Maximizing throughput in a random access radio system by optimal power level choice

Abstract

To enhance the throughput of a slotted random access protocol in a radio communication system, we describe the use of a scheme in which multiple power levels are used at the transmitters. We consider a situation in which n transmitters are simultaneously trying to send a packet to a central receiving station using a time-slotted access protocol, like slotted ALOHA. Each of these transmitters randomly chooses one of m discrete power levels during each attempt to send a packet. One of the simultaneously sent packets can often be successfully received due to the power capture effect. Two types of capture models are presented and analyzed: (1) one in which the transmitter with the largest received power captures the channel and (2) one in which the transmitter captures the channel only if its signal-to-interference ratio is above some threshold when received at the central station. We determine the optimal transmit probabilities for the power levels as well as the optimal values of the power levels when their range is constrained.