Phase noise suppression in OFDM systems in presence of IQ imbalance

The implementation of OFDM system suffers from the effect of phase noise and IQ imbalance, which disturb the orthogonality between subcarriers and cause intercarrier interference (10). When treated separately, effective algorithms, such as the ICI self-cancellation scheme, exist for suppression of phase noise as well as IQ imbalance. However, with both effects present, such algorithms do not lead to effective suppression. In this paper, we propose a novel technique to jointly combat the IQ imbalance and phase noise at baseband. An IQ imbalance estimation and compensation module, which is robust against phase noise, is added in the ICI self-cancellation based OFDM system. After the IQ imbalance has been compensated in the time domain, the ICI self-cancellation scheme of data-conjugate method is used to suppress the phase noise and the residual IQ imbalance. This scheme has a fast convergence and a nearly optimal BER performance even for large IQ imbalance in AWGN channel. In multipath channel, even for large IQ imbalance, this joint suppression scheme offers frequency diversity gain and as a result, the BER performance surpasses that of the conventional OFDM system without IQ imbalance and phase noise.