Research On TCP Cross-layer Optimization Scheme In Cognitive Radio

Currently, with the rapid development of the wireless communication technology, the wireless spectrum resources become more and more scarce. The fixed spectrum allocation mechanism causes a problem that the limited spectrum resources cannot be fully utilized. Cognitive Radio(Cognitive Radio, CR) technology is put forward to solve the conflicts between the limited available spectrum and the low spectral efficiency. To improve the TCP performance in the CR network, this paper researches opportunistic spectrum access and the TCP cross-layer optimization problem.Due to the limitations of the perceived equipment, secondary users cannot obtain the environment’s complete information. To solve this problem, the secondary user’s spectrum sensing and access problem is modeled as a partially observable Markov decision process(Partially Observable Markov Decision Process, POMDP) in this paper. Then the POMDP model is converted to the belief state MDP(BMDP). Finally, in order to help users select the appropriate channel for data transmission, the Sarsa(λ) algorithm is used to achieve the solution of BMDP model. Simulation results show that: the proposed opportunistic spectrum access scheme in this paper can improve the secondary users’ throughput, the effective transmission capacity and spectrum efficiency. At the same time, this scheme can reduce the bit error ratio in data transmission process.To improve the end-to-end transmission performance in CR networks, this paper uses the opportunistic spectrum access scheme based on BMDP to complete the secondary users’ channel selection. The secondary users’ sensing time and transmission time will affect the TCP performance in a CR network. To enhance the adaptability of the TCP Westwood protocol under CR environment, the cross-layer notification mechanism and transport prediction mechanism are added to this protocol. In addition, this paper establishes a TCP throughput’s cross-layer model to find the optimal sensing time in this paper’s simulation scenarios. Simulation results show that: in CR networks, using the improved TCP protocol can receive better performance than using the TCP Reno protocol or the TCP Newreno protocol.