Physical-Layer Network Coding Based Decoding Scheme for Random Access

In this paper, we propose an enhanced low-complexity binary physical-layer network coding (PNC) based decoding scheme for random access systems with binary phase-shift keying modulation to improve the system throughput. In the proposed scheme, the linear combinations of collided users' messages in each time slot are first obtained by exploiting a low-complexity PNC decoding scheme. Based on the decoded linear combinations within a MAC frame, we then propose an enhanced message-level successive interference cancellation algorithm to recover more users' messages. We propose an analytical framework for the PNC-based decoding scheme and derive a tight approximation of the system throughput for the proposed scheme. Subsequently, the number of repeated transmissions of a message, i.e., the number of replicas transmitted by each user, is optimized to further improve the system throughput and energy efficiency. Interestingly, the optimization results show that the optimal number of replicas for maximizing the energy efficiency is a constant for all offered loads. On the other hand, the optimal number of replicas that maximizes the system throughput decreases as the offered load increases. Numerical results show that the derived analytical results closely match with the simulation results. Furthermore, the proposed scheme achieves a considerable throughput improvement, compared to the CRDSA++ scheme.