Performance Analysis And Power Allocation Strategy Of Cooperative Relay System Based On Cognitive Radio

Wireless communication has two major problems i.e. spectrum resource scarity and channel fading effect. With the rapid development of wireless technique and wide usage, the spectrum scarity gets worse. To that end, cognitive radio is proposed to improve the spectrum utilization efficiency by accessing the licensed spectrum in opportunistic way under the premise of quality of service constraints of licensed users. On the other hand, cooperative diversity has emerged as a effective technique to combat channel fading by providing a powerful diversity gain. Therefore, cognitive relaying combined with cooperative relaying and cognitive radio has attracted wide attention for its great improvement on outage performance such as outage performance (OP),ergodic capacity (EC) and symbol error rate(SER).In this paper, we investigate outage performance and optimal power alloction (OPA)strategy of cognitive relaying system in Rayleigh fading, respectively. We consider the system consists of a primary network equipped with several primary users (PU) and a secondary network equipped with multiple secondary users (SU). The transmit powers of SUs are strictly limited by the interference power limits tolerable by PUs. The scenarios of cognitive relaying communication in this paper include multiple relays, single PU/multi-PUs,maximum transmit power limits. On the basis of statistics and information theory, we derive the closed form of OP, EC and SER for various scenarios to analyze the impact of various parameters on outage performance, and OPA strategies are given.The main research work in this paper including: 1.Deriving the closed-form expression for OP, EC and SER of cognitive decode-and-forward (DF) relaying system equipped with single PU with maximal-ratio-combing (MRC)/all-participating (AP); 2.Deriving the closed-form expression for OP of cognitive DF relaying system with multi-PUs and MRC/AP;3.Deriving the closed-form expression for OP of cognitive DF relaying system with single PU and MRC/AP under maximum transmit power limits; 4.Deriving the closed-form expression for OP of cognitive DF relaying system with multi-PUs and MRC/AP under maximum transmit power limits; 5.Deriving the closed-form expression for OP of cognitive amplify-and-forward (AF) relaying system with single PU and selection AF (S-AF)/all-participating AF (AP-AF); 6.Deriving the closed-form expression for OP of cognitive AF relaying system with single PU and S-AF/ AP-AF under maximum transmit power limits;7.Deriving the closed-form expression for OP of cognitive AF relaying system with multi-PUs and S-AF/AP-AF; 8.Giving OPA strategies for cognitive relaying with MRC-DF/S-AF/AP-AF/AP-DF. Finally, the closed-form expressions derived are verified by Monte Carlo simulations, and we compare the numerical outage performance of cognitive relaying system in various scenarios with different parameters to analyze their impact on outage performance. We find that: (1) the diversity gain is equal to the number of cognitive relays, and outage performance gets improved by increasing the number of relays; (2) higher OP is obtained by increasing the number of PUs; (3) outage performance gets improved by extending the maximum transmit power limits.Above all, this paper investigates the outage performance and OPA of cognitive relaying system in different scenarios. By considering the inadequacies in the previous works, we derive the closed-form expressions of several outage performance metrics and give the OPA strategy, which develop the research works in cognitive relaying.