Erasure, Capture, and Random Power Level Selection in Multiple-Access Systems

A communication system with many nodes accessing a common receiver through a time-slotted shared radio channel is considered. Ideally, each transmission of a node is heard by the receiver. In practice, however, due to topological and environmental conditions, the receiver is prone to fail to hear some or all of the packets transmitted in a slot. The phenomena of failing to detect any packet is called erasure, while detecting a single transmission out of many is called capture. This paper introduces multiple-access algorithms that handle erasures as well as captures. The algorithms are evaluated according to the maximal throughput that they can support for a Poisson arrival process. An example is given which shows that, in practice, the positive effect of captures compensates the negative effect of erasures. In addition, we introduce a new approach to effectively exploit the capture phenomena. This approach incorporates a random power level selection scheme that allows each node to randomly choose to transmit in one of several allowable levels of power. Design issues such as number of levels, selection schemes, etc., are discussed. © 1988 IEEE