Research On Cooperative Spectrum Sensing、Cooperative Transmission And Spectrum Handoff In Cognitive Radio Network

With the rapid development of information industry especially the mobile telecommunication industry, the requirement of the wireless spectrum increases rapidly, the conflict becomes much more obviously between the scarcity of wireless spectrum and the low efficiency of the static assignment policy of the wireless spectrum. Enhancing the efficiency of the wireless spectrum has attracted much more attention.Cognitive radio is considered to be one of the most important techniques to improve the efficiency of the wireless spectrum.The accurate sensing of the wireless spectrum is the precondition for the secondary users to use the wireless spectrum and becomes one of the most important research fields of wireless spectrum. Cooperative spectrum sensing can improve the sensing accuracy and has been widely researched. In the period of cooperative spectrum sensing process, multi-users involved in the process will consume much resource for their cooperation. This paper proposes a novel cluster-based sensing strategy related with fuzzy logic neural network to realize the cooperative spectrum sensing. Besides, a new niche genetic algorithm based on improved gradient operators is proposed to select the cluster head.Cooperative communication can improve the system capacity and the network service quality in wireless communication system. The cooperation between users in cognitive radio network (CRN) can greatly improve the expected spectrum efficiency. The broadcast nature of wireless network and character of fountain code suitable to the multicast and time-varying channel in CRN, this paper proposes a novel cooperative scheme based on Raptor coding, the licensed transmitter adopts Raptor encoding process and broadcasts the encoded packets, the cognitive transmitters in a specific location transmit the licensed transmitter’s encoded packets, then each transmitter forwards the encoded packets to the licensed receiver directly, the objective licensed receiver receives the packets both come from the licensed transmitter and the cognitive transmitters.This section proposed another cooperative method based on network coding in cognitive multicast system, a cognitive relay transmitter helps the licensed user transmit data packets, we select the relay who locates in the place that has higher channel gain between the relay and the licensed receiver than that between the licensed transmitter and the licensed receiver, the relay maintains one table of the licensed receiver’s un-received packets, the relay performs network coding and combines these packets into a new combined packet by XOR the licensed receiver’s un-received packets according to the table, and then forwards the new combined packets to the licensed receiver. As for the packets that have not received by the cognitive relay transmitter, the licensed transmitter re-transmits these packets. By way of network coding and cooperative transmission, the whole system can save energy and increases the throughput for the reason that the number of the transmitting packets decreased.Since the fuzzy logic can change the vague uncertain and heterogeneous information into the homogenous and comparable variables which suitable the character of CRN, this paper proposed a spectrum handoff strategy based on fuzzy logic controller to realize the spectrum handoff. The cognitive users utilize the opportunistically listening network coding to get the licensed users’information far away which cannot be detected by themselves. The cognitive user adopts fuzzy logic controller to activate the spectrum handoff on the condition that the interference level beyond the licensed user’s predefined threshold or just to modify the transmitting power and coexist with the licensed users on the condition that the interference level less than the licensed user’s predefined threshold. The simulation results demonstrate that the proposed method can decrease the spectrum handoff rates. To sum up, this paper proposed several methods to improve the spectrum efficiency in CRN, such as cooperative sensing based on the fuzzy logic neural network, the cooperative cognitive relay communication based on Raptor coding, the cooperative multicast strategy based on network coding, and the spectrum handoff based on fuzzy logic controller. The further research fields focus on the confusion of heterogeneous cognitive radio networks and the future ubiquitous networks.