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

TL;DR

This paper introduces a novel frequency-domain compensation scheme for IQ imbalance in OFDM receivers, utilizing a special pilot pattern and efficient estimators to improve noise suppression and reduce complexity, achieving comparable BER performance with fewer training symbols.

Contribution

It proposes a new pilot pattern and combined time-domain and frequency-domain estimators for IQ imbalance compensation in OFDM systems, reducing training overhead and computational complexity.

Findings

Achieves same BER with only two pilot symbols as previous methods with twenty.

Significantly suppresses channel noise by a factor of N/(L+1).

Uses only 2N complex multiplications per OFDM symbol for equalization.

Abstract

A pilot pattern across two OFDM symbols with special structure 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 significantly suppress channel noise by a factor 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 scheme TD-LS/FD-GE 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.