Experimental performance evaluation of IQ imbalance and DC offset estimation and compensation technique for 3GPP LTE base station

In the case of recent wireless communication systems, the need to achieve high performance means that impairments in analog circuits cannot be disregarded. In view of the need for highly accurate compensation, many error compensation techniques using digital signal processing have been studied recently. Digital predistorter (DPD), which can eliminate odd-order distortion caused by PA nonlinearity, is one of the compensation techniques. However, in the case that direct conversion architecture is used in both a forward path and a loop-back path, errors in a quadrature modulator (QMOD) and a quadrature demodulator (QDEMOD) affect the performance of DPD. Previously, we proposed an error estimation technique for a QMOD and a QDEMOD that uses a variable phase shifter and evaluated its performance by an experiment using a narrow-band signal. In this paper, we evaluate the performance of the error estimation technique using the signal based on the 3GPP Long Term Evolution (LTE), whose bandwidth is wider than that in the previous experiment. The results show that image rejection ratio (IRR) after compensation is -59 dBc and error vector magnitude (EVM) is -52 dBc at the output of the QMOD.