Improving Link Quality by Exploiting Channel Diversity in Wireless Sensor Networks

A large percentage of links in low-power wireless sensor networks are of intermediate quality. To the best of our knowledge, opportunistic exploitation is currently the only way to use these links. However, such exploitation requires overhearing which consumes a significant amount of energy. In this paper, we propose a new approach to exploit intermediate quality (IQ) links through channel diversity with a new protocol, called IQ Link Transformation Protocol (ILTP), that does not require overhearing. ILTP transforms IQ links into good links thus allowing us to exploit such links continuously rather than using them only opportunistically. Our key insight is that the packet reception ratios (PRR) across different channels on IQ links are not correlated and it is common on such links to find channels that change in quality on the time scale of a few minutes. Consequently, when the link quality of a channel is bad, it is highly likely that a good channel can be found and its quality will remain good for at least a few minutes. Our evaluations on three large-scale test beds demonstrate that ILTP is able to consistently transform the IQ links into good links. We observe that even a poor link with a PRR of 0.05 can be transformed into a good link with a PRR greater than 0.9. When ILTP is integrated with CTP, the default collection tree protocol for TinyOS, the average number of transmissions per end-to-end packet delivery is reduced by 24% to 58%.