Spread spectrum communication system with frequency-separated message and reference signals
First Claim
1. A spread spectrum communication system comprising:
- a transmitter includinga modulator for modulating an information input signal with a carrier frequency f1,a spreading signal generator,a first mixer for combining the modulated carrier signal with a spreading signal from said spreading signal generator,a second mixer for combining the spreading signal from said spreading signal generator with a second frequency f2 different from said carrier frequency f1, the difference frequency f1 -f2 being sufficiently low that any delay less than a maximum expected delay spread does not result in a 180°
phase shift, anda summer for adding output signals of said first and second mixers to produce a transmitted signal; and
a receiver includingradio frequency receiver means for receiving said transmitted signal from said transmitter,a nonlinear device for squaring an input signal supplied thereto,circuit means coupling said nonlinear device to said radio frequency receiver means, anda demodulator for demodulating the squared output signal at a carrier frequency of f2 -f1.
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Accused Products
Abstract
A method and apparatus for implementing a spread spectrum communication system of the "transmitted reference" type provides both multipath and interference protection with little complexity. Need for a local reference is avoided by transmitting a reference that the receiver can use to perform despreading. In general, the transmitted reference system sends both a message signal and a reference signal to the receiver. The message signal contains the information to be communicated, which has been spread through multiplication with a wide band "spreading waveform". The reference signal consists of the spreading waveform itself which the receiver call use to despread the message signal and recover the information.
26 Citations
8 Claims
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1. A spread spectrum communication system comprising:
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a transmitter including a modulator for modulating an information input signal with a carrier frequency f1, a spreading signal generator, a first mixer for combining the modulated carrier signal with a spreading signal from said spreading signal generator, a second mixer for combining the spreading signal from said spreading signal generator with a second frequency f2 different from said carrier frequency f1, the difference frequency f1 -f2 being sufficiently low that any delay less than a maximum expected delay spread does not result in a 180°
phase shift, anda summer for adding output signals of said first and second mixers to produce a transmitted signal; and a receiver including radio frequency receiver means for receiving said transmitted signal from said transmitter, a nonlinear device for squaring an input signal supplied thereto, circuit means coupling said nonlinear device to said radio frequency receiver means, and a demodulator for demodulating the squared output signal at a carrier frequency of f2 -f1. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A spread spectrum transmitter comprising:
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a modulator for modulating an information input signal with a carrier frequency f1 ; a spreading signal generator; a first mixer for combining the modulated carrier signal with a spreading signal from said spreading signal generator; a second mixer for combining the spreading signal from said spreading signal generator with a second frequency f2 different from said carrier frequency f1, the difference frequency f1 -f2 being sufficiently low that any delay less than a maximum expected delay spread does not result in a 180°
phase shift; anda summer for adding output signals of said first and second mixers to produce a transmitted signal. - View Dependent Claims (8)
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Specification