Throughput optimal communication strategy for wireless random access channel

We consider a wireless time-slotted random access channel where user arrivals are characterized by a Poisson process. Each user comes with a fixed payload, which has to be transmitted in the slot in which it arrives. If the transmission is successful, the user leaves the system, else it is dropped. The receiver and users are assumed to have knowledge of the arrival rate λ, but they are not aware of the actual number of users simultaneously attempting to communicate during a given time slot. In contrast to a conventional slotted ALOHA-based strategy where the channel is partitioned into orthogonal subchannels and each user communicates on a randomly chosen subchannel, we propose a novel strategy whereby users transmit simultaneously over the entire channel resource and the receiver jointly decodes the transmissions. Under the proposed strategy, neither users nor the receiver have prior knowledge of the active user set. Our analysis concretely demonstrates that the proposed strategy is optimal in terms of maximizing the average throughput among all uncoordinated strategies. Numerical results show that the proposal provides an order of magnitude throughput improvement compared to slotted ALOHA in a single-cell environment under a 10% maximum outage constraint.