Providing reference signal to radio heads

• US 6,810,270 B1
• Filed: 11/02/2000
• Issued: 10/26/2004
• Est. Priority Date: 11/02/2000
• Status: Expired due to Fees

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Grohn, Ossi Ilari, Marlborough, Michael Francis, Fugaro, Anthony Salvatore
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): GESESSE, TILAHUN
• Application Number:
  US09/705,093
• Time in Patent Office: 1,454 Days
• Field of Search: 455/562.1, 455/561, 455/422, 455/560, 370/360, 370/514, 370/509, 370/310, 370/465, 340/870.16, 340/870.11
• US Class Current: 455/560
• CPC Class Codes: H04J 3/0647 Synchronisation among TDM nodes

Abstract

A method and apparatus for supplying a timing signal from a central unit to at least one radio head connected to the central unit via a communications link. An external signal, typically generated by a MSC, is received at a first framer of the central unit and the first framer generates a reference clock signal based thereon. This reference clock signal is used as the transmit clock for a second framer, known as the radio head framer. The radio head framer transmits a radio head downlink signal to the radio head(s) via the communications link. The radio head downlink signal typically includes payload information and an associated timing reference signal, typically in the form of an embedded clock signal. This timing reference signal of the downlink is based on the reference clock signal from the first framer, rather than being based on a clock signal from an oscillator within the central unit. The transceivers within the radio head(s) may then control their RF transmissions using the timing reference signal from the radio head framer of the central unit. Accordingly, the radio head(s) are provided with a timing reference signal that is based relatively directly on the signal from the MSC.

Claims

1. A method of supplying a timing signal from a central unit to at least one radio head connected to said central unit via a communications link, said method comprising:

generating a reference clock signal based on an external signal by a first framer of said central unit; and

transmitting a radio head downlink signal from a second framer to said at least one radio head via said communications link, said radio head downlink signal comprising an embedded clock signal based directly on said reference clock signal.

2. The method of claim 1 further comprising:

receiving said external signal also at a third framer of said central unit, said third framer generating a third clock signal and extracting payload information based on said external signal;

an oscillator in said central unit receiving said third clock signal and generating a fourth clock signal based thereon;

processing said payload information at said central unit based on said fourth clock signal;

wherein transmitting said radio head downlink signal from said second framer to said at least one radio head via said communications link comprises transmitting at least a portion of said payload information from said second framer to said at least one radio head via said communications link.

3. The method of claim 2 further comprising transmitting an RF signal by said at least one radio head based on said radio head downlink signal with timing based on said embedded clock signal.

4. A method of supplying a timing signal from a central unit to at least one radio head connected to said central unit via a communications link, said method comprising:

receiving an external signal at a first framer of said central unit and generating a first clock signal based thereon by said first framer;

routing said first clock signal to a second framer as a transmit clock therefor without going through an intervening oscillator; and

transmitting a downlink signal from said second framer to said at least one radio head via said communications link based on said transmit clock.

5. A method of supplying a timing signal from a central unit to at least one radio head connected to said central unit via a communications link, said method comprising:

receiving an external signal at a first framer of said central unit and generating a first clock signal based thereon by said first framer;

using said first clock signal as a transmit clock for a second framer, said second framer transmitting a downlink signal to said at least one radio head via said communications link, said downlink signal comprising a downlink clock signal based on said first clock signal.

6. The method of claim 5 further comprising embedding said downlink clock 1 signal in said downlink signal.

7. The method of claim 5 further comprising:

receiving said external signal also at a third framer of said central unit, said third framer generating a third clock signal and extracting payload information based on said external signal;

receiving, with an oscillator in said central unit, said third clock signal and generating a fourth clock signal based thereon;

processing said payload information at said central unit based on said fourth clock signal; and

thereafter, said second framer transmitting at least a portion of said payload information to said at least one radio head via said communications link with said downlink clock signal.

8. The method of claim 5 wherein said external signal comprises a network downlink clock signal having a long-term accuracy of not less than 0.016 parts per million and wherein receiving said external signal at said first framer of said central unit and generating said first clock signal based thereon by said first framer comprises generating said first clock signal with a long-term accuracy of not less than 0.016 parts per million based on said external signal by said first framer.

9. The method of claim 5 further comprising generating said external signal at a MSC.

10. The method of claim 9 further comprising transmitting said external signal from said MSC to said central unit via a T1 communications link.

11. The method of claim 9 further comprising transmitting said external signal from said MSC to said central unit via an E1 communications link.

12. The method of claim 5 further comprising transmitting an RF signal by said at least one radio head based on said downlink signal with timing based on said first clock signal.

13. The method of claim 5 wherein said communications link is selected from the group consisting of a T1 link and an E1 link.

