Low Delay and Interference Aware Data Gathering Scheme for Battery-Free Wireless Sensor Networks

In Battery-Free Wireless Sensor Network (BF-WSN), nodes are powered by the energy harvested from ambience instead of batteries. The nodes may frequently suffer from insufficient energy so that they need to alternate normal operation (such as transmitting/receiving, etc.) with harvesting energy. This brings in extra packet delay for the nodes to deliver data to the sink(s). Therefore, delivering data with shorter delay is a critical concern for BF-WSN nodes. In this paper, we first define the weight of wireless link that takes into account interference among links, balancing data load among the subtrees of the data gathering tree, and energy harvesting rate (EHR) of the nodes. Then, using the defined weight, we present the heuristic algorithm to build data gathering tree by letting the wireless link with a smaller weight join the tree prior to the ones with greater weights so that the wireless links either tending towards interference with the other ones, bringing in unbalance data load in the subtrees, or having smaller EHR are deferred to join the tree, thus reducing packet delay. Simulation results show the proposed data gathering scheme outperforms the existing scheme in terms of the delay per packet reaching the sink.