PCFG Based Synthetic Mobility Trace Generation

This paper introduces a novel method of generating mobility traces based on Probabilistic Context Free Grammars (PCFGs). A PCFG is a generalization of a context free grammar in which each production rule is augmented with a probability with which this production is applied during sentence generation. A concise PCFG can be inferred from the given real world trace collected from the actual mobile node behaviors. The resulting grammar can be used to generate sequences of arbitrary length mimicking the mobile node behavior. This is important when new protocol designs for mobile networks are tested by simulation. In the paper, we describe the methods developed to construct such grammars from training data (mobility history). We also discuss how to generate the synthetic data with an already constructed grammar. We present the experimental results on two real data sets, measuring similarity of the actual traces with the synthetic ones. We compare our grammar based method to a 2-level Markov Model based trace generation method. The results demonstrate that the grammar based approach works as an excellent compression method for the actual data. On many metrics, the synthetic data generated from the PCFG match the training data much better than the one generated by the Markov Model.