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Wireless Communications, IEEE Transactions on

Issue 1 • Date January 2013

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Displaying Results 1 - 25 of 45
  • Table of contents

    Page(s): c1 - c4
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  • Staff List

    Page(s): c2
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  • End-to-End Secure Multi-Hop Communication with Untrusted Relays

    Page(s): 1 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    A multi-hop line network is considered, where each node can receive signals transmitted by its two neighbors. As such, the model embodies both the interference and broadcast aspects of wireless networks. The leftmost node wishes to send messages to the rightmost node, while keeping these messages confidential from all the intermediate relay nodes. In this setting where any or all of the relay nodes can be eavesdroppers, it is shown that end-to-end secure and reliable communication is possible. Notably, it is shown that an end-to-end secrecy rate that is independent of the number of hops, i.e., intermediate eavesdroppers, is achievable by means of a carefully designed transmission schedule, compute-and-forward relaying and coding strategy utilizing nested lattice codes. The achievable rate obtained indicates that imposing secrecy constraints penalizes the capacity by at most 1 bit per channel use. Therefore, it is concluded that information theoretic secrecy can be guaranteed for this model irrespective of eavesdropping relays and a fixed modest cost for the end-to-end rate. View full abstract»

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  • Coordinated Multicast Beamforming in Multicell Networks

    Page(s): 12 - 21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (762 KB) |  | HTML iconHTML  

    We study physical layer multicasting in multicell networks where each base station, equipped with multiple antennas, transmits a common message using a single beamformer to multiple users in the same cell. We investigate two coordinated beamforming designs: the quality-of-service (QoS) beamforming and the max-min SINR (signal-to-interference-plus-noise ratio) beamforming. The goal of the QoS beamforming is to minimize the total power consumption while guaranteeing that received SINR at each user is above a predetermined threshold. We present a necessary condition for the optimization problem to be feasible. Then, based on the decomposition theory, we propose a novel decentralized algorithm to implement the coordinated beamforming with limited information sharing among different base stations. The algorithm is guaranteed to converge and in most cases it converges to the optimal solution. The max-min SINR (MMS) beamforming is to maximize the minimum received SINR among all users under per-base station power constraints. We show that the MMS problem and a weighted peak-power minimization (WPPM) problem are inverse problems. Based on this inversion relationship, we then propose an efficient algorithm to solve the MMS problem in an approximate manner. Simulation results demonstrate significant advantages of the proposed multicast beamforming algorithms over conventional multicasting schemes. View full abstract»

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  • UHF Propagation Along a Cargo Hold on Board a Merchant Ship

    Page(s): 22 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2177 KB) |  | HTML iconHTML  

    The characterization of a Line of Sight (LOS) and a Non-Line of Sight (NLOS) link is performed over the military Ultra High Frequency (UHF) band (225 to 450 MHz). This is done using experimental results collected inside the cargo hold of a merchant ship. By analyzing the guiding effect associated with the cargo hold and its sub-structures, the channel characteristics of the environment can be determined. This important propagation mechanism is analyzed using the 3-D ray tracing simulator. Path loss for both topologies is studied and linear path loss models are proposed. Small-scale channel characteristics, such as the number of multipath components, decay factor of the multipath components and Root-Mean-Square (RMS) delay spread are studied and compared for the LOS and NLOS scenarios. Due to the guiding effect and multiple reflections along the cargo hold, both the LOS and NLOS scenarios are found to exhibit similar channel characteristics. A linear decay function is proposed to model the average Power Delay Profiles (PDPs). It is concluded that the linear model provides a good representation for the shape of the impulse responses for a cluttered environment with reflective substructures. This study is useful for the implementation of wireless sensor networks for status monitoring in maritime applications. View full abstract»

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  • Auction-Based Power Allocation for Multiuser Two-Way Relaying Networks

    Page(s): 31 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    The overall performance of a cooperative relaying system largely depends on power allocation schemes. In this paper, we address the power allocation problem in a network-coded multiuser two-way relaying network, where multiple pair users communicate with their partners via a common relay node, and compete for the transmit power of the relay. An auction-based power allocation scheme is proposed, in which two users in each pair bid as a single player for a maximum utility of the whole pair, and share the total pair payment in proportion to the amount of power they obtained. The convergence of the proposed auction game (i.e., the convergence to a unique Nash Equilibrium) is theoretically proved by using a standard function. Moreover, the outage behavior is systematically analyzed and a closed form of the pair outage probability is derived. Finally, the performance of the proposed scheme is verified by simulation results. View full abstract»

