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82
Multi-user diversity in a spectrum sharing system
- IEEE Trans Wirel Commun
, 2009
"... Abstract—We investigate the effects of multi-user diversity in a spectrum sharing system where secondary users restrictively utilize a spectrum licensed to primary users only if interference perceived at primary users is regulated below a predetermined level. This interference regulation affects the ..."
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Cited by 37 (6 self)
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Abstract—We investigate the effects of multi-user diversity in a spectrum sharing system where secondary users restrictively utilize a spectrum licensed to primary users only if interference perceived at primary users is regulated below a predetermined level. This interference regulation affects the characteristics of multiuser diversity gains previously known in non-spectrum sharing systems. Our numerical and analytical results show that the multiuser diversity gain in a spectrum sharing sys-tem increases differently according to conditions given by the transmit power of secondary users, P, and a predetermined interference temperature, Q – if P is sufficiently larger than Q, the multiuser diversity gain in terms of capacity scales like log2 (W (Ns)) similarly to a previously known scaling law in the non-spectrum sharing systems, where W(·) and Ns denote a Lambert W function and the number of secondary transmitters, respectively. However, the scaling law of multiuser diversity gain becomes log2(Ns) as P becomes sufficiently larger such that P QNs. Index Terms—Spectrum sharing, cognitive radio, multiuser diversity. I.
Optimal Cognitive Access of Markovian Channels under Tight Collision Constraints
"... Abstract—The problem of cognitive access of channels of primary users by a secondary user is considered. The transmissions of primary users are modeled as independent continuous-time Markovian on-off processes. A secondary cognitive user employs a slotted transmission format, and it senses one of th ..."
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Cited by 23 (7 self)
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Abstract—The problem of cognitive access of channels of primary users by a secondary user is considered. The transmissions of primary users are modeled as independent continuous-time Markovian on-off processes. A secondary cognitive user employs a slotted transmission format, and it senses one of the possible channels before transmission. The objective of the cognitive user is to maximize its throughput subject to collision constraints imposed by the primary users. The optimal access strategy is in general a solution of a constrained partially observable Markov decision process, which involves a constrained optimization in an infinite dimensional functional space. It is shown in this paper that, when the collision constraints are tight, the optimal access strategy can be implemented by a simple memoryless access policy with periodic channel sensing. Analytical expressions are given for the thresholds on collision probabilities for which memoryless access performs optimally. Extensions to multiple secondary users are also presented. Numerical and theoretical results are presented to validate and extend the analysis for different practical scenarios. Index Terms—Cognitive radio, Dynamic spectrum allocation, Cognitive medium access, Markov decision processes.
Dynamic multichannel access with imperfect channel state detection
- IEEE Trans. Signal Process
, 2010
"... Abstract—A restless multi-armed bandit problem that arises in multichannel opportunistic communications is considered, where channels are modeled as independent and identical Gilbert–Elliot channels and channel state detection is subject to errors. A simple structure of the myopic policy is establis ..."
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Cited by 19 (4 self)
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Abstract—A restless multi-armed bandit problem that arises in multichannel opportunistic communications is considered, where channels are modeled as independent and identical Gilbert–Elliot channels and channel state detection is subject to errors. A simple structure of the myopic policy is established under a certain condition on the false alarm probability of the channel state detector. It is shown that myopic actions can be obtained by maintaining a simple channel ordering without knowing the underlying Markovian model. The optimality of the myopic policy is proved for the case of two channels and conjectured for general cases. Lower and upper bounds on the performance of the myopic policy are obtained in closed-form, which characterize the scaling behavior of the achievable throughput of the multichannel opportunistic system. The approximation factor of the myopic policy is also analyzed to bound its worst-case performance loss with respect to the optimal performance. Index Terms—Cognitive radio, dynamic multichannel access, myopic policy, restless multi-armed bandit.
Load-balancing spectrum decision for cognitive radio networks
- IEEE Journal on Selected Areas in Communications
, 2011
"... Abstract—In this paper, we present an analytical framework to design system parameters for load-balancing multiuser spectrum decision schemes in cognitive radio (CR) networks. Unlike the non-load-balancing methods that multiple secondary users may contend for the same channel, the considered load-ba ..."
