Communication

• US 4,351,064 A
• Filed: 01/31/1973
• Issued: 09/21/1982
• Est. Priority Date: 10/30/1970
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Ewanus, Walter
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/328,213
• Time in Patent Office: 3,520 Days
• Field of Search: 325/32, 325/34, 325/42, 325/65, 325/163, 325/145, 325/143, 325/44, 325/47, 325/323, 325/344, 325/349, 325/474, 455/26-29, 375/1
• US Class Current: 380/34
• CPC Class Codes: H04K 1/006 by varying or inverting the phase, at periodic or random intervals

Abstract

There is disclosed frequency modulation (FM) or phase modulation (PM) communication with a receiver having a limiter, in spread-spectrum operation for security purposes. The spectrum is spread on transmission by superimposing a psuedo-noise code modulation on the intelligence modulation of the carrier. On reception the spectrum is collapsed by auto-correlation of the pseudo-noise code. The pseudo-noise spectrum is produced by a digital coder which causes phase modulation of the carrier at the transmitter and the spectrum is collapsed by an identical coder which remodulates the received signal at the receiver which is operated in precise synchronism with the coder at the transmitter. To maintain synchronism a reference oscillator signal which periodically varies the phase of the received carrier is injected into the coder network at the receiver; this reference oscillator signal is processsed so that it passes through the limiter of the receiver. The modulated carrier from the transmitter is received in parallel paths. In one path the received carrier is modulated directly by the code from the coder at the receiver; in the other path, the received carrier is modulated by the code from the coder, periodically delayed in synchronism with a reference oscillator. The resulting so modulated carriers are correlated and the sum of the independently correlated carriers is impressed on the receiver as a carrier which is modulated by the intelligence and in addition is phase modulated in synchronism with the reference oscillator. The phase modulation is not suppressed by the limiter of the receiver and operates through a phase detector, low pass filter and voltage controlled oscillator, which are elements of a tracking loop, to maintain the coder at the receiver in synchronism with the received coder. The spread-spectrum operation disclosed lends itself to embodiment in adapters for converting conventional clear-signal communication equipment constructed in the past to spread-spectrum operation.

Claims

1. Communication apparatus for communicating intelligence including a transmitter unit having

(a) a transmitter network for producing a carrier,

(b) input means, connected to said network, for modulating said carrier with an input signal containing intelligence to be communicated, and

(c) modulator means, connected to said network, for impressing on said carrier a pseudo-noise code,

(d) a receiver unit having a receiver network for receiving the output of said transmitter including said intelligence and conditioning said output to be converted into intelligence perceptable form said receiver network being of the type including means for demodulating a modulated carrier, the said demodulating means including a limiter;

(e) an auto-correlation network including a first correlation branch conducting the modulated carrier and a second correlation branch conducting the modulated carrier;

(f) means connected to said correlation network, for dephasing the output of one of said branches with respect to the output of the other of said branches to produce a signal, dependant on the sum of the outputs of said branches, capable of being passed by said limiter;

(g) means connected to said first and second branches for impressing said sum-dependent signal on said receiver network, and

(h) means, connected to said receiver network and to said correlation network, for impressing on said sum-dependant signal a tracking signal manifested by a variation of the phase of the sum-dependant signal impressed on said receiver network and capable of being passed by said limiter said tracking signal cooperating with said sum-dependant signal to actuate said auto-correlation network to auto-correlate said code; and

communication means between said transmitter network and said receiver network.

2. The apparatus of claim 1 wherein the means for impressing a tracking signal includes a reference oscillator and means, connected to said oscillator, for time-modulating at least one of the carriers passing through at least one of the correlation branches in dependence upon the output of said oscillator;

the said means for impressing a tracking signal also including means comparing the phase relationship of the sum of the outputs of the branches with respect to said oscillator output to produce a parameter dependent on the phase displacement of said last-named outputs with respect to said oscillator output to derive the tracking signal, and means responsive to said tracking signal for maintaining the correlation network in synchronism with the psuedo-noise-code-impressing modulator means.

