[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Scarcity problem of radio spectrum resource stimulates the research on cognitive radio technology, in which dynamic spectrum allocation attracts lots of attention. For higher access efficiency in cognitive radio context, we suggest a fully dynamic access scheme for primary and secondary users, which is modeled by a master-slave stochastic knapsack process. Equilibrium behavior of this knapsack model is analyzed: expressions of blocking probability of both master and slave classes are derived as performance criterion, as well as forced termination probability for the slave class. All the theoretic results are verified by numeric simulations. Compared to traditional opportunistic spectrum access (OSA), which can be regarded as half dynamic due to primary users’ rough preemption, our scheme leads to less termination events for the secondary users while keeping the same performance for the primary class, thus promotes the system access performance. Nonideal spectrum sensing algorithm with detection error is also taken into consideration to evaluate its impact on system access performance, which is a practical issue for implementation.
Mobile Networks and Applications 12/2012; 17(6). · 1.11 Impact Factor
[Show abstract][Hide abstract] 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 2012(1). · 0.54 Impact Factor
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