Abstract: 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 presented an 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 is implanted in the associated zone. Client only needs to communicate with the server when the matrix indicates the rectuirement of the information sharing. The experimental results show that the scheme can eliminate about 70 0 o communication overhead and works well especially for applications with uniformly distributed information.

Key words: Location-aware, Information sharing, Wireless networks, On-demand service