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Cited by 18 (1 self)
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Abstract—In this paper, we present an analytical framework to design system parameters for load-balancing multiuser spectrum decision schemes in cognitive radio (CR) networks. Unlike the non-load-balancing methods that multiple secondary users may contend for the same channel, the considered load-balancing schemes can distribute the traffic loads of secondary users to multiple channels. Based on the preemptive resume priority (PRP) M/G/1 queueing theory, a spectrum decision analytical model is proposed to evaluate the effects of multiple interruptions from the primary user during each link connection, the sensing errors (i.e., missed detection and false alarm) of the secondary users, and the heterogeneous channel capacity. With the objective of minimizing the overall system time of the secondary users, we derive the optimal number of candidate channels and the optimal channel selection probability for the sensing-based and the probability-based spectrum decision schemes, respectively. We find that the probability-based scheme can yield a shorter overall system time compared to the sensing-based scheme when the traffic loads of the secondary users is light, whereas the sensing-based scheme performs better in the condition of heavy traffic loads. If the secondary users can intelligently adopt the best spectrum decision scheme according to sensing time and traffic conditions, the overall system time can be improved by 50 % compared to the existing methods. Index Terms—Cognitive radio, spectrum decision, channel selection, overall system time, preemption, queueing theory. I.
On video multicast in cognitive radio networks
- in Proc. IEEE INFOCOM’09, Rio de Janeiro
, 2009
"... Abstract — We investigate the challenging problem of enabling multicast video service in emerging cognitive radio (CR) net-works. We propose a cross-layer optimization approach to multicast video in CR networks. Specifically, we model CR video multicast as an optimization problem, while considering ..."
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Cited by 17 (7 self)
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Abstract — We investigate the challenging problem of enabling multicast video service in emerging cognitive radio (CR) net-works. We propose a cross-layer optimization approach to multicast video in CR networks. Specifically, we model CR video multicast as an optimization problem, while considering important design factors including scalable video coding, video rate control, spectrum sensing, dynamic spectrum access, modu-lation, scheduling, retransmission, and primary user protection. The objective is to optimize the overall received video quality as well as achieving proportional fairness among multicast users, while keeping the interference to primary users below a prescribed threshold. Although the problem can be solved using advanced optimization techniques, we propose a sequential fixing algorithm and a greedy algorithm with low complexity and proven optimality gap. Our simulations using MPEG-4 fine grained scalability (FGS) demonstrate the efficacy and superior performance of the proposed approach as compared with an alternative equal allocation scheme. I.
Streaming Scalable Videos over Multi-Hop Cognitive Radio Networks
- IEEE Trans. Wireless Communications, Vol 9
"... Abstract—We investigate the problem of streaming mul-tiple videos over multi-hop cognitive radio (CR) networks. Fine-Granularity-Scalability (FGS) and Medium-Grain-Scalable (MGS) videos are adopted to accommodate the heterogeneity among channel availabilities and dynamic network conditions. We obtai ..."
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Cited by 10 (7 self)
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Abstract—We investigate the problem of streaming mul-tiple videos over multi-hop cognitive radio (CR) networks. Fine-Granularity-Scalability (FGS) and Medium-Grain-Scalable (MGS) videos are adopted to accommodate the heterogeneity among channel availabilities and dynamic network conditions. We obtain a mixed integer nonlinear programming (MINLP) problem formulation, with objectives to maximize the overall received video quality and to achieve fairness among the video sessions, while bounding the collision rate with primary users under the presence of spectrum sensing errors. We first solve the MINLP problem using a centralized sequential fixing algorithm, and derive upper and lower bounds for the objective value. We then apply dual decomposition to develop a distributed algorithm and prove its optimality and convergence conditions. The proposed algorithms are evaluated with simulations and are shown to be effective in supporting concurrent scalable video sessions in multi-hop CR networks. Index Terms—Cross-layer optimization, dynamic spectrum access, distributed algorithm, multi-hop cognitive radio networks, video streaming. I.
Performance Analysis of Cognitive Radio Systems under QoS Constraints and Channel Uncertainty
- Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE
, 2010
"... Abstract—In this paper, performance of cognitive transmission over time-selective flat fading channels is studied under quality of service (QoS) constraints and channel uncertainty. Cognitive secondary users (SUs) are assumed to initially perform channel sensing to detect the activities of the prima ..."
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Cited by 8 (6 self)
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Abstract—In this paper, performance of cognitive transmission over time-selective flat fading channels is studied under quality of service (QoS) constraints and channel uncertainty. Cognitive secondary users (SUs) are assumed to initially perform channel sensing to detect the activities of the primary users, and then attempt to estimate the channel fading coefficients through training. Energy detection is employed for channel sensing, and different minimum mean-square-error (MMSE) estimation methods are considered for channel estimation. In both channel sensing and estimation, erroneous decisions can be made, and hence, channel uncertainty is not completely eliminated. In this setting, performance is studied and interactions between channel sensing and estimation are investigated. Following the channel sensing and estimation tasks, SUs engage in data transmission. Transmitter, being unaware of the channel fading coefficients, is assumed to send the data at fixed power and rate levels that depend on the channel sensing results. Under these assumptions, a state-transition model is constructed by considering the reliability of the transmissions, channel sensing decisions and their correctness, and the evolution of primary user activity which is modeled as a two-state Markov process. In the data transmission phase, an average power constraint on the secondary users is considered to limit the interference to the primary users, and statistical limitations on the buffer lengths are imposed to take into account the QoS constraints of the secondary traffic. The maximum throughput under these statistical QoS constraints is identified by finding the effective capacity of the cognitive radio channel. Numerical results are provided for the power and rate policies. Index Terms—Cognitive radio, quality of service constraints, channel sensing, channel estimation, effective capacity, fixed-rate transmissions, state-transition model. I.
