Controlling timing of synchronization updates

• US 20080316996A1
• Filed: 08/24/2007
• Published: 12/25/2008
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Ubiquisys Limited (Cisco Systems, Inc.)
• Inventors: Hatala, Edward
• Granted Patent: US 8,638,774 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0697 Synchronisation in a packet node

Abstract

A base station for use in a mobile communications network may include a frequency synthesizer for generating signals at desired frequencies and a packet data interface for transmitting and receiving packet data signals over a wide area network. The basestation is adapted to determine an elapsed time since it last synchronized the frequency synthesizer to a master device. The basestation is also adapted to request synchronization packet data signals from the master device when the elapsed time exceeds a predetermined holdover period.

Claims

1. A basestation, for use in a mobile communications network, the basestation comprising:

a frequency synthesizer, for generating signals at desired frequencies;

a packet data interface, for transmitting and receiving packet data signals over a wide area network,

wherein the basestation is adapted to determine an elapsed time since it last synchronized the frequency synthesizer to a master device; and

wherein the basestation is adapted to request synchronization packet data signals from the master device when the elapsed time exceeds a predetermined hold-over period.

2. A basestation as claimed in claim 1,wherein the basestation connects into a core network of the mobile communications network through the packet data interface.

3. A basestation as claimed in claim 1,wherein the master device comprises a second basestation in the mobile communications network, and wherein the second basestation connects into the core network of the mobile communications network through the packet data interface.

4. A basestation as claimed in claim 1, 2 or 3, wherein the basestation is adapted to synchronize the frequency synthesizer to the master device on receipt of the synchronization packet data signals from the master device.

5. A basestation as claimed in claim 4, wherein the basestation is adapted to request the master device to stop sending synchronization packet data signals synchronize the frequency synthesizer to the master device.

6. A basestation as claimed in claim 1, 2 or 3, wherein the basestation is adapted to request a specified number of synchronization data packets from the master device.

7. A method of synchronizing a network node, the method comprising, in a synchronization slave node:

determining that further synchronization is required;

sending a request to a synchronization master node for synchronization packets; and

using the requested synchronization packets to achieve frequency synchronization in the synchronization slave node.

8. A method as claimed in claim 7, wherein the step of sending a request to a synchronization master node for synchronization packets comprises sending a request for a specified number of synchronization packets.

9. A method as claimed in claim 7, further comprising sending a request to the synchronization master node to stop sending synchronization packets.

10. A method as claimed in any of claims 7 to 9, wherein the synchronization slave node comprises a basestation of a mobile communications network.

11. A method as claimed in claim 7, 8 or 9, wherein the synchronization master node comprises a second basestation of a mobile communications network.

12. A method as claimed in claim 7, 8 or 9, comprising determining that further synchronization is required based on an elapsed time since a previous synchronization of the synchronization slave node.

13. A method as claimed in claim 7, 8 or 9, comprising determining that further synchronization is required based on a measured temperature within the synchronization slave node.

14. A method of synchronizing a crystal oscillator, the method comprising, at first time intervals:

in operation, receiving synchronization data from a synchronization master;

measuring a time elapsed since the crystal oscillator was last synchronized;

measuring a temperature of the crystal oscillator;

calculating and storing a frequency offset of the crystal oscillator.

15. A method of synchronizing a crystal oscillator, as claimed in claim 14, comprising, at second time intervals:

in operation, receiving synchronization data from a synchronization master;

measuring a temperature of the crystal oscillator;

calculating a frequency offset of the crystal oscillator; and

synchronizing the crystal oscillator based on the calculated frequency offset.

16. A method as claimed in claim 15, wherein the second time intervals exceed the first time intervals.

17. A method as claimed in one of claims 14 to 16, further comprising, in use:

measuring a time elapsed since the crystal oscillator was last synchronized;

measuring a temperature of the crystal oscillator;

determining a frequency offset based on at least one previously stored frequency offset obtained at a similar elapsed time and temperature; and

applying a compensation value to the crystal oscillator based on said determined frequency offset.