Radio irregularity problem in wireless sensor networks: New experimental results

A key design issue in wireless networks is represented by the irregular and dynamic radio coverage at each node. This is especially true for wireless sensor networks, which usually employ low quality radio modules to reduce the cost. It results in irregularity in radio coverage and variations in packet reception in different directions. Due to its likely impact on the upper layer protocols, many services, such as localization, routing and others, needs to be resilient to the irregular and dynamic radio propagation, and to include mechanisms to deal with these problems. As such, accurate models of radio propagation patterns are important for protocol design and evaluation. In this paper, measurements of radio propagation patterns have been carried out using the motes themselves. With empirical data obtained from the Mica2 platforms we were able to observe and further quantify such phenomena. The results demonstrate that the radio pattern is largely random; however, radio signal attenuation varies along different direction, and more importantly, is time-varying while stationary.