Research On Power Allocation For Relay Cooperative Communication In Cognitive Radio

With the rapid development of wireless communication and its wide application, people’s demand on wireless broadband is increasing in an exponential growth. Consequently, spectrum scarcity of radio resource is an urgent problem to solve. However, the utilization of spectrum is not efficient. The primary reason for such paradox is that amount of spectrum has been lain unused though there is a rapid growth of demand spectrum. Cognitive Radio(CR) is seemed as a fundamental way to solve the problem of low utilization. In cognitive radio networks, after cognitive user perceives the state of licensed spectrum, they can utilize some authorized spectrums on the condition that their interference is no destructive impact to authorized users. Though cognitive radio can increase the utilization of frequency spectrum, it is based on that CR users should not cause destructive interference to authorized users. Hence, the CR users’ transmission power should be constrained, which limits communication rate on the CR users. Relay cooperation can not only promote the data transmission efficiently, but also can produce diversity gains, and optimize the performance of communication network greatly as well, which ensure the required rate for CR users with a low power emission. Therefore, cognitive relay cooperative communication has become a research hot-spot in wireless communication domain.For cognitive radio relay cooperative communication system, it should be ensured that CR users’ interference to authorized users is confined to predetermined threshold, and the CR users can reach their required rate. Meanwhile, in order to realize “green” communication, it needs to minimize system power consumption.Combining relay cooperation with cognitive radio technology is one of the effective ways to improve the utilize efficiency of spectrum resources and reduce power consumption further. In this paper, optimal power allocation in relay cooperative cognitive radio systems is discussed. In the context of cognitive radio relay cooperative communication, an algorithm is proposed. By loosely coupling, non-convex optimization which satisfies time sharing condition is converted into its corresponding Lagrange function. Then, using dual decomposition method, the coupling relationship of the constraints is removed from the Lagrange function, and after KKT conditions and sub-gradient method is used to solve the optimization problem, an optimal power allocation algorithm is proposed. This algorithm, which emphasizes on the protection of the authorized users rather than pursuing the maximum throughput of cognitive users, can not only ensure authorized users’ average communication quality and worst communication quality unaffected, but also maximize cognitive users’ communication capacity. Finally, in Rayleigh fading channel, a numerical simulation on Matlab is used to prove the correctness of the proposed algorithm.