RSSI or LQI: Insights from Real-Time Deployments for Underground Sensing and Applications

Abstract

There is a general understanding in the wireless sensor network (WSN) community that the protocol developed solely based on theoretical/simulation considerations do not perform reliably in real-time deployments. This further motivates us to carry out experimental link characterization of WSNs deployed in real-time. In addition, it is more crucial for underground mines, where the reliable operation of a wireless communication system is a concern. While received signal strength indicator (RSSI) and link quality indicator (LQI), a hardware metric of sensor node platform such as CC2420, have been studied in the past for normal terrestrial environment, there has so far been no detailed evaluation reported in underground mines covering different deployment scenarios. In this paper, we present a detailed empirical evaluation of RSSI and LQI to estimate the packet reception rate (PRR) in several underground mine workings. We report our experimental findings from straight, near-face, and curved mine galleries carried out in real-time operational underground coal mine. From our experimental observations, we further provide a discussion on the selection of better link estimator for such high-stress environment. We find that LQI serves as a better candidate over RSSI in all deployment settings. Hence, LQI could be utilized to develop and design communication protocols to be deployed in underground mines. Our results also indicate that a LQI value equal or above 100 and RSSI value equal or above −82 dBm has PRR at least 85% in underground mines.