Performance Analysis Of Cognitive Relay Network

In recent years, with the development of wireless communication, the traditional fixed Spectrum allocation method can not satisfy the increasing demand for wireless communication system. As a revolutionary intelligent spcectrum sharing technology cognitive radio can guarantee the communication system with high reliability and efficient spectrum utilization. For that reason, cognitive radio develops rapidly and gets wide attention. In addition, the cooperative relaying techniques can make the system get as high performance as MIMO. When we apply the cooperative relaying techniques into cognitive networks, a new research topic appears. It can maintain the characteristics of cognitive radio and the reliability of the cooperative relaying techniques. Therefore, in this thesis, we focus on the performance of cognitive relay networks and our main contributions are below as:1. In cognitive relay networks, with multiple relays available for spectrum sensing and data transmission, the system can get better performance than traditional methods. But with the imperfect spectrum sensing in practice, the secondary user’s transmission may interfere with the primary user inevitably. We investigate the impact of imperfect spectrum sensing on PU with distributed spectrum sensing and cooperative spectrum sensing. The exact expressions for interference probability of PU are derived under Rayleigh fading channels. It is shown that the interference from the SU badly degrades the PU’s performance. Simulation resultsand analysis show that increasing the number of relays benefits the PU.2. In spectrum sharing networks, the exact expressions for outage probability of SU are derived under Rayleigh fading channels with the imperfect spectrum sensing and perfect spectrum sensing. Moreover,to evaluate the impact of imperfect spectrum sensing on SU,we put forward the outage probability gap of SU.Simulation results and analysis show that increasing the number of relays benefits the SU.3. The adapitive technique can adjust its parameters with the change of system. When we apply the adaptive technique into cognitive relay networks, it can improve the system performance. So we investigate the performance of adaptive modulation in spectrum sharing cognitive relay networks, where the secondary user (SU) transmits the message by one best relay with amplify and forward (AF) relaying scheme. The capacity of adaptive modulation with opportunistic AF relaying is firstly derived under independent Rayleigh fading channels. Then, with adaptive L-QAM modulation and fixed switching threshold, the outage probability, average spectral efficiency, and the average error bit rate (BER) of the SU are derived. Simulation results validate our analysis and show that adaptive modulation can improve the SU’s performance significantly.