Mobile sensor scheduling for timely sweep coverage

Mobile sensors are a viable choice for providing monitoring service on a set of Points of Interest (PoIs) in a large sensing field. In some applications, each PoI should be covered periodically (sweep coverage), and the collected data should be delivered to the sink node timely (timely transmission), namely both the sensing and transmission delay constraints for each PoI should be satisfied, which we call as timely sweep coverage. We investigate how to optimize the movement path of one mobile sensor to satisfy the two delay constraints for each PoI, so that the required movement velocity for the mobile sensor is minimized. We consider two cases: 1) all PoIs are placed along a straight line (linear case), and 2) all PoIs are arbitrarily placed on a plane (general 2-D case). Under the linear case, the optimal algorithm is presented. Under the general 2-D case, we prove the problem is NP-hard, and two algorithms, STSP and ITSP, are presented. We prove that the approximation ratio of STSP depends on the ratio between the sensing and transmission delay constraints. The ITSP can improve the solution much especially when the two delay constraints differ greatly for each PoI. Extensive simulation results are provided to evaluate our algorithms.