Signal acquisition in a wireless communication system

• US 20050281290A1
• Filed: 12/22/2004
• Published: 12/22/2005
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Agrawal, Avneesh, Khandekar, Aamod
• Granted Patent: US 8,068,530 B2
• Time in Patent Office: Days
• US Class Current: 370/500
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/03866 using scrambling
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 5/0026 Division using four or more dimensions
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

Each base station transmits a TDM pilot 1 having multiple instances of a pilot-1 sequence generated with a PN1 sequence and a TDM pilot 2 having at least one instance of a pilot-2 sequence generated with a PN2 sequence. Each base station is assigned a specific PN2 sequence that uniquely identifies that base station. A terminal uses TDM pilot 1 to detect for the presence of a signal and uses TDM pilot 2 to identify base stations and obtain accurate timing. For signal detection, the terminal performs delayed correlation on received samples and determines whether a signal is present. If a signal is detected, the terminal performs direct correlation on the received samples with PN1 sequences for K₁ different time offsets and identifies K₂ strongest TDM pilot 1 instances. For time synchronization, the terminal performs direct correlation on the received samples with PN2 sequences to detect for TDM pilot 2.

Claims

1. A method of transmitting pilot in a communication system, comprising:

obtaining a pseudo-random number (PN) sequence used to uniquely identify a transmitting entity;

generating a first time division multiplexed (TDM) pilot;

generating a second TDM pilot with the PN sequence;

transmitting the first TDM pilot in a first portion of each transmission interval; and

transmitting the second TDM pilot in a second portion of each transmission interval.

2. The method of claim 1, wherein the generating the first TDM pilot comprises

generating a pilot sequence, and

generating the first TDM pilot with multiple instances of the pilot sequence.

3. The method of claim 1, wherein the generating the second TDM pilot comprises

generating a pilot sequence with the PN sequence, and

generating the second TDM pilot with at least one instance of the pilot sequence.

4. The method of claim 1, wherein the generating the first TDM pilot comprises generating the first TDM pilot in frequency domain with a first set of pilot symbols for a first set of frequency subbands, and wherein the generating the second TDM pilot comprises generating the second TDM pilot in the frequency domain with a second set of pilot symbols for a second set of frequency subbands.

5. The method of claim 1, wherein the obtaining the PN sequence comprises

identifying the PN sequence from among a set of possible PN sequences for the second TDM pilot.

6. The method of claim 1, wherein the transmitting the second TDM pilot comprises transmitting the second TDM pilot in the second portion, after the first portion, of each transmission interval.

7. A method of transmitting pilot in a communication system, comprising:

generating a first time division multiplexed (TDM) pilot with a first pseudo-random number (PN) sequence;

generating a second TDM pilot with a second PN sequence;

transmitting the first TDM pilot in a first portion of each transmission interval; and

transmitting the second TDM pilot in a second portion of each transmission interval.

8. The method of claim 7, wherein the generating the first TDM pilot comprises generating the first TDM pilot with the first PN sequence in time domain, and wherein the generating the second TDM pilot comprises generating the second TDM pilot with the second PN sequence in time domain.

9. The method of claim 7, wherein the generating the first TDM pilot comprises generating the first TDM pilot in frequency domain with a first set of pilot symbols for a first set of frequency subbands, and wherein the generating the second TDM pilot comprises generating the second TDM pilot in the frequency domain with a second set of pilot symbols for a second set of frequency subbands.

10. The method of claim 7, wherein the generating the first TDM pilot comprises

generating a first pilot sequence with the first PN sequence, and

generating the first TDM pilot with a plurality instances of the first pilot sequence.

11. The method of claim 10, wherein the generating the first pilot sequence comprises

generating the first pilot sequence with the first PN sequence and having a length equal to the length of the first PN sequence.

12. The method of claim 7, wherein the generating the first TDM pilot comprises

generating the first TDM pilot with a different first PN sequence for each of a plurality of transmission intervals.

13. The method of claim 7, wherein the generating the first TDM pilot comprises

identifying the first PN sequence from among a set of first PN sequences, the first PN sequence corresponding to a code offset selected from among a plurality of possible code offsets, and

generating the first TDM pilot with the first PN sequence.

14. The method of claim 10, wherein the generating the second TDM pilot comprises

generating a second pilot sequence with the second PN sequence, and

generating the second TDM pilot with at least one instance of the second pilot sequence.

15. The method of claim 14, wherein the generating the second pilot sequence comprises

generating the second pilot sequence with the second PN sequence and having a length equal to the length of the second PN sequence.

16. The method of claim 14, wherein the generating the second pilot sequence comprises

generating the second pilot sequence with the second PN sequence and having a longer length than the first pilot sequence.

17. The method of claim 7, further comprising:

generating a third TDM pilot with a third PN sequence; and

transmitting the third TDM pilot in a third portion of each transmission interval.

18. The method of claim 7, further comprising:

generating a frequency division multiplexed (FDM) pilot; and

transmitting the FDM pilot in a third portion of each transmission interval.

19. The method of claim 7, further comprising:

generating a frequency division multiplexed (FDM) pilot with the second PN sequence; and

transmitting the FDM pilot in a third portion of each transmission interval.

