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2017 Journals

Dr. R. Michael Buehrer | Dr. T. Charles Clancy | Dr. Harpreet Dhillon | Dr. Carl B. Dietrich | Dr. Steven Ellingson | Dr. Y. Thomas Hou
Dr. Lingjia Liu | Dr. Allen B. MacKenzie | Dr. Vuk Marojevic | Dr. Jung-Min "Jerry" Park | Dr. Jeffrey H. Reed | Dr. Walid Saad | Dr. Yaling Yang

Dr. R. Michael Buehrer

Title: Indoor footstep localization from structural dynamics instrumentation

Authors: Jeffrey D Poston, R Michael Buehrer, Pablo A Tarazaga

Abstract: Measurements from accelerometers originally deployed to measure a building's structural dynamics can serve a new role: locating individuals moving within a building. Specifically, this paper proposes measurements of footstep-generated vibrations as a novel source of information for localization. The complexity of wave propagation in a building (e.g., dispersion and reflection) limits the utility of existing algorithms designed to locate, for example, the source of sound in a room or radio waves in free space. This paper develops enhancements for arrival time determination and time difference of arrival localization in order to address the complexities posed by wave propagation within a building's structure. Experiments with actual measurements from an instrumented public building demonstrate the potential of locating footsteps to sub-meter accuracy. Furthermore, this paper explains how to forecast performance in other buildings with different sensor configurations. This localization capability holds the potential to assist public safety agencies in building evacuation and incidence response, to facilitate occupancy-based optimization of heating or cooling and to inform facility security.

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Title: Cooperative Source Node Tracking in Non-Line-of-Sight Environments

Authors: R. M. Vaghefi and R. M. Buehrer, IEEE Transactions on Mobile Computing, vol. 16, no. 5, pp. 1287-1299, May 1 2017

Abstract: The accuracy of localization is highly degraded in indoor and harsh environments where source nodes either do not have connections with a sufficient number of anchor nodes due to strong attenuation or have very poor range estimates due to NLOS propagation. Cooperative localization is a technique in which the source nodes communicate not only with the anchor nodes, but also with each other. Hence, the source nodes can collect several additional measurements which significantly improve the localization performance. Although many studies have examined NLOS-degraded localization of a static node in noncooperative networks, and many others have examined the impact of cooperation for static localization, there is no work which considers cooperative tracking of mobile nodes. To address this open problem, in this work, we examine cooperative tracking, particularly in NLOS environments. More specifically, we develop a novel sensor tracking algorithm based on semidefinite programming (SDP) which has the ability to mitigate NLOS propagation. Our simulations show that the new SDP-based tracking algorithm outperforms the classic extended Kalman filter as well as the other recently proposed algorithms for noncooperative tracking in NLOS environments. We also show that the algorithm can be extended to cooperative networks, and that a substantial performance benefit is realized by cooperation. Google Scholar

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Title: On Jamming Against Wireless Networks

Authors: S. Amuru, H. S. Dhillon and R. M. Buehrer, "On Jamming Against Wireless Networks," in IEEE Transactions on Wireless Communications, vol. 16, no. 1, pp. 412-428, Jan. 2017

Abstract: In this paper, we study jamming attacks against wireless networks. Specifically, we consider a network of base stations (BSs) or access points (APs) and investigate the impact of a fixed number of jammers that are randomly deployed according to a Binomial point process. We investigate the network performance in terms of: 1) the outage probability and 2) the error probability of a victim receiver in the downlink of this wireless network. We derive analytical expressions for both these metrics and discuss in detail how the jammer network must adapt to the various wireless network parameters in order to effectively attack the victim receivers. For instance, we will show that with only 1 jammer per BS/AP: 1) the outage probability of the wireless network can be increased from 1% (as seen in the non-jamming case) to 80% and 2) when retransmissions are used, the jammers cause the effective network activity factor (and hence the interference among the BSs) to be doubled. Furthermore, we show that the behavior of the jammer network as a function of the BS/AP density is not obvious. In particular, a non-trivial behavior is seen, which indicates that the number of jammers required to attack the wireless network must scale with the BS density only until a certain value beyond which it decreases. In the context of error probability of the victim receiver, we study whether or not some recent results related to jamming in the point-to-point link scenario can be extended to the case of jamming against wireless networks. Numerical results are presented to validate all the theoretical inferences presented. Google Scholar

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Dr. T. Charles Clancy

Title: Application-Aware Resource Allocation of Hybrid Traffic in Cellular Networks

Authors: Mo Ghorbanzadeh, Ahmed Abdelhadi, Charles Clancy

Abstract:The hybrid traffic, a composite of elastic and inelastic data generated by delay-tolerant and real-time applications respectively, forms the bulk of what is carried over modern cellular systems. Since a smooth performance of real-time and delay-tolerant applications is tied to their distinctive needs for resources, networks’ intelligence about representative characteristics of applications’ traffic, networks’ ability to prioritize subscribers, and networks’ sophistication to cope with temporal variations in traffic amounts from the real-time and delay-tolerant applications can help efficiently assign resources accordingly to the preceding issues and consequentially elevate the quality-of-experience. To this end, the manuscript at hand aims at concocting a convex proportional fairness resource allocation method for cognitive cellular systems equipped with the intelligence to consider the traffic type, its temporal variations, and user prioritization. The devised method is formalized as mathematically equivalent centralized and distributed formulations with provided solution algorithms and convergence conditions. It is proved that the centralized approach has a lower transmission overhead, whose some lower bounds are derived for the centralized and distributed methods. Analyses of the sensitivity to changes of user equipments quantity and of application usage are presented under a variation of bidding scenarios in the face of the system dynamics. Google Scholar

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Title: On the Latency and Energy Efficiency of Distributed Storage Systems

Authors: Akshay Kumar, Ravi Tandon, T. Charles Clancy

Abstract:The increase in data storage and power consumption at data-centers has made it imperative to design energy efficient distributed storage systems (DSS). The energy efficiency of DSS is strongly influenced not only by the volume of data, frequency of data access and redundancy in data storage, but also by the heterogeneity exhibited by the DSS in these dimensions. To this end, we propose and analyze the energy efficiency of a heterogeneous distributed storage system in which n storage servers (disks) store the data of R distinct classes. Data of class i is encoded using a (n,ki) erasure code and the (random) data retrieval requests can also vary across classes. We show that the energy efficiency of such systems is closely related to the average latency and hence motivates us to study the energy efficiency via the lens of average latency. Through this connection, we show that erasure coding serves the dual purpose of reducing latency and increasing energy efficiency. We present a queuing theoretic analysis of the proposed model and establish upper and lower bounds on the average latency for each data class under various scheduling policies. Through extensive simulations, we present qualitative insights which reveal the impact of coding rate, number of servers, service distribution and number of redundant requests on the average latency and energy efficiency of the DSS. Google Scholar

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Title: Spectral Coexistence of MIMO Radar and MIMO Cellular System

Authors: Jasmin A. Mahal, Awais Khawar, Ahmed Abdelhadi, T. Charles Clancy

Abstract: This paper details designing the precoder of a MIMO-radar spectrally-coexistent with a MIMO cellular system. Spectrum sharing with zero or minimal interference is achieved by using, respectively, the conventional switched null space projection (SNSP) or the newly proposed switched small singular value space projection (SSSVSP). Loss in radar target localization capability due to precoding can be compensated by using SSSVSP instead of SNSP to some extent but increasing the number of radar antenna elements is more effective. Google Scholar

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Title: FSK-Based Reactive Jammer Piggybacking

Authors:Marc Lichtman, T. Charles Clancy, Jeffrey H. Reed

Abstract:The complexity and sophistication of communications jamming will continue to increase over time. The traditional approach to jammer mitigation is to harden radios, often sacrificing communications performance for more advanced jamming protection. To provide an escape from this trend, we propose a jammer exploitation strategy in which the communications system causes an enemy reactive jammer to act as an unwitting relay. This can lead to an improvement in communications as a result of the jamming attack itself. The strategy proposed in this letter revolves around using a frequency-shift keying waveform that is tuned in such a way to exploit the jammer's behavior. We derive the channel capacity when using the waveform along with practical coding, and provide numerical results to gain insight. Google Scholar

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Dr. Harpreet Dhillon

Title: Effect of Cell-Selection on the Effective Fading Distribution in a Downlink K -Tier HetNet

Authors: Mustafa Kishk, Harpreet S. Dhillon

Abstract: This letter characterizes the statistics of effective fading gain in multi-tier cellular networks with strongest base station (BS) cell association policy. First, we derive the probability of association with the n-th nearest BS in the k-th tier. Next, we use this result to derive the probability density function of the channel fading gain (effective fading) experienced by the user when associating with the strongest BS. Interestingly, our results show that the effective channel gain distribution solely depends upon the original channel fading and the path-loss exponent. Moreover, we show that in the case of Nakagami-m fading channels (Gamma distribution), the distribution of the effective fading is also Gamma but with a gain of (α/2) in the shape parameter, where α is the path-loss exponent. Google Scholar

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Title: Stochastic Geometry-Based Comparison of Secrecy Enhancement Techniques in D2D Networks

Authors: Mustafa Kishk, Harpreet S. Dhillon

Abstract: This letter presents a performance comparison of two popular secrecy enhancement techniques in wireless networks: 1) creating guard zones by restricting transmissions of legitimate transmitters whenever any eavesdropper is detected in their vicinity, and 2) adding artificial noise to the confidential messages to make it difficult for the eavesdroppers to decode them. Focusing on a noise-limited regime, we use tools from stochastic geometry to derive the secrecy outage probability at the eavesdroppers as well as the coverage probability at the legitimate users for both these techniques. Using these results, we derive a threshold on the density of the eavesdroppers below which no secrecy enhancing technique is required to ensure a target secrecy outage probability. For eavesdropper densities above this threshold, we concretely characterize the regimes in which each technique outperforms the other. Our results demonstrate that guard zone technique is better when the distances between the transmitters and their legitimate receivers are higher than a certain threshold. Google Scholar

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Title: Tight Lower Bounds on the Contact Distance Distribution in Poisson Hole Process

Authors: Mustafa Kishk, Harpreet S. Dhillon

Abstract: In this letter, we derive new lower bounds on the cumulative distribution function (CDF) of the contact distance in the Poisson hole process (PHP) for two cases: 1) reference point is selected uniformly at random from R2 independently of the PHP and 2) reference point is located at the center of a hole selected uniformly at random from the PHP. While one can derive upper bounds on the CDF of contact distance by simply ignoring the effect of holes, deriving lower bounds is known to be relatively more challenging. As a part of our proof, we introduce a tractable way of bounding the effect of all the holes in a PHP, which can be used to study other properties of a PHP as well. Google Scholar

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Title: Spatio-Temporal Interference Correlation and Joint Coverage in Cellular Networks

Authors: Shankar Krishnan, Harpreet S. Dhillon

Abstract: This paper provides an analytical framework with foundations in stochastic geometry to characterize the spatio-temporal interference correlation as well as the joint coverage probability at two spatial locations in a cellular network. In particular, modeling the locations of cellular base stations (BSs) as a Poisson point process, we study interference correlation at two spatial locations ℓ 1 and ℓ 2 separated by a distance v , when the user follows the closest BS association policy at both spatial locations and moves from ℓ 1 to ℓ 2 . With this user displacement, two scenarios can occur: i) the user is handed off to a new serving BS at ℓ 2 , or ii) no handoff occurs and the user is served by the same BS at both locations. After providing intermediate results, such as probability of handoff and distance distributions of the serving BS at the two user locations, we use them to derive exact expressions for spatio-temporal interference correlation coefficient and joint coverage probability for any distance separation v . We also study two different handoff strategies: i) handoff skipping, and ii) conventional handoffs, and derive the expressions of joint coverage probability for both strategies. The exact analysis is not straightforward and involves a careful treatment of the neighborhood of the two spatial locations and the resulting handoff scenarios. To provide analytical insights, we also provide easy-to-use expressions for two special cases: i) static user ( v=0 ) and ii) highly mobile user ( v→∞) . As expected, our analysis shows that the interference correlation and joint coverage probability decrease with increasing v , with v→∞ corresponding to a completely uncorrelated scenario. Further design insights are also provided by studying the effect of few network/channel parameters, such as BS density and path loss on the interference correlation.

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Title: Stochastic Geometry-Based Modeling and Analysis of Citizens Broadband Radio Service System

Authors: Priyabrata Parida, Harpreet S. Dhillon, Pavan Nuggehalli

Abstract: In this paper, we model and analyze a cellular network that operates in the licensed band of the 3.5-GHz spectrum and consists of a licensed and an unlicensed operator. Using tools from stochastic geometry, we concretely characterize the performance of this spectrum sharing system. We model the locations of the licensed base stations (BSs) as a homogeneous Poisson point process with protection zones (PZs) around each BS. Since the unlicensed BSs cannot operate within the PZs, their locations are modeled as a Poisson hole process. In addition, we consider carrier sense multiple access with collision avoidance-type contention-based channel access mechanism for the unlicensed BSs. For this setup, we first derive an approximate expression and useful lower bounds for the medium access probability of the serving unlicensed operator BS. Furthermore, by efficiently handling the correlation in the interference powers induced due to correlation in the locations of the licensed and unlicensed BSs, we provide approximate expressions for the coverage probability of a typical user of each operator. Subsequently, we study the effect of different system parameters on area spectral efficiency of the network. To the best of our knowledge, this is the first attempt toward accurate modeling and analysis of a citizens broadband radio service system using tools from stochastic geometry. Google Scholar

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Title: Asymptotic Blind-Spot Analysis of Localization Networks Under Correlated Blocking Using a Poisson Line Process

Authors: Sundar Aditya, Harpreet S. Dhillon, Andreas F. Molisch, Hatim Behairy

Abstract: In a localization network, the line-of-sight between anchors (transceivers) and targets may be blocked due to the presence of obstacles in the environment. Due to the non-zero size of the obstacles, the blocking is typically correlated across both anchor and target locations, with the extent of correlation increasing with obstacle size. If a target does not have line-of-sight to a minimum number of anchors, then its position cannot be estimated unambiguously and is, therefore, said to be in a blind-spot. However, the analysis of the blind-spot probability of a given target is challenging due to the inherent randomness in the obstacle locations and sizes. In this letter, we develop a new framework to analyze the worst-case impact of correlated blocking on the blind-spot probability of a typical target; in particular, we model the obstacles by a Poisson line process and the anchor locations by a Poisson point process. For this setup, we define the notion of the asymptotic blind-spot probability of the typical target and derive a closed-form expression for it as a function of the area distribution of a typical Poisson-Voronoi cell. As an upper bound for the more realistic case when obstacles have finite dimensions, the asymptotic blind-spot probability is useful as a design tool to ensure that the blind-spot probability of a typical target does not exceed a desired threshold, ϵ . Google Scholar

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Title: A Stochastic Geometric Analysis of Device-to-Device Communications Operating Over Generalized Fading Channels

Authors: Young Jin Chun, Simon L. Cotton, Harpreet S. Dhillon, Ali Ghrayeb, Mazen O. Hasna

Abstract: Device-to-device (D2D) communications are now considered an integral part of future 5G networks, which will enable direct communication between user equipments and achieve higher throughputs than conventional cellular networks, but with the increased potential for co-channel interference. The physical channels, which constitute D2D communications, can be expected to be complex in nature, experiencing both line-ofsight (LOS) and non-LOS conditions across closely located D2D pairs. In addition to this, given the diverse range of operating environments, they may also be subject to clustering of the scattered multipath contribution, i.e., propagation characteristics which are quite dissimilar to conventional Rayleigh fading environments. To address these challenges, we consider two recently proposed generalized fading models, namely κ-μ and η-μ, to characterize the fading behavior in D2D communications. Together, these models encompass many of the most widely utilized fading models in the literature such as Rayleigh, Rice (Nakagami-n), Nakagami-m, Hoyt (Nakagami-q), and One-sided Gaussian. Using stochastic geometry, we evaluate the spectral efficiency and outage probability of D2D networks under generalized fading conditions and present new insights into the tradeoffs between the reliability, rate, and mode selection. Through numerical evaluations, we also investigate the performance gains of D2D networks and demonstrate their superiority over traditional cellular networks. Google Scholar

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Title: Effect of User Mobility on the Performance of Device-to-Device Networks With Distributed Caching

Authors: Shankar Krishnan , Harpreet S. Dhillon

Abstract: We consider a distributed caching device-to-device network in which a user's file of interest is cached as several portions in the storage of other devices in the network. Assuming that the user needs to obtain all these file portions, the portions cached farther away naturally become the performance bottleneck. This is due to the fact that dominant interferers may be closer to the receiver than the serving device. Using a simple stochastic geometry model, we concretely demonstrate that this bottleneck can be loosened if the users are mobile. Gains obtained from mobility are quantified in terms of coverage probability. Google Scholar

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Title: Enriched K -Tier HetNet Model to Enable the Analysis of User-Centric Small Cell Deployments

Authors: Shankar Krishnan, Harpreet S. Dhillon

Abstract: One of the principal underlying assumptions of current approaches to the analysis of heterogeneous cellular networks (HetNets) with random spatial models is the uniform distribution of users independent of the base station (BS) locations. This assumption is not quite accurate, especially for user-centric capacity-driven small cell deployments where low-power BSs are deployed in the areas of high user density, thus inducing a natural correlation in the BS and user locations. In order to capture this correlation, we enrich the existing K-tier Poisson point process (PPP) HetNet model by considering user locations as Poisson Cluster Process with the BSs at the cluster centers. In particular, we provide the formal analysis of the downlink coverage probability in terms of a general density function describing the locations of users around the BSs. The derived results are specialized for two cases of interest: 1) Thomas cluster process, where the locations of the users around BSs are Gaussian distributed and 2) Matérn cluster process, where the users are uniformly distributed inside a disc of a given radius. Tight closed-form bounds for the coverage probability in these two cases are also derived. Our results demonstrate that the coverage probability decreases as the size of user clusters around BSs increases, ultimately collapsing to the result obtained under the assumption of PPP distribution of users independent of the BS locations when the cluster size goes to infinity. Using these results, we also handle mixed user distributions consisting of two types of users: 1) uniformly distributed and 2) clustered around certain tiers. Google Scholar

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Title: On Jamming Against Wireless Networks

Authors: SaiDhiraj Amuru, Harpreet S. Dhillon , R. Michael Buehrer

Abstract: In this paper, we study jamming attacks against wireless networks. Specifically, we consider a network of base stations (BSs) or access points (APs) and investigate the impact of a fixed number of jammers that are randomly deployed according to a Binomial point process. We investigate the network performance in terms of: 1) the outage probability and 2) the error probability of a victim receiver in the downlink of this wireless network. We derive analytical expressions for both these metrics and discuss in detail how the jammer network must adapt to the various wireless network parameters in order to effectively attack the victim receivers. For instance, we will show that with only 1 jammer per BS/AP: 1) the outage probability of the wireless network can be increased from 1% (as seen in the non-jamming case) to 80% and 2) when retransmissions are used, the jammers cause the effective network activity factor (and hence the interference among the BSs) to be doubled. Furthermore, we show that the behavior of the jammer network as a function of the BS/AP density is not obvious. In particular, a non-trivial behavior is seen, which indicates that the number of jammers required to attack the wireless network must scale with the BS density only until a certain value beyond which it decreases. In the context of error probability of the victim receiver, we study whether or not some recent results related to jamming in the point-to-point link scenario can be extended to the case of jamming against wireless networks. Numerical results are presented to validate all the theoretical inferences presented. Google Scholar

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Title:Nearest-Neighbor and Contact Distance Distributions for Thomas Cluster Process

Authors: Mehrnaz Afshang, Chiranjib Saha, Harpreet S. Dhillon

Abstract: We characterize the statistics of nearest-neighbor and contact distance distributions for Thomas cluster process (TCP), which is a special case of Poisson cluster process. In particular, we derive the cumulative distribution function of the distance to the nearest point of TCP from a reference point for three different cases: 1) reference point is not a part of the point process; 2) it is chosen uniformly at random from the TCP; and 3) it is a randomly chosen point from a cluster chosen uniformly at random from the TCP. While the first corresponds to the contact distance distribution, the other two provide two different viewpoints for the nearest-neighbor distance distribution. Closed-form bounds are also provided for the first two cases. Google Scholar

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Title: Fundamentals of Modeling Finite Wireless Networks Using Binomial Point Process

Authors: Mehrnaz Afshang, Harpreet S. Dhillon

Abstract: Modeling the locations of nodes as a uniform binomial point process, we present a generic mathematical framework to characterize the performance of an arbitrarily located reference receiver in a finite wireless network. Different from most of the prior works where the serving transmitter (TX) is located at the fixed distance from the reference receiver, we consider two general TX-selection policies: 1) uniform TX-selection: the serving node is chosen uniformly at random from amongst all transmitting nodes and 2) k-closest TX-selection: the serving node is the kth closest node (out of all transmitting nodes) to the reference receiver. The key intermediate step in our analysis is the derivation of a new set of distance distributions that lead not only to the tractable analysis of coverage probability but also enable the analysis of wide range of classical and currently trending problems in wireless networks. Using this new set of distance distributions, we further investigate the diversity loss due to SIR correlation in a finite network. We then obtain the optimal number of links that can be simultaneously activated to maximize network spectral efficiency. Finally, we evaluate optimal caching probability to maximize the total hit probability in cache-enabled finite networks. Google Scholar

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Title: Wide-area Wireless Communication Challenges for the Internet of Things

Authors: Harpreet S. Dhillon, Howard Huang, Harish Viswanathan

Abstract: The deployment of Internet of Things (IoT) devices and services is accelerating, aided by ubiquitous wireless connectivity, declining communication costs, and the emergence of cloud platforms. Most major mobile network operators view machine-to-machine (M2M) communication networks for supporting IoT as a significant source of new revenue. In this article, we discuss the need for wide-area M2M wireless networks, especially for short data packet communication to support a very large number of IoT devices. We first present a brief overview of current and emerging technologies for supporting wide area M2M, and then using communication theory principles, discuss the fundamental challenges and potential solutions for these networks, highlighting tradeoffs and strategies for random and scheduled access. We conclude with recommendations for how future 5G networks should be designed for efficient wide-area M2M communications. Google Scholar

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Dr. Carl B. Dietrich

Title: Coexistence of Outdoor Wi-Fi and Radar at 3.5 GHz

Authors: Seungmo Kim, Carl Dietrich

Abstract: Coexistence between radar and outdoor wireless fidelity (Wi-Fi) needs thorough study since the IEEE 802.11 working group (WG) opposed the latest rules in 3550-3700 MHz (the 3.5 GHz band) that require “exclusion zones.” This letter proposes a method that suppresses Wi-Fi-to-radar (WtR) interference, in which a Wi-Fi transmitter (TX) is selected to avoid beam angles toward the victim radar. It is distinguished from prior schemes since it ensures that the Wi-Fi remains operable while suppressing the WtR interference. Google Scholar

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Title: A Geometric Analysis Method for Evaluation of Coexistence between DSRC and Wi-Fi at 5.9 GHz

Authors: Seungmo Kim, Carl Dietrich

Abstract: Channel coexistence between Dedicated Short-Range Communications (DSRC) and Wi-Fi needs thorough study. The reason is that although the 5.850-5.925 GHz (5.9 GHz) band has been reserved for DSRC so far, the U.S. government is moving swiftly on opening the band to be shared with Wi-Fi. However, most prior work lacks sufficient scientific rigor by relying on performance metrics such as packet delivery rate (PDR) and packet delay that cannot accurately measure performance of a vehicular network that primarily uses broadcast in dissemination of packets. Precise analysis of such broadcast operation is essential for rigorous investigation of DSRC-Wi-Fi coexistence because most safety-critical applications of DSRC operate based on broadcast. This paper proposes a new metric that can more accurately characterize the performance of a broadcast-based DSRC network. The new metric is used to (i) characterize coexistence of DSRC with IEEE 802.11ac-based Wi-Fi and (ii) suggest selection of key medium access control (MAC) parameters for DSRC: inter-broadcast interval (IBI) and contention window (CW). Citation Link

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Dr. Steven Ellingson

Title: An Introduction to the GTD Edge Diffraction via Equivalent Currents [Education Corner]

Authors: S. W. Ellingson

Abstract: The geometrical theory of diffraction (GTD) is a popular method for the analysis of diffraction from edges of electrically large conducting surfaces. It is also easy to use, as it involves only algebraic expressions and geometrical considerations. However, GTD is awkward to teach because a rigorous derivation of the diffraction coefficients requires mathematical skills that are beyond the reach of most students and many practitioners. This article presents an alternative derivation of the GTD edge diffraction equations. This approach begins with a relatively simple stationary-phase analysis of a radiation integral formed from equivalent currents postulated to flow along the edge. This analysis yields expressions in GTD form but with unspecified diffraction coefficients. Diffraction coefficients in the original GTD (Keller) form or the uniform GTD (UTD) (Kouyoumjian and Pathak) form can then be introduced as an alternative to the equivalent currents in the final expressions. This approach is suitable for a concise introduction to GTD edge diffraction for students with no previous experience in asymptotic high-frequency methods. Google Scholar

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Dr. Y. Thomas Hou

Title: OFDM-Based Interference Alignment in Single-Antenna Cellular Wireless Networks

Authors: Huacheng Zeng, Yi Shi, Y. Thomas Hou, Wenjing Lou, Xu Yuan, Rongbo Zhu, Jiannong Cao

Abstract: Interference alignment (IA) is widely regarded as a promising interference management technique in wireless networks. Despite its rapid advances in cellular networks, most results of IA are limited to information-theoretic exploration or physical-layer signal design. Little progress has been made so far to advance IA in cellular networks from a networking perspective. In this paper, we aim to fill this gap by studying IA in large-scale cellular networks. For the uplink, we propose an OFDM-based IA scheme and prove its feasibility at the physical layer by showing that all data streams in the IA scheme can be transported free of interference. Based on the IA scheme, we develop a cross-layer IA optimization framework that can fully translate the benefits of IA to throughput gain in cellular networks. Furthermore, we show that the IA optimization problem in the downlink can be solved in the exactly same way as that in the uplink. Simulation results show that our OFDM-based IA scheme can significantly increase the user throughput and the throughput gain increases with user density in the network. Google Scholar

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Title: Location Based Handshake and Private Proximity Test with Location Tags

Authors: Yao Zheng, Ming Li, Wenjing Lou,Y. Thomas Hou

Abstract: Abstract: A location proximity test service allows mobile users to determine whether they are in close proximity to each other, and has found numerous applications in mobile social networks. Unfortunately, existing solutions usually reveal much of users' private location information during a proximity test. They are also vulnerable to location cheating where an attacker reports false locations to gain an advantage. Moreover, the initial trust establishment among unfamiliar users in large scale mobile social networks has been a challenging task. In this paper, we propose a novel scheme that enables a user to perform (1) a location based handshake that establishes secure communications among strangers, who do not have a pre-shared secret, and (2) a privacy-preserving proximity test without revealing the user's actual location to the server or other users not within the proximity. The proposed scheme is based on a novel concept, i.e., spatial-temporal location tags, and we put forward a location tag construction method using environmental signals that provides an unforgeable location proof. We use Bloom filters to efficiently represent users' location tags and vicinity regions. We exploit fuzzy extractor, a lightweight cryptographic primitive, to extract shared secrets between matching location tags. We conduct extensive analysis, simulation, and real experiments to demonstrate the feasibility, security, and efficiency of our scheme. Google Scholar

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Title: Coexistence Between Wi-Fi and LTE on Unlicensed Spectrum: A Human-Centric Approach

Authors: Xu Yuan, Xiaoqi Qin, Feng Tian, Y. Thomas Hou, Wenjing Lou, Scott F. Midkiff , Jeffrey H. Reed

Abstract: In recent years, there has been great interest from the cellular service providers to use the unlicensed spectrum for their service offerings. On the other hand, existing unlicensed users in these bands (e.g., Wi-Fi in the 5-GHz band) have serious concern that such coexistence will jeopardize their service quality. Although there are some proposals on how to achieve coexistence, they are driven by the service providers and as such there remain many issues and skepticism. In this paper, we take a novel human-centric approach to understand coexistence between Wi-Fi and LTE by focusing on human satisfaction. Through mathematical modeling, problem formulation, and extensive simulations studies, we show that in terms of maximizing total human satisfaction function, there does not appear to be any advantage with the coexistence of unlicensed spectrum for Wi-Fi and LTE under static partitioning of unlicensed spectrum. This finding serves as a powerful counter argument to some LTE service providers’ proposal to share the unlicensed spectrum with Wi-Fi through static partitioning. On the other hand, we find that there is a significant improvement in human satisfaction in coexistence between Wi-Fi and LTE under adaptive spectrum partitioning. Since adaptive spectrum partitioning may require a user to change its service provider whenever there is a change among the users, we propose a practical (semi-adaptive) algorithm for implementation without affecting existing users’ service providers. Through performance evaluation, we show that the proposed semi-adaptive algorithm is highly competitive. Google Scholar

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Title: A Distributed Scheduling Algorithm for Underwater Acoustic Networks With Large Propagation Delays

Authors: Huacheng Zeng, Y. Thomas Hou, Yi Shi, Wenjing Lou, Sastry Kompella, Scott F. Midkiff

Abstract: Abstract: Underwater acoustic (UWA) networks are a key form of communications for human exploration and activities in the oceanographic space of the earth. A fundamental issue of UWA communications is large propagation delays due to water medium, which has posed a grand challenge in UWA network protocol design. Conventional wisdom of addressing this issue is to live with this disadvantage by inserting a guard interval to introduce immunity to propagation delays. Recent advances in interference alignment (IA) open up a new direction to address this issue and promise a great potential to improve network throughput by exploiting large propagation delays. In this paper, we investigate propagation delay-based IA (PD-IA) in multi-hop UWA networks. We first develop a set of simple constraints to characterize PD-IA feasible region at the physical layer. Based on the set of PD-IA constraints, we develop a distributed PD-IA scheduling algorithm to greedily maximize interference overlapping possibilities in a multi-hop UWA network. Simulation results show that the proposed PD-IA algorithm yields higher throughput than an idealized benchmark algorithm without propagation delays, indicating that large propagation delays are not adversarial but beneficial for network throughput performance. Google Scholar

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Title: Impact of Full Duplex Scheduling on End-to-End Throughput in Multi-Hop Wireless Networks View Document

Authors: Xiaoqi Qin, Huacheng Zeng, Xu Yuan, Brian Jalaian, Y. Thomas Hou, Wenjing Lou, Scott F. Midkiff

Abstract: There have been some rapid advances on the design of full duplex (FD) transceivers in recent years. Although the benefits of FD have been studied for single-hop wireless communications, its potential on throughput performance in a multi-hop wireless network remains unclear. As for multi-hop networks, a fundamental problem is to compute the achievable end-to-end throughput for one or multiple communication sessions. The goal of this paper is to offer some fundamental understanding on end-to-end throughput performance limits of FD in a multi-hop wireless network. We show that through a rigorous mathematical formulation, we can cast the multi-hop throughput performance problem into a formal optimization problem. Through numerical results, we show that in many cases, the end-to-end session throughput in a FD network can exceed 2x of that in a half duplex (HD) network. Our finding can be explained by the much larger design space for scheduling that is offered by removing HD constraints in throughput maximization problem. The results in this paper offer some new understandings on the potential benefits of FD for end-to-end session throughput in a multi-hop wireless network.Google Scholar

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Title: Beyond Overlay: Reaping Mutual Benefits for Primary and Secondary Networks Through Node-Level Cooperation

Authors: Xu Yuan, Yi Shi, Xiaoqi Qin, Y. Thomas Hou, Wenjing Lou, Sastry Kompella, Scott F. Midkiff, Jeffrey H. Reed

Abstract: Existing spectrum sharing paradigms have set clear boundaries between the primary and secondary networks. There is either no or very limited node-level cooperation between the primary and secondary networks. In this paper, we develop a new and bold spectrum-sharing paradigm beyond the state of the art for future wireless networks. We explore network cooperation as a new dimension for spectrum sharing between the primary and secondary users. Such network cooperation can be defined as a set of policies under which different degrees of cooperation are to be achieved. The benefits of this paradigm are numerous, as they allow integrating resources from two networks. There are many possible node-level cooperation policies that one can employ under this paradigm. For the purpose of performance study, we consider a specific policy called United cooperation of Primary and Secondary (UPS) networks. UPS allows a complete cooperation between the primary and secondary networks at the node level to relay each other's traffic. As a case study, we consider a problem with the goal of supporting the rate requirement of the primary network traffic while maximizing the throughput of the secondary sessions. For this problem, we develop an optimization model and formulate a combinatorial optimization problem. We also develop an approximation solution based on a piece-wise linearization technique. Simulation results show that UPS offers significantly better throughput performance than that under the interweave paradigm. Google Scholar

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Dr. Lingjia Liu

Title: Angle and Delay Estimation for 3-D Massive MIMO/FD-MIMO Systems Based on Parametric Channel Modeling

Authors: Rubayet Shafin; Lingjia Liu; Yan Li; Anding Wang; Jianzhong Zhang

Abstract: In order to meet the challenge of increasing data-rate demand as well as the form factor limitation of the base station (BS), 3-D massive multiple-input multiple-output (MIMO) technology has been introduced as one of the enabling technologies for fifth generation mobile cellular systems. In 3-D massive MIMO systems, a BS will rely on the uplink sounding signals from mobile stations to figure out the spatial information for downlink MIMO operations. Accordingly, multi-dimensional parameter estimation of a MIMO channel becomes crucial for such systems to realize the predicted capacity gains. In this paper, we study the angle and delay estimation for 3-D massive MIMO systems under a parametric channel modeling. To be specific, we first introduce separate low complexity time delay and angle estimation algorithms based on unitary transformation, and analytically characterize the mean squared errors (MSEs) of these estimations for massive MIMO systems. Then, a matrix-based estimation of signal parameters via rotational invariance technique algorithm is applied to jointly estimate the delay and the angles where the MSEs are also analytically characterized. Our results show that the antenna array configuration at the BS plays a critical role in determining the underlying channel estimation performance. Simulation results suggest that the characterized MSEs match well with the simulated ones. Google Scholar

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Title: Enabling Sustainable Cyber Physical Security Systems Through Neuromorphic Computing

Authors: Jialing Li; Lingjia Liu; Chenyuan Zhao; Kian Hamedani; Rachad Atat; Yang Yi

Abstract: As the novel paradigm in the field of machine learning, reservoir computing possesses exceptional performance, e.g. energy efficiency, in tasks in which the traditional von Neumann computing systems cannot incorporate. This makes reservoir computing an ideal candidate to enable the sustainable development of cyber-physical systems (CPS). In the realm of CPS, the tight interaction among physical objects places security threats under the spotlight of attention. For such systems, especially the power grid network, false data injection could potentially lead to catastrophic consequences such as blackouts in large geographical areas. In this paper, we will introduce a reservoir computing architecture, the delayed feedback system, and apply the reservoir computing architecture for anomaly detection. To be specific, detailed design of the three imperative components in the delayed feedback system will be discussed and the corresponding energy efficiency performance will be analyzed. The application of the reservoir computing architecture to anomaly detection in a smart grid network will be introduced. Google Scholar

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Title: Distributed MIMO Precoding for In-band Full-duplex Wireless Backhaul in Heterogeneous Networks

Authors: yi li; Pingzhi Fan; Lingjia Liu; Yang Yi

Abstract: This paper investigates distributed MIMO precoding design to maximize the weighted sum rate in a heterogeneous network (HetNet) where the multiple input multiple output fullduplex (MIMO-FD) small cells reuse the downlink spectrum of the macro base-station (BS) to exchange backhaul information. The multi-antenna BS transmits signals to the cellular users (CUEs) using the dirty paper coding (DPC) technique and the MIMO-FD small cells apply FD precoding structures to effectively balance the received signal, the self-interference (SI), and the co-channel interference (CCI). Since the optimization problem is shown to be nonconvex, obtaining the global optimum is challenging. A low-complexity solution with distributed implementation is introduced with proved convergence. By applying the successive convex approximation technique and the duality between the broadcast channel and the multiple access channel, the original nonconvex problem is decomposed into a sequence of convex subproblems, which can be solved analytically and separately at each small cell and macro BS with limited channel state information exchange. Simulation results confirm the convergence and demonstrate the benefits of the introduced algorithm. It is shown that the SI and CCI can be suppressed effectively with sufficient cancellation power and number of transmit antennas at the FD small cells. Google Scholar

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Dr. Allen B. MacKenzie

Title: Full-duplex or Half-duplex: A Bayesian Game for Wireless Networks with Heterogeneous Self-interference Cancellation Capabilities

Authors: Wessam Afifi; Mohammad J. Abdel-Rahman; Marwan Krunz; Allen B. MacKenzie

Abstract: Recently, tremendous progress has been made in self-interference cancellation (SIC) techniques that enable a wireless device to transmit and receive data simultaneously on the same frequency channel, a.k.a. in-band full-duplex (FD). Although operating in FD mode significantly improves the throughput of a single wireless link, it doubles the number of concurrent transmissions, which limits the potential for coexistence between multiple FD-enabled links. In this paper, we consider the coexistence problem of concurrent transmissions between multiple FD-enabled links with different SIC capabilities; each link can operate in either FD or half-duplex mode. First, we consider two links and formulate the interactions between them as a Bayesian game. In this game, each link tries to maximize its throughput while minimizing the transmission power cost. We derive a closed-form expression for the Bayesian Nash equilibrium and determine the conditions under which no outage occurs at either link. Then, we study the coexistence problem between more than two links, assuming that each link is only affected by its dominant interfering link. We show that under this assumption no more than two links will be involved in a single game. Finally, we corroborate our analytical findings via extensive simulations and numerical results. Google Scholar

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Dr. Vuk Marojevic

Title: Adaptive Pilot Patterns for CA-OFDM Systems in Nonstationary Wireless Channels

Authors: Raghunandan M. Rao, Vuk Marojevic,Jeffrey H. Ree

Abstract: In this paper, we investigate the performance gains of adapting pilot spacing and power for Carrier Aggregation (CA)-OFDM systems in nonstationary wireless channels. In current multi-band CA-OFDM wireless networks, all component carriers use the same pilot density, which is designed for poor channel environments. This leads to unnecessary pilot overhead in good channel conditions and performance degradation in the worst channel conditions. We propose adaptation of pilot spacing and power using a codebook-based approach, where the transmitter and receiver exchange information about the fading characteristics of the channel over a short period of time, which are stored as entries in a channel profile codebook. We present a heuristic algorithm that maximizes the achievable rate by finding the optimal pilot spacing and power, from a set of candidate pilot configurations. We also analyze the computational complexity of our proposed algorithm and the feedback overhead. We describe methods to minimize the computation and feedback requirements for our algorithm in multi-band CA scenarios and present simulation results in typical terrestrial and air-to-ground/ air-to-air nonstationary channels. Our results show that significant performance gains can be achieved when adopting adaptive pilot spacing and power allocation in nonstationary channels. We also discuss important practical considerations and provide guidelines to implement adaptive pilot spacing in CA-OFDM systems. Google Scholar

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Title: Dynamic sounding for multi-user MIMO in wireless LANs

Authors: Xiaofu Ma, Qinghai Gao, Ji Wang, Vuk Marojevic, Jeffrey H. Reed

Abstract: Consumer electronic (CE) devices increasingly rely on wireless local area networks (WLANs). Next generation WLANs will continue to exploit multiple antenna systems to satisfy the growing need for WLAN system capacity. Multipleinput multiple-output (MIMO) antenna systems improve the spectral efficiency and single user throughput. Multi-user MIMO (MU-MIMO) systems exploit the spatial separation of users for increasing the sum-throughput. In an MU-MIMO system, efficient channel sounding is essential for achieving optimal performance. The system analysis in this paper provides insights into the rate at which to perform channel sounding. This paper shows that optimal sounding intervals exist for single user transmit beamforming (SU-TxBF) and MU-MIMO, and proposes a low-complexity dynamic sounding approach for practical MUMIMO WLAN deployments. The proposed approach adjusts the sounding interval adaptively based on the real-time learning outcomes in the given radio environment. Using real over-the-air channel measurements, significant throughput improvements (up to 31.8%) are demonstrated by adopting the proposed dynamic sounding approach, which is compliant with IEEE 802.11ac1.Google Scholar

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Title: Teaching Telecommunication Standards: Bridging the Gap between Theory and Practice

Authors: Antoni Gelonch-Bosch, Ismael Gomez, Vuk Marojevic

Abstract: Telecommunication standards have become a reliable mechanism to strengthen collaboration between industry and research institutions to accelerate the evolution of communications systems. Standards are needed to enable cooperation while promoting competition. Within the framework of a standard, the companies involved in the standardization process contribute and agree on appropriate technical specifications to ensure diversity and compatibility, and facilitate worldwide commercial deployment and evolution. Those parts of the system that can create competitive advantages are intentionally left open in the specifications. Such specifications are extensive, complex, and minimalistic. This makes telecommunication standards education a difficult endeavor, but it is much demanded by industry and governments to spur economic growth. This article describes a methodology for teaching wireless communications standards. We define our methodology around six learning stages that assimilate the standardization process and identify key learning objectives for each. Enabled by software-defined radio technology, we describe a practical learning environment that facilitates developing many of the needed technical and soft skills without the inherent difficulty and cost associated with radio frequency components and regulation. Using only open source software and commercial of-the-shelf computers, this environment is portable and can easily be recreated at other educational institutions and adapted to their educational needs and constraints. We discuss our and our students' experiences when employing the proposed methodology to 4G LTE standard education at Barcelona Tech. Google Scholar

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Title: Enhancing the Robustness of LTE Systems: Analysis and Evolution of the Cell Selection Process

Authors: Mina Labib, Vuk Marojevic, Jeffrey Reed

Abstract: The commercial success of LTE makes it the primary standard for 4G cellular technology, and its evolution paves the path for 5G technology. Furthermore, LTE Unlicensed has been proposed recently to allow cellular network operators to offload some of their data traffic to LTE component carriers operating in the unlicensed band. Hence, it is critical to ensure that the LTE system performs effectively even in harsh signaling environments in both licensed and unlicensed spectrum. This article analyzes the effect of different levels of RF spoofing applied to LTE. RF spoofing affects LTE devices during the initial cell selection process, where a strong nearby cell can impede access to a serving LTE network. This is a serious threat and can be caused unintentionally, in the case of dense and uncoordinated LTE deployment in unlicensed spectrum, or intentionally, where an adversary sets up a fake LTE cell in either licensed or unlicensed LTE spectrum. This article analyzes and experimentally demonstrates the severity of these threats for the evolution of LTE and proposes effective mitigation techniques to prevent denial of service. These mitigation techniques improve the cell selection process at the LTE user equipment, and are backward-compatible with existing LTE networks. We recommend that these modifications be enforced in future releases for increasing the availability and scalability of LTE. Google Scholar

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Title: Understanding Smartphone Sensor and App Data for Enhancing the Security of Secret Questions

Authors: P. Zhao, K. Bian, T. Zhao, X. Song, J. Park, X. Li, F. Ye, and W. Yan

Abstract: Many web applications provide secondary authentication methods, i.e., secret questions (or password recovery questions), to reset the account password when a user’s login fails. However, the answers to many such secret questions can be easily guessed by an acquaintance or exposed to a stranger that has access to public online tools (e.g., online social networks); moreover, a user may forget her/his answers long after creating the secret questions. Today’s prevalence of smartphones has granted us new opportunities to observe and understand how the personal data collected by smartphone sensors and apps can help create personalized secret questions without violating the users’ privacy concerns. In this paper, we present a SecretQuestion based Authentication system, called “Secret-QA”, that creates a set of secret questions on basic of people’s smartphone usage. We develop a prototype on Android smartphones, and evaluate the security of the secret questions by asking the acquaintance/stranger who participate in our user study to guess the answers with and without the help of online tools; meanwhile, we observe the questions’ reliability by asking participants to answer their own questions. Our experimental results reveal that the secret questions related to motion sensors, calendar, app installment, and part of legacy app usage history (e.g., phone calls) have the best memorability for users as well as the highest robustness to attacks. Google Scholar

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Dr. Jung-Min "Jerry" Park

Title: Transmitter Authentication Using Hierarchical Modulation in Dynamic Spectrum Sharing

Authors: V. Kumar, J. Park, and K. Bian

Abstract: One of the critical challenges in dynamic spectrum sharing (DSS) is identifying non-conforming transmitters that violate spectrum access rules prescribed by a spectrum regulatory authority. One approach for facilitating identi cation of the transmitters in DSS is to require every transmitter to embed an uniquely-identi able authentication signal in its waveform at the PHY-layer. In most of the existing PHY-layer authentication schemes, the authentication signal is added to the message signal as noise, which leads to a tradeo between the message signal's signal-to-noise ratio (SNR) and the authentication signal's SNR under the assumption of constant average transmitted power. This implies that one cannot improve the former without sacri cing the latter, and vice versa. In this paper, we propose a novel PHY-layer authentication scheme called Hierarchical Modulation with Modified Duobinary Signaling for Authenti- cation (HMM-DSA), which relaxes the constraint on the aforementioned trade- off. HMM-DSA utilizes a modied duobinary lter to introduce some controlled amount of inter-symbol interference into the message signal, and embeds the authentication signal in the form of filter coefficients. Our results show that the proposed scheme, HMM-DSA, improves the error performance of the message signal as compared to the prior art. Link

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Dr. Jeffrey H. Reed

Title: Extending LTE into the Unlicensed Spectrum: Technical Analysis of the Proposed Variants

Authors: Labib, M., Marojevic, V., Reed, J. H., Zaghloul, A. I., Hayden, P., Nezami, S., ... & Benítez, J.

Abstract: The commercial success of the Long Term Evolution (LTE) and the resulting growth in mobile data demand have urged cellular network operators to strive for new innovations. LTE in unlicensed spectrum has been proposed to allow cellular network operators to offload some of their data traffic by accessing the unlicensed 5 GHz frequency band. Currently, there are three proposed variants for LTE operation in the unlicensed band, namely LTE-U, Licensed Spectrum Access (LAA), and MulteFire. This paper provides a comparative analysis of these variants and explains the current regulations of the 5 GHz band in different parts of the world. We present the technical details of the three proposed versions and analyze them in terms of their operational features and coexistence capabilities to provide an R\&D perspective for their deployment and coexistence with legacy systems. Google Scholar

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Title: Adaptive Pilot Patterns for CA-OFDM Systems in Nonstationary Wireless Channels

Authors: Raghunandan M. Rao, Vuk Marojevic, Jeffrey H. Reed

Abstract: In this paper, we investigate the performance gains of adapting pilot spacing and power for Carrier Aggregation (CA)-OFDM systems in nonstationary wireless channels. In current multi-band CA-OFDM wireless networks, all component carriers use the same pilot density, which is designed for poor channel environments. This leads to unnecessary pilot overhead in good channel conditions and performance degradation in the worst channel conditions. We propose adaptation of pilot spacing and power using a codebook-based approach, where the transmitter and receiver exchange information about the fading characteristics of the channel over a short period of time, which are stored as entries in a channel profile codebook. We present a heuristic algorithm that maximizes the achievable rate by finding the optimal pilot spacing and power, from a set of candidate pilot configurations. We also analyze the computational complexity of our proposed algorithm and the feedback overhead. We describe methods to minimize the computation and feedback requirements for our algorithm in multi-band CA scenarios and present simulation results in typical terrestrial and air-to-ground/air-to-air nonstationary channels. Our results show that significant performance gains can be achieved when adopting adaptive pilot spacing and power allocation in nonstationary channels. We also discuss important practical considerations and provide guidelines to implement adaptive pilot spacing in CA-OFDM systems, Google Scholar

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Title: Performance Analysis of a Mission-Critical Portable LTE System in Targeted RF Interference

Authors: Vuk Marojevic, Raghunandan M Rao, Sean Ha, Jeffrey H Reed

Abstract: Mission-critical wireless networks are being up-graded to 4G long-term evolution (LTE). As opposed to capacity, these networks require very high reliability and security as well as easy deployment and operation in the field. Wireless communication systems have been vulnerable to jamming, spoofing and other radio frequency attacks since the early days of analog systems. Although wireless systems have evolved, important security and reliability concerns still exist. This paper presents our methodology and results for testing. Google Scholar

 

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Title: LTE PHY Layer Vulnerability Analysis and Testing Using Open-Source SDR Tools

Authors: Raghunandan M. RaoSean HaVuk Marojevic, Jeffrey H. Reed

Abstract: This paper provides a methodology to study the PHY layer vulnerability of wireless protocols in hostile radio environments. Our approach is based on testing the vulnerabilities of a system by analyzing the individual subsystems. By targeting an individual subsystem or a combination of subsystems at a time, we can infer the weakest part and revise it to improve the overall system performance. We apply our methodology to 4G LTE downlink by considering each control channel as a subsystem. We also develop open-source software enabling research and education using software-defined radios. We present experimental results with open-source LTE systems and shows how the different subsystems behave under targeted interference. The analysis for the LTE downlink shows that the synchronization signals (PSS/SSS) are very resilient to interference, whereas the downlink pilots or Cell-Specific Reference signals (CRS) are the most susceptible to a synchronized protocol-aware interferer. We also analyze the severity of control channel attacks for different LTE configurations. Our methodology and tools allow rapid evaluation of the PHY layer reliability in harsh signaling environments, which is an asset to improve current standards and develop new robust wireless protocols. Google Scholar

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Title: Intellectual Property and Universities: A Path Forward [Point of View]

Authors: E. William Cowell, Jeffrey H. Reed

Abstract: During the past three decades there has been an increasing focus on the commercialization of technologies developed by academe. Prior to this, research funding by the U.S. Government was skewed toward pure science and mention of commercialization was viewed negatively more often than not. Today’s research funding landscape has reversed the negative view of commercialization, with many Requests for Proposals having specific requirements toward commercialization assessments. This change in mindset has dramatically increased the importance of intellectual property (IP) created by academic research. In fact, most universities have Technology Transfer Offices actively seeking commercialization opportunities for IP created through research activities. The impact of commercialization focus has also affected funding beyond universities. Startup efforts leveraging university IP have become commonplace, with the number of funding mechanisms increasing dramatically. Corporate engagement and interest in university research has evolved as well through the creation of consortia that have expanded the interconnection between industry and academe beyond sponsored research projects. The role of university Technology Transfer Offices has had to evolve to accommodate business engagements at startup and corporate levels, leading to a complex IP landscape that involves universities, startups, and large industrial players. The education of future researchers remains the prime directive of universities, while corporate/startup recruiting is, and will continue to be, a critical component to the relationship between business and academe. Through this Point of View contribution, we provide insight into the cycle of university IP and funding that has evolved through increased commercialization focus for research technologies, highlighting and the resulting relationships between academe, startups, and corporations and offer our opinions on how the future of universities and intellectual property should evolve. Two university IP-based startups from our personal experience are then described to provide examples of possible paths for such efforts. Google Scholar

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Title: Dynamic sounding for multi-user MIMO in wireless LANs

Authors: X. Ma, Q. Gao, J. Wang, V. Marojevic and J. H. Reed

Abstract: Consumer electronic (CE) devices increasingly rely on wireless local area networks (WLANs). Next generation WLANs will continue to exploit multiple antenna systems to satisfy the growing need for WLAN system capacity. Multipleinput multiple-output (MIMO) antenna systems improve the spectral efficiency and single user throughput. Multi-user MIMO (MU-MIMO) systems exploit the spatial separation of users for increasing the sum-throughput. In an MU-MIMO system, efficient channel sounding is essential for achieving optimal performance. The system analysis in this paper provides insights into the rate at which to perform channel sounding. This paper shows that optimal sounding intervals exist for single user transmit beamforming (SU-TxBF) and MU-MIMO, and proposes a low-complexity dynamic sounding approach for practical MUMIMO WLAN deployments. The proposed approach adjusts the sounding interval adaptively based on the real-time learning outcomes in the given radio environment. Using real over-the-air channel measurements, significant throughput improvements (up to 31.8%) are demonstrated by adopting the proposed dynamic sounding approach, which is compliant with IEEE 802.11ac. Google Scholar

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Title: Wireless innovation forum best papers journal issue: our overview

Authors: Bruce Fette, Jeffrey H. Reed

Abstract: In the area of Cognitive Technology, Spectrum and Spectrum Efficiency, Asadi et al. teach means to make use of Meta-Cognition, selection from multiple cognitive engines (CE) to best understand and respond to its environment in both speed (computation), accuracy and ability to deliver communication successfully for a given environmental spectrum activity. Yrjola et al. provide an excellent overview of stakeholder viewpoints and business opportunities in the newly defined Citizens Broadband Radio Service (CBRS) and elements that can help insure the success of this new service. Sohul et al. address a collaborative spectrum sharing auction approach for use by primary and secondary users that make use of Hidden Markov Models to estimate spectrum auction prices that assures spectrum availability, efficiency, cost objectives and quality of service to users. Bastidas et al. develop techniques for Wideband Distributed Spectrum Sharing with Immediate Multiple Access. A channelized radio architecture is proposed and implemented for distributed spectrum sharing that includes spectrum access system, wideband sensing, sophisticated fast rendezvous based on OFDM, and a sophisticated CSMA time slotted MAC protocol. Hirzallah et al. explore methods to enable spectrum sharing between radar and LTE via use of steepest decent or non-steepest decent waveform pre-coders to reduce interference from radar systems. Cai et al. demonstrates the ability to model spectrum usage of a transmitter and associated beam pattern properties of the antennas and corresponding propagation losses in order to be able to predict cross interference between various spectrum users, and thereby achieve greater spectrum allocation efficiency. Google Scholar

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Title: Quality of service assurance-based auction for spectrum sharing systemsls

Authors: Munawwar M. Sohul, Miao Yao, Abdallah S. Abdallah, Matt Carrick, Vuk Marojevic, Jeffrey H. Reed

Abstract:Spectrum sharing has emerged as a promising solution to address the radio frequency spectrum bottleneck. The FCC has recently proposed a spectrum sharing framework that introduces a spectrum access system as the governing entity that manages access to spectrum for primary and secondary users to coexist. An important aspect of dynamic spectrum management is the pricing of spectrum from the perspective of both the primary and secondary users. Existing auction-based spectrum sharing models do not take into consideration an important aspect of successful secondary user operation: the duration of the available spectrum opportunity. In this paper we propose an auction-based spectrum sharing framework that statistically accounts for the accuracy of the estimates of spectrum availability duration. The proposed auctioning process allows both the PU and the SU to iteratively adjust their evaluation about the available spectrum opportunities over time and to achieve a price combination that maximizes their objectives. A method is proposed to statistically assure spectrum availability, supplementing the reporting method. Hidden Markov models and non-stationary hidden Markov models are used to estimate the activity of the spectrum, with simulation results showing high prediction accuracy. Google Scholar

