DIVERSITY COMMUNICATION SYSTEM USING DISTINCT SPECTRAL ARRANGEMENTS FOR EACH BRANCH

• US 3,662,268 A
• Filed: 11/17/1970
• Issued: 05/09/1972
• Est. Priority Date: 11/17/1970
• Status: Expired due to Term

• Current Assignee: Douglas Otto John Reudink, Michael James Gans
• Original Assignee: Douglas Otto John Reudink, Michael James Gans
• Inventors: Reudink, Douglas Otto John, Gans, Michael James
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Weinstein, Kenneth W.
• Application Number:
  US05/090,396
• Time in Patent Office: 539 Days
• Field of Search: 325/56,59,154,156,3,14,51,53,54,58,65,473,479 179/15BP
• US Class Current: 455/504
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence

Abstract

The output of each branch of a diversity system contains a pilot signal and a modulated carrier. The spectrum of each branch output is distinct, but the difference frequency component between the signal and pilot is identical for all branches. The same intelligence is applied to each branch. In a unitary branch combiner, a single mixer performs all cophasing and combining. All of the pilot and carrier signals are beat together to produce in-phase addition of the difference components derived from the individual signal pairs, and the spectra are selected so that negligible interference is generated by cross modulation products.

Claims

1. A diversity transmission system comprising means for generating a plurality of branch outputs, each branch output consisting of a pair of signals, the difference frequency component between the two signals of any pair being identical for all branch outputs, means for applying identical intelligence to each branch output by modulating at least one signal of the pair, mixing means for simultaneously beating together all of the signals of all of the branch outputs to produce difference frequency products among all of the signals, and modulation receiving means tuned to a frequency band containing the identical difference frequency component for detecting the modulation on the difference products derived from two signals of the same branch output, exclusive of the difference products derived from signals of different branch outputs,

2. A diversity transmission system as claimed in claim 1 wherein said means for generating a plurality of branch outputs is arranged to produce a distinct spectrum for each of said plurality of branch outputs.

3. A diversity transmission system as claimed in claim 1 wherein said means for applying intelligence includes means for applying frequency modulation with a selected f.m. index to at least one signal of each signal pair, and said modulation receiving means includes a passband filter tuned to pass said identical difference frequency component and an f.m. detector in which the capture effect suppresses difference frequency products derived from signals of different signal pairs.

4. A diversity transmission system as claimed in claim 3 wherein said means for applying intelligence includes means for modulating the intelligence in part on one signal of said pair of signals and in part on the other signal of said pair of signals.

5. A diversity transmission system in accordance with claim 1 wherein said mixing means produces in-phase difference frequency products of the two signals of each signal pair and randomly phased difference products of two signals in different signal pairs, whereby the randomly phased products are either outside the passband of said modulation receiving means or significantly weak relative to the in-phase product.

6. A diversity transmission system in accordance with claim 1 wherein the spectrum of each of the plurality of signal pairs is selected so that the cross modulation products of all signals, exclusive of those products of the two signals of any single signal pair, are outside the passband defined by the product of the signals of the single signal pair or are significantly weaker than the products of the signals of the single signal pair.

7. A diversity communication system comprising, a plurality of branches, means for applying to each branch a pilot signal and a carrier signal, the difference frequency component between the pilot and carrier on each branch being identical for all braNches, means for applying identical intelligence to each branch by modulating at least one of the two signals, means for simultaneously beating together all of the pilots and carriers of the plurality of branches to produce difference frequency components, means for suppressing the undesired difference frequency components produced by beating together signals other than a pilot and carrier of the same branch. means for detecting the modulation from the difference frequency components produced by beating a pilot and carrier of the same branch.

8. A diversity communication system as claimed in claim 7 wherein said means for applying to each branch a pilot signal and a carrier signal is arranged to produce a distinct spectrum for each branch.

9. A diversity communication system as claimed in claim 8 wherein the spectra are selected so that the cross modulation products of all of the pilots and carriers of the plurality of branches, exclusive of those products of the pilot and carrier of the same branch, are significantly removed in at least frequency or power from those products of a pilot and carrier of any one same branch.

10. A diversity communication system as claimed in claim 7 wherein the frequency of the pilot of a first branch is below the frequency of the carrier of the first branch and the frequency of the pilot of a second branch is above the frequency of the carrier of the second branch so that the spectra of the two branches are reversed, and said means for suppressing the undesired components includes a bandpass filter tuned to pass only the difference frequency and its associated modulation and a modulation detector which suppresses the difference frequency products of corresponding signals in the two branches.

11. A diversity communication system as claimed in claim 7 wherein the spectrum produced by each pilot and carrier pair is widely separated in frequency from the spectrum produced by all other pilot and carrier pairs and said means for suppressing the undesired components includes a bandpass filter tuned to pass only the difference frequency and its associated modulation.

12. A diversity communication system as claimed in claim 7 wherein the spectrum produced by each pilot and carrier is displaced in frequency from the spectrum of the pilot and carrier of any other branch by an amount of at least twice the audio bandwidth, and said means for suppressing the undesired components includes a bandpass filter tuned to pass only the difference frequency and its associated modulation.

13. A diversity communication system as claimed in claim 7 wherein said means for applying identical intelligence includes means for frequency modulating at least one of the two signals in each branch.

14. A diversity communication system as claimed in claim 13 wherein said means for applying identical intelligence includes modulating the intelligence in part on one signal of a pair of signals and in part on the other signal of said pair.

15. A diversity communication system as claimed in claim 7 wherein said means for applying to each branch a pilot signal and a carrier signal is provided at a first station having a transmitter for each of said plurality of branches and antenna means for radiating the output of each transmitter on a diverse transmission path, and said means for beating all of the pilots and carriers of the plurality of branches is provided at a second station having a single antenna and a single mixer connected to said single antenna.

16. A diversity communication system as claimed in claim 7 wherein said means for applying to each branch a pilot signal and a carrier signal is provided by an individual local oscillator producing an output of preselected frequency, each oscillator output being mixed individually with the pilot and the carrier of a single branch to produce a converted output having a desired spectrum, and wherein said means for beating all of the pilots and carriers includes a single mixer into which all of the converted outputs are fed.

17. A diversity transmission system of the type having a plurality of branches, means for applying to each branch a pilot signal and a carrier signal with identical intelligence modulated on each branch and means for mixing the pilot signal and the carrier signal of each branch together to form a difference frequency component between them, characterized in that, said means for mixing is common to all branches and said means for applying a pilot signal and a carrier signal is arranged to provide a distinct spectrum for each branch, the spectra being selected so that all of the difference frequency components from said common mixing means which are derived from a pilot signal and a carrier signal of the same branch are identical and are significantly removed in at least frequency or power from all of the other difference frequency components from said common mixing means.