Estimation of TX I/Q imbalance at the RX side with RX I/Q imbalance and carrier frequency offset for OFDM systems

Milli-meter wave (mmWave) band is attractive for 5G wireless communication systems, due to its free and wide spectrum and the small form factors of its RF components, which make massive MIMO (Multiple-Input Multiple-Output) practical. One of the challenges of mm Wave communication is its severe RF impairments, such as I/Q (In-phase and Quadrature) imbalance. Because of the small form factors of the RF components at mmWave band, the calibration is much more difficult than that in the conventional band. The carrier frequency offset (CFO) will further limits the performance of system especially when it is entangled with the IQ imbalance. When only CFO or IQ imbalance exists, many efficient methods have been offered, but when both of them exist, these methods do not lead to effective estimation. In this paper, two novel preamble structures and the corresponding estimation algorithms are proposed that can treat the CFO and TX/RX I/Q imbalance together. With the proposed methods, we can first estimate the RX I/Q imbalance and CFO without the consideration of the TX I/Q imbalance. After that, we can separately estimate the TX I/Q imbalance and channel coefficients. Simulation results demonstrate that the proposed methods could achieve as competitive performance as the ideal situation which is free of I/Q imbalance.