Digital communications equipment using differential quaternary frequency shift keying
First Claim
1. A communications transmitter for transmitting a digital bit stream, comprising:
- means for converting said digital bit stream to a stream of multi-bit symbols;
means for differentially encoding said stream of multi-bit symbols to produce a stream of differentially encoded symbols; and
means for frequency modulating a carrier signal in accordance with said differentially encoded symbols so as to represent each differentially encoded symbol by one of a plurality of frequencies related in number to a number of bits in said multi-bits symbols.
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Accused Products
Abstract
A digital radio transceiver uses a differential 4-ary frequency shift keying (D4FSK) modulation scheme to achieve a radio that is low cost, miniaturizable, low in power consumption, and high in spectral efficiency. An adaptive digital "slicer" looks at a digitized FM video signal produced in the receiver to determine if the data sent is a 00, 01, 10 or 11. The digitized FM video signal is first processed by a differential decoder, the output of which is input to a peak detector. The peak detector outputs a signal upon the occurrence of a three-step transition, i.e., a peak-to-peak voltage value. Two-step and three-step transitions are separately detected and used to perform digital clock recovery. A carrier detect circuit uses a digital bit filter to produce a carrier detect signal that is reliable and glitch-free. The digital radio transceiver uses frequency hopping spread spectrum transmission. A switchable loop bandwidth frequency synthesizer provides for glitch-free switching between a wide hopping bandwidth and a narrow bandwidth between hops.
209 Citations
25 Claims
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1. A communications transmitter for transmitting a digital bit stream, comprising:
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means for converting said digital bit stream to a stream of multi-bit symbols; means for differentially encoding said stream of multi-bit symbols to produce a stream of differentially encoded symbols; and means for frequency modulating a carrier signal in accordance with said differentially encoded symbols so as to represent each differentially encoded symbol by one of a plurality of frequencies related in number to a number of bits in said multi-bits symbols. - View Dependent Claims (2)
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3. A communications receiver for receiving a digital bit stream, encoded by forming multi-bit symbols and differentially encoding successive pairs of said multi-bit symbols to produce differentially encoded symbols, and frequency modulated so as to represent each differentially encoded symbol by one of a plurality of frequencies related in number to a number of bits of said multi-bit symbols, comprising:
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means for producing in response to an analog radio frequency input signal a demodulated FM signal in which different signal levels correspond to different ones of said plurality of frequencies; means responsive to said demodulated FM signal for adaptively determining a plurality of signal level thresholds corresponding to different ones of said plurality of frequencies and for comparing said demodulated FM signal to said thresholds to determine what particular symbol is being received and to produce a signal indicative thereof; means responsive to said signal for differentially decoding said signal into a stream of multi-bit symbols; and means responsive to said stream of multi-bit symbols for producing said digital bit stream. - View Dependent Claims (4)
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5. A communications transceiver for transmitting and receiving digital information represented as a digital bit stream, comprising:
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means for converting a digital bit stream to be transmitted to a stream of multi-bit symbols; means for differentially encoding said stream of multi-bit symbols to produce a stream of differentially encoded symbols; means for frequency modulating a carrier signal in accordance with said differentially encoded symbols so as to represent each differentially encoded symbol by one of a plurality of frequencies related in number to a number of bits in said multi-bits symbols; means for producing in response to an analog radio frequency input signal a demodulated FM signal, in which different signal levels correspond to different ones of said plurality of frequencies; means responsive to said demodulated FM signal for adaptively determining a plurality of signal level thresholds corresponding to different ones of said plurality of frequencies, and for comparing said demodulated FM signal to said thresholds to determine what particular symbol is being received and to produce a signal indicative thereof; means responsive to said signal for differentially decoding said signal into a stream of multi-bit symbols; and means responsive to said stream of multi-bit symbols for producing a received bit stream. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification