Decode-Quantize-Forward for OFDM-Based Relaying Systems

In this paper, we present a new relaying protocol for coded OFDM-based relaying systems. The classical Decode-Forward (DF) protocol exploits the coding gain within the relay, however the overall performance suffers from error propagation in case of decodings errors at the relay as no reliability information about the source-relay (SR) link can be exploited. This drawback is avoided by the proposed Decode-Quantize-Forward (DQF) scheme, where the code bits estimated by the decoder in the relay are directly forwarded to the destination. Based on the observation, that code bit errors at the relay occur likely on subcarriers with low signal to noise ratio (SNR) on the SR link, we propose a modified maximum ratio combining (cMRC) scheme for the destination. As this approach exploits the varying channel reliability per subcarrier it outperforms the well-known DF protocol significantly.