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Abstract

A communication system having a modulation system for transmitting a symbol set via a single side-band modulated carrier and a demodulation system for recovering the in-phase and quadrature signals from the modulated carrier. The modulation circuit receives M symbol values and generates M time domain samples for each of the in-phase and quadrature signals. The in-phase and quadrature signals can then be combined to generate the single side-band modulated carrier. The modulation circuit includes a transform circuit for generating M transformed symbol values by computing the transform of the M symbol values. A polyphase filter bank having 2M FIR filters is used to process the output of the transform circuit. Each filter has g taps, where g is an integer greater than 1. The outputs of the polyphase filters are combined with the outputs of the polyphase filters generated from a previously received set of M symbols to generate the M time-domain signal values of the in-phase signal. The quadrature signal is generated by a similar circuit having two additional elements. The demodulation circuit recovers symbol sets from the in-phase or quadrature signals generated from M received time-domain signal values. The demodulator includes a memory for storing the 2M most recently received time-domain values, a polyphase filter bank, a polyphase processing circuit, and a transform circuit. The demodulation circuit for recovering a symbol set from the quadrature signal is similar to that for recovering the symbol set from the in-phase signal, except that the polyphase processor combines the outputs of the polyphase filters according to a different set of relationships and the sign of every other output from the transform is changed.

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