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  • Application of Cooperative Diversity to Cognitive Radio Leasing: Model and Analytical Characterization of Resource Gains

    Page(s): 40 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3530 KB) |  | HTML iconHTML  

    This paper studies mutual information in a novel scenario combining cooperative diversity and cognitive radio based on spectrum leasing. In the scenario there is a primary transmitter subject to random channel fading, with full spectrum rights available, and a secondary transmitter without any spectrum rights, which offers its cooperation to the primary transmitter in exchange for a share of the resulting resource gains. Two decision-making schemes, based on different levels of channel knowledge, are considered in the primary transmitter. These are knowledge of the statistics of random fading (averages) and full knowledge of instantaneous channel state. The contributions of this paper are the radio leasing scenario itself, which, unlike previous approaches in cognitive radio, is not based on game theory, and the statistical characterization of the resource gains achieved in this scenario using cooperative diversity for spectrum leasing under diverse channel conditions and the aforementioned decision-making schemes. Analytical expressions are obtained for the probability of cooperation, the mutual information probability density function and its average, and the proportion of resource gains achieved for the statistical and instantaneous channel knowledge schemes. We identify the conditions for resource gains: for statistical channel knowledge to suffice, the primary link must be of low quality, whereas for instantaneous channel knowledge, although resource gains are achieved in any situation, they increase as the primary channel gets worse. View full abstract»

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  • Collision-Tolerant Media Access Control with On-Off Accumulative Transmission

    Page(s): 50 - 59
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (517 KB) |  | HTML iconHTML  

    In this paper, a cross-layer collision-tolerant (CT) media access control (MAC) scheme is proposed for wireless networks. Unlike conventional MAC schemes that discard and retransmit signals colliding at a receiver, the CT-MAC extracts the salient information from the colliding signals with a new on-off accumulative transmission (OOAT) scheme in the physical layer. Users employing OOAT deliver information to the base station (BS) through uncoordinated on-off transmissions of multiple identical sub-symbols (accumulative transmission). Silence periods are inserted between sub-symbols inside a frame to reduce collision probability and render a special signal structure for physical layer detection. Algebraic properties of the on-off transmission patterns, which are represented as cyclic-shifted binary vectors, are analyzed, and the results provide guidelines on the design of OOAT systems and other systems that rely on cyclic-shifted binary vectors. Then, we demonstrate that the structure of the on-off transmission patterns enables a sub-optimum iterative detection method, which improves performance by iteratively exchanging extrinsic soft information between a forward and a backward soft interference cancellation (SIC). Both analytical and simulation results show that the new CT-MAC with OOAT scheme significantly outperforms many existing cross-layer MAC schemes in terms of the number of users supported and the normalized throughput. View full abstract»

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  • Capacity of Wireless Networks with Social Behavior

    Page(s): 60 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB) |  | HTML iconHTML  

    The capacity of a wireless network is studied when nodes communicate with one another in the context of social groups. All the nodes are assumed to have the same number of independent long-range social contacts, one of which each selects randomly as its destination. The Euclidean distance between a source and its social group members follows a power-law distribution and communication between any two nodes takes place only within the physical transmission range resulting in communication over multi-hop paths. The capacity order of such a composite network is derived as a function of the number of nodes, the social-group concentration, and the size of social groups. Our results demonstrate that when each node has constant number of contacts which does not increase with network size growth, and are geographically concentrated, then the network behaves similar to social networks and communication network does not have any effect on the throughput capacity. On the other hand, when the social contact population grows in time, or social connectivity among nodes is highly distributed, then the communication network is the dominant factor and the composite network behaves similar to wireless networks, i.e., the capacity is the same as Gupta and Kumar results. When neither social connectivity nor communication network is dominant, then the throughput capacity results are between these two extreme cases. View full abstract»

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  • Anti-Jamming Message-Driven Frequency Hopping—Part I: System Design

    Page(s): 70 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB) |  | HTML iconHTML  

    This is Part I of a two-part paper that considers anti-jamming system design in wireless networks based on message-driven frequency hopping (MDFH), a highly efficient spread spectrum technique. In this paper, we first analyze the performance of MDFH under hostile jamming. It is observed that while MDFH is robust under strong jamming, it experiences considerable performance losses under disguised jamming from sources that mimic the true signal. To overcome this limitation, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit a secure ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver, it is then exploited by the receiver for effective signal extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming, and is also robust under strong jamming. In addition, we extend AJ-MDFH to the multi-carrier case, which can increase the system efficiency and jamming resistance significantly through jamming randomization and frequency diversity, and can readily be used as a collision-free multiple access system. Part II of the paper focuses on the capacity analysis of MDFH and AJ-MDFH under disguised jamming. View full abstract»

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  • Anti-Jamming Message-Driven Frequency Hopping—Part II: Capacity Analysis Under Disguised Jamming

    Page(s): 80 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (571 KB) |  | HTML iconHTML  

    This is part II of a two-part paper that explores efficient anti-jamming system design based on message-driven frequency hopping (MDFH). In Part I, we point out that under disguised jamming, where the jammer mimics the authorized signal, MDFH experiences considerable performance losses like other wireless systems. To overcome this limitation, we propose an anti-jamming MDFH scheme (AJ-MDFH), which enhances the jamming resistance of MDFH by enabling shared randomness between the transmitter and the receiver using an AES generated ID sequence transmitted along the information stream. In part II, using the arbitrarily varying channel (AVC) model, we analyze the capacity of MDFH and AJ-MDFH under disguised jamming. We show that under the worst case disguised jamming, as long as the secure ID sequence is unavailable to the jammer (which is ensured by AES), the AVC corresponding to AJ-MDFH is nonsymmetrizable. This implies that the deterministic capacity of AJ-MDFH with respect to the average probability of error is positive. On the other hand, due to lack of shared randomness, the AVC corresponding to MDFH is symmetric, resulting in zero deterministic capacity. We further calculate the capacity of AJ-MDFH and show that it converges as the ID constellation size goes to infinity. View full abstract»

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  • Delay Analysis of OFDMA-Aloha

    Page(s): 89 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB) |  | HTML iconHTML  

    OFDMA is the basis of future broadband access, due to its many inherent advantages such as scalability and fine granularity for multi-user access. OFDMA-Aloha combines the flexibility of OFDMA with basic Aloha's collision resolution mechanism over sub-carriers, in an attempt to reduce packet collisions and achieve faster retransmission. However, this comes at the expense of a larger slot size, due to lower channel rates per subcarrier. The above gives rise to a fundamental question: whether to use a single wide-band Aloha channel and retransmit via random back-off in next K time slots, or to retransmit immediately in one of K narrow-band sub-channels which are each 1/K slower (OFDMA-Aloha)? We answer this question, by analyzing the two protocols: Aloha and OFDMA-Aloha under the same total bandwidth and load conditions. We first derive the exact distribution of the packet access delay of OFDMA-Aloha in the saturated case. Then, we extend the analysis to the unsaturated case and derive the mean queue length and packet delay by decomposing the system of interfering queues into multiple independent queues utilizing the symmetry in our system. Our results show that if the network is already saturated, channelization does not bring substantial reduction in the collision rate to the point where it outweighs the effect of expanded slot size. In this case the single channel Aloha performs better than OFDMA-Aloha especially when the gap between the number of channels and the number users is large. On other hand, when the network is lightly loaded, OFDMA-Aloha enjoys smaller packet delays, but not for long as it saturates faster than the single channel Aloha. View full abstract»

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  • Turbo Receiver with ICI-Aware Dual-List Detection for Mobile MIMO-OFDM Systems

    Page(s): 100 - 111
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (907 KB) |  | HTML iconHTML  

    This paper presents a turbo receiver using the proposed ICI-aware Dual-List (IDL) MIMO detection method that can efficiently detect signals deteriorated by both inter-carrier interference (ICI) and inter-antenna interference (IAI). These two interferences often occur simultaneously in mobile multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) communication systems. The IDL detector enhances ICI mitigation and avoids the notorious error propagation problem encountered in conventional interference mitigation/cancellation schemes. In addition, this study proposes three techniques to reduce the required computational complexity by 99.63% in complex additions, 99.69% in complex multiplications, and 67.25% in comparison operations. Simulation results confirm the theoretical upper bound and also show that the bit error rate performance of the receiver in high-mobility channels is comparable to that of a maximum-likelihood MIMO-OFDM receiver in stationary channels, i.e., the ICI-free scenario. View full abstract»

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  • Distributed Control of Multiple Cognitive Radio Overlay for Primary Queue Stability

    Page(s): 112 - 122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (343 KB) |  | HTML iconHTML  

    In this paper, we investigate distributed control of multiple secondary users attempting to access the channel of a high priority primary user. Our aim is to maximize the sum cognitive (secondary) user throughput under the constraint of primary user's queue stability. We consider the effect of primary user link adaptation that allows the primary transmitter (PTx) to adapt its transmission rate in response to the secondary interference-level at the primary receiver (PRx). To control the sum secondary interference to PRx beyond the traditional collision-avoidance paradigm, we propose a novel power-control algorithm for secondary nodes to function. To develop such a distributed algorithm and to improve secondary user adaptability, we allow secondary nodes to monitor primary's radio link control information on the feedback channel. We present practical schemes that approximate the optimum solution without relying on global channel information at each secondary node. View full abstract»

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  • Cooperative Scheduling for Coexisting Body Area Networks

    Page(s): 123 - 133
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (751 KB) |  | HTML iconHTML  

    Body area networks (BANs), referring to embedded wireless systems in, on, and around bodies, are expected to take an important role for health, leisure, sports, and all the facets of our daily life. In many cases, several BANs coexist in a small area, resulting in very strong inter-BAN interference, which seriously disturbs intra-BAN communications. The goal of this paper is to decrease inter-BAN interference by cooperative scheduling, hence increasing packet reception rate (PRR) of intra-BAN communications. Cooperative scheduling here is divided into two sub-problems: single-BAN scheduling as an assignment problem and multi-BAN concurrent scheduling as a game. For the first sub-problem, a low complexity algorithm, horse racing scheduling, is proposed, which achieves near-optimal PRR for the BAN performing scheduling. For the second sub-problem, we prove the existence of a set of mixed strategy Nash equilibria (MSNE). Then, we propose a distributed cooperative scheduling scheme, which efficiently achieves higher PRR than the MSNE without degrading fairness. View full abstract»

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  • Improving Secrecy Rate via Spectrum Leasing for Friendly Jamming

    Page(s): 134 - 145
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB) |  | HTML iconHTML  

    Cooperative jamming paradigm in secure communications enlists network nodes to transmit noise or structured codewords, in order to impair the eavesdropper's ability to decode messages to be kept confidential from it. Such an approach can significantly help in facilitating secure communication between legitimate parties but, by definition, assumes dedicated and/or altruistic nodes willing to act as cooperative jammers. In this paper, it is demonstrated that cooperative jamming leads to meaningful secrecy rate improvements even when this assumption is removed. A distributed mechanism is developed that motivates jamming participation of otherwise non-cooperative terminals, by compensating them with an opportunity to use the fraction of legitimate parties' spectrum for their own data traffic. With the goal of maximizing their data transmission rate priced by the invested power, cooperative jammers provide the jamming/transmitting power that is generally proportional to the amount of leased bandwidth. The fully decentralized framework is facilitated through a game-theoretic model, with the legitimate parties as the spectrum owners acting as the game leader, and the set of assisting jammers constituting the follower. To facilitate the behavior of non-cooperative and competitive multiple jammers, auctioning and power control mechanisms are applied for a follower sub-game in a two-layer leader-follower game framework. View full abstract»

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  • Impact of Unknown Time-varying Fading on the Information Rates of Amplify and Forward Cooperative Systems

    Page(s): 146 - 157
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1095 KB) |  | HTML iconHTML  

    We study information rate penalties for single-relay amplify and forward (AF) cooperative communication in the presence of unknown and time-varying fading. The penalty is defined as the gap between the information rate with perfect channel state information and that when the source-destination, source-relay and relay-destination channels are unknown at the receiving nodes. We prove that this gap in the cooperative system is the sum of gaps in the source-destination (single-hop) and source-relay-destination (dual-hop) channels. Under the assumption that the source and destination are mobile and the relay is stationary, we derive a closed-form accurate approximation for the asymptotic penalty of the mobile-to-mobile single-hop channel, which can also be used in computing asymptotic penalties for the mobile-fixed-mobile dual-hop channel. AF relaying induces non-Gaussian noise at the destination and hence, the penalty of the dual-hop channel is computed semi-analytically. We discuss a numerical technique for evaluation of destination noise entropy. One main observation of this paper is that non-negligible amplified relay noise can increase the cooperation information rate penalty of up to 1.5 times, as compared to non-relayed transmission. We provide extensive simulation results that characterize the behavior of penalty and include other mobility models for the source, relay and destination. View full abstract»

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  • Enabling the Femtocells: A Cooperation Framework for Mobile and Fixed-Line Operators

    Page(s): 158 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (761 KB) |  | HTML iconHTML  

