A new method to simultaneously estimate TX/RX IQ imbalance and channel for OFDM systems

In-phase and Quadrature Imbalance (IQI) exists in both analog IQ modulator and demodulator. When carrier frequency is ultra-high and/or bandwidth is ultra-wide, the impact of IQI on system performance is not negligible. While in most of the literatures, the combined effect of channel, TX, and RX IQI is discussed, in this paper, a method that can separate and simultaneously estimate the three is proposed. The complexity of the proposed method is low, and with estimated TX and RX IQI, simple symbol-by-symbol detection can be used to detect data symbols with negligible performance loss. Compared with the calibration methods, where auxiliary circuits are needed to separate the TX and RX IQI belonging to different communication links inside a transceiver, by exploiting the fact that the wireless channel changes much faster than the IQI, the method proposed here can separate not only the TX and RX IQI but also the channel belonging to the same communication link without any auxiliary circuits. Simulations are carried out to verify the performance of the proposed method.