Understanding the characteristics of low-power wireless links and radios is an essential step towards building robust, efficient and reliable wireless sensor networks. In this project we study and evaluate the fidelity of the Received Signal Strength Indication (RSSI), which the low-power radios use to measure the power of the wireless signal. This value is heavily utilized in many wireless sensor network protocols and applications, such as localization, topology control, link scheduling, and link quality estimation. With extensive experiments, we show that inaccuracies in the RSSI values reported by widely used 802.15.4 radios, such as the CC2420 and the AT86RF230, have profound impact on these protocols and applications. Therefore, we also developed a calibration scheme to effectively minize the adverse effects associated with inaccurate RSSI values.
Stepping up to the link layer, we note that packet loss and energy consumption in sensor networks depend critically on the quality of the network's wireless links. Experimental results have shown that a low-power wireless link can be in one of three states or 'regions', as the inter-node distance increases: connected, transitional (gray), and disconnected. Moreover, the transitional region spans a sigficant portion and is likely to be even larger than the connected region. Therefore, in this project we explore the characteristics of the transitional region and study the possibility of picking reliable links within this region.