    Femtocells' ability to improve the in-building coverage and capacity in a cost-efficient way has drawn significant attention from mobile operators. However, a mobile operator may lack a fixed-line network infrastructure, which is indispensable for enabling femtocell service. In this paper, we propose a hybrid cooperation framework where a mobile operator can collaborate with a fixed-line operator (as a virtual integrated operator) to provide femtocell service to indoor users. The framework consists of sequential game and Nash bargaining. The sequential game models the interactions of the operator and users. Specifically, the operator announces the price for wireless services first and then the users decide their spectrum demands in response to the given price. Then the two operators divide the cooperation benefit according to the Nash bargaining model, which makes the profit sharing fair and cooperation framework amenable to operators. We theoretically derive the unique closed-form equilibrium for the framework as well as the conditions that promote the cooperation. The simulation results verify that the cooperation framework can make more revenue for the operators and the spectrum efficiency is significantly improved. View full abstract»

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  • Exact Non-Gaussian Interference Model for Fading Channels

    Page(s): 168 - 179
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (469 KB) |  | HTML iconHTML  

    This paper derives respective precise bit error probability (BEP) expressions for a two-user binary phase shift keying (BPSK) system in Rayleigh, Nakagami and Rician fading channels. Our expressions allow for different symbol rate and symbol timing asynchronism between the desired user and interfering user. We provide some theoretical results concerning the BEP performance with respect to the fading severity. Comprehensive simulation study and comparison of the BEP performance between the Gaussian and non-Gaussian interference models are also provided. The results show that the Gaussian interference model has limitation in predicting the exact BEP performance in fading channels. It fails in accurately tracking the variation of the BEP with respect to the signal-to-noise ratio (SNR), signal-to-interference ratio (SIR), symbol rate ratio and fading severity. View full abstract»

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  • QoS-Aware and Energy-Efficient Resource Management in OFDMA Femtocells

    Page(s): 180 - 194
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (731 KB) |  | HTML iconHTML  

    We consider the joint resource allocation and admission control problem for Orthogonal Frequency-Division Multiple Access (OFDMA)-based femtocell networks. We assume that Macrocell User Equipments (MUEs) can establish connections with Femtocell Base Stations (FBSs) to mitigate the excessive cross-tier interference and achieve better throughput. A cross-layer design model is considered where multiband opportunistic scheduling at the Medium Access Control (MAC) layer and admission control at the network layer working at different time-scales are assumed. We assume that both MUEs and Femtocell User Equipments (FUEs) have minimum average rate constraints, which depend on their geographical locations and their application requirements. In addition, blocking probability constraints are imposed on each FUE so that the connections from MUEs only result in controllable performance degradation for FUEs. We present an optimal design for the admission control problem by using the theory of Semi-Markov Decision Process (SMDP). Moreover, we devise a novel distributed femtocell power adaptation algorithm, which converges to the Nash equilibrium of a corresponding power adaptation game. This power adaptation algorithm reduces energy consumption for femtocells while still maintaining individual cell throughput by adapting the FBS power to the traffic load in the network. Finally, numerical results are presented to demonstrate the desirable operation of the optimal admission control solution, the significant performance gain of the proposed hybrid access strategy with respect to the closed access counterpart, and the great power saving gain achieved by the proposed power adaptation algorithm. View full abstract»

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  • Performance Analysis of Cyclic Prefixed Single-Carrier Cognitive Amplify-and-Forward Relay Systems

    Page(s): 195 - 205
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    A cyclic prefixed single-carrier (CP-SC) relaying system is considered for cognitive radio networks under spectrum sharing condition. The outage probability of secondary users employing a two-hop amplify-and-forward (AF) relay protocol is investigated under an interference constraint inflicted by the secondary user-source and the secondary user-relay on a primary user (PU). Assuming channel-state-information (CSI) is available, the end-to-end signal-to-noise-ratio (e2e-SNR) is first derived, and then an analytical expression for the cumulative distribution function (CDF) of this e2e-SNR is derived. Based on this derived CDF, analytical expressions for the exact outage probability, the approximate symbol error rate (SER), and approximate achievable rate can be obtained. In addition, to reveal further insights into the impact of channel lengths on the diversity and coding gains, the asymptotic outage probability and SER are provided. It is important to note that the performance of cognitive radio networks is degraded due to the limited power constraint inflicted on the primary network. As such, the optimal power allocation (OPA) is also derived to achieve a better asymptotic outage probability. View full abstract»