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Title: Coexistence Between Wi-Fi and LTE on Unlicensed Spectrum: A Human-Centric Approach

Authors: X. Yuan, X. Qin, F. Tian, Y. Thomas Hou, Wenjing Lou, Scott Midkiff, Jeffrey H. Reed

Abstract: Today there are over 350 million cellular subscribers in the US and 70% of them possess smartphones. The data traffic carried by these subscribers has exceeded 4.8 exabyte per year and is growing at 50% annually. But the radio frequency spectrum that can be used for wireless communications is a finite and extremely valuable resource. With the proliferation of new wireless applications, the use of the radio spectrum has intensified to the point that new spectrum policies are needed. Google Scholar

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Title: Suppressing the Effects of Aliasing and IQ Imbalance on Multiband Spectrum Sensing

Authors: E. Y. Imana, T. Yang and J. H. Reed

Abstract: In cognitive radio networks, secondary users (SUs) can use a frequency band when the primary user (PU) of the band is not transmitting. Spectrum sensing is one of the methods that SUs employ to know if the PU has stopped transmitting. Accurate spectrum sensing boosts the likelihood that an SU detects a spectrum opportunity. However, it will be challenging for affordable receivers to support accurate spectrum sensing due to receiver impairments, including IQ imbalance and aliasing. Several other papers have developed methods that can address the effects of IQ imbalance in spectrum sensing. This paper presents a technique that can address not only IQ imbalance but the effects of aliasing on multiband spectrum sensing as well. We use channelized spectrum-domain modeling of receivers to develop the technique. This paper presents the theoretical development of the receiver modeling technique and the proposed spectrum sensing mechanism. The performance of the proposed mechanism is evaluated using simulations and hardware-based measurements. The results demonstrate that the proposed mechanism significantly enhances the opportunity detection probability of affordable cognitive radios with high IQ imbalance and poor antialiasing filter selectivity performances. Google Scholar

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Title: Enhancing the Robustness of LTE Systems: Analysis and Evolution of the Cell Selection Process

Authors: M. Labib, V. Marojevic, J. H. Reed and A. I. Zaghloul

Abstract:

The commercial success of LTE makes it the primary standard for 4G cellular technology, and its evolution paves the path for 5G technology. Furthermore, LTE Unlicensed has been proposed recently to allow cellular network operators to offload some of their data traffic to LTE component carriers operating in the unlicensed band. Hence, it is critical to ensure that the LTE system performs effectively even in harsh signaling environments in both licensed and unlicensed spectrum. This article analyzes the effect of different levels of RF spoofing applied to LTE. RF spoofing affects LTE devices during the initial cell selection process, where a strong nearby cell can impede access to a serving LTE network. This is a serious threat and can be caused unintentionally, in the case of dense and uncoordinated LTE deployment in unlicensed spectrum, or intentionally, where an adversary sets up a fake LTE cell in either licensed or unlicensed LTE spectrum. This article analyzes and experimentally demonstrates the severity of these threats for the evolution of LTE and proposes effective mitigation techniques to prevent denial of service. These mitigation techniques improve the cell selection process at the LTE user equipment, and are backward-compatible with existing LTE networks. We recommend that these modifications be enforced in future releases for increasing the availability and scalability of LTE. Google Scholar

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Title: FSK-Based Reactive Jammer Piggybacking

Authors: Marc Lichtman, T Charles Clancy, Jeffrey H Reed

Abstract: The complexity and sophistication of communications jamming will continue to increase over time. The traditional approach to jammer mitigation is to harden radios, often sacrificing communications performance for more advanced jamming protection. To provide an escape from this trend, we propose a jammer exploitation strategy in which the communications system causes an enemy reactive jammer to act as an unwitting relay. This can lead to an improvement in communications as a result of the jamming attack itself. Google Scholar

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Title: Beyond Overlay: Reaping Mutual Benefits for Primary and Secondary Networks Through Node-Level Cooperation

Authors: Xu Yuan, Yi Shi, Xiaoqi Qin, Y. Thomas Hou, Wenjing Lou, Sastry Kompella, Scott Midkiff, Jeffrey H. Reed

Abstract: Existing spectrum sharing paradigms have set clear boundaries between the primary and secondary networks. There is either no or very limited node-level cooperation between the primary and secondary networks. In this paper, we develop a new and bold spectrum-sharing paradigm beyond the state of the art for future wireless networks. We explore network cooperation as a new dimension for spectrum sharing between the primary and secondary users. Such network cooperation can be defined as a set of policies under which different degrees of cooperation are to be achieved. The benefits of this paradigm are numerous, as they allow integrating resources from two networks. There are many possible node-level cooperation policies that one can employ under this paradigm. For the purpose of performance study, we consider a specific policy called United cooperation of Primary and Secondary (UPS) networks. UPS allows a complete cooperation between the primary and secondary networks at the node level to relay each other's traffic. As a case study, we consider a problem with the goal of supporting the rate requirement of the primary network traffic while maximizing the throughput of the secondary sessions. For this problem, we develop an optimization model and formulate a combinatorial optimization problem. We also develop an approximation solution based on a piece-wise linearization technique. Simulation results show that UPS offers significantly better throughput performance than that under the interweave paradigm.

 

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Dr. Walid Saad

Title: Distributed Learning for Energy-Efficient Resource Management in Self-Organizing Heterogeneous Networks

Authors: Atefeh Hajijamali Arani, Abolfazl Mehbodniya, Mohammad Javad Omidi, Fumiyuki Adachi, Walid Saad, Ismail Güvenç

Abstract: In heterogeneous networks, a dense deployment of base stations (BSs) leads to increased total energy consumption, and, consequently, increased cochannel interference (CCI). In this paper, to deal with this problem, self-organizing mechanisms are proposed, for joint channel and power allocation procedures, which are performed in a fully distributed manner. A dynamic channel allocation mechanism is proposed, in which the problem is modeled as a noncooperative game, and a no-regret learning algorithm is applied for solving the game. In order to improve the accuracy and reduce the effect of shadowing, we propose another channel allocation algorithm executed at each user equipment (UE). In this algorithm, each UE reports the channel with minimum CCI to its associated BS. Then, the BS selects its channel based on these received reports. To combat the energy consumption problem, BSs choose their transmission power by employing an on–off switching scheme. Simulation results show that the proposed mechanism, which is based on the second proposed channel allocation algorithm and combined with the on–off switching scheme, balances load among BSs. Furthermore, it yields significant performance gains up to about 40.3%  40.3\% , 44.8%  44.8\% , and 70.6%  70.6\% in terms of average energy consumption, UE's rate, and BS's load, respectively, compared to a benchmark based on an interference-aware dynamic channel allocation algorithm. Google Scholar

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Title: Mode Selection and Resource Allocation in Device-to-Device Communications: A Matching Game Approach

Authors: S. M. Ahsan Kazmi, Nguyen H. Tran, Walid Saad, Zhu Han, Tai Manh Ho, Thant Zin Oo, Choong Seon Hong

Abstract: Abstract: Device to device (D2D) communication is considered as an effective technology for enhancing the spectral efficiency and network throughput of existing cellular networks. However, enabling it in an underlay fashion poses a significant challenge pertaining to interference management. In this paper, mode selection and resource allocation for an underlay D2D network is studied while simultaneously providing interference management. The problem is formulated as a combinatorial optimization problem whose objective is to maximize the utility of all D2D pairs. To solve this problem, a learning framework is proposed based on a problem-specific Markov chain. From the local balance equation of the designed Markov chain, the transition probabilities are derived for distributed implementation. Then, a novel two phase algorithm is developed to perform mode selection and resource allocation in the respective phases. This algorithm is then shown to converge to a near optimal solution. Moreover, to reduce the computation in the learning framework, two resource allocation algorithms based on matching theory are proposed to output a specific and deterministic solution. The first algorithm employs the one-to-one matching game approach whereas in the second algorithm, the one-to many matching game with externalities and dynamic quota is employed. Simulation results show that the proposed framework converges to a near optimal solution under all scenarios with probability one. Moreover, our results show that the proposed matching game with externalities achieves a performance gain of up to 35 percent in terms of the average utility compared to a classical matching scheme with no externalities. Google Scholar

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Title: Hardware Trojan Detection Game: A Prospect-Theoretic Approach

Authors: Walid Saad, Anibal Sanjab, Yunpeng Wang, Charles A. Kamhoua, Kevin A. Kwiat

Abstract: Outsourcing integrated circuit (IC) manufacturing to offshore foundries has grown exponentially in recent years. Given the critical role of ICs in the control and operation of vehicular systems and other modern engineering designs, such offshore outsourcing has led to serious security threats due to the potential of insertion of hardware trojans-malicious designs that, when activated, can lead to highly detrimental consequences. In this paper, a novel game-theoretic framework is proposed to analyze the interactions between a hardware manufacturer, acting as an attacker, and an IC testing facility, acting as a defender. The problem is formulated as a noncooperative game in which the attacker must decide on the type of trojan that it inserts while taking into account the detection penalty as well as the damage caused by the trojan. Meanwhile, the resource-constrained defender must decide on the best testing strategy that allows optimizing its overall utility which accounts for both damages and the fines. The proposed game is based on the robust behavioral framework of prospect theory (PT) which allows capturing the potential uncertainty, risk, and irrational behavior in the decision making of both the attacker and defender. For both the standard rational expected utility (EUT) case and the PT case, a novel algorithm based on fictitious play is proposed and shown to converge to a mixed-strategy Nash equilibrium. For an illustrative case study, thorough analytical results are derived for both EUT and PT to study the properties of the reached equilibrium as well as the impact of key system parameters such as the defender-set fine. Simulation results assess the performance of the proposed framework under both EUT and PT and show that the use of PT will provide invaluable insights on the outcomes of the proposed hardware trojan game, in particular, and system security, in general. Google Scholar

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Title: Matching Theory for Distributed User Association and Resource Allocation in Cognitive Femtocell Networks

Authors: Tuan LeAnh, Nguyen H. Tran, Walid Saad, Long Bao Le, Dusit Niyato,Tai Manh Ho, Choong Seon Hong

Abstract: In this paper, a novel framework is proposed to jointly optimize user association and resource allocation in the uplink cognitive femtocell network (CFN). In the considered CFN, femtocell base stations (FBSs) are deployed to serve a set of femtocell user equipments (FUEs) by reusing subchannels used in a macrocell base station (MBS). The problem of joint user association, subchannel assignment, and power allocation is formulated as an optimization problem, in which the goal is to maximize the overall uplink throughput while guaranteeing FBSs overloading avoidance, data rate requirements of the served FUEs, and MBS protection. To solve this problem, a distributed framework based on the matching game is proposed to model and analyze the interactions between the FUEs and FBSs. Using this framework, distributed algorithms are developed to enable the CFN to make decisions about user association, subchannel allocation, and transmit power. The algorithms are then shown to converge to a stable matching and exhibit a low computational complexity. Simulation results show that the proposed approach yields a performance improvement in terms of the overall network throughput and outage probability, with a small number of iterations to converge. Google Scholar

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Title: Stochastic Coalitional Games for Cooperative Random Access in M2M Communications

Authors: Mehdi Naderi Soorki, Walid Saad, Mohammad Hossein Manshaei, Hossein Saidi

Abstract: In this paper, the problem of random access contention between machine type devices (MTDs) in the uplink of a wireless cellular network is studied. In particular, the possibility of forming cooperative groups to coordinate the MTDs’ requests for the random access channel (RACH) is analyzed. The problem is formulated as a stochastic coalition formation game in which the MTDs are the players that seek to form cooperative coalitions to optimize a utility function that captures each MTD’s energy consumption and time-varying queue length. Within each coalition, an MTD acts as a coalition head that sends the access requests of the coalition members over the RACH. One key feature of this game is its ability to cope with stochastic environments in which the arrival requests of MTDs and the packet success rate over RACH are dynamically time-varying. The proposed stochastic coalitional game is composed of multiple stages, each of which corresponds to a coalitional game in stochastic characteristic form that is played by the MTDs at each time step. To solve this game, a novel distributed coalition formation algorithm is proposed and shown to converge to a stable MTD partition. Simulation results show that, on the average, the proposed stochastic coalition formation algorithm can reduce the average fail ratio and energy consumption of up to 36% and 31% for a cluster-based distribution of MTDs, respectively, compared with a noncooperative case. Moreover, when the MTDs are more sensitive to the energy consumption (queue length), the coalitions’ size will increase (decrease). Google Scholar

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Title: Optimal Transport Theory for Cell Association in UAV-Enabled Cellular Networks

Authors: Mohammad Mozaffari,Walid Saad, Mehdi Bennis, Mérouane Debbah

Abstract: In this letter, a novel framework for delay-optimal cell association in unmanned aerial vehicle (UAV)-enabled wireless cellular networks is proposed. In particular, to minimize the average network delay under any arbitrary spatial distribution of the ground users, the optimal cell partitions of the UAVs and terrestrial base stations are determined. To this end, using the powerful mathematical tools of optimal transport theory, the existence of the solution to the optimal cell association problem is proved and the solution space is completely characterized. The analytical and simulation results show that the proposed approach yields substantial improvements in terms of the average network delay. Google Scholar

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Title: Inter-Operator Resource Management for Millimeter Wave Multi-Hop Backhaul Networks

Authors: Omid Semiari, Walid Saad, Mehdi Bennis, Zaher Dawy

Abstract: In this paper, a novel framework is proposed for optimizing the operation and performance of a large-scale multi-hop millimeter wave (mmW) backhaul within a wireless small cell network having multiple mobile network operators (MNOs). The proposed framework enables the small base stations to jointly decide on forming the multi-hop, mmW links over backhaul infrastructure that belongs to multiple, independent MNOs, while properly allocating resources across those links. In this regard, the problem is addressed using a novel framework based on matching theory composed of two, highly inter-related stages: a multi-hop network formation stage and a resource management stage. One unique feature of this framework is that it jointly accounts for both wireless channel characteristics and economic factors during both network formation and resource management. The multi-hop network formation stage is formulated as a one-to-many matching game, which is solved using a novel algorithm, that builds on the so-called deferred acceptance algorithm and is shown to yield a stable and Pareto optimal multi-hop mmW backhaul network. Then, a one-to-many matching game is formulated to enable proper resource allocation across the formed multi-hop network. This game is then shown to exhibit peer effects and, as such, a novel algorithm is developed to find a stable and optimal resource management solution that can properly cope with these peer effects. Simulation results show that, with manageable complexity, the proposed framework yields substantial gains, in terms of the average sum rate, reaching up to 27% and 54%, respectively, compared with a non-cooperative scheme in which inter-operator sharing is not allowed and a random allocation approach. The results also show that our framework improves the statistics of the backhaul sum rate and provides insights on how to manage pricing and the cost of the cooperative mmW backhaul network for the MNOs. Google Scholar

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Title: The 5G Cellular Backhaul Management Dilemma: To Cache or to Serve

Authors: Kenza Hamidouche, Walid Saad, Mérouane Debbah, Ju Bin Song, Choong Seon Hong

Abstract: To reap the benefits of cache-enabled small cell networks, new backaul management mechanisms are needed to prevent the predicted files that are downloaded at the small base stations (SBSs) for caching purposes from jeopardizing the urgent requests that need to be served via the backhaul. Such mechanisms must account for the heterogeneity of the backhaul that will encompass both wireless backhaul links (at various frequency bands) and a wired backhaul component. In this paper, the heterogeneous backhaul management problem is formulated as a minority game in which each SBS has to define the number of predicted files to download, without affecting the required transmission rate of the current requests. For the formulated game, it is shown that a unique fair proper mixed Nash equilibrium (PMNE) exists. A self-organizing reinforcement learning algorithm is then proposed and shown to converge to a unique Boltzmann-Gibbs equilibrium, which approximates the desired PMNE. Simulation results show that the performance of the proposed approach can be close to that of the ideal optimal algorithm while it outperforms a centralized greedy approach in terms of the amount of data that is cached without jeopardizing the quality-of-service of current requests. Google Scholar

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Title: Dynamic Clustering and User Association in Wireless Small-Cell Networks With Social Considerations

Authors: Muhammad Ikram Ashraf ; Mehdi Bennis ; Walid Saad ; Marcos Katz ; Choong-Seon Hong

Abstract: In this paper, a novel social network-aware user association in wireless small cell networks with underlaid deviceto-device (D2D) communication is investigated. The proposed approach exploits strategic social relationships between user equipments (TIEs) and their physical proximity to optimize the overall network performance. This problem is formulated as a matching game between TIEs and their serving nodes (SNs) in which, an SN can be a small cell base station (SCBS) or an important UE with D2D capabilities. The problem is cast as a many-to-one matching game in which TIEs and SNs rank one another using preference relations that capture both the wireless aspects (i.e., received signal strength, traffic load, etc.) and users' social ties (e.g., TIE proximity and social distance). Due to the combinatorial nature of the network-wide TIE-SN matching, the problem is decomposed into a dynamic clustering problem in which SCBSs are grouped into disjoint clusters based on mutual interference. Subsequently, an TIE-SN matching game is carried out per cluster. The game under consideration is shown to belong to a class of matching games with externalities arising from interference and peer effects due to users social distance, enabling TIEs and SNs to interact with one another until reaching a stable matching. Simulation results show that the proposed social-aware user association approach yields significant performance gains, reaching up to 26%, 24%, and 31% for 5th, 50th, and 95th percentiles for TIE throughputs, respectively, as compared to the classical social-unaware baseline. Google Scholar

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Title: Joint Millimeter Wave and Microwave Resources Allocation in Cellular Networks With Dual-Mode Base Stations

