Method for synchronizing the reference frequency oscillator of a metallic-based microcell to a master oscillator

• US 5,469,467 A
• Filed: 10/15/1993
• Issued: 11/21/1995
• Est. Priority Date: 10/15/1993
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Vella-Coleiro, George P.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/138,583
• Time in Patent Office: 767 Days
• Field of Search: 375/106-109, 375/111, 370/17, 370/100.1, 370/103, 370/104.1, 370/108, 455/33.1, 455/51.2, 455/69, 455/71, 455/51.1
• US Class Current: 375/358
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43

Abstract

The present invention involves a device for synchronizing the broadcast frequency of a base station and a microcell linked together by a metallic medium as well as a method for using the device to synchronize the base oscillator and the microcell oscillator. The device comprises a base transmitter which transmits a base time-of-day signal to a microcell comparer, and a microcell clock which sends a microcell time-of-day signal to the microcell comparer. A microcell oscillator provides the microcell clock with a reference frequency. The microcell comparer calculates a time difference which represents a time difference between the base time-of-day signal and the microcell time-of-day signal. The microcell comparer then outputs a correction signal to a digital controller. The digital controller adjusts a microcell oscillator according to the correction signal.

Claims

1. A device for synchronizing the broadcast frequency of a base station and a microcell linked together by a metallic medium, said device comprises:

(a) a base transmitter which transmits a base time-of-day signal to a microcell comparer;

(b) a microcell clock which generates a microcell time-of-day signal, and sends the microcell time-of-day signal to the microcell comparer;

(c) a microcell oscillator which provides said microcell clock with a microcell reference frequency;

(d) the microcell comparer which calculates a time difference between the base time-of-day signal and the microcell time-of-day signal, said microcell comparer outputs a correction signal to a the digital controller; and

(e) the digital controller which adjusts said microcell oscillator according to the correction signal.

2. The device of claim 1 wherein the correction signal is proportional to a change in the time difference, and wherein said digital controller adjusts said microcell oscillator to maintain a constant time difference.

3. The device of claim 1 wherein said digital controller comprises circuitry to reset said microcell clock in the event of a power failure.

4. The device of claim 1 wherein said digital controller comprises circuitry to periodically reset said microcell clock to match the base time-of-day signal by compensating for the time difference.

5. The device of claim 1 wherein said microcell oscillator comprises a crystal type oscillator.

6. The device of claim 1 further comprising:

(f) a base oscillator which provides a base reference frequency to both a base clock and a base RF carrier synthesizer;

(g) the base clock which receives the base reference frequency from said base oscillator and outputs the base time-of-day signal to said base transmitter; and

(h) the base RF carrier synthesizer which receives the base reference frequency from said base oscillator and outputs a base broadcasting signal to a base broadcaster.

7. The device of claim 6 wherein said base oscillator comprises a high stability, rubidium type oscillator.

8. The device of claim 1 further comprising:

(f) an automatic compensating circuit comprising;

(i) a microcell transponder which receives a pulse from said base transmitter and echoes it back to a base receiver

(ii) the base receiver which receives the echoed pulse from said microcell transponder, and sends a return signal to a delay processor;

(iii) the delay processor which calculates a time duration between the pulse and the return signal, divides the time duration in half to arrive at a transmission delay, generates a delay signal proportional to the transmission delay, and sends the delay signal to a delay adjuster; and

(iv) the delay adjuster which advances the base time-of-day signal to compensate for said transmission delay before said base transmitter transmits the base time-of-day signal to said microcell comparer.

9. The device of claim 8 wherein the correction signal is proportional to the time difference, and wherein said digital controller adjusts said microcell oscillator to reduce the time difference to zero.

10. The device of claim 8 wherein said digital controller comprises circuitry to reset said microcell clock in the event of a power failure.

11. The device of claim 8 wherein said digital controller comprises circuitry to periodically reset said microcell clock to match the base time-of-day signal as modified by said delay adjuster.

12. The device of claim 8 wherein said microcell oscillator comprises a crystal type oscillator.

13. The device of claim 8 further comprising:

(g) a base oscillator which provides a base reference frequency to both a base clock and a base RF carrier synthesizer;

(h) the base clock which receives the base reference frequency from said base oscillator and outputs the base time-of-day signal to said base transmitter through the delay adjuster; and

(i) the base RF carrier synthesizer which receives the base reference frequency from said base oscillator and outputs a base broadcasting signal to a base broadcaster.

14. The device of claim 13 wherein said base oscillator comprises a high stability, rubidium type oscillator.

15. A method for synchronizing the broadcast frequency of a base station and a microcell linked together by a metallic medium, said method comprising:

(a) transmitting a base time-of-day signal generated by a base transmitter to a microcell comparer;

(b) sending a microcell time-of-day signal generated by a microcell clock to said microcell comparer;

(c) calculating time difference of the base time-of-day signal with the microcell time-of-day signal by said microcell comparer;

(d) sending a correction signal from said microcell comparer to a digital controller, said correction signal corresponds to a change in the time difference; and

(e) adjusting a microcell oscillator by the digital controller to maintain a constant time difference, said microcell oscillator being connected to said microcell clock and the digital controller.

16. The method of claim 15 further comprising:

(f) resetting said microcell clock by said digital controller in the event of a power outage.

17. The method of claim 15 further comprising:

(f) resetting said microcell clock by said digital controller to match the microcell time-of-day signal to the base time-of-day signal while compensating for the time difference.

18. A method for synchronizing the broadcast frequency of a base station and a microcell linked together by a metallic medium, said method comprising:

(a) transmitting a pulse from a base transmitter to a delay processor and a microcell transponder;

(b) echoing the pulse from said microcell transponder back to a base receiver;

(c) measuring a time duration with said delay processor between the pulse from said base transmitter and the pulse return from said microcell transponder through said base receiver, wherein said time duration is forwarded to from said delay processor to a delay adjuster

(d) calculating transmission delay by said delay processor by dividing the time duration in half;

(e) sending a delay signal from said delay processor to said delay adjuster, the delay signal corresponds to transmission delay;

(f) advancing a base time-of-day signal by said delay adjuster to compensate for the transmission delay before the base transmitter transmits the base time-of-day signal to a microcell comparer;

(g) sending a microcell time-of-day signal generated by a microcell clock to said microcell comparer;

(h) calculating time difference of the base time-of-day signal with the microcell time-of-day signal by said microcell comparer;

(i) sending a correction signal from said microcell comparer to a digital controller, said correction signal corresponds to correction necessary to reduce the time difference to zero; and

(j) adjusting a microcell oscillator by the digital controller to reduce the time difference to zero, said microcell oscillator being connected to said microcell clock and the digital controller.

19. The method of claim 18 further comprising:

(k) resetting said microcell clock by said digital controller in the event of a power outage.

20. The method of claim 18 further comprising:

(k) resetting said microcell clock by said digital controller to match the microcell time-of-day signal to the base time-of-day signal as modified by said delay adjuster.