Preamble design for synchronization and cell search

• US 8,027,329 B2
• Filed: 02/07/2007
• Issued: 09/27/2011
• Est. Priority Date: 02/07/2007
• Status: Active Grant

• Current Assignee: Mahle International GmbH (MAHLE-STIFTUNG GmbH), Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Guey, Jiann-Ching, Hafeez, Abdulrauf
• Primary Examiner(s): Bost; Dwayne
• Assistant Examiner(s): Wyche; Myron
• Application Number:
  US11/672,084
• Publication Number:
  US 20080186949A1
• Time in Patent Office: 1,693 Days
• Field of Search: 370/328, 370/350, 375/260, 375/295, 375/316, 375/356, 375/362
• US Class Current: 370/350
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26132 using repetition
• CPC Class Codes: H04L 27/2659 Coarse or integer frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation

Abstract

A method of synchronizing signals in a wireless network uses a two part preamble transmitted on the downlink between a base station and a mobile station. The preamble includes a common pilot common to a plurality of base stations and a dedicated pilot unique to the transmitting base station. The mobile station performs coarse synchronization based on the common pilot and fine synchronization based on the dedicated pilot. The mobile station also identifies one or more nearby cells based on unique pilot tones in the dedicated pilot transmitted by the nearby cells.

Claims

1. A method of synchronizing signals in a wireless network, the method comprising:

receiving a signal from a transmitting base station, said signal including a preamble having a common pilot common to a plurality of base stations and a dedicated pilot unique to the transmitting base station;

performing coarse synchronization based on the common pilot to determine a coarse timing estimate and a coarse frequency offset for the transmitting base station; and

performing fine synchronization based on the dedicated pilot to determine a fine timing estimate for the transmitting base station.

2. The method of claim 1 wherein performing coarse synchronization comprises:

computing a periodicity metric based on the common pilot; and

determining the coarse timing estimate based on the periodicity metric.

3. The method of claim 2 wherein computing the periodicity metric comprises:

correlating the received signal with itself and with a known coding sequence associated with the common pilot to determine a correlation; and

computing the periodicity metric based on the correlation.

4. The method of claim 2 wherein determining the coarse timing estimate comprises identifying one or more coarse timing estimates that maximize the periodicity metric.

5. The method of claim 1 wherein performing fine synchronization comprises:

computing a fractional timing estimate based on the dedicated pilot; and

determining the fine timing estimate based on the fractional timing estimate and the coarse timing estimate.

6. The method of claim 5 wherein computing the fractional timing estimate comprises:

determining phase differences between pilot tones in the dedicated pilot; and

computing the fractional timing estimate based on the determined phase differences.

7. The method of claim 5 wherein determining the fine timing estimate comprises adjusting the coarse timing estimate based on the fractional timing estimate.

8. The method of claim 1 wherein computing the coarse frequency offset comprises:

correlating the received signal with itself and with a known coding sequence associated with the common pilot to determine a correlation;

determining a phase of the correlation; and

computing the coarse frequency offset based on the phase of the correlation.

9. The method of claim 1 further comprising computing a fine frequency offset based on the dedicated pilot.

10. The method of claim 9 wherein computing the fine frequency offset comprises:

computing a fractional frequency offset based on the dedicated pilot; and

determining the fine frequency offset based on the fractional frequency offset.

11. The method of claim 10 wherein computing the fractional frequency offset comprises:

determining phase differences between pilot tones in the dedicated pilot having the same carrier frequency; and

computing the fractional frequency offset based on the determined phase differences.

12. The method of claim 10 wherein determining the fine frequency offset comprises adjusting the coarse frequency offset using the fractional frequency offset.

13. The method of claim 12 further comprising adjusting a frequency of the mobile station based on one of the coarse and fine frequency offsets associated with a serving base station.

14. The method of claim 12 further comprising reporting one of the coarse frequency offset and the fine frequency offset for one or more neighboring base stations to a serving base station.

