RF Analog Impairments Modeling for Communication Systems Simulation: Application to OFDM-based Transceivers

4.4 IQ Mismatch Estimation and Correction

4.4.1 Principle

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

4.42

in which the ratio β/α is the ISR of the quadrature mixer, with

4.43

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:

4.44

where s_k 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

4.45

In reception, after the DFT processing we obtain the impaired signal in frequency domain (Tubbax et al., 2003, 2004):

4.46

showing that the ideal symbols s_k are corrupted ...