Quick detection of signaling in a wireless communication system

• US 20070060095A1
• Filed: 09/15/2005
• Published: 03/15/2007
• Est. Priority Date: 09/15/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Subrahmanya, Parvathanathan, Chawla, Vivek, Sheshadri, Thejaswi Bharadwaj Madapushi
• Granted Patent: US 8,027,373 B2
• Time in Patent Office: Days
• US Class Current: 455/343.100
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 2201/70709 with discontinuous detection
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0034 using hypothesis testing
• CPC Class Codes: H04L 2027/0065 Frequency error detectors H04L2027/0067 takes precedence
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04W 52/0229 where the received signal is a wanted signal
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Quick frequency tracking (QFT), quick time tracking (QTT), and non-causal pilot filtering (NCP) are used to detect sporadically transmitted signaling, e.g., paging indicators. For QFT, multiple hypothesized frequency errors are applied to an input signal to obtain multiple rotated signals. The energies of the rotated signals are computed. The hypothesized frequency error with the largest energy is provided as a frequency error estimate. For QTT, coherent accumulation is performed on the input signal for a first set of time offsets, e.g., early, on-time, and late. Interpolation, energy computation, and non-coherent accumulation are then performed to obtain a timing error estimate with higher time resolution. For NCP, pilot symbols are filtered with a non-causal filter to obtain pilot estimates for one antenna for non-STTD and for two antennas for STTD. The frequency and timing error estimates and the pilot estimates are used to detect the signaling.

Claims

1. An apparatus comprising:

a controller operative to wake up from sleep to receive signaling during discontinuous reception (DRX) operation;

a processor operative to apply a plurality of hypothesized frequency errors to an input signal to obtain a plurality of rotated signals, to determine energies of the plurality of rotated signals, and to determine a frequency error estimate based on the energies of the plurality of rotated signals; and

a demodulator operative to use the frequency error estimate for detection of the signaling.

2. The apparatus of claim 1, wherein the processor is operative to accumulate each rotated signal over a predetermined period to obtain an accumulated value for the rotated signal and to compute energy of the accumulated value.

3. The apparatus of claim 2, wherein the controller is operative to select the predetermined period based on expected channel conditions.

4. The apparatus of claim 1, wherein the processor is operative to identify a largest energy among the energies of the plurality of rotated signals and to provide a hypothesized frequency error corresponding to the largest energy as the frequency error estimate.

5. The apparatus of claim 1, wherein the controller is operative to distribute the plurality of hypothesized frequency errors uniformly over a range of possible frequency errors.

6. The apparatus of claim 1, wherein the controller is operative to distribute the plurality of hypothesized frequency errors non-uniformly over a range of possible frequency errors and to use smaller frequency error spacing for at least one subrange of frequency errors with higher likelihood of containing an actual frequency error.

7. The apparatus of claim 1, wherein the controller is operative to determine a range of possible frequency errors based on expected channel conditions and to select the plurality of hypothesized frequency errors based on the range of possible frequency errors.

8. The apparatus of claim 1, wherein the demodulator is operative to perform detection for a paging indicator sent at predetermined time interval.

9. The apparatus of claim 1, wherein the processor is operative to receive pilot symbols for the input signal.

10. The apparatus of claim 1, wherein the processor is operative to receive descrambled samples for the input signal.

11. A method comprising:

waking up from sleep to receive signaling during discontinuous reception (DRX) operation;

applying a plurality of hypothesized frequency errors to an input signal to obtain a plurality of rotated signals;

determining energies of the plurality of rotated signals;

determining a frequency error estimate based on the energies of the plurality of rotated signals; and

using the frequency error estimate for detection of the signaling.

12. The method of claim 11, wherein the determining the energies of the plurality of rotated signals comprises

accumulating each rotated signal over a predetermined period to obtain an accumulated value for the rotated signal, and

computing energy of the accumulated value for each rotated signal.

13. The method of claim 11, wherein the determining the frequency error estimate comprises

identifying a largest energy among the energies of the plurality of rotated signals, and

providing a hypothesized frequency error corresponding to the largest energy as the frequency error estimate.

14. The method of claim 11, further comprising:

performing detection for a paging indicator sent at a predetermined time interval.

15. An apparatus comprising:

means for waking up from sleep to receive signaling during discontinuous reception (DRX) operation;

means for applying a plurality of hypothesized frequency errors to an input signal to obtain a plurality of rotated signals;

means for determining energies of the plurality of rotated signals;

means for determining a frequency error estimate based on the energies of the plurality of rotated signals; and

means for using the frequency error estimate for detection of the signaling.

16. The apparatus of claim 15, wherein the means for determining the energies of the plurality of rotated signals comprises

means for accumulating each rotated signal over a predetermined period to obtain an accumulated value for the rotated signal, and

means for computing energy of the accumulated value for each rotated signal.

17. The apparatus of claim 15, wherein the means for determining the frequency error estimate comprises

means for identifying a largest energy among the energies of the plurality of rotated signals, and

means for providing a hypothesized frequency error corresponding to the largest energy as the frequency error estimate.

18. A method comprising:

applying a plurality of hypothesized frequency errors to an input signal to obtain a plurality of rotated signals;

determining energies of the plurality of rotated signals for a first transmit antenna;

determining energies of the plurality of rotated signals for a second transmit antenna;

determining overall energies of the plurality of rotated signals for the first and second antennas; and

determining a frequency error estimate based on the overall energies of the plurality of rotated signals.

19. The method of claim 18, further comprising:

accumulating the plurality of rotated signals separately over a predetermined period to obtain a first plurality of accumulated values used to determine the energies of the plurality of rotated signals for the first transmit antenna;

scaling the plurality of rotated signals with a scaling sequence for the second transmit antenna to obtain a plurality of scaled signals; and

accumulating the plurality of scaled signals separately over the predetermined period to obtain a second plurality of intermediate values used to determine the energies of the plurality of rotated signals for the second transmit antenna.

20. The method of claim 19, wherein the determining the frequency error estimate comprises

identifying a largest overall energy among the overall energies of the plurality of rotated signals, and

providing a hypothesized frequency error corresponding to the largest overall energy as the frequency error estimate.

21. An apparatus comprising:

a controller operative to wake up from sleep to receive signaling during discontinuous reception (DRX) operation;

a processor operative to perform coherent accumulation on an input signal for a first plurality of time offsets, to perform interpolation from the first plurality of time offsets to a second plurality of time offsets, and to perform non-coherent accumulation after the interpolation to obtain a timing error estimate; and

a demodulator operative to use the timing error estimate for detection of the signaling.

22. The apparatus of claim 21, wherein the processor is operative to perform linear interpolation on outputs of the coherent accumulation for the first plurality of time offsets to obtain intermediate values for a second plurality of time offsets and to perform non-coherent accumulation based on the intermediate values.

23. The apparatus of claim 22, wherein the processor is operative to compute energies of the intermediate values for the second plurality of time offsets and to perform non-coherent accumulation based on the energies of the intermediate values for the second plurality of time offsets.

24. The apparatus of claim 23, wherein the processor is operative to identify a largest energy among non-coherently accumulated energies for the second plurality of time offsets and to provide a time offset corresponding to the largest energy as the timing error estimate.

25. The apparatus of claim 21, wherein the processor is operative to perform parabolic interpolation on outputs of the non-coherent accumulation for the first plurality of time offsets.

26. The apparatus of claim 21, wherein the controller is operative to select length of the coherent accumulation and length of the non-coherent accumulation based on expected channel conditions.

27. The apparatus of claim 21, wherein the processor is operative to receive symbols at two times chip rate and to provide the timing error estimate with a resolution of one eighth chip period or better.

