Controlling timing of synchronization updates

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 configured to determine an elapsed time since it last synchronized the frequency synthesizer to a master device;

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

wherein, when the elapsed time does not exceed the predetermined hold-over period, the basestation is configured to determine whether temperature conditions at the basestation meet a predetermined temperature condition threshold, and to determine whether a resynchronization is required for the frequency synthesizer to remain in synchronization;

wherein the basestation is configured to request synchronization packet data signals from the master device when said temperature condition threshold is met;

wherein the basestation is configured to synchronize the frequency synthesizer to the master device on receipt of the synchronization packet data signals from the master device; and

wherein the basestation is configured to request the master device to stop sending synchronization packet data signals to synchronize the frequency synthesizer to the master device.

2. The 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. The 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. The basestation as claimed in claim 1 , wherein the temperature conditions comprise a temperature difference from a specified temperature.

5. The basestation as claimed in claim 1 , wherein the temperature conditions comprise a threshold value for the rate of change of temperature.

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

receiving synchronization data from a synchronization master device;

the method further comprising, when synchronization data is received, measuring a time elapsed since the crystal oscillator was last synchronized;

calculating and storing a first frequency offset of the crystal oscillator, the first frequency offset comprising a difference between a frequency generated by the crystal oscillator and a frequency derived from the synchronization data, and the method further comprising:

measuring a temperature of the crystal oscillator;

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

upon receipt of the synchronization data from the synchronization master device, applying a compensation value to the crystal oscillator based on said determined second frequency offset to synchronize the crystal oscillator to the synchronization master device.

7. The method of synchronizing a crystal oscillator, as claimed in claim 6 , comprising, at second time intervals:

receiving synchronization data from a synchronization master device;

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.

8. A method as claimed in claim 7 , wherein the second time intervals exceed the first time intervals.

9. A method of synchronizing a basestation, the method comprising:

at the basestation, transmitting and receiving packet data signals over a wide area network;

generating signals at desired frequencies using a frequency synthesizer;

determining an elapsed time since the basestation last synchronized the frequency synthesizer to a master device;

when the elapsed time does not exceed a predetermined hold-over period, determining whether temperature conditions at the basestation meet a predetermined temperature condition threshold and determining whether a resynchronization is required for the frequency synthesizer to remain in synchronization;

requesting synchronization packet data signals from the master device when said temperature condition threshold is met;

requesting synchronization packet data signals from the master device when the elapsed time exceeds the predetermined hold-over period;

requesting a specified number of synchronization data packets from the master device;

synchronizing the frequency synthesizer to the master device on receipt of the synchronization packet data signals from the master device; and

requesting the master device to stop sending synchronization packet data signals to synchronize the frequency synthesizer to the master device.

10. The method as claimed in claim 9 , wherein the step of requesting synchronization packet data signals from the master device comprises sending a request for a specified number of synchronization packet data signals.

11. The method as claimed in claim 9 , wherein the basestation connects into a core network of the mobile communications network.

12. The method as claimed in claim 9 , 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.

13. The method as claimed in any one of claims 9 , 11 and 12 , wherein the basestation is configured to synchronize the frequency synthesizer to the master device on receipt of the synchronization packet data signals from the master device.

14. The method as claimed in any one of claims 9 , 11 and 12 , wherein the master device comprises a second basestation of a mobile communications network.

15. The method as claimed in claim 13 , wherein the basestation is configured to request the master device to stop sending synchronization packet data signals to synchronize the frequency synthesizer to the master device.

16. 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 configured to determine an elapsed time since it last synchronized the frequency synthesizer to a master device;

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

wherein, when the elapsed time does not exceed the predetermined hold-over period, the basestation is configured to determine whether temperature conditions at the basestation meet a predetermined temperature condition threshold and to determine whether a resynchronization is required for the frequency synthesizer to remain in synchronization;

wherein the basestation is configured to request synchronization packet data signals from the master device when said temperature condition threshold is met; and

wherein the basestation is configured to request a specified number of synchronization data packets from the master device.

17. The basestation as claimed in claim 16 , wherein the basestation connects into a core network of the mobile communications network through the packet data interface.

18. The basestation as claimed in claim 16 , 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.

19. The basestation as claimed in claim 16 , wherein the temperature conditions comprise a temperature difference from a specified temperature.

20. The basestation as claimed in claim 16 , wherein the temperature conditions comprise a threshold value for the rate of change of temperature.