Achievable rate of dual-hop OFDM relay system with non-regenerative relay without FFT process

We evaluate a dual-hop OFDM relay system with non-regenerative relay without FFT/IFFT processes at the relay node to reduce the processing delay and the complexity of the relay process in terms of the achievable rate and throughput. To maximize the achievable rate, we propose a power allocation scheme to each subcarrier of the source node and the whole subcarrier of the relay node. Due to the flexible power allocation at the source node, the proposed system can attain a higher achievable rate by the method in which more power is allocated to a weaker channel and more power is allocated to the source node when the second hop has stronger channel gains. When OFDM symbol duration is relatively large, the throughput performances that consider the delay due to OFDM signal buffering at the FFT-process and propagation delay reveal that the proposed power allocation scheme outperforms a dual-hop OFDM relay system with subcarrier mapping and sub-optimal power allocation scheme.