Digital transmitter I/Q imbalance calibration: Real-time prototype implementation and performance measurement

Abstract

Nowadays, the direct-conversion and the low-IF transceiver principles are seen as the most promising architectures for future flexible radios. Both of the architectures employ complex I/Q mixing for up- and downconversion. Consequently, the performance of the transceiver architectures can be seriously deteriorated by the phenomenon called I/Q imbalance. I/Q imbalance stems from relative amplitude and phase mismatch between I- and Q-branches of the transceiver. As a result, self-interference or adjacent channel interference is introduced. This paper addresses details of the real-time prototype implementation of the transceiver unit realizing widely-linear least-squares based I/Q imbalance estimation algorithm and corresponding pre-distortion structure proposed earlier by the authors. First the estimation itself is reviewed and a recursive version of it is derived. After that, implementation related practical issues are addressed and implementation platform is also briefly introduced. Finally, implementation details and comprehensive RF measurement results from the real-time implementation are presented.