A hybrid relaying protocol for wireless cooperative networks based on the log-likelihood ratio

Employing different relaying protocols at a relay node in a wireless cooperative network could improve the overall system performance. The choice of amplify-and-forward (AF) or decode-and-forward (DF) depends on the available set of conditions pertaining to each relay node in the system. In this paper, a hybrid relaying protocol is proposed for systems employing BPSK modulation in Rayleigh fading channels. The hybrid protocol in use exploits the best DF has to offer but at a lower complexity, closer to that of the AF. Based on the log-likelihood ratio (LLR) value of the received signal at a relay node, the node decides whether it should follow the AF or the DF relaying protocols or to remain inactive. The reliability of the LLR allows for better hard-decoding due to its higher sensitivity nature. Maximal ratio combining (MRC) is carried out at the destination node to detect all the received signals. The proposed relaying protocol is tested for wireless systems where the relay nodes are symmetrically distributed or randomly distributed. The system performance is measured in terms of the bit error rate and outage probability curves, comparing it with other hybrid relaying systems.