Research On Cooperative Transmission Technology In Cognitive Radio Networks

It has provided a solution to improve the system performance of anti-fading, channel capacity and spectrum utilization by combaining cooperative transmission and cognitive radio. This paper emphatically focuses on the network code technology for cooperative nodes in order to improve system reliability, and discuss optimal power allocation and cooperative strategy in cognitive radio networks.First, by layouting Orthogonal Frequency Division Multiplexing and network coding into coopetative nodes in cognitive radio networks, it effectively improves the system performance under frequency selective channel transmission. And it analyzes the system outage probability and demonstrates the network coding gain by numerical simulation.Secondly, in resource-constrained cognitive radio networks, how to improve the power efficiency of sub-user network is a question worth considering. To address this problem, it first proposes the optimal power allocation algorithm based on the power efficiency of the sub-users in cognitive radio networks. The algorithm not only considers the limit of primary network outage probability on secondary users transmit power , but also the outage probability requirements of secondary network itself at the same time. Besides, it presents a low complexity suboptimal power allocation algorithm by reducing the dimension of the objective optimization problem, converting it into two sub-problems so as to be solved conveniently,which brings only limited performance loss compared to optimal algorithm the sub-optimal algorithm, but saves the computing time and storage space effectively.Finally, it considers the issue when the relay node should assit the source node to transmit information. It proposes a cooperative guideline based on cooperative level. Firstly the notion of cooperative level is defined, then the expressions of system bandwidth utilization and the average symbol error rate are deduced, finally the system performance function is got through the compromise between the coorperative thresholds and power ratio. It also employs particle swarm optimization algorithm to solve optimal cooperative threshold and optimal power ratio.