Multiple channel data link system

• US 4,494,238 A
• Filed: 06/30/1982
• Issued: 01/15/1985
• Est. Priority Date: 06/30/1982
• Status: Expired due to Term

• Current Assignee: General Dynamics Decision Systems, Inc. (General Dynamics Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Groth, Edward J. Jr.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/393,833
• Time in Patent Office: 930 Days
• Field of Search: 375/1, 375/40, 375/100, 375/2.1, 455/49, 455/50, 455/52, 455/59, 455/63, 455/137, 455/139, 455/314, 455/315, 455/316, 371/68, 370/19, 178/22.01, 178/22.1, 178/22.12, 178/22.13, 178/22.14, 178/22.16
• US Class Current: 375/141
• CPC Class Codes: H03J 7/02 Automatic frequency control H03J7/18 takes precedence
• CPC Class Codes: H04B 1/69 Spread spectrum techniques

Abstract

A coherent communications link for simultaneously transmitting intelligence on a plurality of non-contiguous frequency channels by means of a plurality of coherent carrier signals which are connected to a single composite intermediate frequency signal upon reception by a fully coherent receiver. The local oscillator signals in the receiver are maintained coherent with respect to the transmitted carrier signals responsive to the composite IF signal while each of the local oscillator signals is adjusted to maintain coherence of each received carrier in the face of relatively long term drift due to thermal shifts, path effects and hardware drift.

Claims

1. A communications system comprising in combination:

a transmitter further comprising;

means for simultaneously transmitting a plurality of coherently related carrier signals in a like plurality of signal channels, said plurality of signal channels being one of contiguous and non-contiguous; and

means for modulating at least two of said plurality of carrier signals with an identical information bearing modulation signal;

a receiver further comprising;

means for receiving said plurality of coherently related carrier signals;

a single dynamic, carrier tracking, phase locked loop coupled to said receiving means for maintaining all of the received signals coherent;

means coupled into said phase locked loop for coherently combining said plurality of coherently related carrier signals; and

means coupled into said phase locked loop for detecting said coherently combined signals.

2. The communications system according to claim 1 wherein said means for simultaneously transmitting further comprises:

synthesizer means for coherently generating said plurality of carrier signals.

3. The communications system according to claim 1 wherein said transmitter further comprises:

means for modulating each of said plurality of carrier signals with a spectrum spreading signal; and

wherein said receiver further comprises;

means for despreading each of said plurality of spread spectrum carrier signals.

4. The communications system according to claim 3 wherein said means for modulating with a spectrum spreading signal comprises:

first means for generating separate and different spectrum spreading signals for each of said plurality of carrier signals in said transmitter.

5. The communications system according to claim 4 wherein said despreading means further comprises:

second means for generating said each of said separate and different spectrum spreading signals for adaptation as despreading signals in said receiver.

6. The communications system according to claim 5 wherein said despreading means further comprises:

means for generating a like plurality of local oscillator signals, each of said plurality of local oscillator signals being offset in frequency from a corresponding one of said carrier signals by a frequency equal to a predetermined intermediate frequency;

a like plurality of means for mixing one of each of said plurality of local oscillator signals with one of each of said plurality of coherently related carrier signals to produce a like plurality of coherent intermediate frequency signals, each of said plurality of local oscillator signals being coherent with respect to a corresponding one of said plurality of coherently related carrier signals and wherein said mixing means is disposed in said receiver prior to said detection means; and

means for coherently summing said like plurality of coherent intermediate frequency signals for producing a composite coherent intermediate frequency signal.

7. The communications system according to claim 3 wherein said despreading means further comprises:

a plurality of loop means for phase tracking each of said coherently related carrier signals.

8. The communications system according to claim 7 wherein each of said plurality of loop means further comprises a like plurality of orthogonal generating means, each of said like plurality of orthogonal generating means being used to produce one of a set of orthogonal functions, each one of said set of orthogonal functions being adapted to modulate a local oscillator signal and, thus, to identify a specific correction signal in a specific one of said plurality of loop means.

9. The communications system according to claim 8 wherein said modulation is by means of dithering a phase of said local oscillator signal.

10. The communications system according to claim 9 wherein said orthogonal functions are generated by digital means and wherein said modulation is accomplished by digital means.

11. The communications system according to claim 9 further comprising:

shifting means for shifting an element of said modulated signals by substantially ninety degrees; and

means for measuring an amplitude variation of said shifted element, thereby yielding a measure of quality for a corresponding coherently related carrier signal.

12. The communications system according to claim 1 wherein said receiver further comprises:

means for tracking Doppler frequency offsets, and other frequency and phase errors that are proportional to frequency, in a single tracker, said single tracking means being responsive to said coherently combined plurality of carrier signals in said receiver.

