Contention Resolution Diversity Slotted ALOHA with Variable Rate Burst Repetitions

Contention resolution diversity slotted ALOHA is a simple but effective improvement of slotted ALOHA. It relies on MAC bursts repetition and on interference cancellation to increase the throughput of a classic slotted ALOHA access scheme. This improvement permits to achieve a throughput up to T ≃ 0.55, whereas slotted ALOHA is capable of providing T ≃ 0.37. In this paper we show that the iterative interference cancellation process used in contention resolution diversity slotted ALOHA can be described by a bipartite graph. Such representation permits to establish a bridge between the iterative interference cancellation process and the iterative erasure recovery process of graph-based codes. Exploiting this analogy, we show how a higher throughput (close to T ≃ 0.9) can be achieved by selecting variable burst repetition rates, leading to irregular graphs, according to given probability distributions. A framework for the probability distribution optimization is provided as well. Simulation results including the actual interference cancellation mechanism confirm the high efficiency of the proposed approach.