Synchronising base stations

• US 20080075061A1
• Filed: 08/27/2007
• Published: 03/27/2008
• Est. Priority Date: 08/29/2006
• Status: Abandoned Application

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Ubiquisys Limited (Cisco Systems, Inc.)
• Inventors: Hatala, Edward, Keevill, Peter
• Application Number:
  US11/897,006
• Publication Number:
  US 20080075061A1
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04B 7/2693 Centralised synchronisation, i.e. using external universal time reference, e.g. by using a global positioning system [GPS] or by distributing time reference over the wireline network
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase

Abstract

A method for synchronising a clock signal in a basestation of a wireless telecommunications system is described. The basestation has a reference clock signal and is operable to communicate with wireless mobile terminals and with a packet switched network. The method comprises detecting a radio frequency clock synchronisation signal from a wireless telecommunications network, and synchronising the reference clock signal of the basestation in dependence upon the detected radio frequency clock synchronisation signal.

Claims

1. A basestation for use in a wireless telecommunications system, the basestation having a reference clock signal and being operable to communicate with wireless mobile terminals and with a packet switched network, and comprising:

a detector for detecting a radio frequency clock synchronisation signal from a wireless telecommunications network; and

a synchronisation unit operable to synchronise the reference clock signal of the basestation in dependence upon a detected radio frequency clock synchronisation signal, wherein the synchronisation unit is further operable to receive clock synchronisation data packets from a packet switched network, and to synchronise the reference clock signal in dependence upon received clock synchronisation data packets.

2. A basestation as claimed in claim 1, wherein the synchronisation unit is operable to synchronise the reference clock signal using the detected radio frequency clock synchronisation signal from a macrocell basestation, or using received clock synchronisation data packets if no macrocell basestation synchronisation signal can be detected.

3. A basestation as claimed in claim 1, wherein the synchronisation unit is operable to:

receive a start data packet at the basestation;

receive a stop data packet at the basestation;

obtain timestamp information at the basestation, the information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet; and

measure a time between receipt of the start data packet and the stop data packet at the basestation using a reference clock signal of the basestation;

compare the timestamp information with the measured time to produce a comparison value; and

adjust the reference clock signal of the basestation in dependence upon the generated comparison value.

4. A method of operation of a basestation in a wireless telecommunications system, the basestation generating a reference clock signal, the method comprising:

determining whether it is possible to detect a radio frequency clock synchronisation signal from a macrocell basestation of a wireless telecommunications network; and

, if so;

synchronising the reference clock signal of the basestation in dependence upon the detected radio frequency clock synchronisation signal,

or, if not;

receiving clock synchronisation data packets from a packet switched network; and

synchronising the reference clock signal in dependence upon received clock synchronisation data packets.

5. A method as claimed in claim 4, wherein the step of receiving clock synchronisation data packets from the packet switched network comprises:

receiving a start data packet at the basestation;

receiving a stop data packet at the basestation; and

obtaining timestamp information at the basestation, the timestamp information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet;

and the step of synchronising the reference clock signal comprises;

measuring a time between receipt of the start data packet and the stop data packet at the basestation using the reference clock signal of the basestation,

comparing the timestamp information with the measured time to produce a comparison value; and

adjusting the reference clock signal of the basestation in dependence upon the comparison value.

6. A basestation, for use in a wireless telecommunications system, the basestation being adapted to:

generate a reference clock signal;

receive a start data packet from a time server over a packet data network;

receive a stop data packet from the time server over the packet data network;

obtain timestamp information, the timestamp information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet;

measure a time between receipt of the start data packet and the stop data packet at the basestation using the reference clock signal;

compare the timestamp information with the measured time to produce a comparison value; and

adjust the reference clock signal in dependence upon the generated comparison value.

7. A method for synchronising a clock signal in a basestation of a wireless telecommunications system, the basestation having an internal reference clock signal and being operable to communicate with wireless mobile terminals and with a packet switched network, the method comprising detecting a radio frequency clock synchronisation signal from a wireless telecommunications network, and synchronising the reference clock signal of the basestation in dependence upon the detected radio frequency clock synchronisation signal.

8. A method as claimed in claim 7, comprising configuring at least part of the basestation as a mobile terminal operable to obtain clock synchronisation information from a standard wireless telecommunications network.

9. A method as claimed in claim 8, comprising reconfiguring said part of the basestation as a wireless basestation following detection of the radio frequency clock synchronisation signal.

10. A method as claimed in any of claims 7 to 9, wherein the radio frequency clock synchronisation signal is detected from a wireless network different to the wireless network to which the basestation is connected.

11. A method as claimed in claim 7, comprising receiving clock synchronisation data packets from the packet switched network, and synchronising the reference clock signal using the radio frequency clock synchronisation signal in combination with the received clock synchronisation data packets.

12. A method as claimed in claim 11, comprising initially synchronising the reference clock signal using the detected radio frequency clock synchronisation signal, and subsequently using received clock synchronisation data packets to maintain reference clock synchronisation, wherein a radio frequency clock synchronisation signal is detected and used for synchronisation if receipt of the clock synchronisation data packets is interrupted.

13. A method as claimed in claim 11, wherein synchronising the reference clock frequency using received clock synchronisation packets includes the steps of:

receiving a start data packet at the basestation;

starting a timer upon receipt of the start data packet;

receiving a stop data packet at the basestation;

stopping the timer upon receipt of the stop data packet to generate a timer value;

obtaining timestamp information at the basestation, the information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet; and

comparing the timestamp information with the timer value to produce a comparison value; and

adjusting the reference frequency of the base station in dependence upon the generated comparison value.

