Charging Task Scheduling for Directional Wireless Charger Networks

This paper studies the problem of cHarging tAsk Scheduling for direcTional wireless chargEr networks (HASTE), i.e., given a set of rotatable directional wireless chargers on a 2D area and a series of offline (online) charging tasks, scheduling the orientations of all the chargers with time in a centralized offline (distributed online) fashion to maximize the overall charging utility for all the tasks. We prove that HASTE is NP-hard. Then, we prove that a relaxed version of HASTE falls within the realm of maximizing a submodular function subject to a partition matroid constraint, and propose a centralized offline algorithm that achieves (1 - rho)(1 - 1/e) approximation ratio to address HASTE where rho is the switching delay of chargers. Further, we propose a distributed online algorithm and prove it achieves z(1 - rho)(1 - 1/e) competitive ratio. We conduct simulations, and field experiments on a testbed consisting of 8 off-the-shelf power transmitters and 8 rechargeable sensor nodes. The results show that our distributed online algorithm achieves 92.97% of the optimal charging utility, and outperforms the comparison algorithms by up to 26.19% in terms of charging utility.