Power-optimized multi-hop multi-branch amplify-and-forward cooperative systems

Optimal power allocation is a critical approach to realize the full potentials of relay-assisted transmission promised by the recent information-theoretic results. In this paper an optimal power allocation scheme that maximizes the instantaneous signal-to-noise ratio (SNR) in an amplify-an-forward (AF) multi-hop multi-branch transmission system is proposed. By considering an asymptotic expression for the SNR we formulate our optimization problem as two standard geometric programming (GP) problems. By solving these problems we present an optimum power allocation algorithm which at first performs a branch selection phase, and then, derive an optimal power allocation coefficient for source and relay nodes of the selected branches. Optimized power allocation demonstrates a significant performance gain over the uniform power allocation. Simulation results are provided which verify the received SNR and consequently the outage performance are increased with optimal power allocation in Rayleigh fading channel.