Location privacy is one critical factor concerned by mobile users of Location Based Service (LBS). Location privacy of mobile users includes two parts: current position information and trajectory information. The problem of position anonymity in Ad Hoc & sensor networks has been widely studied during past years. Nevertheless, most of existing privacy preserving solutions either need a third part server or require a large number of users. This paper proposes a simple and distributed trajectory preserving strategy, called Virtual Avatar (VAvatar). VAvater adopts a virtual path programming resolution, which does not need any third-part server (agent), to achieve trajectory information anonymity for continuous querying users of LBS. On the other hand, attackers may have strong ability to make mobility predictions by analyzing spatio-temporal relation of historical communication data. In order to prevent users from such threatening, VAvatar takes following two strategies: noisy location selecting strategy and query scheduling strategy to interrupt spacial and temporal relationships between position data. Theoretical analysis and experiments show that VAvatar provides efficient protection of trajectory privacy for mobile users with tolerable energy cost.
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