Authors: Omid Semiar, Walid Saad, Mehdi Bennis

Abstract: The use of dual-mode base stations that can jointly exploit millimeter wave (mmW) and microwave (μW) resources is a promising solution for overcoming the uncertainty of the mmW environment. In this paper, a novel dual-mode scheduling framework is proposed that jointly performs user applications (UAs) selection and scheduling over μW and mmW bands. The proposed scheduling framework allows multiple UAs to run simultaneously on each user equipment (UE) and utilizes a set of context information, including the channel state information per UE, the delay tolerance and required load per UA, and the uncertainty of mmW channels, to maximize the quality-of-service (QoS) per UA. The dual-mode scheduling problem is then formulated as an optimization problem with minimum unsatisfied relations problem, which is shown to be challenging to solve. Consequently, a long-term scheduling framework, consisting of two stages, is proposed. Within this framework, first, the joint UA selection and scheduling over the μW band is formulated as a one-to-many matching game between the μW resources and UAs. To solve this problem, a novel scheduling algorithm is proposed and shown to yield a two-sided stable resource allocation. Second, over the mmW band, the joint contextaware UA selection and scheduling problem is formulated as a 0-1 Knapsack problem and a novel algorithm that builds on the Q-learning algorithm is proposed to find a suitable mmW scheduling policy while adaptively learning the UEs' line-of-sight probabilities. Furthermore, it is shown that the proposed scheduling framework can find an effective scheduling solution, over both μW and mmW, in polynomial time. Simulation results show that, compared with conventional scheduling schemes, the proposed approach significantly increases the number of satisfied UAs while improving the statistics of QoS violations and enhancing the overall users' quality-of-experience. Google Scholar

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Title: Offloading in HetNet: A Coordination of Interference Mitigation, User Association, and Resource Allocation

Authors: Thant Zin Oo, Nguyen H. Tran, Walid Saad, Dusit Niyato, Zhu Han, Choong Seon Hong

Abstract: The use of heterogeneous small cell-based networks to offload the traffic of existing cellular systems has recently attracted significant attention. One main challenge is solving the joint problems of interference mitigation, user association, and resource allocation. These problems are formulated as an optimization which is then analyzed using two different approaches: Markov approximation and log-linear learning. However, finding the optimal solutions of both approaches requires complete information of the whole network which is not scalable with the network size. Thus, an approach based on a Markov approximation with a novel Markov chain design and transition probabilities is proposed. This approach enables the Markov chain to converge to the bounded near optimal distribution without complete information. In the game-theoretic approach, the payoff-based log-linear learning is used, and it converges in probability to a mixed-strategy ε-Nash equilibrium. Based on the principles of these two approaches, a highly randomized self-organizing algorithm is proposed to reduce the gap between optimal and converged distributions. Simulation results show that all of the proposed algorithms effectively offload more than 90 percent of the traffic from the macrocell base station to small cell base stations. Moreover, the results also show that the algorithms converge quickly irrespective of the number of possible configurations. Google Scholar

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Title: Echo State Networks for Proactive Caching in Cloud-Based Radio Access Networks With Mobile Users

Authors: Mingzhe Chen,Walid Saad, Changchuan Yin, Mérouane Debbah

Abstract: In this paper, the problem of proactive caching is studied for cloud radio access networks (CRANs). In the studied model, the baseband units (BBUs) can predict the content request distribution and mobility pattern of each user and determine which content to cache at remote radio heads and the BBUs. This problem is formulated as an optimization problem, which jointly incorporates backhaul and fronthaul loads and content caching. To solve this problem, an algorithm that combines the machine learning framework of echo state networks (ESNs) with sublinear algorithms is proposed. Using ESNs, the BBUs can predict each user's content request distribution and mobility pattern while having only limited information on the network's and user's state. In order to predict each user's periodic mobility pattern with minimal complexity, the memory capacity of the corresponding ESN is derived for a periodic input. This memory capacity is shown to capture the maximum amount of user information needed for the proposed ESN model. Then, a sublinear algorithm is proposed to determine which content to cache while using limited content request distribution samples. Simulation results using real data from Youku and the Beijing University of Posts and Telecommunications show that the proposed approach yields significant gains, in terms of sum effective capacity, that reach up to 27.8% and 30.7%, respectively, compared with two baseline algorithms: random caching with clustering and random caching without clustering. Google Scholar

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Title: Fuzzy-Based Game Theoretic Mobility Management for Energy Efficient Operation in HetNets

Authors: Karthik Vasudeva; Sener Dikmese; İsmail Güven; Abolfazl Mehbodniya; Walid Saad; Fumiyuki Adachi

Abstract: The dense deployment of heterogeneous networks (HetNets) has shown to be a promising direction to cope with the capacity demands in the future 5G wireless networks. The large number of small cell base stations (SBSs) in HetNets intended to help in achieving the capacity requirement of 5G networks can also result in a significant increase in energy consumption. This is due to the fact that there might be few associated users in certain SBSs, intelligently switching them to low energy consumption modes, or turning them off without seriously degrading system capacity is desirable in order to improve the energy savings in the HetNets. Also, the unnecessary handovers caused due to this dynamic power level switching in the SBS should not be neglected. In this paper, fuzzy logic-based game-theoretic framework is utilized to address these issues and examine the energy efficiency improvements in HetNets. We design fuzzy inference rules for handover decisions, and target base station selection is performed through a fuzzy ranking technique, while simultaneously considering both energy/spectral efficiency and signaling overhead. The results show that energy consumption can be improved considerably especially for high user velocities, while also managing ping-pong handovers. Google Scholar

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Title: Caching in the Sky: Proactive Deployment of Cache-Enabled Unmanned Aerial Vehicles for Optimized Quality-of-Experience

Authors: Mingzhe Chen, Mohammad Mozaffari,Walid Saad, Changchuan Yin, Mérouane Debbah, Choong Seon Hong

Abstract: In this paper, the problem of proactive deployment of cache-enabled unmanned aerial vehicles (UAVs) for optimizing the quality-of-experience (QoE) of wireless devices in a cloud radio access network is studied. In the considered model, the network can leverage human-centric information, such as users' visited locations, requested contents, gender, job, and device type to predict the content request distribution, and mobility pattern of each user. Then, given these behavior predictions, the proposed approach seeks to find the user-UAV associations, the optimal UAVs' locations, and the contents to cache at UAVs. This problem is formulated as an optimization problem whose goal is to maximize the users' QoE while minimizing the transmit power used by the UAVs. To solve this problem, a novel algorithm based on the machine learning framework of conceptor-based echo state networks (ESNs) is proposed. Using ESNs, the network can effectively predict each user's content request distribution and its mobility pattern when limited information on the states of users and the network is available. Based on the predictions of the users' content request distribution and their mobility patterns, we derive the optimal locations of UAVs as well as the content to cache at UAVs. Simulation results using real pedestrian mobility patterns from BUPT and actual content transmission data from Youku show that the proposed algorithm can yield 33.3% and 59.6% gains, respectively, in terms of the average transmit power and the percentage of the users with satisfied QoE compared with a benchmark algorithm without caching and a benchmark solution without UAVs. Google Scholar

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Title: Online Ski Rental for ON/OFF Scheduling of Energy Harvesting Base Stations

Authors: Gilsoo Lee,Walid Saad, Mehdi Bennis, Abolfazl Mehbodniya, Fumiyuki Adachi

Abstract: The co-existence of small cell base stations (SBSs) with conventional macrocell base station is a promising approach to boost the capacity and coverage of cellular networks. However, densifying the network with a viral deployment of SBSs can significantly increase energy consumption. To reduce the reliance on unsustainable energy sources, one can adopt self-powered SBSs that rely solely on energy harvesting. Due to the uncertainty of energy arrival and the finite capacity of energy storage systems, self-powered SBSs must smartly optimize their ON and OFF schedule. In this paper, the problem of ON/OFF scheduling of self-powered SBSs is studied, in the presence of energy harvesting uncertainty with the goal of minimizing the operational costs consisting of energy consumption and transmission delay of a network. For the original problem, we show that an algorithm can solve the problem in the illustrative case. Then, to reduce the complexity of the original problem, an approximation is proposed. To solve the approximated problem, a novel approach based on the ski rental framework, a powerful online optimization tool, is proposed. Using this approach, each SBS can effectively decide on its ON/OFF schedule autonomously, without any prior information on future energy arrivals. By using competitive analysis, a deterministic online algorithm and a randomized online algorithm (ROA) are developed. The ROA is then shown to achieve the optimal competitive ratio in the approximation problem. Simulation results show that, compared with a baseline approach, the ROA can yield performance gains reaching up to 15.6% in terms of reduced total energy consumption of SBSs and up to 20.6% in terms of per-SBS network delay reduction. The results also shed light on the fundamental aspects that impact the ON time of SBSs while demonstrating that the proposed ROA can reduce up to 69.9% the total cost compared with a baseline approach. Google Scholar

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Title: Toward Massive Machine Type Cellular Communications

Authors: Zaher Dawy, Walid Saad, Arunabha Ghosh, Jeffrey G. Andrews, Elias Yaacoub

Abstract: Cellular networks have been engineered and optimized to carrying ever-increasing amounts of mobile data, but over the last few years, a new class of applications based on machine-centric communications has begun to emerge. Automated devices such as sensors, tracking devices, and meters, often referred to as machine-to-machine (M2M) or machine-type communications (MTC), introduce an attractive revenue stream for mobile network operators, if a massive number of them can be efficiently supported. The novel technical challenges posed by MTC applications include increased overhead and control signaling as well as diverse application-specific constraints such as ultra-low complexity, extreme energy efficiency, critical timing, and continuous data intensive uploading. This article explains the new requirements and challenges that large-scale MTC applications introduce, and provides a survey of key techniques for overcoming them. We focus on the potential of 4.5G and 5G networks to serve both the high data rate needs of conventional human-type communication (HTC) subscribers and the forecasted billions of new MTC devices. We also opine on attractive economic models that will enable this new class of cellular subscribers to grow to its full potential. Google Scholar

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Title:A Multi-Game Framework for Harmonized LTE-U and WiFi Coexistence over Unlicensed Bands

Authors: Kenza Hamidouche, Walid Saad, Mérouane Debbah

Abstract:The introduction of LTE over unlicensed bands (LTE-U) will enable LTE base stations to boost their capacity and offload their traffic by exploiting the underused unlicensed bands. However, to reap the benefits of LTE-U, it is necessary to address various new challenges associated with LTE-U and WiFi coexistence. In particular, new resource management techniques must be developed to optimize the usage of the network resources while handling the interdependence between WiFi and LTE users and ensuring that WiFi users are not jeopardized. To this end, in this article, a new game theoretic tool, dubbed the multi-game framework, is proposed as a promising approach for modeling resource allocation problems in LTE-U. In such a framework, multiple coexisting and coupled games across heterogeneous channels can be formulated to capture the specific characteristics of LTE-U. Such games can be of different properties and types, but their outcomes are largely interdependent. After introducing the basics of the multi-game framework, two classes of algorithms are outlined to achieve the new solution concepts of multi-games. Simulation results are then conducted to show how such a multi-game can effectively capture the specific properties of LTE-U and make of it a “friendly” neighbor to WiFi. Google Scholar

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Title: Echo State Networks for Self-Organizing Resource Allocation in LTE-U With Uplink–Downlink Decoupling

Authors: Mingzhe Chen,Walid Saad, Changchuan Yin

Abstract: Uplink-downlink decoupling in which users can be associated to different base stations in the uplink and downlink of heterogeneous small cell networks (SCNs) has attracted significant attention recently. However, most existing works focus on simple association mechanisms in LTE SCNs that operate only in the licensed band. In contrast, in this paper, the problem of resource allocation with uplink-downlink decoupling is studied for an SCN that incorporates LTE in the unlicensed band. Here, the users can access both licensed and unlicensed bands while being associated to different base stations. This problem is formulated as a noncooperative game that incorporates user association, spectrum allocation, and load balancing. To solve this problem, a distributed algorithm based on the machine learning framework of echo state networks (ESNs) is proposed. This proposed algorithm allows the small base stations to autonomously choose their optimal resource allocation strategies given only limited information on the network's and users' states. It is shown that the proposed algorithm converges to a stationary mixed-strategy distribution, which constitutes a mixed strategy Nash equilibrium for their studied game. Simulation results show that the proposed approach yields significant gain, in terms of the sum-rate of the 50th percentile of users, that reaches up to 167% compared with a Q-learning algorithm. The results also show that the ESN significantly provides a considerable reduction of information exchange for the wireless network. Google Scholar

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Title: Leveraging Social Communities for Optimizing Cellular Device-to-Device Communications

Authors: Md Abdul Alim, Tianyi Pan, My T. Thai, Walid Saad

Abstract: Device-to-device (D2D) communications over the licensed wireless spectrum has been recently proposed as a promising technology to meet the capacity crunch of next generation cellular networks. However, due to the high mobility of cellular devices, establishing and ensuring the success of D2D transmission become a major challenge. To this end, in this paper, a novel framework is proposed to enable devices to form multi-hop D2D connections in an effort to maintain sustainable communication in the presence of device mobility. To solve the problem posed by device mobility, in contrast to existing works, which mostly focus on physical domain information, a durable community-based approach is introduced taking social encounters into context. It is shown that the proposed scheme can derive an optimal solution for time sensitive content transmission while also minimizing the cost that the base station pays in order to incentivize users to participate in D2D. Simulation results show that the proposed social community aware approach yields significant performance gain, in terms of the amount of traffic offloaded from the cellular network to the D2D tier, compared with the classical social-unaware methods. Google Scholar

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Title: Overlapping coalition formation games for emerging communication networks

Authors: Tianyu Wang, Lingyang Song, Zhu Han, Walid Saad

Abstract: Modern cellular networks are witnessing an unprecedented evolution from classical centralized and homogenous architectures into a mix of various technologies, in which the network devices are densely and randomly deployed in a decentralized and heterogenous architecture. This shift in network architecture requires network devices to become more autonomous and, potentially, cooperate with one another. Such cooperation can, for example, take place between interfering small access points that seek to coordinate their radio resource allocation, nearby single-antenna users that can cooperatively perform virtual MIMO communications, or even unlicensed users that wish to cooperatively sense the spectrum of licensed users. Such cooperative mechanisms involve the simultaneous sharing and distribution of resources among a number of overlapping cooperative groups or coalitions. In this article, a novel mathematical framework from cooperative games, dubbed overlapping coalition formation games (OCF games), is introduced to model and solve such cooperative scenarios. First, the concepts of OCF games are presented, and then several algorithmic aspects are studied for two main classes of OCF games. Subsequently, two example applications, interference management and cooperative spectrum sensing, are discussed in detail to show how the proposed models and algorithms can be used in future scenarios of wireless systems. Finally, we conclude by providing an overview on future directions and applications of OCF games. Google Scholar

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Title: Efficient Deployment of Multiple Unmanned Aerial Vehicles for Optimal Wireless Coverage

Authors: Mohammad Mozaffari,Walid Saad, Mehdi Bennis, Mérouane Debbah

Abstract: In this letter, the efficient deployment of multiple unmanned aerial vehicles (UAVs) acting as wireless base stations that provide coverage for ground users is analyzed. First, the downlink coverage probability for UAVs as a function of the altitude and the antenna gain is derived. Next, using circle packing theory, the 3-D locations of the UAVs is determined in a way that the total coverage area is maximized while maximizing the coverage lifetime of the UAVs. Our results show that, in order to mitigate interference, the altitude of the UAVs must be properly adjusted based on the beamwidth of the directional antenna as well as coverage requirements. Furthermore, the minimum number of UAVs needed to guarantee a target coverage probability for a given geographical area is determined. Numerical results evaluate various tradeoffs. Google Scholar

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Dr. Yaling Yang

Title: -P2 -SAS: Privacy-Preserving Centralized Dynamic Spectrum Access System

Authors: Yanzhi Dou, Kexiong Zeng, He Li, Yaling Yang

Abstract: Centralized spectrum management is one of the key dynamic spectrum access (DSA) mechanisms proposed to govern the spectrum sharing between government incumbent users (IUs) and commercial secondary users (SUs). In the current centralized DSA designs, the operation data of both government IUs and commercial SUs need to be shared with a central server. However, the operation data of government IUs are often classified information and the SU operation data may also be commercial secrets. The current system design dissatisfies the privacy requirement of both IUs and SUs, since the central server is not necessarily trustworthy for holding such sensitive operation data. To address the privacy issue, this paper presents a privacy-preserving centralized DSA system (P2-SAS), which realizes the complex spectrum allocation process of DSA through efficient secure multi-party computation. In P2-SAS, none of the IU or SU operation data would be exposed to any snooping party, including the central server itself. We formally prove the correctness and privacy-preserving property of P2-SAS and evaluate its scalability and practicality using experiments based on real-world data. Experiment results show that P2-SAS can respond an SU's spectrum request in 6.96 s with communication overhead of less than 4 MB. Google Scholar

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2017 Conferences

Dr. R. Michael Buehrer | Dr. A.A. Louis Beex | Dr. T. Charles Clancy | Dr. Harpreet Dhillon | Dr. Carl B. Dietrich | Dr. Y. Thomas Hou
Dr. Allen B. MacKenzie | Dr. Vuk Marojevic | Dr. Jung-Min "Jerry" Park | Dr. Jeffrey H. Reed | Dr. Walid Saad | Dr. Yaling Yang

Dr. R. Michael Buehrer

Conference: 2017 IEEE International Conference on Communications (ICC)

Title: Bandit strategies for blindly attacking networks

Authors: S. Amuru, R. M. Buehrer, M. van der Schaar

Abstract:

Can we optimally attack networks (in terms of disrupting the ability of the nodes in the network from communicating) when the network topology is unknown? In this paper, we show that it is not always possible to do so when the network topology is unknown a priori. Specifically, we develop multi armed bandit-based techniques that enable the attacker to learn the best network attack strategies and also discuss the potential limitations that the attacker faces in such blind scenarios. Google Scholar

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Conference: 2017 IEEE International Conference on Communications Workshops (ICC Workshops)

Title: Towards a characterization of localization performance in networks with random geometries,

Authors: C. E. O'Lone, R. M. Buehrer

Abstract:

Localization in cellular networks has become a topic of great interest. With increased cell phone use indoors, as well as in urban canyons, an unobstructed view of GPS satellites is becoming less common. In order to localize in the presence of these increasingly complex environments, reliance on the network infrastructure for localization purposes has become necessary. As a consequence, localization in cellular networks, in the absence of GPS, has begun to garner attention. As these networks were originally designed for communication purposes, a complete analytical characterization of these types of networks, regarding their viability for the purposes of localization, has yet to be presented. Google Scholar

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Conference: 2017 IEEE Wireless Communications and Networking Conference (WCNC)

Title: Sensitivity Analysis of Localization Using Discrete Astronomical Radio Sources

