**3. Model**

In this section, the conventional TMC model is firstly introduced, then it is gradually equipped with more sophisticated structures, i.e., applying Gaussian mixture to TMC to obtain the TMC-GMM model and then applying semi-Markov structure to TMC-GMM to obtain the SemiTMC-GMM model. Afterward, a detailed description of on-line EM algorithm suited for SemiTMC-GMM is given. As a matter of fact, these additional processes can be naturally added because of the high generality of the TMC model through the flexibility of the auxiliary processes.
