Markov Modeling for Data Block Transmission of OFDM Systems over Fading Channels

Orthogonal frequency-division multiplexing (OFDM) is a promising technique for high data rate wireless access networks. Modeling OFDM systems for the analysis of network performance is very challenging, because of the complexity of the modulation/coding schemes and the wideband wireless channel fading in both the time and frequency domains. In this paper, a novel packet-level model based on a two-dimensional Markov chain is proposed for OFDM systems over time-varying (Nakagami-m fading), frequency-selective channels. First, the level cross rate (LCR) of the amplitude of channel frequency response is derived. Then, we develop a methodology to map the received signal-to-noise ratio (SNR) of the subcarriers into a finite number of channel states with different packet error rate (PER). The proposed model presents directly the performance of the OFDM systems and incorporates the time- and frequency-domain correlations of the fading channels. Channel coding is also considered in evaluating PER. Simulations have verified that the statistics of the BER presented by our model are consistent with those of waveform simulations. The proposed Markov model can be an effective tool to study and optimize upper-layer protocols of OFDM-based wireless networks, via both analysis and simulation.