Design of Location Service for a Hybrid Network of Mobile Actors and Static Sensors

Location services are essential to many applications running on a hybrid of wirelessly-networked mobile actors and static sensors, such as surveillance systems and the pursuer and evader game (PEG). To our best knowledge, there has been no previous location service protocol for wireless sensor networks. A number of location service protocols have been proposed for mobile ad hoc networks, but they are not applicable to sensor networks due to the usually large per-hop latency between sensors. This paper presents a distributed location service protocol (DLSP) for wireless sensor networks. Using a rigorous analysis of DLSP, we derive the condition for achieving a high packet-delivery ratio, and show how to configure the protocol parameters to ensure the scalability of DLSP. We find that DLSP is scalable if the mobile's speed is below a certain fraction of the packet-transmission speed, which depends on a movement threshold. For example, if the movement threshold for the location servers at the lowest level equals the radio range, the speed limit is one-tenth of the packet-transmission speed. The mobile's theoretical speed limit is one-fifth of the packet-transmission speed, beyond which DLSP cannot scale regardless of the movement threshold. Because of the high location-update overhead of DLSP, we propose an optimization, DLSP-SN, which can reduce the overhead by over 70%, while achieving high packet-delivery ratios. However, due to the griding effect, the packet's path length of DLSP-SN may be longer than that of DLSP, incurring higher data-delivery cost