Signal acquisition in a wireless communication system

• US 8,068,530 B2
• Filed: 12/22/2004
• Issued: 11/29/2011
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Agrawal, Avneesh, Khandekar, Aamod
• Primary Examiner(s): Ha; Dac
• Assistant Examiner(s): Guarino; Rahel
• Application Number:
  US11/022,519
• Publication Number:
  US 20050281290A1
• Time in Patent Office: 2,533 Days
• Field of Search: 375/142, 375/149, 375/150, 375/343, 375/133, 375/130, 375/134, 375/141, 375/146, 375/33, 370/280, 370/292, 370/294, 370/321, 370/337, 370/347, 370/443, 370/441, 370/458, 370/500, 370/510, 370/350, 370/345, 370/442, 370/508, 370/512, 370/537, 370/327
• US Class Current: 375/130
• 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 performing signal acquisition in a communication system, comprising:

performing a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence;

when the first TDM pilot is detected, performing a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence; and

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

2. The method of claim 1, wherein the PN sequence is one of a set of PN sequences available for the second TDM pilot.

3. The method of claim 1, wherein the performing the first correlation comprises:

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

4. The method of claim 1, 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.

5. The method of claim 4, 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.

6. The method of claim 1, further comprising:

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

7. The method of claim 1, further comprising:

deriving an adaptive threshold based on the received samples; and

detecting the first TDM pilot based on the adaptive threshold.

8. The method of claim 1, further comprising:

detecting the first TDM pilot based on a fixed threshold.

9. The method of claim 1, further comprising:

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

10. The method of claim 1, wherein the performing the second correlation comprises:

performing direct correlation based on the received samples for at least one hypothesis, each hypothesis corresponding to a particular time offset and a hypothesized 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.

11. The method of claim 1, wherein the identifying the transmitter comprises identifying the transmitter of the first and second TDM pilots based further on the first pilot sequence for the first TDM pilot.

12. The method of claim 1, further comprising:

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

13. The method of claim 1 further comprising:

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

correcting the estimated frequency error.

14. The method of claim 1, further comprising:

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

15. The method of claim 1, further comprising:

identifying a data value associated with the PN sequence used for the second correlation.

16. The method of claim 1, wherein the first TDM pilot comprises the at least one instance of the first pilot sequence sent in time domain, and wherein the second TDM pilot comprises the at least one instance of the second pilot sequence sent in time domain.

17. The method of claim 1, wherein the first TDM pilot comprises a first set of pilot symbols generated based on the at least one instance of the first pilot sequence and sent on a first set of subcarriers, and wherein the second TDM pilot comprises a second set of pilot symbols generated based on the at least one instance of the second pilot sequence and sent on a second set of subcarriers.

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

performing a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence; and

when the first TDM pilot is detected, performing a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence, wherein the performing the second correlation comprises;

performing direct correlation based on the received samples with at least one hypothesized pseudo-random number (PN) sequence for the second TDM pilot.

19. The method of claim 18, further comprising:

if the first TDM pilot is detected, performing a third correlation based on the received samples to identify the first pilot sequence.

20. The method of claim 19, wherein the performing the third correlation based on the received samples comprises performing the third correlation based on the received samples in time domain.

21. The method of claim 19, wherein the performing the third correlation based on the received samples comprises performing the third correlation based on the received samples in frequency domain.

22. The method of claim 19, wherein the performing the third correlation comprises:

performing direct correlation between the received samples and at least one hypothesized pseudo-random number (PN) sequence for the first TDM pilot, for a plurality of time offsets,

identifying K largest direct correlation results obtained for the plurality of time offsets and the at least one hypothesized PN sequence for the first TDM pilot, where K is an integer of 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 the first pilot sequence being associated with a particular time offset and a particular hypothesized PN sequence for the first TDM pilot.

23. The method of claim 18, 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.

24. The method of claim 18, further comprising:

detecting a first PN sequence from among a set of M1 possible first PN sequences for the first TDM pilot;

detecting a second PN sequence from among a set of M2 possible second PN sequences for the second TDM pilot, the set of M2 possible second PN sequences being associated with the detected first PN sequence, where M1 is one or greater and M2 is greater than one; and

identifying a transmitter of the first and second TDM pilots based on the detected first PN sequence and the detected second PN sequence.

25. An apparatus for performing signal acquisition in a communication system, comprising:

a first correlator operative to perform a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence;

a second correlator operative to, when the first TDM pilot is detected, perform a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence; and

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

26. The apparatus of claim 25, wherein the PN sequence is one of a set of PN sequences available for the second TDM pilot.

