Patent ID: 7085328

Claim:
An apparatus for converting a quadrature amplitude modulated (QAM) signal representing a first sequence of complex elements into a hard decision sequence of complex elements matching corresponding elements of the first sequence, the apparatus comprising: an analog-to-digital converter (ADC) for digitizing the QAM signal to produce a digital waveform sequence representing amplitudes of successive samples of the QAM signal; digital signal processing (DSP) circuit processing the digital waveform sequence to produce a soft decision sequence of complex elements, each being of value that is a higher resolution approximation of a value of a corresponding element of the first sequence, wherein the DSP circuit provides quadrature amplitude demodulation for which a quadrature demodulation phase angle is controlled by input phase angle control data, provides an adjustable gain controlled by gain control data, and provides equalization in accordance with a set of equalization filter coefficients, each controlled by separate coefficient control data; a slicer for converting each soft decision sequence element into a corresponding element of the hard decision sequence, each hard decision sequence element being of a value that is a lower resolution representation of a value of its corresponding hard decision sequence element; and an adaptation circuit evaluating a plurality of expressions having the hard and soft decision sequences as independent variables, wherein each expression computes successive values for a separate one of the phase control data, the gain control data, and the coefficient control data for each filter coefficient so as to minimize a first cost function having soft and hard sequence elements as independent variables, wherein the adaptation circuit sets the phase control data, the gain control data, and the coefficient control data for each filter coefficient to the successive values chosen by the plurality of expressions.