Semi-Blind Iterative Joint Estimation of Frequency Selective I/Q-Imbalance and Modulator Offset Error in Direct-Conversion Transmitters

The compensation of frequency selective I/Q-imbalance and modulator (MOD) offset error can improve the performance of direct-conversion transmitters significantly. For effective compensation of these two effects, the parameter estimation is crucial. In many applications, ``semi-blind´´ estimation is desired i.e. not dedicated pilot signals but the communication signals are used for estimation. Conventionally, Least-Square Estimation (LSE) is applied. However, if the communication signal has spectral gaps (e.g. due to oversampling), the LSE will suffer from ill-conditioned matrix problem, which results in severe estimation error. To overcome this problem, we propose an Iterative Frequency Domain Estimation (IFDE) technique, which operates adaptively according to the spectral characteristic of the communication signal and can provide good calibration performance. The effectiveness of the IFDE and its advantage over conventional LSE are verified by numerical simulations.