Research On Transmission Performance Of Cognitive Radio System Based On Cooperative Communication

With the rapid development of wireless communications services, the contradiction between the spectrum resource scarcity and inefficient utilization under the current fixed spectrum allocation policy is becoming increasingly acute. Great attention has been paid to cognitive radio technology, which can dynamically reuse idle spectrum resources on the premise of the interference to the primary users avoided or limited to an acceptable level, improve spectrum efficiency and achieve open spectrum sharing policy. Besides, the cooperative communication technique can get spatial diversity gain and improve system performance effectively by converging the diversity and cooperative relay techniques. For this purpose, the dissertation focuses on the contribution of improving spectrum efficiency and system performance by combining cognitive radio and cooperative communication technologies. The major work is summarized as follows:1?By investigating the two-hop cooperative cognitive network in overlay sharing(OS) mode, a cooperative detection strategy for multiple cognitive user system is considered and outage probability formulation on the Amplify-and-Forward(AF) protocol is deduced. By optimizing the parameters such as sensing time and threshold, an optimization scheme has been proposed, which is proven to minimize the outage probability and improve transmission reliability of cognitive network on the premise of guarantee fixed detection performance.2?By analyzing the two-hop cooperative cognitive network in underlay sharing(US) mode, an approximate outage probability formulation and diversity order have been derived for amplify-and-forward with relay selection(AFRS) and decode-and-forward with relay selection(DFRS) protocol. On this condition, hybrid protocol with relay selection(HPRS) is proposed. Meanwhile, the approximate outage probability formulation and diversity order for HPRS were deduced. Compared with AFRS and DFRS protocol, the HPRS can achieve better outage performance and higher reliability.3?By analyzing the multi-hop cooperative cognitive diversity network in OS mode, an approximate outage probability formulation has been derived for decode-and-forward(DF) protocol in high signal-to-noise ratio. An optimal scheme is proposed, which can improve outage performance and transmission reliability of multi-hop cognitive system by optimizing sensing time.4?By analyzing the multi-hop cooperative cognitive diversity network in US mode, an approximate outage probability formulation and diversity order has been derived for DF protocol in high signal-to-noise ratio. As DF protocol cannot achieve space diversity gain, modified multi-hop selective decode-and-forward(SDF) protocol is proposed. An approximate outage probability formulation and diversity order are deduced for SDF protocol in high signal-to-noise ratio. Contrasted with DF protocol, SDF protocol can decrease outage probability and achieve the full space diversity.