I/Q Imbalance Calibration Method for 5G Ultra-Wideband Transceivers

We propose a novel joint frequency-dependent I/Q imbalance calibration method through novelty of training signals and imbalance extraction method, applicable to the ultra-wideband wireless transceivers, such as 5G millimeter wave systems. First, we formulate the frequency-dependent I/Q imbalance of both transmitter (Tx) and receiver (Rx) as a function of input training signals, loopback response, and output signals. We then derive compensation filters as a unique solution of linear equations by constraining the training signals and loopback control. The training signals are designed to have a specific phase relation for providing unique solution of the compensation filters, which are then implemented by complex finite impulse response (FIR) filters. Simulations show that the proposed method can accurately estimate and compensate I/Q imbalance for both Tx and Rx. Laboratory experiments with a state of the art 5G transceiver on a hardware platform show that the imbalance strongly depends on frequency. Our method is able to suppress the frequency-dependent image of new radio (NR) signal below the thermal noise level over the full 1.4 GHz bandwidth.