3. A pseudo-noise adapter for the receiver unit of a communication system for communicating intelligence and having a transmitter unit producing a carrier to be modulated, the said receiver unit having a receiver network for receiving the output of said transmitter including said intelligence and conditioning said output to be converted into intelligence-perceptable form having a limiter, the said transmitter unit including a first pseudo-noise coder, a first modulator connected in carrier-modulating relationship with said coder, and first timing means for actuating said coder periodically;

the said adapter including a second pseudo-noise coder and modulator means connected in a network with said second coder, the said last-named network to be connected to said receiver network with said second coder correlation-modulating said carrier, to supply its output to said receiver network, and second timing means for actuating said second coder periodically, said second coder when so actuated producing a code substantially the same as the code produced by said first coder, the said adapter also including means, connected to said network including said modulator means, for producing a tracking signal capable of being passed, retaining its phase and deviation properties, by the limiter of said receiver network and detector means for deriving from the tracking signal after it is passed by said receiver network, a signal measuring the departure of said second coder from synchronism with said first coder, and the said adapter including means, connected to said second timing means, responsive to said departure-measuring signal, for reducing the departure of said second coder from synchronism with said first coder.

4. The method of deriving the intelligence communicated by the transmitter unit of a communications system transmitting a carrier modulated by said intelligence and also by pseudo-noise modulation with receiving unit including a receiver network having a limiter, a pseudo-noise coder and modulator means connected to said coder;

the said method comprising

(a) correlating the transmitted pseudo-noise code by cooperation of said coder and said modulator means to produce a first signal including a carrier modulated by said intelligence;

(b) impressing a periodic delay on the output of said pseudo-noise coder, said delay having a frequency outside of the frequency bandwidth of the communicated intelligence;

(c) correlating the delayed output of said pseudo-noise coder by cooperation of said output and said modulator means to produce a second signal including a carrier modulated by said intelligence;

(d) dephasing said first and second signals relative to each other;

(e) adding said dephased first and second signals to derive a composite signal including a carrier modulated by said intelligence and also having a phase modulation dependent on the periodicity of said delay;

(f) impressing said composite signal in the input of said receiver to derive, at the output of said receiver, said communicated intelligence and also a signal of the periodicity of said delay displaced in phase with reference to the impressed periodic delay;

(g) deriving an error signal dependent on the displacement in phase of said signal of the periodicity of said delay; and

(h) controlling the pseudo-noise coder in accordance with said error signal to maintain said coder in synchronism with the pseudo-noise modulation modulating said transmitted carrier.

5. A pseudo-noise adapter for the receiver unit of a communication system having a transmitter unit producing a carrier to be modulated, the said receiver unit having a receiver network having a limiter, the said transmitter unit including a first pseudo-noise coder, a first modulator connected in carrier-modulating relationship with said first coder, and first timing means for actuating said coder periodically;

the said adapter including a second pseudo-noise coder and modulator means including second and third modulators connected in parallel in a network with said second coder, the said last-named network to be connected to said receiver network, with said second coder correlation-modulating said carrier, and second timing means for actuating said second coder periodically, said second coder when so actuated producing a code substantially the same as the code provided by said first coder, said second timing means including a time modulator interposed between the second coder and the third modulator, for passing the output of the second coder to the third modulator delayed by intervals set by the time modulator, said last-named network also including means for shifting the phase of the outputs of said second and third modulators with respect to each other and means for summing the dephased outputs of said second and third modulators;

the said adapter also including means, connected to said network including said modulator means, for producing a tracking signal capable of being passed, retaining its phase and deviation properties, by the limiter of said receiver network and detector means for deriving from the tracking signal, after it is passed by said receiver network, a signal measuring the departure of said second coder from synchronism with said first coder, the tracking-signal-producing means including a reference oscillator and also including means, connecting said oscillator to said time modulator, to set the delaying intervals of said time modulator in accordance with the oscillations of said oscillator, said tracking-signal-producing means also including means, connecting said reference oscillator to said detector means in comparison relationship with the output of the receiver network, to produce the departure-measuring signal and the said adapter including means, connected to said second timing means, responsive to said departure-measuring signal, for reducing the departure of said second coder from synchronism with said first coder.

6. The adapter of claim 5 wherein the detector means is a phase detector which determines the phase and deviation relationship between the output of the reference oscillator and the tracking signal output of the receiver network and the departure-measuring signal is dependent on the said phase and deviation relationship.