Digital image signal rejection in WCDMA receivers based on adaptive interference cancellation

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 direct-conversion and low-IF type front-ends are gaining more and more interest. One crucial aspect is the amplitude and phase matching of the analog I and Q signal branches. Especially in the low-IF scheme, which the paper also considers, I/Q mismatches result in incomplete image signal or mirror frequency attenuation which needs to be enhanced using additional analog or digital signal processing. The paper presents and analyzes a novel interference cancellation based technique for digital image suppression. The approach is practically oriented taking into account the effects of realistic signaling environments, such as carrier synchronization errors and low signal-to-noise ratios. The novelty of the presented structure is demonstrated using measured front-end signals complying with the current WCDMA system specifications.