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A cellular subscriber modem for receiving CCITT-type quadrature amplitude modulated (QAM) signals. The cellular modem includes a novel symbol detector that converts received symbol information to polar notation. The detector\s constellation thresholds include a circular threshold having a radius gre

A cellular subscriber modem for receiving CCITT-type quadrature amplitude modulated (QAM) signals. The cellular modem includes a novel symbol detector that converts received symbol information to polar notation. The detector\s constellation thresholds include a circular threshold having a radius greater than the magnitude of the innermost symbols, but less than the magnitude of the outermost symbols, and radially spaced thresholds, which further discriminate between the outermost symbols. As a result, special cellular-compatible modem equipment need not be connected between the public-access switched telephone network and the computer equipment at the other end, which means that a CCITT-compatible cellular subscriber modem can then be treated as any other type of CCITT-modem. The detector may be implemented in the software of a standard modem processor, or as several analog comparator circuits.

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A cellular subscriber modem for receiving a quadrature amplitude modulated (QAM) signal, the QAM signal consisting of a plurality of symbols selected from a two-dimensional orthogonal signaling constellation which includes an innermost and a plurality of outer symbols within each of four quadrants,

A cellular subscriber modem for receiving a quadrature amplitude modulated (QAM) signal, the QAM signal consisting of a plurality of symbols selected from a two-dimensional orthogonal signaling constellation which includes an innermost and a plurality of outer symbols within each of four quadrants, the modem comprising: means for sampling a received cellular radio frequency (RF) signal containing the QAM signal, and for providing a pair of in-phase (i) and quadrature (q) received signal samples thereof; means for determining a radial magnitude and a phase for each pair of i and q signal samples; and means for comparing the radial magnitude and the phase for each pair of i and q signal samples against magnitude and phase constellation threshold values to determine which one of the plurality of symbols is represented by each pair of i and q signal samples, wherein the means for comparing further comprises means for selecting the magnitude threshold value such that the probability of correct symbol detection is maximized by equalizing the probability that an inner-most symbol within a given quadrant will be mistakenly identified as an outer symbol to the probability that an outer symbol will be mistakenly identified as the inner-most symbol.