A multicarrier QAM modulator for WCDMA basestation

A multicarrier QAM modulator for the wideband code division multiple access (WCDMA) basestation has been designed. The multicarrier modulator performs pulse shaping filtering for four baseband I and Q data streams. The filtered data is interpolated in three stages each interpolating with a factor of two. The modulation of four independent carriers is performed with the numerically controlled oscillators (NCO) which are based on the CORDIC vector rotation algorithm. The multi-carrier output is formed by summation of the modulated carriers. The SINC-attenuation effect of the D/A-converter is canceled by an inverse-SINC predistortion filter. The goal of the design process was to make the performance of the modulator limited by the 14-bit D/A-converter which can be considered as the state of the art available at IF frequencies.