Privacy-Preserving Multiple Tensor Factorization for Synthesizing Large-Scale Location Traces

With the widespread use of LBSs (Location-based Services), synthesizing location traces plays an increasingly important role in analyzing spatial big data while protecting users' privacy. Although location synthesizers have been widely studied, existing synthesizers do not provide utility, privacy, or scalability sufficiently, hence are not practical for large-scale location traces. To overcome this issue, we propose a novel location synthesizer called PPMTF (Privacy-Preserving Multiple Tensor Factorization). We model various statistical features of the original traces by a transition-count tensor and a visit-count tensor. We simultaneously factorize these two tensors via multiple tensor factorization, and train factor matrices via posterior sampling. Then we synthesize traces from reconstructed tensors using the MH (Metropolis-Hastings) algorithm. We comprehensively evaluate the proposed method using two datasets. Our experimental results show that the proposed method preserves various statistical features, provides plausible deniability, and synthesizes large-scale location traces in practical time. The proposed method also significantly outperforms the state-of-the-art with regard to the utility, privacy, and scalability.