Joint TX/RX IQ Mismatch Compensation Based on a Low-IF Internal Feedback Architecture

Modern radios use in-phase (I) and quadrature-phase (Q) channels for transmission and reception. However, IQ matching for high image rejection ratio is difficult and costly to realize by pure analog circuit techniques. Therefore, digital-assisted IQ compensation is required. This paper presents a novel joint TX/RX IQ compensation (JTRC) algorithm for low-IF feedback architecture. Conventional approaches are based on time-domain processing of test tones or frequency-domain processing of pilots in orthogonal frequency-division multiplexing (OFDM) systems. In contrast, JTRC employs time-domain blind source separation (BSS) for both OFDM and non-OFDM based systems without placing a specific requirement on the type of test signal. For example, JTRC supports both tones and modulated signals. Moreover, JTRC can be performed in the background during normal transmission mode using the actual transmitted signal. Unlike other BSS approaches that can only compensate for RX IQ mismatches while assuming a matched transmitter, JTRC can jointly compensate for both TX and RX IQ mismatches. We present an in-depth analysis that validates the JTRC algorithm and show simulation results that demonstrate its effectiveness.