DecTDMA: A Decentralized-TDMA - With Link Quality Estimation for WSNs.

In wireless sensor networks (WSNs), different motes may transmit packets concurrently, i.e., having overlapping transmission periods. As a result of this contention, there are no packet reception guarantees and significant bandwidth can be lost. This contention can have a strong impact on the performance together with other kinds of interference sources, e.g., ambient noise. As a result, WSN's connectivity tends to have a very dynamic nature. In this paper, we devise DecTDMA (Decentralized-TDMA), a fully decentralized medium access controller (MAC) that significantly reduces contention. It is based on a self-stabilizing algorithm for time division multiple access (TDMA). This self-stabilizing TDMA algorithm uses no external assistance or external references, such as wireless access points (WAPs) and globally-synchronized clocks. We present the design and implementation of DecTDMA and report encouraging results: our Cooja simulations and Indriya testbed experiments show stable connectivity and high medium utilization in both single and multi-hop networks. Since DecTDMA has favorable characteristics with respect to connection stability, we show that common link quality estimation (LQE) techniques further improve the operation of DecTDMA in the dynamic environment of low- power wireless networks.