Multiuser cognitive access of continuous time markov channels: maximum throughput and effective bandwidth regions
- in Proc. 2010 Information Theory and Applications Workshop
, 2010
"... Abstract—The problem of sharing multiple channels owned by primary users with multiple cognitive users is considered. Each primary user transmits on its dedicated channel, and its occupancy is modeled by a continuous time Markov process. Each cognitive user is capable of sensing one channel at a tim ..."
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Cited by 8 (6 self)
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Abstract—The problem of sharing multiple channels owned by primary users with multiple cognitive users is considered. Each primary user transmits on its dedicated channel, and its occupancy is modeled by a continuous time Markov process. Each cognitive user is capable of sensing one channel at a time and it transmits according to a slotted structure. The transmissions of cognitive users on each channel are subject to a prescribed collision constraint. Under tight collision constraints, the maximum throughput region is obtained by a policy referred to as Orthogonalized Periodic Sensing with Memoryless Access (OPS-MA). Characterizations of the maximum throughput region are also provided when the collision constraints are loose. It is shown that the OPS-MA policy achieves the maximum sum-rate under all collision constraints when the number of cognitive users equals to that of the primary users. Inner and outer bounds for the effective bandwidth region are formulated as a pair of convex optimizations. When there are only two channels, corner points (the single user scenario) of the optimal effective bandwidth region are also obtained. Index terms—Cognitive radio networks, dynamic spectrum access, opportunistic multiaccess, effective bandwidth, Constrained POMDP, queueing networks. I.
Scalable Video Multicast in Cognitive Radio Networks
"... Abstract—We investigate the problem of scalable video multi-cast in emerging cognitive radio (CR) networks. Although consid-erable advances have been made in CR research, such important problems have not been well studied. Naturally, “bandwidth-hungry ” multimedia applications are excellent candidat ..."
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Cited by 8 (5 self)
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Abstract—We investigate the problem of scalable video multi-cast in emerging cognitive radio (CR) networks. Although consid-erable advances have been made in CR research, such important problems have not been well studied. Naturally, “bandwidth-hungry ” multimedia applications are excellent candidates for fully capitalizing the potential of CRs. We propose a cross-layer optimization approach to multicast video in CR networks. Specifically, we consider an infrastructure-based CR network col-located with N primary networks and model CR video multicast over the N channels as a mixed integer nonlinear programming (MINLP) problem. The objective is three-fold: to optimize the overall received video quality; to achieve proportional fairness among multicast users; and to keep the interference to primary users below a prescribed threshold. We propose a sequential fixing algorithm and a greedy algorithm to solve the MINLP, while the latter has low complexity and proven optimality gap. Our simulations with MPEG-4 fine grained scalability (FGS) video demonstrate the efficacy and superior performance of the proposed algorithms. Index Terms—Video multicast, cognitive radio networks, dy-namic spectrum access, cross-layer optimization I.
Cognitive Frequency Hopping Based on Interference Prediction: Theory and Experimental Results
, 2009
"... Wireless services in the unlicensed bands are proliferating but frequently face high interference from other devices due to a lack of coordination among heterogeneous technologies. In this paper we study how cognitive radio concepts enable systems to sense and predict interference patterns and adapt ..."
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Cited by 7 (0 self)
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Wireless services in the unlicensed bands are proliferating but frequently face high interference from other devices due to a lack of coordination among heterogeneous technologies. In this paper we study how cognitive radio concepts enable systems to sense and predict interference patterns and adapt their spectrum access accordingly. This leads to a new cognitive coexistence paradigm, in which cognitive radio implicitly coordinates the spectrum access of heterogeneous systems. Within this framework, we investigate coexistence with a set of parallel WLAN bands: based on predicting WLAN activity, the cognitive radio dynamically hops between the bands to avoid collisions and reduce interference. The development of a real-time test bed is presented, and used to corroborate theoretical results and model assumptions. Numerical results show a good fit between theory and experiment and demonstrate that sensing and prediction can mitigate interference effectively.
