In this contribution, the Bit Error Rate (BER) performance of OFDM systems using coherent demodulation over time-variant flat Nakagami-m fading channels is analyzed. In a rapidly fading environment the orthogonality of the OFDM subcarrier signals may be destroyed and this phenomenon potentially results in InterCarrier Interference (ICI). The novel contribution of the paper is that the desired signal is shown to be accurately modelled as a function of the sum of two correlated Nakagamim variables, provided that the Doppler shift is moderate. It is also shown that the ICI can be modelled as a function of the difference of two correlated Nakagami-m variables. Finally, it is demonstrated that the assumption of having a near-Gaussian ICI distribution is inaccurate, hence leading to an inaccurate BER estimate, which is associated with a pessimistically high BER-floor.
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