Optimal relay location and power allocation for Rayleigh-fading channels in cognitive relay networks

Cognitive relay networks have been studied for the advantages of improving the throughput of secondary users. Relay location and power allocation are the key issues in cognitive relay networks, which impact on the system performance. In this paper, we analyze the problem of optimal relay location and power allocation in cognitive relay networks. Firstly, we deduce an ergodic capacity formula for the secondary users reuse the resource of one primary user in Rayleigh-fading channels, and the formula is used in the terms of high signal-to-noise ratio (SNR) and high interference-to-noise ratio (INR). Then, the expressions for optimal relay location and power allocation are derived from the deduced formula when the distances among primary users and secondary users are known. At last, an ergodic algorithm for finding the results is given. The simulation proves the proposed ergodic capacity formula is correct. The ergodic algorithm is also verified by simulation, and the optimal relay location and power can be also determined.