Increasing Deadline-Constrained Throughput in Multi-Channel ALOHA Networks via Non-Stationary Multiple-Power-Level Transmission Policies.

Abstract

Multi-channel Slotted ALOHA is currently used primarily in satellite-based networks for transaction processing (e.g., credit card payments at cash registers). For these applications, maximization of attainable throughput while adhering to a maximum-delay constraint with a required probability reflects both the user's requirements, the network owner's desires, and the non-deterministic nature of ALOHA. This paper explores the judicious use of multiple power levels as a priority mechanism; e.g., the last transmission attempt uses higher power. It focuses on the practical and relevant range of three transmission attempts, up to three power levels, and maximum values of the permissible probability of missing the deadline (Pe) in the range 10-5 < Pe < 102. Our scheme increases the attainable delay-constrained throughput by 84-355% (two power levels) and 140-762% (three levels) over classical slotted ALOHA. An optimized combination of multiple copies and two power levels outperforms classical slotted ALOHA by 144-1240%. The smaller Pe, the greater the improvement. The benefit of our schemes is thus dramatic, and far exceeds the contribution of power capture to (unconstrained) capacity of ALOHA.