Efficient Valid Scope for Location-Dependent Spatial Queries in Mobile Environments

In mobile environments, mobile clients can access information with respect to their locations by submitting Location-Dependent Spatial Queries (LDSQs) to Location- Based Service (LBS) servers. Owing to scarce wireless channel bandwidth and limited client battery life, frequent LDSQ submission from clients must be avoided. Observing that LDSQs issued from a client located at nearby positions would likely return the same query results, we explore the idea of valid scope , which represents a spatial area in which a set of LDSQs will retrieve exactly the same set of query results. With a valid scope derived and an LDSQ result cached, a client can assert whether the new LDSQs can be answered with the maintained LDSQ result, thus eliminating the need of sending LDSQs to the server. Contention on the wireless channel and client energy consumed for data transmission can be considerably reduced. In this paper, we design efficient algorithms to compute the valid scope for common types of LDSQs, including nearest neighbor queries, range queries and window queries. Through an extensive set of experiments, our proposed valid scope computation algorithms are shown to outperform existing approaches.