Collaborative Transmission over Intermediate Links in Duty-Cycle WSNs

This paper studies the performance bottleneck of tree-based wireless sensor networks. Based on our findings, we propose a collaborative transmission paradigm which opportunistically shifts some node traffics to intermediate links beyond the tree topology. We experimentally demonstrate that the quality of intermediate links can even out over multiple transmissions. Low-Power-Listening based MACs can increase the packet reception ratio of data delivery, but may also introduce asymmetry issues on intermediate link, leading to redundant packet transmissions. To overcome the problem, we select good-SINR links that ensure high reliability with at most k retransmissions for communication. We compute the ratio of tree-link and intermediate long-link transmissions in a distributed way, aiming at minimizing the maximum load in the neighborhood. We implement the method in TinyOS as an independent component named LLC, and evaluate LLC via both simulation and testbed experiments. Results show that LLC can reduce the energy consumption by up to 50%, while retaining the high retransmission reliability.