Cooperative Relay Selection In Cognitive Radio Network

It can be found from the development of mobile communication system that it is an eternal theme in the field of wireless communication to meet people’s increasing need of wireless data service. With the advanced mobile communication technologies continuing to emerge, the shortage of spectrum resources is becoming increasingly serious. However, the current fixed spectrum allocation policy exists extreme imbalance in spectrum utilization: some spectrum resource is idle most of time, while others may be overcrowded. Cognitive radio emerged in this situation. This technology can sense the wireless environment, and find the idle spectrum resource, and then chance transmission parameters dynamically, which aimed at re-using the spectrum resource. Now, cognitive radio is regarded as the most promising technology of wireless communication.In cognitive radio network, the primary system co-exists with secondary system in the same area. On one hand, the secondary system should avoid interfering the primary system, on the other hand, the secondary system also need to guarantee the quality of secondary users’ communication. Due to these reasons, introducing the relay communication into cognitive radio secondary system can firstly improve the performance of spectrum detection by utilizing the independence of wireless channels and secondly improve spectrum utilization by forwarding the data. Hence, the relay selection has become the hot topic in cognitive radio network.This paper researches on relay selection in the scene of cooperation cognitive radio network aiming at improving the quality of service for secondary user. It finds that random relay selection scheme only consider the interference to primary user with low complexity. However the selected relay may not match the needed data rate of transmitter, and thus lead to communication outage. The best SNR relay selection scheme considers both interference to primary user and quality of wireless, but it ignores the characteristic of dynamic changes for the available spectrum holes in the selected relay. Therefore, the location of relay and the activities of primary users may affect the number of available spectrum holes which used to forward resource data, and then result in outage of secondary users. So, this paper studies both the affection of primary activities and the quality of different wireless channels, and propose the combined quality of channel and spectrum resource relay selection scheme. Both theory analysis and computer simulation show that the proposed relay selection scheme can improve the throughput of secondary system, decrease the outage of secondary user, and guarantee the quality of user’s communication.