SEP Analysis and Optimal Power Allocation of Multi-Node Amplify-and-Forward Cooperation Systems

In this paper, symbol error probability (SEP) performance analysis and optimal power allocation (OPA) are considered for uncoded multi-node relay network employing amplify-and-forward (AF) cooperation protocol over independent but not identically distributed Rayleigh fading channels. By taking advantage of the approximate probability density function (PDF) and cumulative distribution function (CDF) of the harmonic mean of two independent exponential random variables, we obtain a closed-form SEP formulation for the AF cooperation system with M-PSK and M- QAM signals, respectively. Moreover, an approximation is presented which is asymptotically tight at high SNR. Based on the asymptotically tight SEP approximation, an OPA is provided to minimize the SEP under the total power constraints. It turns out that the optimal allocation for AF cooperation system is not dependent on the modulation modes and the direct link between the source and the destination, but it depends only on the links related to the relays.