Study On Cooperative Behavior In Cognitive Radio Networks

With the rapid development of wireless communication networks, wireless spectrum resource is becoming increasingly scarce. Now wireless spectrum is divided into two parts by the nation, which are the licensed frequency band (LFB) and unlicensed frequency band (UFB) respectively. The fixed spectrum approach has hindered the development of the communication network. The utilization of licensed spectrum is very low, and the new emerging wireless technology is mostly used in the unlicensed bands. The limited available spectrum and the low utilization of the spectrum has expedited a new communication pattern, named cognitive radio technology.Except for spectrum utilization, advanced wireless technologies are essential required to achieve high data transport rate and quality of service (QoS). Recently, the multi-hop transmissions, especially the cooperation diversity technology, have brought up a prevalent attention in wireless community. We can enhance the performance, for example, link reliability and network throughput by nodes'cooperation. In cognitive radio networks, a cognitive user cannot access a primary channel until it senses idle channel. Thus, the cooperation scheme in cognitive radio networks is more difficult than general ad hoc networks because of channel dynamics. In this thesis, we study the optimization design for cooperative diversity in cognitive radio networks.Firstly, we study the problem of optimal configuration and power allocation in cognitive radio networks. Considering the outage performance metric, we discuss the best position of the relay node under optimal power allocation. Experimental results ensure that the system outage performance is improved. Moreover, we provide an efficient procedure for the location of relay nodes.Secondly, we investigate the outage performance in industrial cognitive radio network with multi-relays. To minimize the outage probability in the cooperative diversity system, one best relay node will be selected and besides, optimal power allocation is performed between the source and relay. Moreover, a new joint optimization of relay selection and power allocation algorithm is proposed.In the end, we focus on the resource allocation for the orthogonal frequency division multiplexing access (OFDMA) technology based cognitive cooperation relay network. The joint resource allocation scheme based on particle swarm optimization (PSO) incorporates subchannel allocation, power allocation and QoS constrains. Simulation results show that the proposed method can maximize the system throughput.