QAM receiver having joint gain, carrier recovery and equalization adaptation system

摘要

A quadrature amplitude modulation (QAM) receiver digitizes an analog QAM signal representing a transmitted sequence of complex elements to produce a digital waveform sequence representing amplitudes of successive samples of the QAM signal. The QAM receiver employs a digital signal processing (DSP) circuit to process the digital waveform sequence to produce a soft decision sequence of complex elements, each of value that is a higher resolution approximation of a value of a corresponding transmitted sequence element. A pair of slicers then convert each soft decision sequence element into a lower resolution hard decision sequence element matching the corresponding complex element of the transmitted sequence. In processing the digital waveform sequence, the DSP circuit provides quadrature demodulation with a demodulation phase angle controlled by a control data sequence theta_n provides a gain controlled by control data g_n and provides equalization using a set of equalization filter coefficients, each i^th filter coefficient being of value controlled by separate control data f_i. DSP circuit adjusts control data sequence theta_n and control data g_n and f_i in accordance with separate algorithms, but the algorithms all minimize the same cost function relative to the soft and hard decision sequences.