Carrier-modulated coherency monitoring system

• US 4,048,563 A
• Filed: 10/17/1975
• Issued: 09/13/1977
• Est. Priority Date: 10/17/1975
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Osborne, Eugene F.
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Psitos, Aristotelis M.
• Application Number:
  US05/623,539
• Time in Patent Office: 697 Days
• Field of Search: 178/69.5 R, 178/69.1, 340/146.1, 325/4, 325/41, 325/321, 325/65, 325/58, 343/10, 179/15 BS
• US Class Current: 375/367
• CPC Class Codes: G01S 11/10 using Doppler effect

Abstract

A radio information system is described which uses the exact mathematical tios and the unique periodic angular coherence of the residual RF carrier and the digitally encoded modulation spectral components of the electromagnetic wave as emitted by a source transmitter (or transmitters) to enhance system performance and to provide new instrumentation and measurement capabilities at the receiver apparatus. The digital modulation synchronizing code occupies a wide frequency bandwidth and is encoded for precise repetitive transmission to provide, for example in a satellite navigation system, a means of accurate synchronization and measurement of time and range parameters. Many encoded sequences of either discrete or pseudo-random types may be used as the synchronizing code. However in the description herein the pseudo-random noise (PRN) codes are used for their added advantage in spread spectrum discrimination against intentional interference. The total or composite RF signal typically also includes non-interfering information or message modulation.

Claims

1. In a radio transmission system for transmitting information between spaced location, the combination comprising:

signal source means for generating a carrier signal of radio frequency, f_rf,

source means for generating a synchronizing code having a repetitive time frame which is numerically related to the period, 1/f_rf, of said carrier signal by a predetermined fixed multiplier,

modulator means connected to said carrier signal source and said synchronizing code source for modulating said carrier signal with said synchronizing code,

transmitter means for transmitting said modulated carrier signal,

receiver means for receiving said modulated carrier signal and including means for recovering said carrier signal and said synchronizing code from said modulated carrier signal, and

measurement means responsive to said recovered carrier signal and synchronizing code and including counter means and counter control means, said counter control means being responsive to said synchronizing code for controlling said counter means to register a count of the number of whole and fractional cycles of said carrier signal received in a measurement time interval corresponding to the repetitive time frame of said synchronizing code as received.

2. The apparatus specified in claim 1 wherein said counter control means includes means to select a time interval multiplier, whereby said counter means registers a count of the number of whole and fractional cycles of said carrier signal received in a measurement time interval equal to a multiple of the time frame of said synchronizing code.

3. The apparatus specified in claim 1 wherein said recovery means comprises a phase-locked loop to recover the carrier signal component of said received mmodulated carrier signal, and a delay-locked loop to recover the synchronizing code component of said received modulated carrier signal.

4. The apparatus specified in claim 1 further including a source of message code and means for modulating said carrier signal with said meassage code, and wherein said receiver means includes means responsive to said modulated carrier signal for demodulating said modulated carrier signal to recover said message code from said modulated carrier signal.

5. The apparatus specified in claim 1 wherein said signal source means includes,

means for generating a pseudo-random noise code as said synchronizing code, and

means connected to said pseudo-random noise code generating means for modulating said carrier signal with said pseudo-random noise code.

6. The apparatus specified in claim 1 further including timing means for producing a local time reference and wherein said counter means comprises,

first means receiving as input said recovered carrier signal and responsive to said counter control means for registering a count of the number of whole cycles of said carrier signal received in said measurement time interval,

second means receiving an input signal defining the time of reception of said synchronizing code and responsive to said timing means for measuring the time of reception of said synchronizing code relative to said local time reference,

third means responsive to the measurement provided by said second means for demarcating the beginning and ending time limits of a plurality of successive time frames of said synchronizing code, said third means being connected to said first means to control the value of said measurement time interval during which said first means counts whole cycles of said recovered carrier signal, and

fourth means responsive to said third means for registering the duration of any fractional cycle of said recovered carrier signal occurring in said measurement time interval.

7. The apparatus specified in claim 6 wherein the count registered by said first means is dependent upon zero crossing detection of said carrier signal during said measurement time interval and wherein said fourth means includes a zero crossing detector responsive to said carrier signal and rendered effective at the beginning time limit of said measurement time interval and timing means for registering the time interval occurring between the beginning of said measurement time interval and the first zero crossing of said carrier signal within said measurement time interval.

8. The apparatus specified in claim 1 wherein said signal source means comprises

a stable oscillator means for generating a carrier frequency signal,

a code generator means, and

a divider circuit means connected between said stable oscillator means and said code generator means for dividing said carrier frequency signal to produce a control signal whose period is longer by a fixed multiple than the period of said carrier frequency signal, said control signal being applied to said code generator means and establishing the repetitive time frame of said code generator means.

9. The apparatus specified in claim 3 wherein said carrier signal phase-locked recovery loop and said synchronizing code delay-locked recovery loop are interconnected with

a signal developed in the delay-locked loop during tracking of the synchronizing code applied to aid the phase-locked loop in tracking the carrier signal, and

a signal developed in the phase-locked loop during tracking of the carrier signal applied to aid the delay-locked loop in tracking the synchronizing code.

10. The apparatus specified in claim 9 wherein said signal source means is mounted aboard an orbiting satellite and said receiver means is located at a ground station and further including means connected to each of said phase-locked recovery loop and said delay-locked recovery loop for providing programmed aiding to each of said loops in accordance with the predicted location of said orbiting satellite.