Research And Implementation On A Privacy-Aware Location Based Active Information Sharing System

Frequent location updates from mobile clients make the server a bottleneck for severe communication and processing overhead in large scale location-based information sharing system. From our observation, implanted information is not distributed uniformly in geography, which leads to some blank zones. In existing systems, the client needs to update its location on the server periodically no matter whether any information needs to be shared, which brings extra communication overhead. We present a Grid-based indexing mechanism(GIM), providing on-demand information request for mobile clients. In this mechanism, an information matrix is built in the server and synchronized to clients, in which each element indicates whether information implanted in the associated zone. Client only needs to communicate with the server when the matrix indicates the requirement of the information sharing. The experimental results show that the scheme can eliminate about60%communication overhead and works well especially for applications with uniformly distributed information.Traditional spatial cloaking methods are carried out by a trusted proxy known as location trusted server (LTS) to generate a region that contains at least k users for every request. The LTS is assumed to know the location of all users at all times, and perform the cloaking for all user requests. There are a number of disadvantages of relying on a single service for privacy preservation, including the scalability concern and the appropriate worry that this service "knows too much". To ameliorate this single-service problem, in-device spatial cloaking may be more desirable. With cloud services, it may be appropriate to assume that user-density information is available from cloud servers. These servers may collect user location information for different regions, or may use sophisticated method to estimate user densities for different places. When a request needs to be anonymized, the device goes to the cloud to acquire appropriate user density information to perform spatial cloaking. This paper proposes and studies a new algorithm and reports performance evaluation of the new algorithm and its optimized version, aiming at provably safe cloaking with minimized communication cost. Experimental results show that the new algorithms work well in the realistic evaluation environment and easy to merge with location based active information sharing system.We have built campus-level demo system to evaluate our mechanisms and algorithms. The result based on real students show that our method is effective.