Remote monitoring and calibration of system reference clock using network timing reference

• US 7,738,611 B2
• Filed: 08/07/2006
• Issued: 06/15/2010
• Est. Priority Date: 08/07/2006
• Status: Active Grant

• Current Assignee: Aviat U.S., Inc. (Aviat Networks Incorporated)
• Original Assignee: Harris Stratex Networks, Inc.
• Inventors: Detwiler, Thomas F.
• Primary Examiner(s): Ghebretinsae; Temesghen
• Application Number:
  US11/499,639
• Publication Number:
  US 20080032724A1
• Time in Patent Office: 1,408 Days
• Field of Search: 375354-376, 370/350
• US Class Current: 375/354
• CPC Class Codes: G04G 5/002 brought into action by radio
• CPC Class Codes: G04G 7/02 by radio
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 7/0004 Initialisation of the receiver H04L7/0075 and H04L7/10 take precedence

Abstract

A systematic and method for calibrating a local radio reference clock for a radio operating in a radio network having a network reference clock. The method comprises determining at the radio an offset between the local clock and the network clock, placing the local clock in a calibration mode, and calibrating the local clock using a radio link to reduce the offset.

Claims

1. A method of calibrating a local radio reference clock for a radio operating in a radio network, the radio network having a main unit with a network reference clock, comprising the steps of:

determining an alarm condition triggered when a frequency of the local radio reference clock is different from a predetermined setpoint by more than a prescribed amount;

transmitting the alarm condition to the main unit;

determining a frequency offset between the local clock and the network reference clock, based in part on the determination of the alarm condition;

placing the local clock in a calibration mode; and

calibrating the local clock by reducing sufficiently slowly the frequency offset between the local clock and the network reference clock to enable continued radio communication with a node during calibration.

2. The method of claim 1 wherein information representative of the frequency offset is transmitted from the radio to the main unit and the main unit places the local clock in the calibration mode.

3. The method of claim 2 wherein the node comprises the main unit.

4. The method of claim 1 wherein the frequency offset is determined as a function of measurements taken by the main unit.

5. The method of claim 1 wherein the network reference clock is a reference clock for a synchronous communication protocol.

6. The method of claim 1 wherein the radio network communicates using an asynchronous communication protocol and the network reference clock is replaced by a network reference clock signal injected into a data-carrying communication channel.

7. The method of claim 4 wherein the measurements are taken at predefined intervals.

8. The method of claim 4 wherein the measurements are taken continuously.

9. The method of claim 2 wherein the information is the alarm condition.

10. The method of claim 1 wherein the step of determining further comprises the steps of:

summing n frequency offsets; and

dividing the sum by n.

11. The method of claim 10 wherein the step of determining further comprises comparing the sum divided by n to a predetermined threshold.

12. The method of claim 1 wherein the network reference clock is selected from the group comprising:

a Global Positioning System signal, a Pulse Code Modulated signal, a crystal oscillator, an oven controlled crystal oscillator, an oven voltage controlled crystal oscillator, and a voltage controlled oscillator.

13. The method of claim 1 wherein the local oscillator is selected from the group comprising:

an oven controlled crystal oscillator and an oven voltage controlled crystal oscillator.

14. The method of claim 1 further comprising communicating information representative of the frequency offset from the main unit to the radio.

15. The method of claim 1 further comprising communicating information representative of the frequency offset from the radio to the main unit and placing the local clock in calibration mode by the main unit.

16. The method of claim 1 wherein the frequency offset is determined as a function of measurements taken by the main unit.

17. A radio network comprising:

a local reference clock in a radio;

a network reference clock remote from the radio;

a component configured to determine an alarm condition triggered when a frequency of the local radio reference clock is different from a predetermined setpoint by more than a prescribed amount and to determine a frequency offset between the local clock and the network reference clock, based in part on the determination of the alarm condition;

a transceiver configured to transmit the alarm condition to a main unit;

a command unit for generating a command to place the radio in a calibration mode; and

a calibration unit for calibrating the local reference clock during the calibration mode by reducing the frequency offset sufficiently gradually to enable continued radio communication with a node during calibration.