Asymmetry-aware link layer services in wireless sensor networks

Recent studies in wireless sensor networks (WSNs) have observed that the irregular link quality is a common phenomenon, rather than an anomaly. The irregular link quality, especially link asymmetry, has significant impacts on the design of WSN protocols. In this paper, we propose two asymmetry-aware link layer services, including the neighborhood link quality service (NLQS) and the link relay service (LRS). The novelty of the NLQS service is taking the link asymmetry into consideration, providing timeliness link quality and distinguishing the inbound and outbound neighbors with the support of LRS, which builds a relay framework to alleviate the effects of link asymmetry. To demonstrate the proposed link layer service, we design and implement two example applications, building the shortest-hop routing path (SHRT) and the best path reliability routing path (BRRT), on the TinyOS platform. We found that the performance of two example applications is improved substantially. More than 40% of nodes identify more outbound neighbors and the percentage of increased outbound neighbors is between 14% and 100%. In SHRT, more than 15% of nodes reduce hops of the routing path and the percentage of reduced hops is between 14% and 100%. In BRRT, more than 16% of nodes improve the path reliability of the routing path and the percentage of the improved path reliability is between 2% to 50%.