Optimum Power Allocation for LDPC Coded Soft Forwarding Scheme in Wireless Networks

This paper proposes a new power efficient multilevel threshold based soft quantization (MLT- SQ+PA) scheme for a multiple access relay system (MARS). In the proposed MLTSQ+ PA protocol, the relay computes the reliabilities, expressed as log-likelihood ratios (LLRs), of the received signals from the two sources. We provide an analytical closed form expression for the optimized power allocation factor at the relay. The relay evaluates the LLRs of the network-coded packet, quantizes and scales these using the optimum power allocation factor, forwarding the resulting "quantized soft symbols" to the destination. Compared to competing schemes, the performance of our system is superior in terms of BER when the same amount of channel state information (CSI) is exploited.