A Cooperative LDPC-Aided Detection Scheme for Uplink NOMA Systems

This paper investigates a two-user uplink non-orthogonal multiple access (NOMA) system operating over narrowband fading channels. Both users transmit simultaneously on the same resource, generating mutual interference at two spatially separated base stations (BSs). To improve reliability under fading and asymmetric link conditions, we introduce a cooperative successive interference cancellation (SIC) architecture in which each BS monitors the reliability of its own decoding stage and activates cooperation only when decoding failures are detected. The use of LDPC coding provides both strong error-correction capability and a natural reliability indicator that drives cooperation. Numerical results show that the proposed approach yields substantial gains in error-rate performance compared with conventional non-cooperative NOMA receivers, and provides competitive or superior performance with respect to cooperative schemes based solely on cyclic redundancy check (CRC)-based error detection.