On Improving the Reliability of Packet Delivery in Dense Wireless Sensor Networks

Wireless sensor networks (WSN) built using current Berkeley Mica motes exhibit low reliability for packet delivery. There is anecdotal evidence of poor packet delivery rates from several field trials of WSN deployment. All-to-one communication pattern is a dominant one in many such deployments. As we scale up the size of the network and the traffic density in this communication pattern, improving the reliability of packet delivery performance becomes very important. This study is aimed at two things. Firstly, it aims to understand the factors limiting reliable packet delivery for all-to-one communication pattern in dense wireless sensor networks. Secondly, it aims to suggest enhancements to well-known protocols that may help boost the performance to acceptable levels. We first postulate the potential reasons hampering packet delivery rates with current CSMA-based MAC layer used by the radios deployed in WSN. We then propose a set of enhancements that are aimed to mitigate the ill-effects of these factors. We pick three protocols, namely, Flooding, AODV, and Geographic routing as candidates for this study. Using TOSSIM, we perform a detailed study of these protocols and the proposed enhancements. This study serves several purposes. First, it helps us to quantify the detrimental effects of these factors. Second, it helps us to quantify the extent to which our proposed enhancements improves packet delivery performance. Concretely, we show that using Geographic routing in a WSN with 225 nodes spread over 150 feet times 150 feet, the proposed enhancements yield a 23-fold improvement in packet delivery performance over the baseline. Further, the enhancements result in fairness (measured by the number of messages received from each node at the destination). Lastly, we show that the overhead (in terms of retransmissions, acknowledgement messages, and control messages) is reasonable.