Joint Adaptive Compensation of Transmitter and Receiver IQ Imbalance Under Carrier Frequency Offset in OFDM-Based Systems

Zero-intermediate frequency (IF)-based orthogonal frequency division multiplexing (OFDM) transmitters and receivers are gaining a lot of interest because of their potential to enable low-cost terminals. However, such systems suffer from front-end impairments such as in-phase/quadrature-phase (IQ) imbalance which may have a huge impact on the performance. Moreover, since OFDM is very sensitive to a carrier frequency offset, this distortion needs to be taken into account in the derivation and analysis of any IQ imbalance estimation/compensation scheme. In this paper, the effect of both transmitter and receiver IQ imbalance under carrier frequency offset in an OFDM system is studied and an algorithm is developed to compensate for such distortions in the digital domain. The algorithm involved is a very efficient post-FFT adaptive equalization which is shown to lead to near ideal compensation.