A LS estimation algorithm on quadrature modulation correction scheme for LTE/WCDMA RF transceiver

Although the quadrature mixing radio front-end offers an attractive way to perform frequency translation, its image-rejection capability is severely affected by the gain and phase imbalances (I/Q imbalances) between its two analog signal paths. Digital signal processing techniques based on the preamble or training signals have widely been proposed to compensate for these mixer imperfections. However, these methods are not suitable for the communication systems without the specified training signals. In this paper, we propose a LS (Least Square) estimation algorithm which can be utilized in any quadrature modulation communication system. The algorithm is based on the baseband signal pre-correction methodology, and the QMC (qudrature modulation correction) parameters can be estimated on line or offline depending on the working mode. The proposed algorithm has been thoroughly tested in the RF transceiver system. The test result shows that the ACLR performance outperforms the WCDMA standard with about 6dB margin with single carrier and at least 5dB margin with four carriers and can eliminate the QM distortion effectively.