Spread spectrum communications system
First Claim
1. A method of transmitting digital data, comprising the steps of:
- a) generating a high frequency carrier at a first carrier frequency;
b) modulating the frequency of said carrier with data bits assembled in data packets of predetermined format;
c) generating a high frequency carrier at a first carrier frequency and shifting the nominal frequency of said carrier by a frequency increment DF to obtain a second carrier frequency, whereDF=K*1/Ts+dF,dF=approximately L/(2*Ts),K is an integer,L is an odd integer, andTs is a PN (pseudo noise) sequence period;
d) modulating the frequency of said carrier in step c) with said data bits assembled in data packets of said predetermined format;
e) spreading said carrier at said first and said second frequency, during a transmission time, by a predetermined PN sequence having a period Ts related to a bit time Tb whereTb=N * Ts, N being an integer >
1 whereby a spread carrier spectrum comprising many spectral components separated by 1/Ts is obtained, the amplitudes of said components being reduced by said spreading function, said components and the modulation imposed upon them being separable from other components by a narrow band filter.
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Accused Products
Abstract
A spread spectrum communication system for direct sequence transmission of digital information having a modulation format which is particularly suitable for indoor communication within residential, office and industrial structures. The modulation format combines BPSK or MSK spreading with FM carrier modulation by data bits and a carrier frequency shift whose magnitude is related to both a chip rate and a spreading sequence length. The carrier, chip clock and data clock are all synchronous and the sequence length is an integral submultiple of the bit length. The system reduces the frequency error between the transmitter chip clock and the receiver chip clock to permit the elimination of a code phase tracking loop in the receiver to reduce the receiver complexity. The receiver has an extended dynamic range which makes possible the reception of very strong signal without an automatic gain control loop (AGC) as well as reducing the time needed for code phase acquisition. The transmission system is highly resistant to CW jamming and short distance multipath effects.
195 Citations
36 Claims
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1. A method of transmitting digital data, comprising the steps of:
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a) generating a high frequency carrier at a first carrier frequency; b) modulating the frequency of said carrier with data bits assembled in data packets of predetermined format; c) generating a high frequency carrier at a first carrier frequency and shifting the nominal frequency of said carrier by a frequency increment DF to obtain a second carrier frequency, where DF=K*1/Ts+dF, dF=approximately L/(2*Ts), K is an integer, L is an odd integer, and Ts is a PN (pseudo noise) sequence period; d) modulating the frequency of said carrier in step c) with said data bits assembled in data packets of said predetermined format; e) spreading said carrier at said first and said second frequency, during a transmission time, by a predetermined PN sequence having a period Ts related to a bit time Tb where Tb=N * Ts, N being an integer >
1whereby a spread carrier spectrum comprising many spectral components separated by 1/Ts is obtained, the amplitudes of said components being reduced by said spreading function, said components and the modulation imposed upon them being separable from other components by a narrow band filter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A transmitter for transmitting digital data comprising:
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a) carrier frequency generator means for generating a carrier frequency signal at a first frequency.; b) modulator means for modulating said carrier with data bits; c) frequency shift means for generating a second carrier frequency offset from said first carrier frequency by DF, where DF=K*1/Ts+dF, dF=approximately L/(2*Ts), K is an integer, L is an odd integer, and Ts is a PN (pseudo noise) sequence period; d) pseudo random sequence generator means for generating a predetermined PN sequence; d) carrier spread means for spreading power of said first and second carrier frequencies by said pseudo noise sequence. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A receiver for a spread spectrum signal comprising:
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a) a wideband receiving means for receiving a spread carrier radio signal for generating a spread carrier electrical signal; b) means for generating a predetermined PN (pseudo noise) sequence; c) multiplying means coupled to said receiving means and said generating means for multiplying said spread carrier electrical signal by said predetermined PN sequence, for collapsing a bandwidth of the received spread carrier when the local PN sequence phase is in agreement with the sequence phase imposed on the received spread carrier by a transmitter means, thereby spreading any jamming signals which are received along with the transmitted spread signal into many components separated by 1/Ts intervals and reduced in amplitude by the spreading function; d) narrow band FM receiver means coupled to an output of said multiplying means for recovering data; e) means coupled to said wideband receiving means for alternately receiving a radio signal on one of two preselected frequencies; and f) frequency switch means coupled to said means for alternately receiving for switching the received frequency between a first and a second of said preselected frequencies at predetermined time intervals. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25)
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26. A system for transmitting and receiving digital data, comprising:
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a) means for generating a high frequency carrier at a first carrier frequency; b) means for modulating the frequency of said carrier with data bits assembled in data packets of predetermined format; c) means for shifting the nominal frequency of said carrier by a frequency increment DF to obtain a second carrier frequency, where DF=K*1/Ts+dF, dF=approximately L/(2*Ts), K is an integer, L is an odd integer, and Ts is a PN (pseudo noise) sequence period; d) means for spreading said carrier at said first and said second frequency, during a transmission time, by a predetermined PN sequence having a period Ts related to a bit time Tb where Tb=N * Ts, N being an integer >
1whereby a spread carrier spectrum comprising many spectral components separated by 1/Ts is obtained, the amplitudes of said components being reduced by said spreading function, e) means for receiving the transmitted data; and f) means for multiplying said transmitted spread carrier in said receiver means by a locally generated predetermined PN sequence, for collapsing the bandwidth of the received spread carrier when the local PN sequence phase in agreement with the sequence phase imposed on the received spread carrier. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34)
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35. In a spread spectrum transmitter having a phase-lock loop for generating a carrier signal at a first frequency, said phase-lock loop including a voltage controlled oscillator having an output coupled to a frequency divider and an input coupled to an output of a phase detector, said phase detector having one input coupled to the output of said divider and a second input coupled to an output of a reference oscillator;
- frequency shift means for generating a second carrier frequency offset from said first carrier frequency; and
means for generating a spread spectrum signal from said first and said second carrier and a spreading signal, the improvement comprising said frequency driver consisting of a dual modulus prescaler.
- frequency shift means for generating a second carrier frequency offset from said first carrier frequency; and
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36. In a spread spectrum transmitter having a phase-lock loop for generating a carrier signal at a first frequency, said phase-lock loop including a voltage controlled oscillator having an output coupled to a frequency divider and an input coupled to an output of a phase detector, said phase detector having one input coupled to the output of said divider and a second input coupled to an output of a reference oscillator;
- means for receiving a second carrier frequency offset from said first carrier frequency;
means for generating a spread spectrum signal from said first and said second carrier and a spreading signal; and
means for despreading an incoming RF signal utilizing said spread spectrum signal, the improvement comprising said frequency divider consisting of a dual modulus prescale.
- means for receiving a second carrier frequency offset from said first carrier frequency;
Specification