20. The method of claim 7, further comprising:

generating a frequency division multiplexed (FDM) pilot with a third PN sequence; and

transmitting the FDM pilot in a third portion of each transmission interval.

21. The method of claim 7, further comprising:

identifying the first PN sequence from among a set of M₁ possible first PN sequences; and

identifying the second PN sequence from among a set of M2 possible second PN sequences associated with the first PN sequence, where M₁ is one or greater and M2 is greater than one.

22. The method of claim 7, further comprising:

identifying the second PN sequence assigned to a base station transmitting the first and second TDM pilots, wherein neighboring base stations in the systems are assigned different second PN sequences.

23. The method of claim 7, wherein the generating the second TDM pilot comprises

selecting the second PN sequence from among a plurality of second PN sequences assigned to a base station, wherein each of the plurality of second PN sequences corresponds to a different data value.

24. A method of transmitting pilot in a communication system, comprising:

generating a plurality of time division multiplexed (TDM) pilots with a plurality pseudo-random number (PN) sequences, one PN sequence for each TDM pilot; and

transmitting the plurality of TDM pilots in a plurality of time intervals of each transmission interval with TDM pilot transmission.

25. The method of claim 24, further comprising:

identifying a PN sequence for each of the plurality of TDM pilots from among a set of PN sequences available for the TDM pilot.

26. The method of claim 24, further comprising:

identifying a first PN sequence for a first TDM pilot from among a set of PN sequences available for the first TDM pilot; and

for each remaining TDM pilot among the plurality of TDM pilots,

determining a subset of PN sequences associated with a PN sequence used for another TDM pilot transmitted in a prior time interval, and

identifying a PN sequence for the remaining TDM pilot from among the subset of PN sequences.

27. An apparatus in a communication system, comprising:

a processor operative to generate a first time division multiplexed (TDM) pilot with a first pseudo-random number (PN) sequence and to generate a second TDM pilot with a second PN sequence; and

a multiplexer operative to multiplex the first TDM pilot in a first portion of each transmission interval and to multiplex the second TDM pilot in a second portion of each transmission interval.

28. The apparatus of claim 27, wherein the processor is operative to generate a first pilot sequence with the first PN sequence, generate the first TDM pilot with a plurality of instances of the first pilot sequence, generate a second pilot sequence with the second PN sequence, and generate the second TDM pilot with least one instance of the second pilot sequence.

29. The apparatus of claim 27, wherein the processor is operative to identify the first PN sequence from among a set of M1 possible first PN sequences and to identify the second PN sequence from among a set of M2 possible second PN sequences associated with the first PN sequence, where M1 is one or greater and M2 is greater than one.

30. The apparatus of claim 27, further comprising:

a transmitter unit operative to transmit the first and second TDM pilots aligned in time with first and second TDM pilots from at least one other base station.

31. The apparatus of claim 27, further comprising:

a transmitter unit operative to transmit the first and second TDM pilots asynchronously with respect to first and second TDM pilots from at least one other base station.

32. The apparatus of claim 27, further comprising:

a transmitter unit operative to transmit the first and second TDM pilots staggered in time with respect to first and second TDM pilots from at least one other base station.

33. The apparatus of claim 32, wherein the first and second TDM pilots for each base station are transmitted in a time interval assigned to the base station.

34. The apparatus of claim 32, wherein neighboring base stations in the system use the same first PN sequence and the same second PN sequence.

35. The apparatus of claim 27, wherein neighboring base stations in the system are assigned different second PN sequences.

36. The apparatus of claim 27, wherein the communication system utilizes orthogonal frequency division multiplexing (OFDM).

37. An apparatus in a communication system, comprising:

means for generating a first time division multiplexed (TDM) pilot with a first pseudo-random number (PN) sequence;

means for generating a second TDM pilot with a second PN sequence;

means for transmitting the first TDM pilot in a first portion of each transmission interval; and

means for transmitting the second TDM pilot in a second portion of each transmission interval.

38. The apparatus of claim 37, wherein the means for generating the first TDM pilot comprises means for generating a first pilot sequence with the first PN sequence and means for generating the first TDM pilot with a plurality of instances of the first pilot sequence, and

wherein the means for generating the second TDM pilot comprises means for generating a second pilot sequence with the second PN sequence and means for generating the second TDM pilot with at least one instance of the second pilot sequence.

39. The apparatus of claim 37, wherein neighboring base stations in the system are assigned different second PN sequences.

40. A method of performing acquisition in a communication system, comprising:

performing a first correlation on received samples to detect for a first time division multiplexed (TDM) pilot comprised of a plurality of instances of a first pilot sequence; and

if the first TDM pilot is detected, performing a second correlation on the received samples to detect for a second TDM pilot comprised of at least one instance of a second pilot sequence.

41. The method of claim 40, wherein the performing the first correlation on the received samples comprises performing the first correlation on the received samples with a first pseudo-random number (PN) sequence, and wherein the performing the second correlation on the received samples comprises performing the second correlation on the received samples with a second PN sequence.

