Joint I/Q Mismatch and Distortion Compensation in Direct Conversion Transmitters

Analog and radio frequency (RF) front-end circuit impairments such as mismatches between in-phase (I) and quadrature (Q) branches can severely degrade performance of wireless communications systems. In this paper, we propose a technique to compensate for both frequency-independent and frequency-dependent impairments in direct conversion transmitters (DCTs). The technique employs a recursive algorithm to estimate the impairments from instantaneous power of the transmitted RF signal, and it jointly mitigates the mismatches/imbalances between the I and Q branches and the distortions in each of the I and Q branches. It is applicable to wireless communications systems that employ different modulation techniques. Theoretical analyses are presented for identifiability and convergence properties of the technique. Effects of imperfect measurement are discussed. Both computer simulation and prototype experimentation are carried out to demonstrate that the proposed technique accurately determines and compensates for the DCT impairment, and improves the transmitted signal quality.