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New methods for Opportunistic Spectrum Access in Multi-user Cognitive Radio Networks

Saleh Kaleybar, Saber | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42080 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Pakravan, Mohammad Reza
  7. Abstract:
  8. In this dissertation, we design channel access strategies for opportunistic spectrum access in cognitive radio networks. It is assumed that the secondary transmitter and receiver hop across spectrum opportunities synchronously. This synchronization between the transmitter and the receiver can be separated in two phases: In the first phase, two Secondary Users (SUs) meet each other for the first time in a spectrum opportunity and exchange control messages. In the second phase, two SUs hop across available channels to transfer data. Rendezvous algorithm can facilitate the first meeting of two SUs. For the first phase, we propose a blind rendezvous algorithm and study its features. We show that the maximum time to rendezvous for the proposed algorithm is at least three times lower than other related works. For the second phase, we consider two models for the dynamic behavior of channels’ occupation: Markov and Bernoulli models. Assuming Markov model for the channels, we propose a joint policy for SUs. This joint policy not only tries to maximizes network throughput but also guarantee quality of service constraints. In addition, we define an upper bound for a specific class of strategies in Markov model which is called myopic policy. We compare it with simulation data to show its tightness. In the case of Bernoulli model for the channels, we prove that the optimal mixed strategy is in a specific set and it can be extracted by mixed integer linear programming. Unfortunately, this solution requires complete information about the network in each SU. Hence, we propose a distributed algorithm and study its features such as regret and convergence issues. To the best of our knowledge, the proposed algorithm is the first kind of distributed graph coloring which is employed to obtain appropriate mixed strategies for SUs. Besides, simulation results show that the proposed algorithm has better performance than the other related works in practical scenarios. At last, we obtain first and second moments of SUs’ queues for a random access strategy with an approximation approach. We also discuss about optimal access strategies and buffer management problem in the considered network. The main advantage of this queue analysis is that it considers exact time slots in contrast to other related works which consider fluid approximation for time slots in deriving moments of queue lengths. Furthermore, the proposed moments of SUs’ queues are closer to simulation results rather than the other related work in this feild. To the best of our knowledge, the buffer management analysis in cognitive radio networks has been studied for the first time in this thesis and simulation results verify our analysis.
  9. Keywords:
  10. Cognitive Radio ; Opportunistic Spectrum Access ; Rendezvous Algorithm ; Access Strategies

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