Opportunistic Processing and Query of Motion Trajectories in Wireless Sensor Networks

Abstract

Abstract-We study the problem of in-network processing and queries of trajectories of moving targets in a sensor network. The main idea is to exploit the spatial coherence of target trajectories for opportunistic information dissemination with no or small extra communication cost, as well as for efficient probabilistic queries searching for a given target signature in a real-time manner. Sensors near a moving target are waken up to record information about this target and take the communication opportunities to exchange their knowledge with preceding and descending sensor nodes along the trajectory. Thus a moving target's information is naturally detected, recorded, and disseminated along its trajectory, as well as the motion trajectories that enter the sensor field afterwards.We analyzed and through simulations tested the dissemination cost and query success rate for randomly generated data sets. Trajectories of reasonable length can be discovered by probabilistic in-network queries with high probability. Compared with the scheme without opportunistic dissemination, the in-network processing of trajectories, with modest cost on dissemination, allows substantially reduced query cost and delay.

Target Trajectory Querying in Wireless Sensor Networks

“…If the target signature is propagated wider in the network, a random query has a high probability to hit a sensor that contains the target signature in the process of forwarding the query message along a direction. The simulation of reference [2] shows that in the opportunistic propagation schemes, when either the age or the length of a target trajectory is large enough, the random query number is close to 1. Otherwise, the repeat count of random query processes will be relatively large to discover the given target signature.…”

“…There are two kinds of target trajectory queries of moving targets [2], namely, existence query, and trajectory reporting query, respectively: (a) Was there a blue truck entering the field in the past half hour? (b) If yes, return its trajectory.…”

“…There are two query methods regarding target trajectory, which use the data-centric storage policy to store and process data in a distributed sensor network, namely, IBQ (index-based query) [7] and RQ (random query) [2].…”

“…Zhou and Gao [2] proposed an opportunistic processing and query schemes, in which sensors exploit existing communication opportunities to propagate their respective signature of previously detected targets. There is no index node, and thus, no index for target trajectory.…”

“…We propose a storage and querying protocol of target trajectories, which is based on RQ (random query) and IBQ (index-based query) [2], [7]. The main idea of our storage protocol is: (1) to apply the local storage policy to store the tracking data near detection sensors, and maintain the relationship of sensors, which detect the same target to help the trajectory reporting query, (2) to apply the data-centric storage policy to store the index of each target trajectory, which only includes the target ID and the sensor ID (the sensor ID is the first sensor ID that detected the target), and (3) to apply the opportunistic propagation in the tracking process to make the target signature wider in the the network.…”