Equal Opportunity MAC Scheme for Contending Sensor Nodes in Wireless Passive Sensor Networks

Abstract

In a wireless passive sensor network, RF sources wirelessly supply energy to sensor nodes. Against theoretical expectations for an abundance of energy, a wireless passive sensor network suffers from a scarcity of energy in practice. By such a scarcity, a wireless passive sensor network is obliged to adopt a contending-type MAC scheme, which inevitably brings about packet collision and hence capture phenomenon. Unfortunately, the capture phenomenon places a sensor node which is far off from the sink node at a distinct disadvantage. In this paper, we propose a MAC scheme, rooted in framed and slotted ALOHA, which provides every sensor node with an equal opportunity for succeeding in packet delivery. In a case study, we prove the existence of an equal opportunity MAC scheme and construct such a MAC scheme explicitly. In addition, we develop an exact expression of the throughput attained by the proposed scheme in a closed form. Using the throughput formula, we then demonstrate that the proposed scheme is able to achieve a higher total throughput than a conventional scheme.