A power-efficient method to increase common rate in AF multi-way relay channels

Multi-way relaying is a cooperative scheme for communication scenarios where several users want to share their data with each other. While the capacity of multi-way relay channels (MWRCs) is still unknown to completely understand their potentials, the achievable data rates of MWRCs have been studied for specific setups. In this work, we aim to get a better understanding of the achievable data rates of an amplify-and-forward (AF) MWRC. To this end, we first present an achievable upper bound for the common data rate of an AF MWRC and discuss how users´ power allocation affects the common rate. While full power transmission at the users assures reaching the maximum achievable common rate in one-way relaying, we show that it is not the case for MWRCs. Thus, we formulate an optimization problem to find the optimal users´ power allocation to gain the maximum common rate. Finding an optimal solution for this optimization problem is quite complex since the number of constraints grows exponentially with the number of users. We then focus on a relaxed version of the rate optimization problem and propose a suboptimal algorithm to solve it. Our simulation results show that the proposed algorithm can achieve rates higher than the ones achieved through full power transmission with noticeably lower transmit power at the users.