Effects of channel estimation errors on BER performance of DFT-precoded OFDM systems

We study the effects of channel estimation errors on bit error rate (BER) performance of a DFT-precoded OFDM system with frequency domain linear minimum mean square error (MMSE) equalizer, by analytically studying the effects of channel estimation errors on the mean square error (MSE) of the equalizer output, which can be related to the BER performance using a Gaussian approximation. We first obtain an approximate expression for the BER performance in terms of the MSE of the equalizer output with channel estimation errors, which is found to be a sum of the equalizer output MSE for the known channel frequency response and the scaled MSE of the channel frequency estimates. For a fixed MSE of channel frequency estimates, the degradation of the equalizer output signal-to-noise ratio (SNR) increases as E_s/N_o increases. We also propose a semi-analytical approach to obtain the BER performance, by modeling the frequency channel estimates as the actual channel estimates plus a Gaussian random variable with zero mean and a variance of the averaged MSE of the channel frequency estimates. Simulation results show that both proposed approaches can accurately estimate the BER performance of DFT-precoded OFDM systems with channel estimation errors.