Active Interference Cancelation for user coexistence in the presence of I/Q imbalance

Secondary wide-band users have to guarantee that they will not disturb the in-band narrow-band primary users with allocated spectrum. There are techniques proposed to limit the leakage power of secondary wide-band users in the specified in-band narrow bands. Active Interference Cancelation (AIC) can flexibly solve this problem in the digital domain and hence remove the need for extra analog hardware. The main challenge is that the final depth of a nulled band is severely degraded by RF impairments such as PA non-linearity, phase noise, and I/Q mismatch. In this paper, we investigate the effect of I/Q imbalance on the performance of active interference cancelation techniques. Our analysis shows that for a transmitter with 3° phase imbalance and 0.1dB gain imbalance, the null depth will decrease from 40dB (provided in the digital domain) to 28.7dB (at the out of the radio transmitter). Then we introduce a compensation techniques and demonstrate an improvement of 5 - 10dB in the null depth depending on the severity of I/Q imbalance.