13. The communications system according to claim 1 wherein said receiver further comprises:

means for generating and controlling a phase of a plurality of local oscillator signals corresponding in number to said plurality of coherently related carrier signals, for reducing short term errors, such as Doppler errors and other errors which are a function of frequency, in said coherently combined plurality of carrier signals, said generating and controlling means being responsive to said coherently combined carrier signals.

14. The communications system according to claim 13 wherein said receiver further comprises:

a plurality of narrow band means for correcting long term frequency drift in each of said plurality of local oscillator signals, each of said plurality of said narrow band means being responsive to an amplitude portion of said coherently combined signal.

15. The communications system according to claim 1 wherein said receiver further comprises:

means for generating and controlling the phase of a plurality of local oscillator signals corresponding in number to said plurality of coherently related carrier signals, for reducing short term errors, such as Doppler errors and other errors which are a function of frequency, in said coherently combined pourality of carrier signals, said generating and controlling means being responsive to said coherently combined carrier signals; and

a plurality of narrow band means for correcting long term frequency drift in each of said plurality of local oscillator signals, each of said plurality of said narrow band means being responsive to an amplitude portion of said coherently combined signal.

16. The communications system according to claim 15 wherein said means for coherently combining further comprises:

means for generating a like plurality of local oscillator signals, each of said plurality of local oscillator signals being offset in frequency from a corresponding one of said carrier signals by a frequency equal to a preselected intermediate frequency;

a like plurality of means for mixing one of each of said plurality of said coherently related carrier signals to produce a like plurality of coherent intermediate frequency signals, each of said plurality of local oscillator signals being coherent with respect to a corresponding one of said plurality of coherently related carrier signals and wherein said mixing means is disposed in said receiver prior to said detector means; and

means for coherently summing said like plurality of coherent intermediate frequency signals for producing a composite coherent intermediate frequency signal.

17. The communications system according to claim 16 wherein said receiver further comprises:

a plurality of loop means for phase tracking each of said coherently related carrier signals.

18. The communications system according to claim 17 wherein each of said plurality of loop means further comprises a like plurality of orthogonal generating means, each of said like plurality of orthogonal generating means being used to produce one of a set of orthogonal functions, each one of said set of orthogonal functions being adapted to modulate a local oscillator signal and, thus, identify a specific correction signal in a specific one of said plurality of loop means.

19. The communications system according to claim 18 wherein each of said orthogonal functions are adapted to modulate one of said correction signals by means of dithering a phase of each of said correction signals, respectively.

20. The communications system according to claim 19 wherein said orthogonal functions are generated by digital means and wherein said modulation is accomplished by digital means.

21. The communications system according to claim 20 wherein said receiver further comprises:

means for tracking Doppler frequency offsets, and other frequency and phase errors that are proportional to frequency, in a single tracker, said single tracking means being responsive to said coherently combined plurality of carrier signals in said receiver.

22. The communications system according to claim 21 wherein said receiver further comprises:

means for generating and controlling the phase of a plurality of local oscillator signals corresponding in number to said plurality of coherently related carrier signals, for reducing short term errors, such as Doppler errors and other errors which are a function of frequency in said coherently combined plurality of carrier signals, said generating and controlling means being responsive to said coherently combined carrier signals.

23. A receiver for receiving a plurality of coherently related radio frequency signals, the plurality of radio frequency signals being one of contiguous and non-contiguous, the radio frequency signals each being modulated with an information bearing signal, said information bearing signals being identical each to every other information bearing signal, the receiver comprising:

a single dynamic, carrier tracking, phase locked loop for maintaining all of the received signals coherent;

means coupled into said phase locked loop for coherently and simultaneously combining at least two of the received radio frequency signals; and

means coupled into said phase locked loop for detecting said combined signals, said means for detecting being responsive to said combined radio frequency signals subsequent to said combining.

24. The receiver according to claim 23 wherein said received plurality of radio frequency signals is modulated with spectrum spreading signals, each of said spectrum spreading signals being unique, the receiver further somprising:

means for simultaneously and coherently despreading said plurality of spread spectrum modulated radio frequency signals.

25. A receiver for receiving a plurality of radio frequency signals, the plurality of radio frequency signals being one of contiguous and non-contiguous, the radio frequency signals being modulated with spectrum spreading signals, each of said spectrum spreading signals being unique but related in a predetermined way to a master spectrum spreading signal, said received plurality of spread spectrum radio frequency signals being modulated with an information bearing signal, each of said information bearing signals being identical to every other information bearing signal, the receiver comporising:

means for simultaneously and coherently despreading said plurality of spread spectrum modulated radio frequency signals;

means coupled to said despreading means for coherently and simultaneously combining at least two of the received radio frequency signals; and

means for detecting said combined signals, said means for detecting being operable on said combined radio frequency signals subsequent to said combining.

