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Multi-layer partition for query location anonymization

Due to the proliferation of Global Position System (GPS) and smart phone technology, Location-Based Service (LBS) has attained tremendous growth in recent years. Spatial queries retrieving nearest Point-Of-Interests (POI) require actual user locations for services. However, sharing such sensitive personal location information with potentially malicious servers may cause concerns about user privacy. The current obfuscation-based approach addressing this problem cannot provide binding privacy guarantees as a trusted third-party anonymizer is required. On the other hand, the data-encryption-based and cPIR-based approaches incur costly computation overheads. Recently, the secure hardware-aided PIR-based technique has been shown to be superior to formers, but it did not consider the characteristics of data distribution of searching domain. In this work, we propose two schemes: MSQL, NSQL, based on flexible multi-layer grids and non-empty lookup table for efficient storage and retrieval on non-uniform distribution of POI data, so that improved performance of PIR-based techniques could be achieved. Numerical experiments demonstrate that the proposed techniques indeed deliver better efficiency under various criteria.