Planning the trajectories of multiple mobile sinks in large-scale, time-sensitive WSNs

Controlled sink mobility has been shown to be very beneficial in lifetime prolongation of wireless sensor networks (WSNs) by avoiding the typical hot-spot problem near the sink. Besides striving for elongated lifetimes, many applications of WSNs are time-sensitive, i.e., they strongly benefit from bounds on the message transfer delay. Further, large WSNs require multiple sinks in order to scale well with respect to delay and lifetime. Therefore, it becomes very interesting to investigate how to plan the trajectories of multiple mobile sinks such that lifetime and delay goals are met simultaneously. To that end, we propose a geometrically principled heuristic for finding good trajectories of multiple mobile sinks in large-scale, time-sensitive WSNs. First, we discuss the high analytical challenges of optimally planning the trajectories of multiple mobile sinks. Based on this, we relax the problem by transforming it into a geometric design problem, which, subsequently, is solved in closed form. In simulations, we investigate how well this geometric heuristic for sink trajectories of multiple mobile sinks performs with respect to delay and lifetime. We find that it excels especially in large-scale WSNs, for example in a WSN with 500 nodes and 20 sinks, it roughly cuts delay bounds by 50% while tripling the lifetime compared to the sinks following random walks. Hence planning the sink trajectories carefully really pays off.