Dynamic Range Low-power Wireless Protocols for Environmental Monitoring

Abstract

In the rapidly advancing world of wireless embedded systems, sensor networks (WSNs) are becoming increasingly more applicable for data gathering applications. When designed for such applications, the design goals are most often defined in terms of communication reliability, flexible data-rates, and network life-time. One of the application domains that will benefit from improvement in these metrics, is the area of environmental monitoring. Of particular interest is the use of sensor networks in cryosphere research. To monitor the stability of high-alpine mountain slopes, several low-power wireless communication protocols have been proposed and deployed over time. Among them are the Low-Power Wireless Bus (LWB) and Dozer protocols, introduced by the TIK research group at ETH Zurich. In their own way, both LWB and Dozer have proven to be efficient and reliable means of wireless communication. Being tested in the field, these state of the art communication protocols have been operational in previous monitoring systems for over a decade. However, even whilst being functional, these prior deployment’s processing, bandwidth, and storage capacities remain limited. In an effort to construct a new monitoring system, the aim is to include a communication protocol that shows favorable scaling properties in battery life (duty cycle) versus bandwidth. Determining which protocol to choose, however, remains problematic due to the lack of appropriate performance data. To address this issue, this report studies the currently deployed solutions (LWB and Dozer) by deriving predictive models and comparing both protocols’ performance in terms of duty cycle versus bandwidth. In doing so, this report shows that: (i) given a 10-node network, the Dozer and LWB analytical models can predict the duty cycle with approximately 95 percent accuracy when compared to the actual implementation; (ii) an alteration of the topology control for Dozer (in a 10-node network) can lead to improvements in duty cycle of up to 40 percent without significantly impacting the stability; (iii) LWB shows more favorable results in terms of duty cycle when compared to the normal Dozer implementation, but is only favorable in low bandwidth situations when compared to Dozer with improved topology control; (iv) given a 10-minute window, Dozer experiences less instability events, such as packet re-transmissions or beacon misses. LWB shows more stability issues, but the additional radio on-time is limited as the slot sizes are of fixed duration. Both protocols are reliable in the sense that no packets are lost. With previous findings taken into consideration, if it is possible to adjust the topology control for Dozer for a given network, a combination of LWB and Dozer might offer the most optimal solution.