Modem for RF subscriber telephone system
First Claim
1. A multiple phase demodulator comprisingan input means to provide a phase-modulated input signal;
- a generator for generating a steady-state signal comprising a sine wave alternatley shifted ninety degrees;
a mixing means for combining said steady-state signal with said input signal to form a resultant signal;
an analog-to-digital converter for converting said resultant signal to digital form;
means including a digital memory means to conform the converted resultant signal to signals of predetermined frequencies; and
recovery means to recover the digital information from said conformed resultant signal, thereby producing a digital bit stream as output.
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Accused Products
Abstract
A modem including a modulator section for converting a bit stream, wherein each given number of successive bits defines a symbol, into a phase modulated intermediate frequency (IF) signal, the symbols in the modulator section being phase modulated and then digitally filtered to provide a filtered signal that, when converted into an analog signal, provides a modulation signal of a frequency that is centered about a predetermined frequency and deviates therefrom in accordance with the value of the phase modulated symbol, the analog signal then being filtered and passed to a mixer for up conversion to an IF signal; and a demodulator section for converting the IF signal into a bit stream, the demodulator section including a microprocessor which not only filters received digital signals but contains a memory for storing filter coefficients for use in the filtering of received digital signals; the modem being also operable in a training mode wherein a sequence of predetermined symbols is provided to the filter in the modulator section and the resultant phase modulated IF signal is receivable in the demodulator section, the microprocessor acting to adjust the filter coefficients stored in its memory until the reconstructed phase modulated symbols correspond to the sequence of predetermined symbols provided to the filter in the modulator section.
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Citations
24 Claims
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1. A multiple phase demodulator comprising
an input means to provide a phase-modulated input signal; -
a generator for generating a steady-state signal comprising a sine wave alternatley shifted ninety degrees; a mixing means for combining said steady-state signal with said input signal to form a resultant signal; an analog-to-digital converter for converting said resultant signal to digital form; means including a digital memory means to conform the converted resultant signal to signals of predetermined frequencies; and recovery means to recover the digital information from said conformed resultant signal, thereby producing a digital bit stream as output. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A modem comprising a multiple phase modulator and a multiple phase demodulator;
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said modulator comprising means for converting an input constituting a digitized bit stream into symbols, each symbol being defined by a given number of successive bits; a phase modulation means for phase modulating each symbol; a digitally implemented filter for shaping and generating a waveform from each of said symbols in accordance with the specifications of the frequency channel over which said symbols are transmitted, each of each waveforms constituting a transmitted symbol; and a digital-to-analog converter for converting each of said transmitted symbols to an analog signal; said demodulator comprising an input means to apply a phase-modulated input signal from said modulator; a generator for generating a steady-state signal containing both in-phase (I) and quadrature phase (Q) waveforms that are alternately phase shifted ninety degrees from each other; a mixing means for combining said steady-state signal with said input signal to form a resultant signal; an analog-to-digital converter for converting the resultant signal to digital form; means including a digital memory means to conform the converted resultant signal to signals of predetermined frequencies; and recovery means to recover the digital information from said conformed resultant signal, thereby producing a digital bit stream as an output. - View Dependent Claims (9)
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10. A system for converting a bit stream, wherein each given number of successive bits defines a symbol, into a phase modulated intermediate frequency (IF) signal at a predetermined IF frequency, comprising
phase modulating means for phase modulating each of said symbols; -
filtering means for digitally filtering each phase modulated symbol to provide a filter output comprising time-shared digital in-phase (I) and quadrature phase (Q) waveforms, said filter output, when converted to an analog signal, providing a modulation signal of a modulation frequency that is centered about a predetermined frequency and that deviates therefrom in accordance with the value of the phase modulated symbol; means for converting the filter output into an analog signal to provide a modulation signal; and means for multiplying said modulation signal by a fixed predetermined frequency having sin and cos components. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification