Trunk and Trail: Wireless Sensor Network Services For Distributed Object Tracking

In-network observation and control of mobile objects via static wireless sensors demands consistent, timely information. In this paper, we present two wireless network (WSN) services that support such observation and control: Trunk provides a global snapshot of the locations of all mobile objects at well-known times to all innetwork subscribers, and Trail provides the location of a particular mobile object upon demand to an in-network subscriber. We design both services to be energy efficient, reliable, and fault-tolerant despite the network dynamics typically associated with WSNs. Because Trunk service times are well-known and subscribers demand consistent information, Trunk operates readily in a synchronous model and achieves energy-efficiency by scheduling radio transmissions and receptions. By way of contrast, as Trail service times are unknown and subscribers demand timely information, Trail basically operates in an asynchronous model and achieves low latency via a distributed data structure that is updated only locally when objects move and offers a find time that increases linearly with the distance from an object. In the asynchronous model however, concurrent “where” operations can interfere with each other and receivers are always on, so we consider an extension to Trail for the synchronous model, which yields better reliability and energy efficiency but at the cost of latency. We provide experimental results on the performance of these services in a network of 105 motes (specifically XSMs) in our Kansei WSN testbed and describe an example object tracking system that we demonstrated based on these services which involved an intruder-interceptor game for perimeter protection WSNs.