Authors: Gaber, R. H. Tillman, R. M. Buehrer, S. Ellingson

Abstract: Although GPS is the most common method used for localization, it is sometimes insufficient due to its unavailability or unreliability. Therefore, signals of opportunity (SOP) arise as a promising alternative solution in such situations. In this paper, we examine a new technique for determining the location of devices based on novel (and naturally occurring) signals of opportunity rather than a fixed infrastructure. Precisely, our technique is based on tracking the sidereal motion of discrete astronomical radio sources (e.g., supernova remnants or radio galaxies). Unlike other types of SOP and GPS alternatives, our technique has the advantage of using permanent sources. In other words, since the sources are naturally occurring, they have the advantage of being permanent; they can't be disabled or shot down, and don't have any maintenance issues. These sources are also readily detectable at radio frequencies over a continuous range from HF through SHF, making jamming difficult. Given two antennas acting as an interferometer, the fringe rate (the rate at which the phase of the correlation of the discrete astronomical radio source being tracked for localization purposes changes) is estimated, and used for identifying the interferometer location in latitude and longitude. In this paper, building on our previous work, we perform a sensitivity analysis of our proposed technique. Specifically, we examine the impact of the baseline geometry, the estimation of the interferometer baseline, and the impact of the specific fringe rate value on the performance of the technique. Our results demonstrate the potential usefulness of the technique. Google Scholar

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Dr. A. A. Louis Beex

Conference: 2017 IEEE EMBS International Conference on Biomedical & Health Informatics (BHI)

Title: Classification of ADHD and Non-ADHD using theta/beta power ratio features

Authors: J. L. L. Marcano, M. A. Bell, A. A. L. Beex

Abstract: As of today, ADHD is diagnosed through subjective evaluation of symptoms, which overlap with those of other conditions. To address this issue and increase the accuracy of diagnoses, quantitative methods for the diagnosis of ADHD have been developed in the last 20 years. Recently, the US FDA approved the use of one of these methods, the θ/β power ratio (TBPR), in a device intended to support the diagnosis of ADHD. The TBPR, along with classification algorithms, is used to investigate the effectiveness of TBPR as a feature to classify ADHD and Non-ADHD subjects. Google Scholar

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Dr. Charles Clancy

Conference: 2017 19th International Conference on Advanced Communication Technology (ICACT)

Title: Semi-supervised radio signal identification

Authors: Timothy J. O'Shea, Nathan West, Matthew Vondal, T. Charles Clancy

Abstract: Radio emitter recognition in dense multi-user environments is an important tool for optimizing spectrum utilization, identifying and minimizing interference, and enforcing spectrum policy. Radio data is readily available and easy to obtain from an antenna, but labeled and curated data is often scarce making supervised learning strategies difficult and time consuming in practice. We demonstrate that semi-supervised learning techniques can be used to scale learning beyond supervised datasets, allowing for discerning and recalling new radio signals by using sparse signal representations based on both unsupervised and supervised methods for nonlinear feature learning and clustering methods. Google Scholar

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Dr. Harpreet Dhillon

Conference: Wireless Communications and Networking Conference (WCNC)

Title: D2D Underlaid Cellular Networks with User Clusters: Load Balancing and Downlink Rate Analysis

Authors: Chiranjib Saha, Harpreet Shillon

Abstract: Abstract: In this paper we develop a comprehensive analytical framework for a cellular network enhanced with in-band device-to-device (D2D) communication capability where the D2D links reuse the downlink resources of the cellular links. The locations of the cellular base stations (BSs) are modeled as a Poisson point process (PPP). The user positions are modeled as a Thomas cluster process (TCP) to capture the inherent tendency of users to be located at close proximity to each other. The bandwidth allocated to D2D transmission is fixed and to cellular transmission is dynamic dependent on the load (the number of users) served by the macro BS. The users inside a cluster can either establish a D2D connection with a potential D2D transmitter (Tx) containing the file of interest within the same cluster if it is located closer than certain distance threshold or otherwise connects to the cellular network. By increasing this distance threshold, cellular traffic can be offloaded to D2D connections which in turn increases the interference from simultaneously active D2D Txs. We characterize the downlink rate coverage probability for this setup. Our analysis shows that there exists an optimum distance threshold for which rate coverage is maximized. Google Scholar

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Conference: Wireless Communications and Networking Conference Workshops (WCNCW),

Title: Stochastic Geometry Perspective of Unlicensed Operator in a CBRS System

Authors:Priyabrata Parid ,Harpreet S. Dhillon, Pavan Nuggehalli

Abstract: In this work, we model and analyze a cellular system that operates in the licensed band of the 3.5 GHz spectrum and consists of a licensed and an unlicensed operator. Using tools from stochastic geometry, we study the co-existence of these networks from the perspective of the unlicensed operator. We model the licensed base station (BS) locations as a homogeneous Poisson point process with protection zones (PZs) around each BS. Since the unlicensed BSs can not operate within PZs, their locations are modeled as a Poisson hole process. In addition, we also consider contention-based channel access mechanism for the unlicensed BSs. We provide useful lower bound for the medium access probability for a typical BS of the unlicensed operator. Further, approximate results for coverage probability are also presented, by effectively handling the correlation in the interference powers induced due to correlation in locations of the licensed and unlicensed BSs. Using the derived expressions, we study the effect of the density of licensed BSs on the average number of active unlicensed BSs per unit area and coverage probability for a typical unlicensed user. To the best of our knowledge, this work presents the first comprehensive stochastic geometry-based analysis of the CBRS system. Google Scholar

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Conference: Wireless Communications and Networking Conference (WCNC)

Title: Exact Characterization of Spatio-Temporal Joint Coverage Probability in Cellular Networks

Authors: Shankar Krishnan, Harpreet S. Dhillon

Abstract: In this paper, we characterize the joint coverage probability at two spatial locations in a cellular network. In particular, modeling the locations of cellular base stations (BSs) as a Poisson Point Process (PPP), we study interference correlation at two spatial locations L1 and L2 separated by a distance v, when user follows closest BS association policy at both spatial locations and moves from L1 to L2. With this user displacement, two scenarios can occur: i) the user is handed off to a new serving BS at L2, or ii) no handoff occurs and the user is served by the same BS at both locations. After providing intermediate results such as probability of handoff and distance distributions of the serving BS at the two user locations, we derive exact expressions for the joint coverage probability for any distance separation v. The exact analysis is not straightforward and involves a careful treatment of the neighborhood of the two spatial locations and the resulting handoff scenarios. As expected, joint coverage probability decreases with the separation in the two locations. Google Scholar

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Conference: Wireless Communications and Networking Conference (WCNC),

Title: k-Coverage Probability in a Finite Wireless Network

Authors: Mehrnaz Afshang ; Harpreet S. Dhillon

Abstract: We present a general mathematical framework to characterize the performance of an arbitrarily-located reference receiver in a finite wireless network. Modeling the locations of nodes as a uniform binomial point process (BPP), we derive the general k-coverage probability, which is the distribution of the signal-to-interference ratio (SIR) at the reference receiver when it connects to its k-th closest transmitting node. This k-coverage result for an arbitrarily- located reference receiver significantly generalizes existing works on finite networks, which usually assume that the reference receiver connects to a pre-selected transmitter located at a fixed distance that may not be a part of the BPP (ad hoc network setup). A particular special case of interest is that of k=1, which can be interpreted as the downlink coverage probability in a finite cellular network modeled as a BPP. To the best of our understanding, the exact characterization of this result for finite cellular networks is not known. The mathematical analysis of k-coverage probability is enabled by the derivation of joint distance distributions from interfering and serving nodes to the reference receiver. As expected, our results demonstrate that the k-coverage probability strongly depends upon the location of the reference receiver. This observation highlights the importance of location information of the reference receiver for the accurate analysis of finite wireless networks. Google Scholar

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Conference: Wireless Communications and Networking Conference (WCNC)

Title: New Stochastic Geometry-Based Analysis of Uplink Massive MIMO in Asymptotic Antenna Regime

Authors: Priyabrata Parida, Harpreet S. Dhillon

Abstract: In his seminal paper [1], Marzetta demonstrated that having sufficiently large number of antennas at the base stations (BSs) eliminates the deleterious effect of channel fading and additive noise while negating the effect of network interference. As termed by him, massive multiple input multiple output (MIMO) is one of the revolutionary approaches to achieve the steep targets of fifth generation wireless communication systems. On the other hand, adhering to the concept of network densification, the BS deployments are following increasingly irregular pattern. Hence, it is a mere inevitability that future wireless networks are going to be served by randomly deployed BSs with large number of antennas. Therefore, performance analysis of such networks is of prime importance. In recent years, stochastic geometry has emerged as a powerful tool to analyze such random networks that can be leveraged to analyze the massive MIMO network performance as well. Since for a massive MIMO system, involvement of uplink (UL) during channel state information (CSI) acquisition phase is unavoidable (assuming a time division duplexed (TDD) system), successful analysis of massive MIMO system hinges on accurate modeling and analysis of the UL. Google Scholar

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Conference: Information Theory and Applications Workshop (ITA),

Title: Poisson cluster process: Bridging the gap between PPP and 3GPP HetNet models

Authors: Chiranjib Saha, Mehrnaz Afshang, Harpreet S. Dhillon

Abstract: The growing complexity of heterogeneous cellular networks (HetNets) has necessitated the need to consider variety of user and base station (BS) configurations for realistic performance evaluation and system design. This is directly reflected in the HetNet simulation models considered by standardization bodies, such as the third generation partnership project (3GPP). Complementary to these simulation models, stochastic geometry-based approach modeling the user and BS locations as independent and homogeneous Poisson point processes (PPPs) has gained prominence in the past few years. Despite its success in revealing useful insights, this PPP-based model is not rich enough to capture all the spatial configurations that appear in real-world HetNet deployments (on which 3GPP simulation models are based). In this paper, we bridge the gap between the 3GPP simulation models and the popular PPP-based analytical model by developing a new unified HetNet model in which a fraction of users and some BS tiers are modeled as Poisson cluster processes (PCPs). This model captures both non-uniformity and coupling in the BS and user locations. For this setup, we derive exact expression for downlink coverage probability under maximum signal-to-interference ratio (SIR) cell association model. As intermediate results, we define and evaluate sum-product functionals for PPP and PCP. Special instances of the proposed model are shown to closely resemble different configurations considered in 3GPP HetNet models. Our results concretely demonstrate that the performance trends are highly sensitive to the assumptions made on the user and SBS configurations. Google Scholar

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Conference: Wireless Communications and Networking Conference (WCNC) Date of Conference: 19-22 March 2017

Title: Modeling and Analysis of Ambient RF Energy Harvesting in Networks with Secrecy Guard Zones

Authors: Mustafa A. Kishk, Harpreet S. Dhillon

Abstract: This paper studies the secrecy performance in wireless networks (primary network) overlaid with an ambient RF energy harvesting network (secondary network). The nodes in the secondary network are assumed to be solely powered by ambient RF energy harvested from transmissions of the primary network. We assume that the secondary nodes can eavesdrop on the primary transmissions due to which the primary network uses secrecy guard zones. The primary transmitter goes silent if any secondary receiver is detected within its guard zone. Using tools from stochastic geometry, we first derive the optimal guard zone radius that minimizes the probability of going silent while ensuring a predefined minimum secure connection probability. Clearly, when more secondary nodes are deployed, more primary transmitters will remain silent for a given guard zone radius, thus impacting the amount of energy harvested by the secondary network. This introduces an interesting coupling between the performance of the two networks. We study this coupling using tools from game theory and propose an algorithm that can assist the two networks to converge to Nash equilibrium. Our results demonstrate the convergence of the proposed algorithm to the Nash equilibrium in finite number of iterations. Overall, this work forms one of the few concrete works that symbiotically merge tools from stochastic geometry and game theory. Google Scholar

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Conference: 2017 IEEE Wireless Communications and Networking Conference (WCNC)

Title: A New Clustered HetNet Model to Accurately Characterize User-Centric Small Cell Deployments

Authors: Mehrnaz Afshang; Harpreet S. Dhillon

Abstract: This paper develops a comprehensive framework for the performance analysis of user-centric capacity-driven small cell deployments, where small cell BSs (SBSs) are deployed at the places of high user density, i.e., user hotspots. In order to incorporate the correlation between user and SBS locations, we model the geographical centers of user hotspots as a homogeneous Poisson point process (PPP) around which users and SBSs are clustered following two independent general distributions. The macrocell base station (BS) locations are modeled by an independent PPP. A key intermediate step of our analysis is the derivation of a new set of distance distributions, which enable the exact characterization of coverage probability and throughput. For numerical evaluation, we specialized the setup to the case where users and SBSs are clustered with two independent normal distributions. Our analysis demonstrates that as the number of SBSs reusing the same resource block increases (higher frequency reuse), coverage probability decreases whereas throughput increases. Thus the same resource block can be aggressively reused by more SBSs as long as the coverage probability remains acceptable. Google Scholar

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Dr. Carl Dietrich

Conference: Proceedings of the 22nd International Conference on 3D Web Technology

Title: Evaluating multi-view representations of a Web3D streaming server

Authors: Ayat Mohammed, Nicholas F Polys, Vuk Marojevic, Richard M Goff, Carl B Dietrich

Abstract: Analysis of multivariate data in space and time (spatio-temporal) has gained distinctive importance in all research domains. The development of new solutions that enhance massive 3D scientific visualizations on the Web is still growing. In this paper, we combine computing power, human visual perception and interaction and real-time Web3D rendering to develop a 3D visualization for multivariate data through CORNET-3D. CORNET-3D is a software tool, which dynamically displays live wireless signal spectra, i.e. magnitudes vs. radio frequency (RF), of cognitive radio nodes in the CORNET testbed through a browser. Real time visualization of the electromagnetic spectrum activities for wireless communications provides a visually perceivable representation of the cognitive radio nodes' power and occupancy in the frequency domain. This work compares user performance between three representations (views) of multivariate scientific data to mitigate the trade-off between proximity and occlusion in CORNET-3D. The three views are Colored-Spectrum, Colored-Bars and Colored-Spectrum-with-Bars. For both types of questions (power or bandwidth), the results show that it is easy for people to carry out visual discrimination in multi-variate data visualization using the Colored Spectrum-with-Bars view. But to get accurate judgments, the Colored spectrum view should be used. Google Scholar

 

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Conference: Wireless Communications and Networking Conference (WCNC), 2017 IEEE, 1-6

Title: Propagation Measurements at 5.8 GHz for Railroad Intelligent Transportation Systems

Authors: Thomas W Tedesso, Christopher Rowe, Christopher R Anderson, Carl B Dietrich

Abstract: Unprotected grade crossings encompass up to 80% of U.S. railroad grade crossings. Train-vehicle collision occurs about once every 90 minutes in the U.S.; these catastrophic accidents cause significant injury and financial losses and are attributed to drivers lack of awareness of approaching trains. Wireless early warning vehicle-to-vehicle and vehicle-to-infrastructure technologies have emerged rapidly in recent years, however, there have been very limited efforts to apply these to improve railroad crossing safety, in part due to a lack of knowledge of the unique propagation conditions encountered in railroad environments. In this paper, we present measurement results and empirical models for 5.8 GHz signal propagation in a railroad environment to investigate train-to-infrastructure communication links in both clear and cluttered environments. Over 10 000 measurements were recorded on two different test tracks for wayside transmitter heights between 2.0m and 12.2m and at train speeds of 20, 50, and 79 MPH. Large-scale path loss exponents ranged from 2.0 to 2.9; small-scale fading analysis indicated these signals experience Rician fading with K-factors ranging from 9.8-14.0. Multipath analysis demonstrated that RMS Delay Spreads ranged from nearly zero to a maximum of 260 nsec; RMS Doppler Spreads ranged from 310-1130 Hz. These data suggest that signals at this frequency, even in moderately cluttered environments, should be able to operate over relatively long distances and experience minimal fading or spectral distortion. Google Scholar

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Conference: Consumer Communications & Networking Conference (CCNC), 2017 14th IEEE Annual

Title: Analysis of directional antenna for railroad crossing safety applications

Authors: X. Ma and S. Guha and J. Choi and C. R. Anderson and R. Nealy and J. Withers and J. H. Reed and C. Dietrich

Abstract: A rapidly deployable and cost-effective railroad crossing early warning system integrated  with the railway system is attractive due to its protection of the unmanned grade crossings,  which requires a warning system with long-distance communication link. In this paper, we  investigate the problem of suitable antenna selection for such a railway warning system  First, the antenna criteria for railroad crossing safety applications are described based on  practical system considerations, the safe distances on the road and on the railway. Google Scholar

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Dr. Y. Thomas Hou

Conference: IEEE INFOCOM 2017 - IEEE Conference on Computer Communications

Title:When gene meets cloud: Enabling scalable and efficient range query on encrypted genomic data

Authors: Wenhai Sun, Ning Zhang, Wenjing Lou, Y. Thomas Hou

Abstract: As the cost of human full genome sequencing continues to fall, we will soon witness a prodigious amount of human genomic data in the public cloud. To protect the confidentiality of the genetic information of individuals, the data has to be encrypted at rest. On the other hand, encryption severely hinders the use of this valuable information, such as Genome-wide Range Query (GRQ), in medical/genomic research. While the problem of secure range query on outsourced encrypted data has been extensively studied, the current schemes are far from practical deployment in terms of efficiency and scalability due to the data volume in human genome sequencing. In this paper, we investigate the problem of secure GRQ over human raw aligned genomic data in a third-party outsourcing model. Our solution contains a novel secure range query scheme based on multi-keyword symmetric searchable encryption (MSSE). The proposed scheme incurs minimal ciphertext expansion and computation overhead. We also present a hierarchical GRQ-oriented secure index structure tailored for efficient and large-scale genomic data lookup in the cloud while preserving the query privacy. Our experiment on real human genomic data shows that a secure GRQ request with range size 100,000 over more than 300 million encrypted short reads takes less than 3 minutes, which is orders of magnitude faster than existing solutions. Google Scholar

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Conference :IEEE INFOCOM 2017 - IEEE Conference on Computer Communications

Title: Privacy-preserving pattern matching over encrypted genetic data in cloud computing