15. The method of claim 1 further comprising reporting one of the coarse timing estimate, the coarse frequency estimate, and the fine timing estimate for one or more neighboring base stations to a serving base station.

16. The method of claim 1 further comprising identifying a base station based on pilot tones in the dedicated pilot.

17. The method of claim 16 wherein identifying the base station based on pilot tones in the dedicated pilot comprises:

determining a detection metric for each of one or more base stations based on the dedicated pilot of the signals received from each base station; and

selecting the base station having a maximum detection metric as a serving base station for the mobile station.

18. The method of claim 17 further comprising:

smoothing the detection metric for each of the one or more base stations; and

selecting the serving base station based on the smoothed detection metric.

19. The method of claim 18 further comprising:

determining a fine frequency offset based on the dedicated pilot;

smoothing the fine frequency offset; and

adjusting a frequency of the mobile station based on the smoothed fine frequency offset.

20. The method of claim 17 further comprising identifying one or more neighboring base stations based on the detection metrics.

21. A mobile station in a wireless network for receiving signals from one or more base stations, the mobile station comprising:

a transceiver to receive a signal from a transmitting base station, wherein said received signal includes a preamble having a common pilot common to a plurality of base stations and a dedicated pilot unique to the transmitting base station; and

a processor configured to;

determine a coarse timing estimate and a coarse frequency offset for the transmitting base station based on the common pilot; and

determine a fine timing estimate for the transmitting base station based on the dedicated pilot.

22. The mobile station of claim 21 wherein the processor is configured to determine the coarse timing estimate by:

computing a periodicity metric based on the common pilot; and

determining the coarse timing estimate based on the periodicity metric.

23. The mobile station of claim 22 wherein the processor is configured to compute the periodicity metric by:

correlating the received signal with itself and with a known coding sequence associated with the common pilot to determined a correlation; and

computing the periodicity metric based on the correlation.

24. The mobile station of claim 22 wherein the processor is configured to determine the coarse timing estimate by identifying one or more coarse timing estimates that maximize the periodicity metric.

25. The mobile station of claim 21 wherein the processor is configured to determine the fine timing estimate by:

computing a fractional timing estimate based on the dedicated pilot; and

determining the fine timing estimate based on the fractional timing estimate and the coarse timing estimate.

26. The mobile station of claim 25 wherein the processor is configured to compute the fractional timing estimate by:

determining phase differences between pilot tones in the dedicated pilot; and

computing the fractional timing estimate based on the determined phase differences.

27. The mobile station of claim 25 wherein the processor is configured to determine the fine timing estimate by adjusting the coarse timing estimate based on the fractional timing estimate.

28. The mobile station of claim 21 wherein the processor is configured to compute the coarse frequency offset by:

correlating the received signal with itself and with a known coding sequence associated with the common pilot to determined a correlation;

determining a phase of the correlation; and

computing the coarse frequency offset based on the phase of the correlation.

29. The mobile station of claim 21 wherein the processor is further configured to compute a fine frequency offset based on the dedicated pilot.

30. The mobile station of claim 29 wherein the processor is configured to compute the fine frequency offset by:

computing the fractional frequency offset based on the dedicated pilot; and

determining the fine frequency offset based on the fractional frequency offset.

31. The mobile station of claim 30 wherein the processor is configured to compute the fractional frequency offset by:

determining the phase differences between pilot tones in the dedicated pilot having the same carrier frequency; and

computing the fractional frequency offset based on the determined phase differences.

32. The mobile station of claim 30 wherein the processor is configured to determine the fine frequency offset by adjusting the coarse frequency offset using the fractional frequency offset.

33. The mobile station of claim 32 wherein the processor is further configured to adjust a frequency of the mobile station based on one of the coarse and fine frequency offsets associated with a serving base station.

34. The mobile station of claim 30 wherein the processor is further configured to report one of the coarse frequency offset and the fine frequency offset for one or more neighboring base stations to a serving base station.

35. The mobile station of claim 21 wherein the processor is further configured to report one of the coarse timing estimate and the fine timing estimate for one or more neighboring base stations to a serving base station.

