An optimal graph approach for optimizing OFDMA relay networks

This paper considers a relay-assisted cooperative network where multiple relays assist the communication of multiple users using orthogonal frequency-division multiple-access (OFDMA). Our goal is to improve system performance by exploring full potential of the network in various dimensions, including user, relay, channel, and transmission mode. We formulate the joint optimization of subcarrier pairing, subcarrier assignment, relay selection, and transmission mode selection. We show that this combinatorial optimization problem can be transformed into a minimum cost network flow (MCNF) problem with integer solutions in graph theory. Then the linear optimal distribution (LOD) algorithm is applied to find the optimal solution in polynomial time. Simulations show that the proposed algorithm can significantly enhance the overall system throughput.