A POMDP Based Distributed Adaptive Opportunistic Spectrum Access Strategy for Cognitive Ad Hoc Networks
ABSTRACT In this letter, we propose a Partially Observable Markov Decision Process (POMDP) based Distributed Adaptive Opportunistic Spectrum Access (DA-OSA) Strategy for Cognitive Ad Hoc Networks (CAHNs). In each slot, the source and destination choose a set of channels to sense and then decide the transmission channels based on the sensing results. In order to maximize the throughput for each link, we use the theories of sequential decision and optimal stopping to determine the optimal sensing channel set. Moreover, we also establish the myopic policy and exploit the monotonicity of the reward function that we use, which can be used to reduce the complexity of the sequential decision.
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ABSTRACT: With the rapid development of wireless communications technologies, radio spectrum has become a type of extremely scarce resources in meeting the increasing demands for broadband wireless services. However, the traditional static spectrum allocation policy leads to severe spectrum underutilization and spectrum shortage problems. The cognitive radio (CR) technology can detect the occupancy of the spectrum and enable the dynamic spectrum access (DSA) to fill the spectrum hole caused by the static allocation policy, and thus has been widely recognized as an efficient approach to solve the above problems. The distributed cognitive wireless network (CWN), which does not have central entities, is one of the major networking architectures applying the CR technology. Correspondingly, the design of DSA in distributed CWNs is crucial, yet challenging, to increasing the utilization efficiency of the wireless spectrum with dynamically-varying occupancy statuses. In this article, we present a survey on DSA protocols for distributed CWNs. In particular, we first address the challenges in the design and implementation of distributed DSA protocols. Then, we categorize the existing distributed DSA protocols based on different criteria, such as spectrum sharing modes, spectrum allocation behaviors, spectrum access modes, the usage of common control channel, spectrum usage strategies, the number of radios, and spectrum sensing techniques. We also discuss the advantages and disadvantages of each category under diverse classification criterion. Moreover, we make a comprehensive survey of the state-of-the-art distributed DSA protocols using different spectrum access modes, which can be categorized into contention-based, time-slotted, and hybrid protocols. Through the study, we find out that most of distributed DSA protocols fall into the contention-based and hybrid protocols. In addition, the ongoing standardization efforts are also reviewed. Finally, several open research issues for the distributed DSA protocols are presented, such as spectrum handoff based protocols, spectrum prediction based protocols, adaptation of the spectrum-sharing modes, protocols with cooperative spectrum sensing, as well as distributed collision avoidance mechanisms.EURASIP Journal on Wireless Communications and Networking 01/2012; 2012(1). DOI:10.1186/1687-1499-2012-60 · 0.72 Impact Factor
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ABSTRACT: In cognitive radio networks (CRNs), TCP goodput is one of the key issues to measure it's performance. However, most existing research efforts on TCP performance improvement have two weaknesses as follows: first of all, most of them only consider the underlying parameters to optimize the physical performance, the TCP performance have been neglected; Second, they are largely formulated as a Markov Decision Process (MDP), which requires a complete knowledge of network and cannot be directly applied to distributed CRNs. To solve the above problems, a Q-BMDP algorithm is proposed in this paper: Each user in CRN autonomously decides modulation type and transmitting power in PHY, channels to access in MAC to find the best TCP goodput. Due to the existence of perception error of environment, this issue is formulated as a Partial Observable Markov Decision Process (POMDP) which is then converted to belief state MDP, with Q-value iteration to find the optimal strategy. Simulation results show that the network can learn optimal strategy to effectively improve TCP goodput in dynamic wireless network.Engineering and Technology (S-CET), 2012 Spring Congress on; 05/2012
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ABSTRACT: In an opportunistic spectrum sharing system, secondary users (SUs) opportunistically access the white space spectrum that is not occupied by the primary user (PU). Some analytical performance models have been available based on Markov chain modeling. In these models, SUs and PUs access the spectrum by randomly selecting the available channels with equal probability. However, how SUs and PUs use the spectrum are controlled by the access strategy designed in their MAC layer in an ad-hoc network or centralized radio resource management layer in an infrastructure-based network. To analyze the grade of service (GoS) of the secondary system under consideration for the access strategy, we propose an access rule transition matrix to model the access behavior of radio resource management, and apply it into the continuous-time Markov chain model. It was proved that the proposed model is equivalent to the original models assuming the random access strategy by simulation. Moreover, we analyzed the GoS performance of the secondary system by assuming an ordered hunt access strategy. The results showed that the GoS performance of secondary systems can be improved greatly if it knows the spectrum access strategy of the primary system. Copyright © 2011 John Wiley & Sons, Ltd.Concurrency and Computation Practice and Experience 08/2012; 24(11):1200-1212. DOI:10.1002/cpe.1890 · 1.00 Impact Factor