Fairness-aware shared relay assignment for cooperative communications

The choice of relay nodes significantly affects the performance of wireless cooperative networks. Previous research mostly focused on dedicating one relay node to a source node in the network. However, fairness can be improved by sharing each relay node among more than one source node. This paper first defines the shared relay assignment for (max-min) fairness (SRAF) problem, and formalizes it using a mixed integer program. We then propose a heuristic algorithm (RRA) to solve this problem. The algorithm mainly uses the binary search and rounding mechanisms to implement the shared relay assignment, so that the minimum throughput of all source nodes is improved. The theoretical analysis proves that the proposed algorithm can reach the approximate performance of 2+ε, where ε is an arbitrarily small positive number. An improved version of RRA, called IRRA, can improve the minimum throughput while still preserving the worst-case performance. Our simulations show that the IRRA algorithm can achieve about 18% improvement over the best existing approach in the minimum throughout among the source nodes.