Joint subchannel-relay assignment and bit allocation for multi-user cooperative OFDMA systems based on fairness

Joint bit allocation, relay selection, and sub-channel assignment are critical and challenging for achieving full benefits of OFDM based cooperative relay networks. In this paper, we study such a problem in an OFDM cooperative network comprising of multi battery-operated source-destination pairs and multiple relays with an objective of minimizing overall transmitting power under a total power and target data rate constraints. Assuming knowledge of the instantaneous channel gains for all links in the entire network, we propose several fairness criteria aiming at providing attractive trade-offs between network lifetime and users´ outage probability. Numerical studies are conducted to evaluate the performance of the proposed algorithms in two practical scenarios. Simulation results show that the proposed allocation algorithms achieve good tradeoff between the network lifetime and users´ outage.