On optimal relay selection and subcarrier assignment in OFDMA relay networks with QoS guarantees

This paper investigates QoS-aware relay selection and subcarrier assignment in cooperative OFDMA networks. In contrast to some existing works, which solve the sum-rate maximization problem directly, we first simplify it by exploiting the structure of the optimal solution, then we solve the simplified problem. To characterize the optimal network sum-rate performance, we solve the simplified problem optimally by the branch-and-cut method. In addition to the sum-rate maximization problem, we demonstrate that its two variants can also be similarly simplified and then be solved optimally by the branch-and-cut method. The optimal method serving as the benchmark is particularly suitable for moderate scale problems. Simulations show that the branch-and-cut method can locate the optimal solution effectively, which may in turn provide some insights into the performance of the heuristic method.