A Frequency-domain Compensation Scheme for IQ-Imbalance in OFDM Receivers

A special pilot pattern across two OFDM symbols is devised for channel estimation in OFDM systems with IQ imbalance at receiver. Based on this pilot pattern, a high-efficiency time-domain (TD) least square (LS) channel estimator is proposed to suppress channel noise by a factor of N/(L+1) in comparison with the frequency-domain LS one in [1] where N and L+1 are the total number of subcarriers and the length of cyclic prefix, respectively. Following this, a low-complexity frequency-domain (FD) Gaussian elimination (GE) equalizer is proposed to eliminate IQ distortion by using only 2N complex multiplications per OFDM symbol. From simulation, the proposed TD-LS/FD-GE scheme using only two pilot OFDM symbols achieves the same bit error rate ( BER) performance under ideal channel knowledge and no IQ imbalances at low and medium signal-to-noise ratio (SNR) regions whereas these compensation schemes including FD-LS/Post-FFT LS, FD-LS/Pre-FFT Corr, and SPP/Pre-FFT Corr in [1] require about twenty OFDM training symbols to reach the same performance where A/B denotes compensation scheme with A being channel estimator and B being equalizer.