Joint estimation and compensation of transmitter and receiver IQ imbalances in millimeter-wave SC-FDE systems

For millimeter-wave (MMW) communications, the in-phase quadrature imbalance (IQI) at the transmitter (TX) and the receiver (RX) may severely degrade the system performance, if not compensated. This paper addresses the joint estimation and compensation of TX and RX IQIs for single carrier frequency domain equalization (SC-FDE) systems. In particular, we introduce a concept called channel variation energy (CVE) to characterize the smoothness of channel frequency response observed at the receiver. By minimizing the CVE, the expressions relating the TX and RX IQIs are derived in closed form. Based on the expressions obtained, two schemes are proposed to estimate the TX and RX IQIs: i) Rosenbrock search based scheme; 2) least-square (LS) scheme. Once the IQIs are estimated, the channel information can be easily obtained by simple substitution. Therefore, the proposed schemes can separately estimate TX IQI, RX IQI and channel information, which is necessary for SC-FDE. Through simulations compliant with IEEE 802.11ad standard, it is shown that the proposed schemes can achieve the performance close to the ideal case without IQIs.