We have seen in Section 2.7 that the quadrature mixer amplitude and phase mismatches can severely degrade zero-IF OFDM transceiver performance by generating a complex conjugate image superimposed on the original signal. We demonstrated that the complex baseband signal including the IQ mismatch effect on the ideal signal x(t) can be expressed as
in which the ratio β/α is the ISR of the quadrature mixer, with
where ΔG and Δϕ are the amplitude and phase imbalances, respectively, and (.)* denotes the complex conjugate.
Let us suppose an ideal OFDM symbol not affected by the channel propagation:
where sk are the data symbols, k is the subcarrier index, and N is the total number of subcarriers.
Applying the IQ mismatch from Equation 4.42, we obtain
In reception, after the DFT processing we obtain the impaired signal in frequency domain (Tubbax et al., 2003, 2004):
showing that the ideal symbols sk are corrupted ...