Blind Moment Estimation Techniques for I/Q Imbalance Compensation in Quadrature Receivers

Abstract

When targeting receiver integrability and flexibility, the choice of the front-end architecture is in key position. Instead of the traditional superheterodyne architecture, more recent I/Q or quadrature receiver front-ends are receiving increasingly more interest. One crucial aspect in quadrature receiver front-ends is the amplitude and phase matching of the analog I and Q signal branches. I/Q mismatches result in incomplete image signal or mirror frequency attenuation which must be enhanced using additional analog or digital signal processing. This paper presents and analyzes a novel DSP-based blind (non-data-aided) technique for I/Q imbalance compensation, utilizing a property of the ideal baseband equivalent called circularity. The weights of the compensator are computed directly from the estimates of the second-order moments of the mismatched baseband equivalent received signal. This algorithm is further simplified, with minimal loss in performance, yielding an extraordinarily simple yet effective compensation technique which ideally triples the dB value of the analog front-end image rejection ratio. The algorithms are applicable to any I/Q receiver structure, whether single-channel or multi-channel, and are in fact totally independent of any specific structure or characteristic (other than circularity) of the ideal baseband equivalent signal