36. The mobile station of claim 21 wherein the processor is further configured to identify a base station based on pilot tones in the dedicated pilot.

37. The mobile station of claim 36 wherein the processor is configured to identify the base station based on pilot tones in the dedicated pilot by:

determining a detection metric for each of one or more base stations based on the dedicated pilot of the signals received from each base station; and

selecting the base station having a maximum detection metric as a serving base station for the mobile station.

38. The mobile station of claim 37 wherein the processor is further configured to:

smooth the detection metric for each of the one or more base stations; and

select the serving base station based on the smoothed detection metric.

39. The mobile station of claim 38 wherein the processor is further configured to:

determine a fine frequency offset based on the dedicated pilot;

smooth the fine frequency offset; and

adjust a frequency of the mobile station based on the smoothed fine frequency offset.

40. The mobile station of claim 37 wherein the processor is further configured to identify one or more neighboring base stations based on the detection metrics.

41. A synchronization method for a wireless network, the method comprising:

transmitting a common pilot as a first part of a preamble transmitted with a signal from a base station to a mobile station in said wireless network, said common pilot common to a plurality of base stations in the wireless network;

transmitting a dedicated pilot as a second part of said preamble, said dedicated pilot unique to the base station transmitting the signal; and

receiving synchronization data derived by said mobile station based on said transmitted preamble, wherein said synchronization data comprises a fine timing estimate derived from said dedicated pilot, and a coarse timing estimate and a coarse frequency estimate derived from said common pilot.

42. The method of claim 41 wherein the common pilot comprises a Barker-encoded repeated training sequence.

43. The method of claim 42 wherein the Barker-encoded repeated training sequence includes a plurality of evenly spaced pilot tones.

44. The method of claim 43 further comprising randomly phase modulating the pilot tones in the common pilot.

45. The method of claim 41 wherein the dedicated pilot includes a set of pilot tones unique to the base station transmitting the signal.

46. The method of claim 45 wherein the dedicated pilot includes two symbols, wherein the set of pilot tones are distributed across the two symbols according to an alternating pattern.

47. The method of claim 46 wherein the set of pilot tones comprises multiple pairs of adjacent pilot tones and multiple single pilot tones alternately spaced within each symbol.

48. The method of claim 41 wherein the signal comprises an OFDM signal.

58. The method of claim 41 further comprising synchronizing a timing of the base station to that of one or more neighboring base stations based on the received synchronization data.

49. A base station in a wireless network, the base station comprising:

a processor configured to generate a preamble for the signal, said preamble comprising a common pilot comprising a symbol common to a plurality of base stations in the wireless network and a dedicated pilot unique to the base station transmitting the signal;

a transceiver to transmit the preamble with the signal to the mobile station and to receive synchronization data derived by said mobile station based on said transmitted preamble, wherein said synchronization data comprises a fine timing estimate derived from said dedicated pilot, and a coarse timing estimate and a coarse frequency estimate derived from said common pilot.

50. The base station of claim 49 wherein the common pilot comprises a Barker-encoded repeated training sequence.

51. The base station of claim 50 wherein the Barker-encoded repeated training sequence includes a plurality of evenly spaced pilot tones.

52. The base station of claim 51 wherein the pilot tones are randomly phase modulated.

53. The base station of claim 49 wherein the dedicated pilot includes a set of pilot tones unique to the base station transmitting the signal.

54. The base station of claim 53 wherein the dedicated pilot includes two symbols, wherein the set of unique pilot tones are distributed across the two symbols according to an alternating pattern.

55. The base station of claim 54 wherein the set of unique pilot tones comprises multiple pairs of adjacent pilot tones and multiple single pilot tones alternately spaced within each symbol.

56. The base station of claim 49 wherein the signal comprises an OFDM signal.

57. The base station of claim 49 wherein the processor is further configured to synchronize a timing of the base station to that of one or more neighboring base stations based on the received synchronization data.