14. A method as claimed in claim 13, wherein the timestamp information is derived from information included in the start data packet and the stop data packet.

15. A method as claimed in claim 13, wherein the timestamp information is included in a timestamp data packet received by the basestation.

16. A method as claimed in claim 11, wherein the synchronising the reference clock signal does not require transmission of feedback data packets from the basestation to the packet switched network.

17. A method as claimed in any of claims 7 to 9, wherein the packet switched network is an Internet protocol based network.

18. A basestation for use in a wireless telecommunications system, the basestation having a reference clock signal and being operable to communicate with wireless mobile terminals and with a packet switched network, and comprising:

a detector for detecting a radio frequency clock synchronisation signal from a wireless telecommunications network; and

a synchronisation unit operable to synchronise the reference clock signal of the basestation in dependence upon a detected radio frequency clock synchronisation signal.

19. A basestation as claimed in claim 18, comprising synchronisation unit is operable to configure at least part of the basestation as a mobile terminal operable to obtain clock synchronisation information from a standard wireless telecommunications network.

20. A basestation as claimed in claim 19, wherein the synchronisation unit is operable to reconfigure said part of the basestation as a wireless basestation following detection of the radio frequency clock synchronisation signal.

21. A basestation as claimed in any one of claims 18 to 20, wherein the radio frequency clock synchronisation signal is detected from a wireless network different to the wireless network to which the basestation is connected.

22. A basestation as claimed in claim 18, wherein the synchronisation unit is operable to receive clock synchronisation data packets from a packet switched network, and to synchronise the reference clock signal using a radio frequency clock synchronisation signal in combination with received clock synchronisation data packets.

23. A basestation as claimed in claim 22, wherein the synchronisation unit is operable to synchronise the reference clock signal initially using the detected radio frequency clock synchronisation signal, and subsequently using received clock synchronisation data packets to maintain reference clock synchronisation, and to detect and use a radio frequency clock synchronisation signal for synchronisation if receipt of the clock synchronisation data packets is interrupted.

24. A basestation as claimed in claim 22, wherein the synchronisation unit is operable to:

receive a start data packet at the basestation;

start a timer upon receipt of the start data packet;

receive a stop data packet at the basestation;

stop the timer upon receipt of the stop data packet to generate a timer value;

obtain timestamp information at the basestation, the information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet; and

compare the timestamp information with the timer value to produce a comparison value; and

adjust the reference clock signal of the basestation in dependence upon the generated comparison value.

25. A basestation as claimed in claim 24, wherein the timestamp information is derived from information included in the start data packet and the stop data packet.

26. A basestation as claimed in claim 24, wherein the timestamp information is included in a timestamp data packet received by the basestation.

27. A basestation as claimed in any one of claims 22, wherein the basestation is not operable to transmit feedback data packets to the packet switched network following reception of clock synchronisation data packets therefrom.

28. A basestation as claimed in any one of claims 18 to 20, wherein the packet switched network is an Internet protocol based network

29. A method for synchronising a clock signal in a basestation of a wireless telecommunications system, the basestation having an internal reference clock signal, and being operable to communicate with wireless mobile terminals and with a packet switched network, the method comprising receiving clock synchronisation data packets transmitted from the packet switched network, and synchronising the reference clock signal of the basestation in dependence upon the received clock synchronisation packets, wherein the method does not require transmission of feedback data packets from the basestation to the packet switched network.

30. A method as claimed in claim 29, wherein the packet switched network is an Internet protocol based network.

31. A method as claimed in claim 29, comprising the steps of:

receiving the start data packet at the basestation;

starting a timer upon receipt of the start data packet;

receiving the stop data packet at the basestation;

stopping the timer upon receipt of the stop data packet to generate a timer value;

obtaining timestamp information at the basestation, the information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet; and

comparing the timestamp information with the timer value to produce a comparison value; and

adjusting the reference frequency of the base station in dependence upon the generated comparison value.

32. A method as claimed in claim 31, wherein the timestamp information is derived from information included in the start data packet and the stop data packet.

33. A method as claimed in claim 31, wherein the timestamp information is included in a timestamp data packet received by the basestation.

34. A method as claimed in claim 29, wherein the timestamp information is derived from information included in the start data packet and the stop data packet.

35. A method as claimed in claim 29, wherein the timestamp information is included in a timestamp data packet received by the basestation.

36. A basestation for use in a wireless telecommunications system, the basestation having an internal reference clock signal, and being operable to communicate with wireless mobile terminals and with a packet switched network, and comprising a synchronisation unit operable to receive clock synchronisation data packets transmitted from the packet switched network, and to synchronise the reference clock signal of the basestation in dependence upon received clock synchronisation packets, synchronising the reference clock signal does not require transmission of feedback data packets to the packet switched network.

37. A basestation as claimed in claim 36, wherein the packet switched network is an Internet protocol based network.

38. A basestation as claimed in claim 36 or 37, wherein the synchronisation unit is operable to:

receive a start data packet at the basestation;

start a timer upon receipt of the start data packet;

receive a stop data packet at the basestation;

stop the timer upon receipt of the stop data packet to generate a timer value;

obtain timestamp information at the basestation, the information including a time indication of time period between the sending of the start data packet and the sending of the stop data packet; and

compare the timestamp information with the timer value to produce a comparison value; and

adjust the reference clock signal of the base station in dependence upon the generated comparison value.