Direct sequence spread spectrum (DSSS) communications system with frequency modulation utilized to achieve spectral spreading
First Claim
1. A spread spectrum transmission apparatus comprising:
- means for accepting a baseband signal containing information,means for generating a spreading waveform,means for combining the spreading waveform with the baseband signal to produce by the sum thereof a spread spectrum signal that is frequency modulated.
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Abstract
Hardware complexity of transmitting and receiving equipment in a CDMA (Code Division Multple Access) cellular radio transmission system, embodying the principles of the invention, is reduced by the use of frequency modulation (FM) techniques to achieve spectral spreading in combination with signal modulation.
The spectral spreading technique of a CDMA cellular radio telephone communications system is generalized by extending the range of values allotted to the spreading waveform code signal to include complex numbers of unity magnitude. This permits the addition of a baseband version of the information signal and spreadying waveforms instead of the conventional multiplication of the two signals in existing DSSS (Direct Sequence Spread Spectrum) communications sytems. The resultant summed signal is used to control a VCO (Voltage Controlled Oscillator) to produce a frequency modulated spread signal to be transmitted. This arrangement permits improved and more efficient implementations of the transmitting and receiving equipment.
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Citations
18 Claims
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1. A spread spectrum transmission apparatus comprising:
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means for accepting a baseband signal containing information, means for generating a spreading waveform, means for combining the spreading waveform with the baseband signal to produce by the sum thereof a spread spectrum signal that is frequency modulated.
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2. A spread spectrum transmission apparatus comprising:
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means for accepting a baseband signal containing information, means for generating a spreading waveform, means for combining the spreading waveform with the baseband signal to produce by the sum thereof a spread spectrum signal that is frequency modulated, the means for combining including; means for summing the base band signal and the spreading waveform, and a voltage controlled oscillator responsive to the means for summing. - View Dependent Claims (3)
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4. A radio transmitter for a spread spectrum cellular telephone system, comprising:
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means for accepting a baseband signal containing information, means for generating a spreading waveform, means for summing the spreading waveform with the baseband signal, means responsive to the means for summing for producing a frequency modulated signal with spread spectrum, and means for transmitting the frequency modulated signal.
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5. A radio transmitter for a spread spectrum cellular telephone system, comprising:
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means for accepting a base band signal containing information, means for generating a spreading waveform, means for summing the spreading waveform with the baseband signal, means responsive to the means for summing for producing a frequency modulated signal with spread spectrum, and means for transmitting the frequency modulated signal, filtering means for producing a continuous spreading waveform prior to application to the means for summing. - View Dependent Claims (6)
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7. A spread spectrum receiving apparatus comprising:
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means for generating a replica of a spreading signal used for spreading a transmitted signal, means for frequency modulating a signal in response to the replica of a spreading signal, means for receiving a signal with spread spectrum, means for mixing the frequency modulated signal and the received spread spectrum signal to produce a signal of an intermediate frequency less than that of the received spread spectrum signal, means for recovering an original information signal from the signal of an intermediate frequency. - View Dependent Claims (8, 9, 10, 11)
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12. A spread spectrum transmission apparatus comprising:
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an input for accepting a signal; a spreading waveform generator; a summing circuit for combining the signal and a spreading waveform of the spreading waveform generator; a frequency generator having a frequency dependent on an applied signal, and coupled to receive an output of the summing circuit; an output circuit coupled to receive an output of the frequency generator. - View Dependent Claims (13)
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14. A spread spectrum receiving apparatus comprising:
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an input for accepting a spread spectrum signal; a frequency generator having a frequency dependent on an applied signal; a mixing circuit coupled to receive signals from the input and from the frequency generator; an FM demodulator coupled to receive output from the mixing circuit a de-spreading waveform generator; a de-spreading waveform control loop responsive to an output of the FM demodulator;
including;timing control circuitry for controlling timing of an output of the de-spreading waveform generator; and an amplitude control circuit for controlling an amplitude of an output of the de-spreading waveform generator.
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15. A method of generating a frequency modulated spread spectrum signal,
comprising the steps of: - summing a signal and a spreading signal;
generating a signal varying in frequency about a center frequency in response to an amplitude of the sum of the signal and the spreading signal.
- summing a signal and a spreading signal;
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16. A method of recovering information from an FM spread spectrum signal;
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comprising the steps of; generating a replica of a spreading signal used in transmitting the signal; generating a signal varying in frequency about a center frequency in response to the replica of a spreading signal for use as a de-spreading signal; combining by mixing the FM spread spectrum signal and the de-spreading signal; FM demodulating the signal produced by mixing. - View Dependent Claims (17, 18)
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Specification