Optimizing relay selection and power allocation for orthogonal multiuser downlink systems

This paper studies the relay assignment and power allocation for orthogonal multiuser systems using amplify-and-forward (AF) relays in the downlink. Our objective is to maximize the sum-rate of all users, subject to individual and total power constraints on the relays and a relay assignment constraint. For fixed relay selection, the power allocation problem is convex and can be optimally solved, whereas the joint optimization of relay selection and power allocation appears to be non-convex and is not known to be tractable. To tackle this, we propose an algorithm using Markov chain Monte-Carlo (MCMC) in combination with cross-entropy optimization (CEO). Results show that the scheme outperforms significantly a greedy approach and achieves near-optimal performance at very low complexity.