Structuring contention-based channel access in wireless sensor networks

Abstract

In a wireless network using CSMA for MAC, packet collisions can result either because of the vulnerability stemming from the idle channel detection delay of the radio device or because of the hidden terminal problem. Both of these collision scenarios can be addressed by applying some additional structure to carrier sense-based channel access, sacrificing throughput to improve collision protection. Specifically, we assign a unique time slice to each contending transmitter that is designed to allow collision-free access to each data slot while still using carrier sense as the mechanism to determine channel state. The width of each time slice is equal to the idle channel detection delay of the radio. We prepend a fixed-length time interval to each transmitted packet whose length is proportional to the idle channel detection delay of the radio device and the node density. We discuss this method of channel access including tradeoffs and requirements, and analyze the performance in comparison with existing MAC strategies.