A design of QAM modulator for multicode WCDMA

A QAM modulator using multiple four-output FIR filters based on look-up table (LUT) is proposed for downlink of wideband CDMA systems, and its functions are verified by stand-alone tests by means of the test equipment that achieves the functions of a QAM receiver system. Because a modulator employs the multicode modulation and M-QAM unlike QPSK modulation, the FIR filter for pulse shaping requires the multi-bit input word. So we propose the filter structure with multi-bit input word, which consists of multiple four-output FIR filter and bit-weighted accumulators. It is easy to extend the filter structure as increase of input bit word without higher clock frequency. We measure the spectrum of the implemented modulator by using a spectrum analyzer. Also, the demodulated signal constellation is obtained in the case of 16, 64 and 256-QAM as increase of multicode number.