LDPC Coded Angular Modulation Scheme for Cooperative Wireless Networks

This paper investigates a new methodology for soft information forwarding (SIF) based on a novel technique known as soft angular modulation (SAM). In this new relay scheme, the soft symbols are embedded into phases at the relay. This is more advantageous as we refrain to forward real values (under bandwidth constraints) via wireless channels. This makes the proposed scheme practically feasible. The proposed system provides a means of using distributed low-density parity- check (LDPC) coding in conjunction with a new soft encoding scheme (puncturing), which is useful even under indigent source-relay link conditions. This also precludes the amplitudes of generated symbols descent to zero, as happens with most of the existing soft forwarding methods. Ordinarily, such schemes suffer from error propagation to the destination when the signal-to-noise ratio (SNR) of the source-relay link is low; however, our system avoids this problem by regenerating soft versions of the source symbols at the relay. Furthermore, we also propose a computationally efficient formula for log-likelihood ratio (LLR) at the destination. Simulation results demonstrate that the proposed scheme can maintain very good performance under poor source relay SNR conditions.