27. The apparatus of claim 25, further comprising:

a third correlator operative to, if the first TDM pilot is detected, perform a third correlation based on the received samples to identify the first pilot sequence.

28. The apparatus of claim 25, wherein the first correlator is operative to perform a delayed correlation between the received samples and delayed received samples.

29. The apparatus of claim 25, wherein the controller is operative to identify the transmitter of the first and second TDM pilots based further on the first pilot sequence for the first TDM pilot.

30. The apparatus of claim 25, wherein the first TDM pilot comprises the at least one instance of the first pilot sequence sent in time domain, and wherein the second TDM pilot comprises the at least one instance of the second pilot sequence sent in time domain.

31. The apparatus of claim 25, wherein the first TDM pilot comprises a first set of pilot symbols generated based on the at least one instance of the first pilot sequence and sent on a first set of subcarriers, and wherein the second TDM pilot comprises a second set of pilot symbols generated based on the at least one instance of the second pilot sequence and sent on a second set of subcarriers.

32. An apparatus in a communication system, comprising:

means for performing a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence;

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

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

33. The apparatus of claim 32, wherein the PN sequence is one of a set of PN sequences available for the second TDM pilot.

34. The apparatus of claim 32, further comprising:

means for, if the first TDM pilot is detected, performing a third correlation based on the received samples to identify the first pilot sequence.

35. The apparatus of claim 32, wherein the means for performing the first correlation comprises:

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

36. The apparatus of claim 32, wherein the means for identifying the transmitter comprises means for identifying the transmitter of the first and second TDM pilots based further on the first pilot sequence for the first TDM pilot.

37. The apparatus of claim 32, wherein the first TDM pilot comprises the at least one instance of the first pilot sequence sent in time domain, and wherein the second TDM pilot comprises the at least one instance of the second pilot sequence sent in time domain.

38. The apparatus of claim 32, wherein the first TDM pilot comprises a first set of pilot symbols generated based on the at least one instance of the first pilot sequence and sent on a first set of subcarriers, and wherein the second TDM pilot comprises a second set of pilot symbols generated based on the at least one instance of the second pilot sequence and sent on a second set of subcarriers.

39. An apparatus for performing signal acquisition in a communication system, comprising:

a first correlator operative to perform a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence; and

a second correlator operative to, when the first TDM pilot is detected, perform a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence, wherein the second correlator is operative to perform direct correlation based on the received samples with at least one hypothesized pseudo-random number (PN) sequence for the second TDM pilot.

40. The apparatus of claim 39, further comprising:

a controller operative to detect a first PN sequence from among a set of M1 possible first PN sequences for the first TDM pilot, to detect a second PN sequence from among a set of M2 possible second PN sequences for the second TDM pilot, the set of M2 possible second PN sequences being associated with the detected first PN sequence, where M1 is one or greater and M2 is greater than one, and to identify a transmitter of the first and second TDM pilots based on the detected first PN sequence and the detected second PN sequence.

41. An apparatus in a communication system, comprising:

means for performing a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence; and

means for, when the first TDM pilot is detected, performing a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence, wherein the means for performing the second correlation comprises;

means for performing direct correlation based on the received samples with at least one hypothesized pseudo-random number (PN) sequence for the second TDM pilot.

42. The apparatus of claim 41, further comprising:

means for detecting a first PN sequence from among a set of M1 possible first PN sequences for the first TDM pilot;

means for detecting a second PN sequence from among a set of M2 possible second PN sequences for the second TDM pilot, the set of M2 possible second PN sequences being associated with the detected first PN sequence, where M1 is one or greater and M2 is greater than one; and

means for identifying a transmitter of the first and second TDM pilots based on the detected first PN sequence and the detected second PN sequence.

43. A computer program product, comprising:

a non-transitory processor-readable medium comprising;

code for causing at least one processor to perform a first correlation based on received samples to detect a first time division multiplexed (TDM) pilot comprised of at least one instance of a first pilot sequence,

code for causing the at least one processor to, when the first TDM pilot is detected, perform a second correlation based on the received samples to detect a second TDM pilot comprised of at least one instance of a second pilot sequence, and

code for causing the at least one processor to identify a transmitter of the first and second TDM pilots based at least on a pseudo-random number (PN) sequence used for the second correlation to detect the second TDM pilot.