14. The method of claim 5 wherein said at least one radio head belongs to a first radio head chain and wherein said downlink signal is a first downlink signal and wherein said downlink clock signal is a first downlink clock signal and wherein said central unit connects to a second radio head chain via a second communications link, said method further comprising:

using said first clock signal as a transmit clock for a third framer, said third framer transmitting a second downlink signal to said second radio head chain via said second communications link, said second downlink signal comprising a second downlink clock signal based on said first clock signal.

15. The method of claim 14 further comprising transmitting an RF signal by said first radio head chain based on said first downlink clock signal and transmitting an RF signal by said second radio head chain based on said second downlink clock signal.

16. The method of claim 5 wherein said central unit is a first central unit and further comprising:

using said first clock signal as a transmit clock for said first framer, said first framer transmitting to a second central unit based on said first clock signal;

supplying timing reference from said second central unit to at least one radio head associated with said second central unit;

transmitting an RF signal by said at least one radio head associated with said second central unit timing based on said first clock signal.

17. A method of supplying a timing signal from a central unit to at least one radio head connected to said central unit via a communications link, said method comprising:

receiving an external signal at a first framer of said central unit, said first framer generating a reference clock signal based on said external signal;

transmitting a radio head downlink signal from a second framer to said at least one radio head via said communications link using said reference clock signal as a transmit clock for said second framer.

18. The method of claim 17 wherein transmitting said downlink signal from said second framer to said at least one radio head via said communications link using said reference clock signal as said transmit clock for said second framer comprises generating an embedded clock signal for said downlink signal based on said reference clock signal.

19. The method of claim 18 further comprising:

receiving said external signal also at a third framer of said central unit, said third framer generating a third clock signal and extracting payload information based on said external signal;

receiving, with an oscillator in said central unit, said third clock signal and generating a fourth clock signal based thereon;

processing said payload information at said central unit based on said fourth clock signal; and

thereafter, said second framer transmitting at least a portion of said payload information to said at least one radio head via said communications link with said embedded clock signal.

20. The method of claim 19 wherein said external signal comprises a network downlink clock signal having a long-term accuracy of not less than 0.016 parts per million and wherein said first framer generating said reference clock signal based on said external signal comprises said first framer generating said reference clock signal with a long-term accuracy of not less than 0.016 parts per million based on said external signal.

21. The method of claim 20 further comprising transmitting an RF signal by said at least one radio head based on said radio head downlink signal with timing based on said reference clock signal.

22. The method of claim 21 wherein said communications link is selected from the group consisting of a T1 link and an E1 link.

23. The method of claim 20 wherein said at least one radio head belongs to a first radio head chain and wherein said radio head downlink signal is a first radio head downlink signal and wherein said central unit connects to a second radio head chain via a second communications link, said method further comprising:

transmitting a second radio head downlink signal from a fourth framer to said second radio head chain via said second communications link using said reference clock signal as a transmit clock for said fourth framer.

24. The method of claim 23 further comprising transmitting an RF signal by said first radio head chain based on said first radio head downlink signal and transmitting an RF signal by said second radio head chain based on said second radio head downlink signal.

25. A communications assembly, comprising:

a central unit communicating with at least one radio head via a communications link;

said central unit comprising a first framer and a second framer;

said first framer receiving a signal generated external to said central unit and generating a reference clock signal based thereon;

said second framer receiving said reference clock generated by said first framer as a transmit clock and transmitting a radio head downlink signal to said at least one radio head based thereon;

said at least one radio head comprising a transceiver, said transceiver transmitting an RF communications signal based on said radio head downlink signal.

26. The assembly of claim 25 wherein said downlink signal comprises an embedded clock signal based directly on said reference clock generated by said first 1:

5 framer.

27. The assembly of claim 26 wherein said communications link between said central unit and said at least one radio head is selected from the group consisting of a T1 link and an E1 link.

28. The assembly of claim 25 wherein said central unit further comprises an oscillator receiving a clock signal derived from said signal generated external to said central unit and generating a second clock signal based thereon, said central unit processing payload information associated with said signal generated external to said central unit based on said second clock signal, wherein said radio head downlink signal comprises at least a portion of said payload information.

29. The assembly of claim 25 wherein said at least one radio head belongs to a first radio head chain and wherein said radio head downlink signal is a first radio head downlink signal, said assembly further comprising:

a second radio head chain connected to said central unit via a second communications link; and

wherein said central unit further comprises a third framer, said third framer receiving said reference clock generated by said first framer as a transmit clock and transmitting a second radio head downlink signal to said second radio head chain based thereon.

30. The assembly of claim 25 wherein said central unit is a first central unit and further comprising:

a second central unit connected to said first central unit via said first framer and having a radio head chain associated therewith;

said first framer transmitting said reference clock signal to said second central unit by using said reference clock signal as its own transmit clock; and

said second central unit further comprising a third framer, said third framer receiving said reference clock via said first framer as a transmit clock and transmitting a second radio head downlink signal to said radio head chain based thereon.