An Angular Soft Forwarding Scheme for Wireless Cooperative Relay Networks

In this paper, we propose a new methodology for soft forwarding which is based on a novel technique known as soft angular modulation (SAM). This is effective even under poor source-relay link conditions. The new treatment presented here allows a more flexible system design. This makes soft forwarding, which is not practical with current infrastructure, a feasible approach. In this work, we convert soft information from the soft domain into the angular domain. We then forward unity amplitude symbols using wireless fading channels. Due to the analogue nature of the probabilistic content (or soft information), the soft information relaying (SIR) scheme is not treated as a practically feasible relay protocol. We offer a remedy to this by forwarding unity amplitude symbols from the relay. Using the expression of soft noise variance, we deduct an approximate log likelihood ratio (LLR) expression for a parallel relay network employing SAM scheme. It is shown that the derived BER of SAM and numerical BER are closely aligned. The proposed scheme yields improved BER performance as compared to other conventional schemes.