# Blind Compensation of \(I/q\) Impairments in Wireless Transceivers
## 5 Experimental Results  
After evaluating the performance of the proposed methodology using extensive simulations, the next step required experimental validation. The experimental setup is shown in Figure 12. Since the proposed mitigation strategy deals with frequency independent \(I/Q\) imbalances, the test signal selected was a 16-QAM signal with a narrow bandwidth of 10 KHz to minimize the effect of the frequency response, expected from the experimental setup. As many as 20,000 data points were generated and modulated using quadrature amplitude modulation. A raised cosine filter with a roll off factor of 0.3 and a filter delay of 3 was used to limit the bandwidth of the signal. The signal was then up-sampled by a factor of 8 (the sampling rate was 80 KHz). The \(I\) and \(Q\) components had the same variance and zero mean, thereby meeting the assumptions in Section 2.2. This signal was then shiftedto a low IF of 20 KHz in the digital processing unit and loaded to a vector signal generator (VSG, Agilent E4438C, Keysight Technologies, Santa Rosa, CA, USA) through a general-purpose interface bus (GPIB). For direct conversion transceivers, the image lies exactly on the band of interest, and the image suppression cannot be seen clearly. Hence, conversion to low IF enables visualization of the image band.  
The VSG performed digital modulation, digital-to-analog conversion, and frequency up-conversion. In order to add modulator imperfections, a gain imbalance of 1 dB and a phase imbalance of 5 degrees were added to this signal to voluntarily add \(I/Q\) imbalance to the VSG. This signal was then transmitted at a carrier frequency of 2.14 GHz and captured using a vector signal analyzer (VSA, Agilent E4440A, Keysight Technologies, Santa Rosa, CA, USA) with a span of 62.5 KHz and a resolution bandwidth of 15.2 Hz. The VSA served as a receiver in this case. The receiver performed frequency down-conversion, analog-to-digital conversion and finally demodulation and adds its inherent imbalance. This captured signal, with a time length of 250 ms, was loaded into the digital signal processor without any compensation for time delay or phase mismatch. Finally, the proposed post compensation technique was applied to this signal. The imbalanced and corrected waveform were captured by the spectrum analyzer, and a snapshot of the spectrum is shown in Figure 13. It can be seen that before compensation, the image suppression was around \(-20\) dB. However, after application of the proposed post-compensation algorithm, the image was reduced by around 30 dB, resulting in an image suppression of more than \(-50\) dB. Finally, Figure 14 shows the corrupted and recovered constellation using the proposed methodology. It can be seen in Figure 13 that the inherent DC offset of the device still showed up in the compensated output. This issue can be resolved by subtracting the mean of the compensated signal from the signal, thus reducing the DC offset due to local oscillator leakage [32].  
Figure 12: Measurement setup for evaluating the performance of proposed methodology.  
that the variation in EVM due to \(I/Q\) imbalance has been corrected using the proposed scheme and the NMSE is reduced considerably. The results obtained using the measurements were also compared to the simulations using the same values of imbalance parameters as in the measurement setup.