Authors: Bing Wang, Wei Song, Wenjing Lou, Y. Thomas Hou

Abstract: Personalized medicine performs diagnoses and treatments according to the DNA information of the patients. The new paradigm will change the health care model in the future. A doctor will perform the DNA sequence matching instead of the regular clinical laboratory tests to diagnose and medicate the diseases. Additionally, with the help of the affordable personal genomics services such as 23andMe, personalized medicine will be applied to a great population. Cloud computing will be the perfect computing model as the volume of the DNA data and the computation over it are often immense. However, due to the sensitivity, the DNA data should be encrypted before being outsourced into the cloud. In this paper, we start from a practical system model of the personalize medicine and present a solution for the secure DNA sequence matching problem in cloud computing. Comparing with the existing solutions, our scheme protects the DNA data privacy as well as the search pattern to provide a better privacy guarantee. We have proved that our scheme is secure under the well-defined cryptographic assumption, i.e., the sub-group decision assumption over a bilinear group. Unlike the existing interactive schemes, our scheme requires only one round of communication, which is critical in practical application scenarios. We also carry out a simulation study using the real-world DNA data to evaluate the performance of our scheme. The simulation results show that the computation overhead for real world problems is practical, and the communication cost is small. Furthermore, our scheme is not limited to the genome matching problem but it applies to general privacy preserving pattern matching problems which is widely used in real world. Google Scholar

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Conference: 2017 IEEE International Conference on Communications (ICC)

Title: AugAuth: Shoulder-surfing resistant authentication for augmented reality

Authors: Ruide Zhang, Ning Zhang, Changlai Du, Wenjing Lou, Y. Thomas Hou, Yuichi Kawamoto

Abstract: As computing system continues to play an increasing role in daily life, user authentication is now an important component. One of the most widely accepted methods for user authentication is through proof of knowledge of a piece of secret information, such as password. However, entering this non-mutable secret for authentication in public space often allows attackers to steal the secret by shoulder surfing or video recording. We observe that it is possible to block attacker's access to user input using augmented reality (AR) display, which is only available to the user. Based on this intuition, we present AugAuth, an authentication scheme in AR using commercial off-the-shelf(COTS) gesture control sensors as an input device. AugAuth can resist against shoulder surfing by presenting user input interface that is only visible to the user and is unique every time. To enable user input with finger movement using the gesture control armband, Myo, we have solved several challenges in electromyogram signal processing, such as annotating the start of signal and finger classification. The experiment results for our input system of a group of volunteers show that our finger classification function has high accuracy and AugAuth is practical for use in real life authentication scenarios. Google Scholar

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Conference: 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

Title: Spectrum attacks aimed at minimizing spectrum opportunities

Authors: Andrey Garnaev ; Wade Trappe ; Y. Thomas Hou ; Wenjing Lou

Abstract: Unutilized spectrum, i.e. spectrum holes, are opportunities that may be used for communication or other RF services. In this paper, we explore adversarial attacks that reduce the size of spectrum holes by showing their advantage compared to a random jammer. Using a game-theoretical approach, we design an optimal scanning strategy that provides an increased probability of detecting such an attack. The advantage of our strategy is achieved by focusing scanning efforts on bands that are more likely to be attacked, and neglecting the others. However, such focused scanning is a disadvantage since, if the adversary has a different objective, he can safely sneak usage of the bands neglected by such a specially-tuned spectrum scanner. To deal with this problem, we also derive the optimal scanning allocation that balances between applying the anti-spectrum holes attack scanning strategy and scanning the neglected bands so as to prevent the possibility of the adversary using those bands without being detected. Google Scholar

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Conference: Consumer Communications & Networking Conference (CCNC), 2017 14th IEEE Annual

Title: Prototypes of using directional antenna for railroad crossing safety applications

Authors:X. Ma and S. Guha and J. Choi and C. R. Anderson and R. Nealy and J. Withers and J. H. Reed and C. Dietrich

Abstract: In this demonstration proposal, we present a prototype of a rapidly deployable and cost-effective railroad crossing early warning system integrated with the railway system. Specifically, the proposed demonstration deal with the safety applications based on dedicated short range communications (DSRC) protocol and devices using our different antennas. We will demonstrate the feasibility and advantages of our proposed system, including the antenna design, system deployment, the over-the-air transmission, and the software applications that we developed for the end users. Google Scholar

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Dr. Allen MacKenzie

Conference: Computer Communication and Networks (ICCCN), 2017 26th International Conference on Computer Communication and Networks

Title: Robust Controller Placement and Assignment in Software-Defined Cellular Networks

Authors: M. J. Abdel-Rahman, E. A. Mazied, K. Teague, A. B. MacKenzie and S. F. Midkiff

Abstract: Software-defined cellular networks (SDCN) have been recently introduced to enable flexible cellular network design that facilitates fulfilling 5G design requirements. Placement of controllers within the SDCN plays a crucial role in optimizing its performance. In this paper, we study the controller placement problem in SDCN, considering the uncertainty in cellular user locations. Specifically, our contributions are as follows. First, we develop C3P2, a static joint stochastic controller placement and evolved node B (eNB)- controller assignment problem. The objective of C3P2 is to minimize the number of controllers needed to control all eNBs, while ensuring that the response time to each eNB will exceed delta seconds with probability less than 1 - beta. Second, we develop CPPA, a joint stochastic controller placement and adaptive eNB controller assignment problem. In contrast to C3P2, in CPPA the eNB controller assignment adapts to variations in the eNB request rates, resulting from the variations in the cellular user locations. Finally, we use sample average approximation combined with various linearization techniques to solve and evaluate C3P2 and CPPA under various system parameters. Our results demonstrate the advantages of (i) joint compared to sequential optimization, (ii) stochastic compared to deterministic optimization, and (iii) adaptive compared to static optimization. Google Scholar

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Conference: 2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt)

Title: Optimal distributed allocation of almost blank subframes for LTE/WiFi coexistence

Authors: S. Chatterjee, M. J. Abdel-Rahman and A. B. MacKenzie

Abstract: Since LTE in unlicensed spectrum (LTE-U) was proposed by Qualcomm, it has drawn considerable interest because of its potential to increase the capacity of existing LTE networks by utilizing existing infrastructure in the unlicensed band. But, Wi-Fi technology, already operating in the unlicensed 5 GHz band, creates several potential challenges for managing the activities of these two different technologies in the same band. In this context, we propose an adaptive coexistence scheme between LTE and WiFi by utilizing almost blank subframes (ABS). An ABS is an LTE subframe of duration 1 ms (containing two time slots of 0.5 ms duration) with reduced downlink activity. LTE allocates ABSs over 20 MHz channels in 5 GHz band to allow WiFi to access the spectrum. In the proposed coexistence scheme, each LTE cell optimally distributes ABSs over the frame to provide certain quality of service (QoS) guarantees for WiFi traffic while ensuring the performance of its own users. Google Scholar

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Conference: 2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt)

Title: Joint access point deployment and assignment in mmWave networks with stochastic user orientation,

Authors: M. N. Soorki, M. J. Abdel-Rahman, A. MacKenzie and W. Saad

Abstract: Millimeter wave (mmWave) communication is a promising solution for providing high capacity wireless access to regions with high traffic demands. The main challenge of mmWave communications is the availability of directional line of sight links between access points and mobile devices which stochastically change due to high attenuation in mmWave propagation and severe blockage of mmWave links with obstacles such as human bodies. In this paper, a novel framework for optimizing the deployment of mmW access points, while being cognizant of the mobile devices orientation, is proposed. In the studied model, the locations of potential access points and users are assumed as predefined parameters while the orientation of the users is changing stochastically. To minimize the number of access points while satisfying the line of sight coverage of mobile devices, first, a joint access point placement and mobile device assignment problem is proposed, assuming that the orientation of each user is deterministically known. This formulation is then extended to the case in which the orientation of the user is stochastic. Finally, the proposed deterministic and stochastic joint access point placement and mobile device assignment schemes are evaluated under various system parameters. Simulation results demonstrate the advantage of the proposed stochastic scheme to the deterministic scheme, in terms of reducing the load on access points. Moreover, on average, the proposed stochastic scheme can increase the probability of user satisfaction up to 24% for 0.95 requested coverage probability compared to the deterministic case.Google Scholar

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Conference: Wireless Communications and Networking Conference (WCNC), 2017 IEEE

Title: On Stochastic Controller Placement in Software-Defined Wireless Networks

Authors:M. J. Abdel-Rahman, E. A. Mazied, A. MacKenzie, S. Midkiff, M. R. Rizk and M. El-Nainay

Abstract: Software-defined networking (SDN) abstracts and centralizes the network control functions in a software entity that runs on a server, known as SDN controller. The controller needs to respond to its controlled elements in a strictly timely manner, and the controller placement has a prominent effect on its response time. Originally, all SDN architectures assumed a physical wired connection between the SDN controller and its controlled elements, and the controller placement problem (CPP) has been only studied under such wired settings. Recently, novel SDN architectures have been proposed in which a direct wireless connection is assumed between the controller and its controlled elements. In this paper, we consider the 'wireless CPP,' when the link between the controller and the controlled element is wireless. Specifically, our contributions are as follows. First, we propose two joint controller placement and assignment formulations, assuming wired links between the controllers and their controlled elements; the first formulation considers an average response time constraint, whereas the second one considers a per-link response time constraint. Then, using chance- constrained stochastic programming (CCSP), we extend our formulation to the case when the links between the controllers and their controlled elements are wireless. Finally, we evaluate our joint placement and assignment schemes under various system parameters. Our results demonstrate the advantage of our joint scheme, in terms of reducing the required number of controllers, compared to a recent sequential assignment and placement scheme in the literature. They also show the ability of our CCSP-based scheme in probabilistically satisfying the controllers response time constraints. Google Scholar

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Conference: Virtualization and Programmability in Mobile Wireless Networks: Architecture and Resource Management, Proceedings of the Workshop on Mobile Edge Communications

Title: Virtualization and Programmability in Mobile Wireless Networks: Architecture and Resource Management

Authors: Kleber V Cardoso, Mohammad J Abdel-Rahman, Allen B MacKenzie, Luiz A DaSilva

Abstract: We present a high-level end-to-end architecture for virtualization and programmability in next-generation mobile wireless networks. Our architecture envisions three major players: Service Providers, who wish to orchestrate wireless networks with particular characteristics to support particular applications; Resource Providers, who contribute resources such as spectrum, access points, backhaul infrastructure, and computing; and Virtual Network Builders, who marshal resources into networks for Service Providers. We take into account resource sharing and investigate how virtualization and programmability affect resource management. We show that: (i) virtualization reduces cost significantly, (ii) this cost reduction does not degrade the user satisfaction, and (iii) non-virtualized networks need to keep a large amount of idle capacity to satisfy coverage. Link

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Dr. Vuk Marojevic

Conference: 2017 IEEE Wireless Communications and Networking Conference (WCNC)

Title: Software-Defined LTE Evolution Testbed Enabling Rapid Prototyping and Controlled Experimentation

Authors: Vuk Marojevic, Deven Chheda, Raghunandan M. Rao, Randall Nealy, Jung-Min Park, Jeffrey H. Reed

Abstract: The long-term evolution (LTE) has spread around the globe for deploying 4G cellular networks for commercial use. These days, it is gaining interest for new applications where mobile broadband services can be of benefit to society. Whereas the basic concepts of LTE are well understood, its long-term evolution has just started. New areas of R&D look into operation in unlicensed and shared bands, where new versions of LTE need to coexist with other communication systems and radars. Virginia Tech has developed an LTE testbed with unique features to spur LTE research and education. This paper introduces Virginia Tech's LTE testbed, its main features and components, access and configuration mechanisms, and some of the research thrusts that it enables. It is unique in several aspects, including the extensive use of software-defined radio technology, the combination of industry-grade hardware and software-based systems, and the remote access feature for user-defined configurations of experiments and radio frequency paths. Google Scholar

 

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Dr. Jung-Min "Jerry" Park

Conference: IEEE International Conference on Communications (ICC)

Title: Coexistence of DSRC and Wi-Fi: Impact on the performance of vehicular safety applications

Authors: J. Liu, G. Naik, and J. Park

Abstract: To adequately support high-throughput applications in next-generation WLANs, more spectrum will be needed to accommodate wider channels. To address this issue, spectrum regulators and stakeholders from the wireless industry and the intelligent transportation system communities are exploring possible band sharing approaches in the 5.9 GHz band. Such approaches include techniques that enable the harmonious coexistence of Dedicated Short Range Communications (DSRC) networks and IEEE 802.11ac networks. In this paper, we provide in-depth discussions on how the coexistence of DSRC and 802.11ac impacts the performance of DSRC applications, with a particular focus on vehicular safety applications. We propose an analytical model that provides valuable insights on DSRC network performance and its vulnerability to interference induced by other DSRC nodes as well as 802.11ac nodes. Using the analytical results derived from the model and extensive simulation results, we also propose a methodology for adjusting 802.11ac parameters that enables a DSRC network to meet the performance requirements of safety applications. Using simulations, we also analyze the throughput of the coexisting 802.11ac network. Google Scholar

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Conference: IEEE Int’l Conference on Computer Communications (INFOCOM)

Title: Coexistence of Dedicated Short Range Communications (DSRC) and Wi-Fi: Implications to Wi-Fi performance

Authors: ​G. Naik, J. Liu, and J. Park

Abstract: The 5.9 GHz band is being actively explored for possible spectrum sharing opportunities between Dedicated Short Range Communications (DSRC) and IEEE 802.11ac networks in order to address the increasing demand for bandwidth-intensive Wi-Fi applications. In this paper, we study the implications of this spectrum sharing to the performance of Wi-Fi systems. Through experiments performed on our testbed, we first investigate band sharing options available for Wi-Fi devices. Using experimental results, we show the need for using conservative Wi-Fi transmission parameters to enable harmonious coexistence between DSRC and Wi-Fi. Moreover, we show that under the current 802.11ac standard, certain channelization options, particularly the high bandwidth ones, cannot be used by Wi-Fi devices without causing interference to the DSRC nodes. Under these constraints, we propose a Real-time Channelization Algorithm (RCA) for Wi-Fi Access Points (APs) operating in the shared spectrum. Evaluation of the proposed algorithm using a prototype implementation on commodity hardware as well as via simulations show that informed channelization decisions can significantly increase Wi- Fi throughput compared to static channelization schemes. Google Scholar

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Conference: 2017 IEEE Int’l Symposium on Dynamic Spectrum Access Networks (DySPAN),

Title: TESSO: An analytical tool for characterizing aggregate interference and enabling spatial spectrum sharing

Authors: S. Bhattarai, J. Park, W. Lehr, B. Gao

Abstract: Radio propagation models play a crucial role in realizing effective spectrum sharing. Unlike propagation models that do not use the exact details of terrain, terrain-based propagation models are effective in identifying spatial spectrum sharing opportunities for the secondary users (SUs) around an incumbent user (IU). Unfortunately, terrain-based propagation models, such as the Irregular Terrain Model (ITM) in point-to-point (PTP) mode, are computationally expensive, and they require precise geo-locations of the SUs. Such requirements render them challenging, if not impractical, to implement in real-time applications, such as geolocation database (GDB)-driven spectrum sharing. To address this problem, we propose a pragmatic approach called Tool for Enabling Spatial Spectrum Sharing Opportunities (TESSO). TESSO characterizes the aggregate interference caused by the SUs and identifies spatial spectrum sharing opportunities effectively. It is computationally efficient, and does not require precise geo-locations of the SUs. Our results show that TESSO provides the same level of interference protection guarantee to the IU as that offered by the terrain-based models. TESSO can be implemented in GDB-driven spectrum sharing ecosystems for effectively exploiting spatial spectrum sharing opportunities. Google Scholar

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Dr. Jeffrey H. Reed

Conference: 2017 IEEE International Conference on Communications (ICC),

Title: On scalability and interference avoidance in nonlinear adjacent channel interference networks,

Authors: A. V. Padaki, R. Tandon and J. H. Reed

Abstract:

Wireless spectrum is a scare natural resource and maximizing its utilization is of at most importance to meet the ever increasing demands in data rate and bandwidth. Spectrum Sharing and Dynamic Spectrum Access (DSA) have been identified as key technologies to make efficient use of the spectrum [1]–[5]. With new spectrum opening up for sharing [6], [7], diverse Radio Access Technologies (RAT) and allied services will access the same spectrum band in the future. Google Scholar

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Conference: 2017 IEEE Wireless Communications and Networking Conference (WCNC)

Title: Software-Defined LTE Evolution Testbed Enabling Rapid Prototyping and Controlled Experimentation

Authors: V. Marojevic, D. Chheda, R. M. Rao, R. Nealy, J. M. Park and J. H. Reed

Abstract: The long-term evolution (LTE) has spread around the globe for deploying 4G cellular networks for commercial use. These days, it is gaining interest for new applications where mobile broadband services can be of benefit to society. Whereas the basic concepts of LTE are well understood, its long-term evolution has just started. New areas of R&D look into operation in unlicensed and shared bands, where new versions of LTE need to coexist with other communication systems and radars. Virginia Tech has developed an LTE testbed with unique features to spur LTE research and education. This paper introduces Virginia Tech's LTE testbed, its main features and components, access and configuration mechanisms, and some of the research thrusts that it enables. It is unique in several aspects, including the extensive use of software-defined radio technology, the combination of industry-grade hardware and software-based systems, and the remote access feature for user-defined configurations of experiments and radio frequency paths. Google Scholar

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Conference: 2017 14th IEEE Annual Consumer Communications & Networking Conference (CCNC)

Title: Analysis of directional antenna for railroad crossing safety applications

Authors: Xiaofu Ma, Sayantan Guha, Junsung Choi, Jeffrey H . Reed

Abstract:A rapidly deployable and cost-effective railroad crossing early warning system integrated with the railway system is attractive due to its protection of the unmanned grade crossings, which requires a warning system with long-distance communication link. In this paper, we investigate the problem of suitable antenna selection for such a railway warning system First, the antenna criteria for railroad crossing safety applications are described based on practical system considerations, the safe distances on the road and on the railway. Then, the optimal antenna pattern is derived theoretically to get the smallest size which fits for the practical installation. We also conducted a feasibility study of an array antenna through measurements on a near field scanner. Google Scholar

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Conference: Consumer Communications & Networking Conference (CCNC), 2017 14th IEEE Annual

Title: Prototypes of using directional antenna for railroad crossing safety applications

Authors: Xiaofu Ma, Sayantan Guha, Junsung Choi, Jeffrey H . Reed

Abstract:In this demonstration proposal, we present a prototype of a rapidly deployable and cost-effective railroad crossing early warning system integrated with the railway system. Specifically, the proposed demonstration deal with the safety applications based on dedicated short range communications (DSRC) protocol and devices using our different antennas. We will demonstrate the feasibility and advantages of our proposed system, including the antenna design, system deployment, the over-the-air transmission, and the software applications that we developed for the end users. Google Scholar

