BER Minimization in Relay-Assisted OFDM Systems by Subcarrier Permutation

The authors consider relay-assisted communications from a source to a destination based on OFDM. The relay performs subcarrier permutation by exploiting full Channel State Information (CSI), in addition to conventional amplify-and-forwarding. That is, the relay permutes the received signals over the subcarriers in the frequency domain, then amplifies and forwards the data to the destination. In this paper, the authors obtain optimal subcarrier permutations that minimize the uncoded BER for several relaying scenarios. From these insights, they develop a low-complexity ordering-based subcarrier permutation for the general relaying scenario. Simulations indicate that the proposed subcarrier permutation outperforms a random subcarrier permutation (where CSI is not exploited), and performs close to an optimal subcarrier permutation (which incurs a high complexity).