unction is based on a Taylor series, where the output transmitted signal is represented as y(n) = (n) where xm(n) is the ideal passband analog signal for the digital representation of x(t). It can Chapter 3 TX radio TX radio processing processing Self-interference signal AUX TX AUX RX radio Digital SIC radio processing processing Self-interference signal RX radio RX radio processing processing Self-interference cancelation signal Self-interference cancelation signal Figure 3.40 Auxiliary transmit/receive chain in full-duplex systems (40,41]. be shown that for practical wireless systems, only the odd orders of the polynomial contrib- ute to the in-band distortion. Furthermore, only a limited number of odd orders contribute to the distortion, and higher orders can be neglected. The nonlinearity is typically character- ized by the third-order intercept point, which is defined as the point at which the power of the third harmonic is equal to the power of the first harmonic. Another source of impairment is IQ imbalance which is caused by the gain and phase mismatches between I and Q branches of the transmitter and receiver chains. This imbalance results in the com- plex conjugate of the ideal signal to be superimposed with some level of attenuation. Thus the output of an imperfect IQ mixer is a transformation of an input signal x(t) where both direct and conjugated signals are filtered and then summed together. The IQ imbalance can be modeled and compensated using widely linear filters. The results of studies suggest that the oscillator phase noise is one of the main self- interference cancellation challenges that limit the performance of full-duplex systems. It was assumed that when transmitter and receiver use a common local oscillator, the level of phase noise would remain at a tolerable level. However, this consideration is not always valid, especially in the case of OFDM systems. The studies show that with a phase noise variance between 0.4 and 1.0 degrees, the reduction in self-interference cancellation perfor- 