通过实验和观察发现,现有的基于位置的信息共享系统中存在严重的空间冗余和内容冗余问题.这些冗余的存在极大地增加了系统的通信和计算开销,干扰了客户的个性化使用.提出冗余削减的按需服务机制,它由如下两部分组成:基于网格划分的信息索引机制(GIM,Grid-based Index Mechanism)实现按需的位置更新；基于分类的信息定制机制(CISM,Classification-based Information Selection Mechanism)使客户有权选择自己所需信息类别进行按需的信息共享.实验表明,信息分类按需定制机制可以极大地消减冗余信息共享带来的系统负载；信息索引机制可以节约大约70％的位置更新引发的通信开销,在信息分布极其不均匀的应用中性能提升更加明显.%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 requirement of the information sharing. The experimental results show that the scheme can eliminate about 70% communication overhead and works well especially for applications with uniformly distributed information.
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