Spectral spatial equalization for OFDM in time-varying frequency-selective multipath channels

Abstract

Orthogonal frequency division multiplex (OFDM) transmission over a time-variant frequency-selective multipath fading channel suffers from significant attenuation on faded frequency regions as well as inter-channel interference (ICI) due to the loss of subchannel orthogonality. To mitigate signal fading and ICI, we introduce a frequency-space domain equalization (FSDE) using an antenna array. Unlike conventional combining diversity or selection diversity, this scheme differs in that it attempts to prevent the occurrence of the frequency-selective fading and ICI rather than compensates for them. A FSDE on the received OFDM signal is performed by space-time Fourier transform (STFT) and frequency-domain equalization (FDE). While a time-domain Fourier transform in STFT demodulates OFDM signals, a space-domain Fourier transform attenuates the OFDM signals arriving at the antenna array through unwanted paths. This approach includes the blind estimation of the direction-of-arrival (DOA) for the multiple paths by employing the cyclostationarity of the OFDM signal. A FDE is applied to the output of the STFT to compensate for the effect of the remaining ICI. The effectiveness of FSDE is examined in terms of the resulting frequency-selective fading, ICI and SINR gain.