Recently, orthogonal frequency division multiplexing (OFDM) has been considered the most promising solution for beyond 3G, and the related research has not been constrained in the physical layer any longer. However, taking too many details of physical layer into consideration will make the problem so complicated that both the analysis and simulation of higher layers become impossible. We use constrained hidden Markov model (CHMM) to model burst errors of physical layer in OFDM system. The effective scaling method for CHMM parameter estimation algorithm, i.e., modified Baum-Welch algorithm (BWA), is presented in this paper to avoid underflow in computer programming, which is critical for the realization of CHMM. By computer simulations, we discuss how to choose proper state number of CHMM and provide a group of CHMM for OFDM system in HIPERLAN/2 indoor wireless channel, which can be used to facilitate the comparison of different coding schemes and analysis of high-level protocol performance.
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