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Dr. Walid Saad

Conference: 2017 IEEE Symposium on Computers and Communications (ISCC)

Title: Truthful spectrum auction for efficient anti-jamming in cognitive radio networks

Authors: Mohammad Aghababaie, Alavijeh Behrouz Maham, Zhu Han, Walid Saad

Abstract: One significant challenge in cognitive radio networks is to design a framework in which the selfish secondary users are obliged to interact with each other truthfully. Moreover, due to the vulnerability of these networks against jamming attacks, designing anti-jamming defense mechanisms is equally important. In this paper, we propose a truthful mechanism, robust against the jamming, for a dynamic stochastic cognitive radio network consisting of several selfish secondary users and a malicious user. In this model, each secondary user participates in an auction and wish to use the unjammed spectrum, and the malicious user aims at jamming a channel by corrupting the communication link. A truthful auction mechanism is designed among the secondary users. Furthermore, a zero-sum game is formulated between the set of secondary users and the malicious user. This joint problem is then cast as a randomized two-level auctions in which the first auction allocates the vacant channels, and then the second one assigns the remaining unallocated channels. Simulation results show that the distributed algorithm can achieve a performance that is close to the centralized algorithm. Google Scholar

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Conference: European Wireless 2017; 23th European Wireless Conference

Title: Minority Games for Backhaul Management in Cache-Enabled Small Cell Networks

Authors: Kenza Hamidouche; Walid Saad; Merouane Debbah

Abstract: In this paper, a new backhaul management approach is proposed for cache-enabled small cell networks (SCNs). Such networks are composed of a set of small base stations (SBSs) that are equipped with storage units and have to serve predicted and current requests. The predicted requests are served from the cache of the SBSs and each SBS has to download the related files ahead of time, while the current requests are served by the SBSs instantaneously from the backhaul. Due to the capacity-limited backhaul links, the SBSs cannot serve all the files with a given required rate. Indeed, the higher is the number of requested files in the network, the lower is the assigned backhaul capacity to each SBS. Since the predicted files are not urgent, the number of related files that are requested by the SBSs must be limited by the total capacity of the backhaul links and the number of current requests. Moreover, the backhaul links of SCNs can be heterogeneous and thus they can encompass a number of technologies such as fiber optical, millimeter Wave and sub-6 GHz bands. This problem is formulated as a minority game in which each SBS has to define the number of predicted files to download at a given time period, without affecting the required transmission rate of the current requests. For the formulated game, it is shown that there exists a unique fair proper mixed Nash equilibrium. Simulation results show that users can experience a transmission rate that is up to 4 times higher than the allocated rate in the conventional model in which the SBSs request all their predicted files. Google Scholar

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Conference: European Wireless 2017; 23th European Wireless Conference

Title: Deep Learning for Proactive Resource Allocation in LTE-U Networks

Authors: Ursula Challita, Li Dong, Walid Saad

Abstract: LTE in unlicensed spectrum (LTE-U) is a promising approach to overcome the wireless spectrum scarcity. However, to reap the benefits of LTE-U, a fair coexistence mechanism with other incumbent WiFi deployments is required. In this paper, a novel deep learning approach is proposed for modeling the resource allocation problem of LTE-U small base stations (SBSs). The proposed approach enables multiple SBSs to perform dynamic channel selection, carrier aggregation, and fractional spectrum access proactively while guaranteeing fairness with existing WiFi networks and other LTE-U operators. SBSs are modeled as Homo Egualis agents that aim at predicting a sequence of future actions and thus achieving long-term equal weighted fairness with WLAN and other LTE-U operators over a given time horizon. Simulation results using real data traces show that the proposed scheme can yield up to 28% gains over a conventional reactive approach. The results also show that the proposed framework prevents WiFi performance degradation for a densely deployed LTE-U network. Google Scholar

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Conference: 2017 IEEE International Conference on Communications (ICC)

Title: An online secretary framework for fog network formation with minimal latency

Authors: Gilsoo Lee, Walid Saad, Mehdi Bennis

Abstract: Fog computing is seen as a promising approach to perform distributed, low-latency computation for supporting Internet of Things applications. However, due to the unpredictable arrival of available neighboring fog nodes, the dynamic formation of a fog network can be challenging. In essence, a given fog node must smartly select the set of neighboring fog nodes that can provide low-latency computations. In this paper, this problem of fog network formation and task distribution is studied considering a hybrid cloud-fog architecture. The goal of the proposed framework is to minimize the maximum computational latency by enabling a given fog node to form a suitable fog network, under uncertainty on the arrival process of neighboring fog nodes. To solve this problem, a novel approach based on the online secretary framework is proposed. To find the desired set of neighboring fog nodes, an online algorithm is developed to enable a task initiating fog node to decide on which other nodes can be used as part of its fog network, to offload computational tasks, without knowing any prior information on the future arrivals of those other nodes. Simulation results show that the proposed online algorithm can successfully select an optimal set of neighboring fog nodes while achieving a latency that is as small as the one resulting from an ideal, offline scheme that has complete knowledge of the system. The results also show how, using the proposed approach, the computational tasks can be properly distributed between the fog network and a remote cloud server. Google Scholar

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Conference: 2017 IEEE International Conference on Communications (ICC)

Title: Prospect theory for enhanced cyber-physical security of drone delivery systems: A network interdiction game

Authors: Anibal Sanjab, Walid Saad, Tamer Başar

Abstract: The use of unmanned aerial vehicles (UAVs) as delivery systems of online goods is rapidly becoming a global norm, as corroborated by Amazon's “Prime Air” and Google's “Project Wing” projects. However, the real-world deployment of such drone delivery systems faces many cyber-physical security challenges. In this paper, a novel mathematical framework for analyzing and enhancing the security of drone delivery systems is introduced. In this regard, a zero-sum network interdiction game is formulated between a vendor, operating a drone delivery system, and a malicious attacker. In this game, the vendor seeks to find the optimal path that its UAV should follow, to deliver a purchase from the vendor's warehouse to a customer location, to minimize the delivery time. Meanwhile, an attacker seeks to choose an optimal location to interdict the potential paths of the UAVs, so as to inflict cyber or physical damage to it, thus, maximizing its delivery time. First, the Nash equilibrium point of this game is characterized. Then, to capture the subjective behavior of both the vendor and attacker, new notions from prospect theory are incorporated into the game. These notions allow capturing the vendor's and attacker's (i) subjective perception of attack success probabilities, and (ii) their disparate subjective valuations of the achieved delivery times relative to a certain target delivery time. Simulation results have shown that the subjective decision making of the vendor and attacker leads to adopting risky path selection strategies which inflict delays to the delivery, thus, yielding unexpected delivery times which surpass the target delivery time set by the vendor. Google Scholar

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Conference: 2017 European Conference on Networks and Communications (EuCNC)

Title: Proactive edge computing in latency-constrained fog networks

Authors: Mohammed S. Elbamby, Mehdi Bennis, Walid Saad

Abstract: In this paper, the fundamental problem of distribution and proactive caching of computing tasks in fog networks is studied under latency and reliability constraints. In the proposed scenario, computing can be executed either locally at the user device or offloaded to an edge cloudlet. Moreover, cloudlets exploit both their computing and storage capabilities by proactively caching popular task computation results to minimize computing latency. To this end, a clustering method to group spatially proximate user devices with mutual task popularity interests and their serving cloudlets is proposed. Then, cloudlets can proactively cache the popular tasks' computations of their cluster members to minimize computing latency. Additionally, the problem of distributing tasks to cloudlets is formulated as a matching game in which a cost function of computing delay is minimized under latency and reliability constraints. Simulation results show that the proposed scheme guarantees reliable computations with bounded latency and achieves up to 91% decrease in computing latency as compared to baseline schemes. Google Scholar

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Conference: 2017 European Conference on Networks and Communications (EuCNC)

Title: Towards low-latency and ultra-reliable vehicle-to-vehicle

Authors: Muhammad Ikram Ashraf, Chen-Feng Liu, Mehdi Bennis , Walid Saad

Abstract: Recently vehicle-to-vehicle (V2V) communication emerged as a key enabling technology to ensure traffic safety and other mission-critical applications. In this paper, a novel proximity and quality-of-service (QoS)-aware resource allocation for V2V communication is proposed. The proposed approach exploits the spatial-temporal aspects of vehicles in terms of their physical proximity and traffic demands, to minimize the total transmission power while considering queuing latency and reliability. Due to the overhead caused by frequent information exchange between vehicles and the roadside unit (RSU), the centralized problem is decoupled into two interrelated subproblems. First, a novel RSU-assisted virtual clustering mechanism is proposed to group vehicles in zones based on their physical proximity. Given the vehicles' traffic demands and their QoS requirements, resource blocks are assigned to each zone. Second, leveraging techniques from Lyapunov stochastic optimization, a power minimization solution is proposed for each V2V pair within each zone. Simulation results for a Manhattan model have shown that the proposed scheme outperforms the baseline in terms of average queuing latency reduction up to 97% and significant improvement in reliability. Google Scholar

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Conference: 2017 IEEE International Conference on Communications Workshops (ICC Workshops)

Title: Adaptive mode selection in cognitive buffer-aided full-duplex relay networks with imperfect self-interference cancellation for power and delay limited cases

Authors: Mostafa Darabi, Nima Namvar, Behrouz Maham, Walid Saad, Merouane Debbah

Abstract: In this paper, a cognitive radio network is considered in which the secondary network (SN) consists of a source, a buffer-aided full-duplex decode-and-forward relay, and a destination, underlaid over a primary network (PN). An imperfect self-interference (SI) cancellation is assumed at the secondary relay (SR), such that the SI power is proportional to the transmit power of the SR. For the SN with limited power expenditure, a novel joint mode selection and power allocation policy is proposed to maximize the secondary throughput under the constraints of secondary power consumption and a limited average induced interference power at the primary destination. For delay sensitive SN applications, a statistical delay constraint is imposed in which the queue length at the SR can only exceed a specified threshold with a limited probability. In the two proposed policies, the SN decides optimally when to operate in half duplex mode and/or in full duplex mode, and be silent. To avoid data loss in the SN, buffer is used at the SR for data storage. Simulation results show that, for a given interference threshold and statistical delay constraint, the proposed policy outperforms the non-buffer full-duplex, buffer-aided half-duplex, and non-buffer half-duplex policies in terms of the average secondary throughput, the average secondary delay, and the secondary power expenditure. Google Scholar

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Conference: 2017 IEEE International Conference on Communications Workshops (ICC Workshops)

Title: Fuzzy logic game-theoretic approach for energy efficient operation in HetNets

Authors: Karthik Vasudeva, Sener Dikmese, İsmail Güvenç, Abolfazl Mehbodniya, Walid Saad, Fumiyuki Adachi

Abstract: Densely-deployed heterogeneous networks (HetNets) with large number of small cell base stations (SBSs) will constitute one of the main pillars of emerging 5G wireless systems. While such dense deployments of HetNets can help in achieving capacity requirements of 5G networks, they can also result in a significant increase in energy consumption. Since there may not be many associated users in certain SBSs, intelligently turning them off while not seriously degrading system throughput and handover performance can improve energy savings in HetNets. In this paper, we consider a fuzzy logic based game-theoretic framework for energy efficiency improvements in HetNets. We develop fuzzy decision rules for handovers and target base station selection while simultaneously considering the energy/spectral efficiency and handover performance. Our results show that energy consumption can be improved considerably especially for small number of active users and for high user velocities, while also managing ping-pong handovers and cell loads. Google Scholar

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Conference: 2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt)

Title: Joint access point deployment and assignment in mmWave networks with stochastic user orientation

Authors: Mehdi Naderi Soorki, Mohammad J. Abdel-Rahman, Allen MacKenzie, Walid Saad

Abstract: Millimeter wave (mmWave) communication is a promising solution for providing high capacity wireless access to regions with high traffic demands. The main challenge of mmWave communications is the availability of directional line of sight links between access points and mobile devices which stochastically change due to high attenuation in mmWave propagation and severe blockage of mmWave links with obstacles such as human bodies. In this paper, a novel framework for optimizing the deployment of mmW access points, while being cognizant of the mobile devices orientation, is proposed. In the studied model, the locations of potential access points and users are assumed as predefined parameters while the orientation of the users is changing stochastically. To minimize the number of access points while satisfying the line of sight coverage of mobile devices, first, a joint access point placement and mobile device assignment problem is proposed, assuming that the orientation of each user is deterministically known. This formulation is then extended to the case in which the orientation of the user is stochastic. Finally, the proposed deterministic and stochastic joint access point placement and mobile device assignment schemes are evaluated under various system parameters. Simulation results demonstrate the advantage of the proposed stochastic scheme to the deterministic scheme, in terms of reducing the load on access points. Moreover, on average, the proposed stochastic scheme can increase the probability of user satisfaction up to 24% for 0.95 requested coverage probability compared to the deterministic case. Google Scholar

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Conference: 2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt)

Title: Robust Bayesian learning for wireless RF energy harvesting networks

Authors: Nof Abuzainab, Walid Saad, Behrouz Maham

Abstract: In this paper, the problem of adversarial learning is studied for a wireless powered communication network (WPCN) in which a hybrid access point (HAP) seeks to learn the transmission power consumption profile of an associated wireless transmitter. The objective of the HAP is to use the learned estimate in order to determine the transmission power of the energy signal to be supplied to its associated device. However, such a learning scheme is subject to attacks by an adversary who tries to alter the HAP's learned estimate of the transmission power distribution in order to minimize the HAP's supplied energy. To build a robust estimate against such attacks, an unsupervised Bayesian learning method is proposed allowing the HAP to perform its estimation based only on the advertised transmisson power computed in each time slot. The proposed robust learning method relies on the assumption that the device's true transmission power is greater than or equal to advertised value. Then, based on the robust estimate, the problem of power selection of the energy signal by the HAP is formulated. The HAP optimal power selection problem is shown to be a discrete convex optimization problem, and a closed-form solution of the HAP's optimal transmission power is obtained. The results show that the proposed robust Bayesian learning scheme yields significant performance gains, by reducing the percentage of dropped transmitter's packets of about 85% compared to a conventional Bayesian learning approach. The results also show that these performance gains are achieved without jeopardizing the energy consumption of the HAP. Google Scholar

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Conference: 2017 IEEE/ACM Second International Conference on Internet-of-Things Design and Implementation (IoTDI)

Title: Demo Abstract: Cyber-Physical Fingerprinting for Internet of Things Authentication

Authors: Yaman Sharaf-Dabbagh, Walid Saad

Abstract: Current security and privacy solution to fail to meet the IoT requirements due to computational restrictions and portable nature of IoT objects. In this demo, a novel authentication framework is proposed that exploits the device-specific information to authenticate each object in the IoT. The framework is shown to effectively track the physical environment effects on objects. The experiment shows a sample IoT environment consisting of multiple Raspberry PI units operating as IoT objects. The proposed framework monitors the changes of the physical environment surrounding objects by examining the changes in the device-specific information of each IoT object. The scenario of an emulation attacker is presented in the demo as a case study. The attacker is capable of replicating all the transmitted messages and security keys of one of the IoT objects. Our proposed framework is able to effectively detect such an attack and improve the authentication accuracy for all IoT objects. -Demo Abstract. Google Scholar

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Conference: 2017 International Conference on Computing, Networking and Communications (ICNC)

Title: SDR based indoor localization using ambient WiFi and GSM signals

Authors: Varun Nambiar, Edwin Vattapparamban, Ali I. Yurekli, İsmail Güvenç, Mohammad Mozaffari, Walid Saad

Abstract: In this paper, experimental results with software defined radios (SDRs) for capturing and localizing WiFi and GSM users are developed. First, a detailed overview on various SDR equipment and software, such as embedded and networked USRPs, WiFi Pineapple, GNU Radio, OpenBTS, and Wireshark is presented. Sufficient details are provided on how to configure and operate the SDR equipment and the associated software. Measurement data is then collected from both WiFi and GSM signals, and least squares localization techniques are used for finding the target device's location. The obtained indoor localization accuracies are shown to be reasonable, considering that off-the-shelf equipment has been used with passive sniffing of a target user's signal strength. Google Scholar

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Dr. Yaling Yang

Conference: Proceedings of the 18th International Workshop on Mobile Computing Systems and Applications

Title: A Practical GPS Location Spoofing Attack in Road Navigation Scenario

Authors: KC Zeng, Y Shu, S Liu, Y Dou, Y Yang

Abstract: High value of GPS location information and easy availability of portable GPS signal spoofing devices incentivize attackers to launch GPS spoofing attacks against location-based applications. In this paper, we propose an attack model in road navigation scenario, and develop a complete framework to analyze, simulate and evaluate the spoofing attacks under practical constraints. To launch an attack, the framework first constructs a road network, and then searches for an attack route that smoothly diverts a victim without his awareness. In extensive data-driven simulations in College Point, New York City, we managed to navigate a victim to locations 1km away from his original destination. Link

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Books

In alphabetical order by author's last name:

Dr. Steven Ellingson

Dr. Steve EllingsonDr. Steve Ellingson has a new book on Radio Systems Engineering, released through Cambridge University Press.

Abstract: "Using a systems framework, this textbook provides a clear and comprehensive introduction to the performance, analysis and design of radio systems for students and practicing engineers. Presented within a consistent framework, the first part of the book describes the fundamentals of the subject: propagation, noise, antennas and modulation. The analysis and design of radios, including RF circuit design and signal processing, is covered in the second half of the book."


Bio: Dr. Ellingson is an associate professor in the Bradley Department of Electrical and Computer Engineering. He received his PhD in Electrical Engineering from Ohio State University and is a core faculty member of Wireless @ Virginia Tech leading the research thrusts in RF Analysis and Technologies. Dr. Ellingson is also an avid amateur radio operator.


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Dr. Walid Saad

Dr. Walid Saad has a new book titled Overlapping Coalition Formation Games in Wireless Communication Networks available through SpringerBriefs Press.

Abstract: "This brief introduces overlapping coalition formation games (OCF games), a novel mathematical framework from cooperative game theory that can be used to model, design and analyze cooperative scenarios in future wireless communication networks."

 

Bio: Dr. Saad is an assistant professor and Steven O. Lane Junior Faculty Fellow with the Bradley Department of Electrical and Computer Engineering and a core faculty member of Wireless @ Virginia Tech.

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