Cyclic Prefix Update for OFDM Amplify-and-Forward Relay Systems

We consider half-duplex amplify-and-forward (AF) relaying for increasing network coverage and spectrum efficiency of an OFDM-based cellular system. Due to the fact that OFDM symbols are transmitted over two serial multipath channels (i.e., the source-relay link and the relay-destination link) via AF relaying, the time spread of the received signal at destination nodes is introduced by both source-relay and relay-destination channels. Consequently, cyclic prefix (CP) added at the source node should have a much longer length than that of one-hop OFDM transmission to avoid inter-symbol interference. However, the increased CP length leads to the reduced spectrum efficiency of OFDM communications. In this paper, we propose a novel CP update scheme for achieving efficient and reliable multi-hop transmission in OFDM-based AF relay systems. By enabling the additional CP discarding and CP re-adding functionalities to relay nodes, the proposed scheme significantly reduces the required CP length without causing extra loss in the bit error rate performance, and therefore improves achievable end-to-end throughput and spectrum utilization efficiency. Simulation results confirm the theoretical analysis and illustrate the effectiveness of the proposed scheme.