No abstract

FlexiTP is a novel TDMA protocol that offers a synchronized and loose slot structure. Nodes in the network can build, modify, or extend their scheduled number of slots during execution, based on their local information. Nodes wake up for their scheduled slots; otherwise, they switch into power-saving sleep mode. This flexible schedule allows FlexiTP to be strongly fault tolerant and highly energy efficient. FlexiTP is scalable for a large number of nodes because its depth-first-search schedule minimizes buffering, and it allows communication slots to be reused by nodes outside each other's interference range. Hence, the overall scheme of FlexiTP provides end-to-end guarantees on data delivery (throughput, fair access, and robust self-healing) while also respecting the severe energy and memory constraints of wireless sensor networks. Simulations in ns-2 show that FlexiTP ensures energy efficiency and is robust to network dynamics (faults such as dropped packets and nodes joining or leaving the network) under various network configurations (network topology and network density), providing an efficient solution for data-gathering applications. Furthermore, under high contention, FlexiTP outperforms Z-MAC in terms of energy efficiency and network performance.

No abstract

Wireless sensor network technology promises to reveal finegrained, dynamic changes in monitored variables of an outdoor landscape. But there are significant problems to be overcome in translating this vision to working systems. This paper describes the design and implementation of a reactive, event driven network for environmental monitoring of soil moisture and evaluates the effectiveness of this solution. A novel feature of our solution is its reactivity to the environment: when rain falls and soil moisture is changing rapidly, measurements are collected frequently, whereas during dry periods between rainfall events measurements are collected much less often. Reactivity allows us to focus on dynamic responses and limit the amount of useless data gathered, as well as improving robustness and network lifetime. The main contribution of the paper is to demonstrate that a reactive sensor network can deliver useful data on soil moisture responses to rainfall. Field trial results on the reactivity, robustness and longevity of the network are evaluated, and future improvements proposed.