26. A receiver for receiving a plurality of radio frequency signals, the plurality of radio frequency signals being one of contiguous and non-contiguous, the receiver comprising:

a single dynamic, carrier tracking, phase locked loop for maintaining all of the received signals coherent;

means coupled into said phase locked loop for simultaneously and coherently combining said plurality of radio frequency signals; and

means coupled into said phase locked loop for coherently controlling phases of a plurality of different local oscillator signals responsive to an average long term phase shift in the plurality of radio frequency signals such as shifts due to thermal, aging and dispersion effects.

27. A communications method comprising the steps of:

generating a plurality of coherently related radio frequency signals, said plurality of radio frequency signals being one of contiguous and non-contiguous;

modulating said plurality of radio frequency signals with a like plurality of information bearing signals, every one of said like plurality of information bearing signals being identical with every other one of said like plurality of information bearing signals;

combining said plurality of modulated radio frequency signals into a composite signal;

transmitting said composite signal to a receiver;

receiving said composite signal;

splitting said composite signal into a plurality of composite signals;

generating a like plurality of coherently related local oscillator signals, each of said plurality of local oscillator signals being offset in frequency by a predetermined intermediate frequency from a corresponding one of said plurality of radio frequency signals;

mixing each of said plurality of local oscillator signals with a different one of said plurality of composite signals to produce a plurality of converted composite signals;

summing said plurality of converted composite signals coherently;

amplifying and filtering said plurality of summed signals in an intermediate amplifier to produce a single information bearing signal; and

detecting said information bearing signal coherently.

28. The method according to claim 27 further comprises the steps of:

spreading the spectrum of each of said plurality of radio frequency signals with a plurality of different spectrum spreading signals, each of said spectrum spreading signals being unique with respect to every other of said plurality of spectrum spreading signals; and

despreading said plurality of spread spectrum radio frequency signals in said receiver to produce a despread converted composite signal.

29. The method according to claim 28 wherein said despreading step further comprises the steps of:

modulating each of the plurality of local oscillator signals with a like plurality of unique functions, each of said unique functions being related to all others of said plurality of unique functions orthogonally; and

tracking a phase of each of said plurality of unique function modulated local oscillator signals in a plurality of phase locked loops to control a phase of each of said plurality of local oscillator signals to be coherent with a corresponding phase of a corresponding one of said received radio frequency signals by recognizing each of the plurality of loop signals by means of the orthogonal function modulated upon its corresponding signal.

30. The method according to claim 29 further comprising the steps of:

shifting the phase of at least one of said plurality of unique function modulated local oscillator signals substantially by ninety degrees, thereby shifting a corresponding element of said converted composite signal; and

measuring an amplitude variation of said shifted converted composite element signal thereby yielding a measure of quality for a corresponding coherently related radio frequency signal.

31. A communications method comprising the steps of:

generating a plurality of radio frequency signals, said radio frequency signals being one of contiguous and non-contiguous;

modulating said plurality of radio frequency signals with a like plurality of spectrum spreading signals, all of said like plurality of spectrum spreading signals being different from every other one of said plurality of spectrum spreading signals, each of said plurality of spectrum spreading signals being modified from a master spectrum spreading signal in a predetermined way;

combining said plurality of modulated radio frequency signals into a composite signal;

transmitting said composite signal to a receiver;

receiving said composite signal;

splitting said composite signal into a plurality of composite signals;

generating a like plurality of coherent local oscillator signals, each of said plurality of local oscillator signals being offset in frequency by a predetermined frequency from a corresponding one of said plurality of radio frequency signals;

mixing each of said plurality of local oscillator signals with a different one of said plurality of composite signals to produce a plurality of converted composite signals;

amplifying and filtering said plurality of converted composite signals in an intermediate amplifier;

generating a plurality of spectrum despreading signals which are each identical, respectively, to each of said plurality of spectrum spreading signals;

applying each of said plurality of despreading signals to each corresponding one of said plurality of local oscillator signals for producing a plurality of local oscillator signals for despreading said plurality of spread spectrum signals;

despreading said plurality of spectrum spread radio frequency signals by means of said plurality of local oscillator despreading signals; and

detecting said composite despread signals coherently.

32. A method for coherently combining a plurality of first coherently related signals comprising the steps of:

generating a first plurality of coherently related local oscillator signals;

generating an offset reference signal;

mixing each of said plurality of said first local oscillator signals in a mixer with said offset reference signal to produce a plurality of second local oscillator signals;

multiplying, coherently, each of said second local oscillator signals by a factor of k to produce a third plurality of local oscillator signals, said third plurality of local oscillator signals being coherently related to the first coherently related signals; and

mixing each of said third plurality of local oscillator signals each with a corresponding one of said first plurality of coherently related signals to produce a plurality of coherent intermediate signals.