Shared relay assignment in cooperative communications for bandwidth maximization

Previous research mostly focused on mutually assigning one relay node for a source node to explore the transmission gains of cooperative communications. However, sharing a relay among multiple source nodes can improve the utilization of the relay node. This paper first defines the shared relay assignment for max–min bandwidth (SRA-MMB) problem and max–total bandwidth (SRA-MTB) problem, and formalizes them using integer programs. For the SRA-MMB problem, we propose a heuristic shared relay assignment algorithm (called RRA-MB) using binary search and rounding methods to maximize the minimum bandwidth of all the sources. The theoretical analysis proves that, in the worst case, the proposed algorithm can reach the approximate performance of \(2 + \varepsilon\), where \(\varepsilon\) is an arbitrarily small positive number. For the SRA-MTB problem, we propose a 2-approximation algorithm based on the rounding method to maximize the total bandwidth when each source has a relay usage time limit. Moreover, an optimal algorithm is designed to solve the special instance of SRA-MTB, in which all the source nodes have the same (i.e., uniform) limit on its relay usage time. Our simulations show that the proposed algorithms can achieve about 18 and 27 % improvements over the existing approaches in terms of minimum and total bandwidths respectively.