A Spherical Hidden Markov Model for Semantics-Rich Human Mobility Modeling

Authors

  • Wanzheng Zhu University of Illinois at Urbana–Champaign
  • Chao Zhang University of Illinois at Urbana–Champaign
  • Shuochao Yao University of Illinois at Urbana–Champaign
  • Xiaobin Gao University of Illinois at Urbana–Champaign
  • Jiawei Han University of Illinois at Urbana–Champaign

Keywords:

Mobility Modeling, vMF distribution

Abstract

We study the problem of modeling human mobility from semantic trace data, wherein each GPS record in a trace is associated with a text message that describes the user's activity. Existing methods fall short in unveiling human movement regularities for such data, because they either do not model the text data at all or suffer from text sparsity severely. We propose SHMM, a multi-modal spherical hidden Markov model for semantics-rich human mobility modeling. Under the hidden Markov assumption, SHMM models the generation process of a given trace by jointly considering the observed location, time, and text at each step of the trace. The distinguishing characteristic of SHMM is the text modeling part. We use fixed-size vector representations to encode the semantics of the text messages, and model the generation of the l2-normalized text embeddings on a unit sphere with the von Mises-Fisher (vMF) distribution. Compared with other alternatives like multi-variate Gaussian, our choice of the vMF distribution not only incurs much fewer parameters, but also better leverages the discriminative power of text embeddings in a directional metric space. The parameter inference for the vMF distribution is non-trivial since it involves functional inversion of ratios of Bessel functions. We theoretically prove, for the first time, that: 1) the classical Expectation-Maximization algorithm is able to work with vMF distributions; and 2) while closed-form solutions are hard to be obtained for the M-step, Newton's method is guaranteed to converge to the optimal solution with quadratic convergence rate. We have performed extensive experiments on both synthetic and real-life data. The results on synthetic data verify our theoretical analysis; while the results on real-life data demonstrate that SHMM learns meaningful semantics-rich mobility models, outperforms state-of-the-art mobility models for next location prediction, and incurs lower training cost.

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Published

2018-04-29

How to Cite

Zhu, W., Zhang, C., Yao, S., Gao, X., & Han, J. (2018). A Spherical Hidden Markov Model for Semantics-Rich Human Mobility Modeling. Proceedings of the AAAI Conference on Artificial Intelligence, 32(1). Retrieved from https://ojs.aaai.org/index.php/AAAI/article/view/11777