Analysis of the demodulation techniques for OFDM signals under correlated Rayleigh fading

The complex channel fading process cannot be assumed constant over one OFDM symbol duration when the symbol interval is long enough. In other words, the faded samples within one OFDM symbol are not highly correlated. We propose a novel OFDM demodulation technique by multiplying the received signal with the conjugate of the channel gain at each time instant before performing FFT. The probability density function (PDF) of the multiplicative distortion is expressed as the inverse Laplace transform of its moment generating function (MGF). This allows us to calculate the bit error rate (BER) analytically. Both analytical and simulation results show that the proposed demodulation method gives better performance than the conventional demodulation method when the product of Doppler spread and sample duration (f_d T_s) is small