Mean squared error analysis for OFDMA signals under joint Tx/Rx IQ imbalance

In this paper, a normalized mean squared error (NMSE) expression is derived for an orthogonal frequency division multiple access link under the effects of joint transmitter (Tx) and receiver (Rx) in-phase/quadrature imbalance (IQI). Two special cases of Tx-only and Rx-only IQI are also studied. The considered type of IQI is frequency independent. Additionally, asymptotic analysis under the assumption of high signal-to-noise ratio (SNR) is performed where in some cases, the NMSE metric increases as the SNR increases. To rectify this behavior, we propose a regularization parameter that can be added to the minimum mean square error channel equalizer to force the NMSE metric to converge as the SNR increases.