PAPR reduction of amplify-and-forward relay OFDM system using subcarrier pairing method

Best-to-worst (BTW) subcarrier pairing (SCP) has been discussed as a technique in orthogonal frequency division multiplexing (OFDM)-based amplify-and-forward (AF) relay networks, owing to a good bit error rate (BER) performance. However, the technique does not consider peak to average power ratio (PAPR), where the PAPR must be kept as low as possible to use a low cost power amplifier (PA) at relay node (RN). PAPR reduction technique should be applied in RN, because lower PAPR in source node (SN) using PAPR reduction technique might not be maintained in RN owing to channel effects between SN and RN. We propose a new approach of BTW SCP technique, S-BTW (shifted BTW) that can perform a low PAPR as well as good BER performance. After BTW reordering, we calculate PAPR and compare the value with a threshold value. If the PAPR cannot achieve the required PAPR value, the subcarrier is one-by-one circularly shifted until reaching a maximum number of shifts. For the case that the required PAPR cannot be achieved after reaching maximum number of shifts, we propose a combination of the S-BTW and clipping. Both simulation and theoretical analysis is performed to prove the validity of our proposal.