Joint Compensation of OFDM Frequency Selective Transmitter and Receiver IQ Imbalance

Direct conversion architectures are currently receiving a lot of interest in OFDM based wireless transmission systems. However such systems are very sensitive to in-phase/quadrature-phase (IQ) imbalances in the front-end analog processing. In this paper the joint effect of frequency selective IQ imbalances at both transmitter and receiver is studied. When the cyclic prefix is long enough to accommodate the combined channel, transmitter and receiver filter impulse, we propose a low complexity two tap equalizer with LMS based adaptation. When the cyclic prefix is not sufficiently long, this results in inter-block-interference (IBI) between the OFDM symbols. In this case we propose a frequency domain per-tone equalizer (PTEQ) initialized by RLS based adaptation. Both algorithms provide a very efficient post-FFT adaptive equalization and their performance is close to the ideal case.