In this paper we describe T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks. Applications for these networks have some characteristics (low message rate, insensitivity to latency) that can be exploited to reduce energy consumption by introducing an active/sleep duty cycle. To handle load variations in time and location T-MAC introduces an adaptive duty cycle in a novel way: by dynamically ending the active part of it. This reduces the amount of energy wasted on idle listening, in which nodes wait for potentially incoming messages, while still maintaining a reasonable throughput. We discuss

Applications for wireless sensor networks have notably different characteristics and requirements from standard WLAN applications. Low energy consumption is the most important consideration. The low message rate that is typical for sensor network applications and the relaxed latency requirements allow for significant reductions in energy consumption of the radio. In this article we study the energy saved by two MAC protocols optimized for wireless sensor networks, S-MAC and T-MAC, in comparison to standard CSMA/CA, We also report on the effects of low-power listening, a physical layer optimization, in combination with these MAC protocols. The comparison is based on extensive simulation driven by traffic that varies over time and location; sensor nodes are inactive unless they observe some physical event, or send status updates to the sink node providing the connection to the wired world. T-MAC in combination with low-power listening saves most energy, but can not handle the same peak loads as CSMA/CA and S-MAC.

Localisation is required for many ad-hoc sensor network applications. Therefore, much work has been done regarding techniques for localisation, mainly using anchors (nodes with known locations). However, there has been little study of how anchors are likely to be distributed in applications, and how to perform localisation with more realistic anchor distributions. In this paper