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  • A Framework for Uplink Intercell Interference Modeling with Channel-Based Scheduling

    Page(s): 206 - 217
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB) |  | HTML iconHTML  

    This paper presents a novel framework for modeling the uplink intercell interference (ICI) in a multiuser cellular network. The proposed framework assists in quantifying the impact of various fading channel models and state-of-the-art scheduling schemes on the uplink ICI. Firstly, we derive a semi-analytical expression for the distribution of the location of the scheduled user in a given cell considering a wide range of scheduling schemes. Based on this, we derive the distribution and moment generating function (MGF) of the uplink ICI considering a single interfering cell. Consequently, we determine the MGF of the cumulative ICI observed from all interfering cells and derive explicit MGF expressions for three typical fading models. Finally, we utilize the obtained expressions to evaluate important network performance metrics such as the outage probability, ergodic capacity, and average fairness numerically. Monte-Carlo simulation results are provided to demonstrate the efficacy of the derived analytical expressions. View full abstract»

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  • Linear Network Coding Strategies for the Multiple Access Relay Channel with Packet Erasures

    Page(s): 218 - 227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    The multiple access relay channel (MARC) where multiple users send independent information to a single destination aided by a single relay under large-scale path loss and slow fading is investigated. At the beginning, the users take turns to transmit their packets. The relay is not aware of the erasure status of each packet at the destination but has the knowledge of the average signal-to-noise-ratio (SNR) of every communication link. With this knowledge, the relay applies network coded retransmission on the overheard packets so as to maximize the expected total number of recovered packets or minimize the average packet loss rate at the destination. Several network coding (NC) strategies at the relay are designed. In particular, for the case where the relay is given only one time slot for retransmission, an optimal NC construction is derived. For the multiple-slot case, three sub-optimal schemes are investigated, namely network coding with maximum distance separable (MDS) code (NC-MDS), the worst-user-first (WUF) scheme and a hybrid of NC-MDS and WUF. We prove that NC-MDS and WUF are asymptotically optimal in the high and low SNR regimes, respectively. A lower bound on the average packet loss rate has been derived. Numerical studies show that, in a cellular system, the hybrid scheme offers significant performance gain over a number of existing schemes in a wide range of SNR. We also observe that performance curves of both WUF and the hybrid scheme touch the derived lower bound in the low SNR regime. View full abstract»

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  • Zero-Forcing Beamforming in Multiuser MISO Downlink Systems Under Per-Antenna Power Constraint and Equal-Rate Metric

    Page(s): 228 - 236
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (715 KB) |  | HTML iconHTML  

    In this paper, we analyze the average sum rate of downlink multi-antenna systems with zero-forcing beamforming (ZFBF). In practical implementations, each antenna is equipped with its own power amplifier and is limited individually by linearity of the amplifier. Thus, this paper adopts a more realistic per-antenna power constraint instead of conventional sum-power constraint on transmit antennas. To this end, we first show that a distribution of the received signal-to-noise ratio (SNR) of the ZFBF scheme with per-antenna power constraint and equal-rate metric can be approximated as a minimum of chi-square random variables. Based on this result, we present an accurate formula of the average sum rate in a closed form. Furthermore, employing extreme value theory, an expression of the asymptotic average sum rate with large numbers of transmit antennas and users is derived from the limiting distribution of the received SNR. Simulation results verify the validity of our analysis even with not so large numbers of transmit antennas and users. View full abstract»

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  • An Auction Approach to Distributed Power Allocation for Multiuser Cooperative Networks

    Page(s): 237 - 247
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (838 KB) |  | HTML iconHTML  

    This paper studies a wireless network where multiple users cooperate with each other to improve the overall network performance. Our goal is to design an optimal distributed power allocation algorithm that enables user cooperation, in particular, to guide each user on the decision of transmission mode selection and relay selection. Our algorithm has the nice interpretation of an auction mechanism with multiple auctioneers and multiple bidders. Specifically, in our proposed framework, each user acts as both an auctioneer (seller) and a bidder (buyer). Each auctioneer determines its trading price and allocates power to bidders, and each bidder chooses the demand from each auctioneer. By following the proposed distributed algorithm, each user determines how much power to reserve for its own transmission, how much power to purchase from other users, and how much power to contribute for relaying the signals of others. We derive the optimal bidding and pricing strategies that maximize the weighted sum rates of the users. Extensive simulations are carried out to verify our proposed approach. View full abstract»

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Cullen Trust for Higher Education Endowed Professor of Engineering