Two-Way DF Relaying for OFDMA System

Wireless communication has become widely used in recent years acquiring higher demand of efficient wireless systems effectively competing various wireless complications. Cooperative communication is thought as one method to compete the effects of fading and enhancing the throughput of wireless transmission where the use of relay nodes randomly distributed introduces a rich spatial diversity to accomplish a better system performance and improve the coverage for the users near the edge of the cell. In this paper, a Two-way Decode and Forward Relaying for orthogonal frequency division multiple access (OFDMA) mobile systems (TWR-DF-OFDMA) is proposed. The system consists of mobile terminals (MTs) divided into near nodes and far nodes in which the base station directly transmits to the near nodes and indirectly transmits to the far nodes by the cooperation of the near nodes which act as relays. A multi relay selection scheme is proposed in which NNs with the best channel conditions are chosen for a particular FN. Another scheme is further proposed in which MTs are classified into near nodes, far nodes, and direct nodes. The effect of channel estimation error on the performance of the proposed scheme is investigated. The performance of the system is measured in terms of the bit error rate and the sum rate. It is found that the performance of TWR-DF-OFDMA is much better than that of direct transmission case. Furthermore, it is shown that the number of NNs in the system affects the performance of TWR-DF-OFDMA and an optimum number was found to give the highest performance of TWR-DF-OFDMA compared to direct transmission case.