Tree-based multi-channel convergecast in Wireless Sensor Networks

The use of Wireless Sensor Networks (WSN) in application domains such as industrial automation poses strict requirements in terms of communication delay, reliability, etc. Time Division Multiple Access (TDMA) is the preferred access scheme for the above applications, and leading industry standards such as WirelessHART employ it by centrally generating convergecast schedules. Despite the fact that techniques such as multi-channel communication and spatial re-use are currently not harnessed to their full potential, existing scheduling heuristics are often complex while performing far from the optimal solution. We investigate the tree convergecast scheduling with multiple channels (TCMC) problem. In particular, we derive an integer programming-based optimal solution to the min length and buffer size scheduling as well as the min length and channel number scheduling. We further describe TCMC scheduling as a decision problem, which allows us to create a general scheduling framework that is flexible and requires minimal code modification for implementing different TCMC scheduling strategies. Within our framework, we propose and implement four heuristics. Our novel busy-sender-first heuristic is significantly better than the state-of-the-art heuristic in both schedule length (within 0.22% of the optimum) and memory consumption, as well as being conceptually much simpler. Finally, based on the evaluation results of the busy-sender-first heuristic, we derive guidelines on the choice of number of channels and configuration of tree topology, respectively.