42. The method of claim 40, wherein the performing the first correlation comprises

performing a delayed correlation between the received samples and delayed received samples.

43. The method of claim 40, wherein the performing the first correlation comprises, for each sample period,

performing a delayed correlation between the received samples and delayed received samples,

computing a delayed correlation metric,

comparing the delayed correlation metric against a threshold, and

declaring detection of the first TDM pilot if the delayed correlation metric exceeds the threshold.

44. The method of claim 43, further comprising:

if the first TDM pilot is detected, detecting for a peak in delayed correlation results for different sample periods and providing location of the peak as an estimated location of the first TDM pilot.

45. The method of claim 40, further comprising:

averaging correlation results from the first correlation for a plurality of transmission intervals.

46. The method of claim 40, further comprising:

deriving an adaptive threshold based on the received samples; and

detecting for the first TDM pilot based on the adaptive threshold.

47. The method of claim 40, further comprising:

detecting for the first TDM pilot based on the fixed threshold.

48. The method of claim 40, further comprising:

detecting for the first TDM pilot based on a highest correlation result provided by the first correlation in each transmission interval.

49. The method of claim 41, wherein the performing the second correlation comprises

performing direct correlation on the received samples with at least one hypothesized second PN sequence.

50. The method of claim 41, wherein the performing the second correlation comprises

performing direct correlation on the received samples for at least one hypothesis, each hypothesis corresponding to a particular time offset and a hypothesized second PN sequence for the second TDM pilot,

computing a direct correlation metric for each of the at least one hypothesis,

comparing the direct correlation metric for each hypothesis against a threshold, and

declaring detection of the second TDM pilot if the direct correlation metric for any one of the at least one hypothesis exceeds the threshold.

51. The method of claim 41, further comprising:

if the first TDM pilot is detected, performing a third correlation on the received samples to identify at least one instance of the first pilot sequence.

52. The method of claim 51, wherein the performing the third correlation on the received samples comprises performing the third correlation on the received samples in time domain with a first pseudo-random number (PN) used to generate the first TDM pilot.

53. The method of claim 51, wherein the performing the third correlation on the received samples comprises performing the third correlation on the received samples in frequency domain with a first pseudo-random number (PN) used to generate the first TDM pilot.

54. The method of claim 51, wherein the performing the third correlation comprises

performing direct correlation between the received samples and at least one hypothesized first PN sequence, for a plurality of time offsets,

identifying K largest direct correlation results obtained for the plurality of time offsets and the at least one first PN sequence, where K is an integer one or greater, and

providing K detected instances of the first pilot sequence corresponding to the K largest direct correlation results, each detected instance of first pilot sequence being associated with a particular time offset and a particular first PN sequence.

55. The method of claim 40, further comprising:

identifying a transmitter of the first and second TDM pilots based on a pseudo-random number (PN) sequence used for the second correlation to detect for the second TDM pilot.

56. The method of claim 40, further comprising:

identifying a transmitter of the first and second TDM pilots based on a time interval in which the first and second TDM pilots are detected.

57. The method of claim 40, further comprising:

if the first TDM pilot is detected, performing a third correlation on the received samples to detect for a frequency division multiplexed (FDM) pilot sent on a plurality of frequency subbands.

58. The method of claim 40, further comprising:

estimating frequency error in the received samples based on result of the first correlation; and

correcting the estimated frequency error.

59. The method of claim 40, further comprising:

if the second TDM pilot is detected, decoding a control channel to verify detection of the second TDM pilot.

60. The method of claim 40, further comprising:

identifying a data value associated with a pseudo-random number (PN) sequence used for the second correlation.

61. An apparatus in a communication system, comprising:

a first correlator operative to perform a first correlation on received samples to detect for a first time division multiplexed (TDM) pilot comprised of a plurality of instances of a first pilot sequence; and

a second correlator operative to, if the first TDM pilot is detected, perform a second correlation on the received samples to detect for a second TDM pilot comprised of at least one instance of a second pilot sequence.

62. The apparatus of claim 61, wherein the first correlator is operative to perform the first correlation on the received samples with a first pseudo-random number (PN) sequence, and wherein the second correlator is operative to perform the second correlation on the received samples with a second PN sequence.

63. The apparatus of claim 61, further comprising:

a third correlator operative to, if the first TDM pilot is detected, perform a third correlation on the received samples to identify at least one instance of the first pilot sequence.

64. An apparatus in a communication system, comprising:

means for performing a first correlation on received samples to detect for a first time division multiplexed (TDM) pilot comprised of a plurality of instances of a first pilot sequence; and

means for, if the first TDM pilot is detected, performing a second correlation on the received samples to detect for a second TDM pilot comprised of at least one instance of a second pilot sequence.

65. The apparatus of claim 64, wherein the means for performing the first correlation on the received samples comprises means for performing the first correlation on the received samples with a first pseudo-random number (PN) sequence, and wherein the means for performing the second correlation on the received samples comprises means for performing the second correlation on the received samples with a second PN sequence.

66. The apparatus of claim 64, further comprising:

means for, if the first TDM pilot is detected, performing a third correlation on the received samples to identify at least one instance of the first pilot sequence.