Cooperative communications using reliability-forwarding relays

This study presents a new relay strategy and associated diversity combining technique for improving the communication performance in semi-blind cooperative networks. In constructing the network model, it is assumed that each relay can obtain the perfect channel state information (CSI) from the source to itself, and the destination can acquire the perfect CSI from all the relays to itself, but does not require the CSI from the source to the participating relays. In performing the considered semi-blind cooperative communications, the relays forward their reliability to the destination using a quantized reliability-relaying (QRR) scheme. Specifically, the relays partition their reliability into three levels in accordance with the log-likelihood ratio (LLR) value of the received signal, and forward a regenerative symbol to the destination if the quantized reliability falls within the "send +1" or "send-1" region; and remain silent otherwise. It is shown theoretically that the QRR scheme achieves a higher deflection coefficient than the regular decode-and-forward (DF) scheme, in which all the participating relays forward their regenerative messages to the destination irrespective of their reliability. Moreover, the simulation results show that given the same semi-blind model, the QRR scheme achieves a lower bit error rate (BER) than existing relay selection DF schemes for all considered values of the average input signal-to-noise ratio (SNR).