Blind I/Q imbalance compensation in OFDM receivers based on adaptive I/Q signal decorrelation

Due to its simple structure and relaxed requirements for radio frequency (RF) filtering, the so called direct-conversion or zero-IF architecture is gaining more and more interest in radio receiver design. One practical problem in the analog I/Q processing section is the amplitude and phase matching of the I and Q signal branches. With reasonable design and implementation costs, amplitude and phase mismatches in the order of 1-5% and 1-5° are feasible. The performance degradation due to these levels of I/Q mismatches is, however, considerable, especially in case of OFDM signals, where the mismatches cause certain type of intercarrier interference (ICI). In this paper, a novel structure for I/Q mismatch compensation is proposed for OFDM systems. The proposed compensator operates in the time domain and is based on adaptive I/Q decorrelation. It has low computational complexity and is basically independent of other receiver and system related nonidealities, especially frequency offsets and multipath propagation. Furthermore, the compensator is blind in the sense that no known training signals are needed. The effectiveness of the proposed structure is illustrated using computer simulations, showing impressive performance in practical signaling environments.