Enhancing CRDSA with Transmit Power Diversity for Machine-Type Communication

Contention resolution diversity slotted ALOHA (CRDSA) is a promising solution to meet the challenge of designing efficient random access in future wireless networks. In this paper, we consider CRDSA with transmit power diversity where each packet copy from a device is transmitted at a randomly selected power level. This results in interslot received power diversity, which is exploited by employing a signal-to-interference-plus-noise ratio based successive interference cancellation (SIC) receiver. Leveraging edge-weighted bipartite graph representation, we propose a novel graph-based message passing algorithm to model the SIC decoding. We derive an expression to characterize the recovery-error probability of the scheme. We also formulate and solve an optimization problem to determine the optimal transmit power distribution. The results show that by enhancing the capture effect, the optimal transmit power distribution leads to considerable performance improvement.