28. A method comprising:

waking up from sleep to receive signaling during discontinuous reception (DRX) operation;

performing coherent accumulation on an input signal for a first plurality of time offsets;

performing interpolation from the first plurality of time offsets to a second plurality of time offsets;

performing non-coherent accumulation after the interpolation;

deriving a timing error estimate based on outputs of the non-coherent accumulation; and

using the timing error estimate for detection of the signaling.

29. The method of claim 28, wherein the performing interpolation on the first plurality of time offsets comprises

performing linear interpolation on outputs of the coherent accumulation for the first plurality of time offsets to obtain intermediate values for a second plurality of time offsets, and wherein the non-coherent accumulation is performed based on the intermediate values.

30. The method of claim 29, further comprising:

computing energies of the intermediate values for the second plurality of time offsets, and wherein the non-coherent accumulation is performed based on the energies of the intermediate values for the second plurality of time offsets.

31. The method of claim 30, further comprising:

identifying a largest energy among non-coherently accumulated energies for the second plurality of time offsets; and

providing a time offset corresponding to the largest energy as the timing error estimate.

32. The method of claim 28, wherein the performing interpolation on the first plurality of time offsets comprises

performing parabolic interpolation on outputs of the non-coherent accumulation for the first plurality of time offsets.

33. An apparatus comprising:

means for waking up from sleep to receive signaling during discontinuous reception (DRX) operation;

means for performing coherent accumulation on an input signal for a first plurality of time offsets;

means for performing interpolation from the first plurality of time offsets to a second plurality of time offsets;

means for performing non-coherent accumulation after the interpolation;

means for deriving a timing error estimate based on outputs of the non-coherent accumulation; and

means for using the timing error estimate for detection of the signaling.

34. The apparatus of claim 33, wherein the means for performing interpolation on the first plurality of time offsets comprises

means for performing linear interpolation on outputs of the coherent accumulation for the first plurality of time offsets to obtain intermediate values for a second plurality of time offsets.

35. The apparatus of claim 34, further comprising:

means for computing energies of the intermediate values for the second plurality of time offsets, and wherein the non-coherent accumulation is performed based on the energies of the intermediate values for the second plurality of time offsets;

means for identifying a largest energy among non-coherently accumulated energies for the second plurality of time offsets; and

means for providing a time offset corresponding to the largest energy as the timing error estimate.

36. A method comprising:

performing coherent accumulation on an input signal for a first transmit antenna at a first plurality of time offsets;

performing coherent accumulation on the input signal for a second transmit antenna at the first plurality of time offsets;

performing interpolation from the first plurality of time offsets to a second plurality of time offsets for each of the first and second transmit antennas;

determining energies for the second plurality of time offsets for each of the first and second transmit antennas;

combining the energies for the first and second transmit antennas for each of the second plurality of time offsets;

performing non-coherent accumulation of the energies for the second plurality of time offsets; and

obtaining a timing error estimate based on outputs of the non-coherent accumulation.

37. The method of claim 36, wherein the performing interpolation comprises

performing linear interpolation on outputs of the coherent accumulation for the first transmit antenna to obtain intermediate values at a second plurality of time offsets for the first transmit antenna, and

performing linear interpolation on outputs of the coherent accumulation for the second transmit antenna to obtain intermediate values at the second plurality of time offsets for the second transmit antenna.

38. The method of claim 36, further comprising:

identifying a largest energy among non-coherently accumulated energies for the second plurality of time offsets; and

providing a time offset corresponding to the largest energy as the timing error estimate.

39. An apparatus comprising:

a controller operative to wake up from sleep to receive signaling during discontinuous reception (DRX) operation; and

a demodulator operative to filter pilot symbols with a non-causal filter to obtain pilot estimates and to perform detection for the signaling based on the pilot estimates.

40. The apparatus of claim 39, wherein the demodulator is operative to filter the pilot symbols with a non-causal finite impulse response (FIR) filter having equal number of taps on both sides of each signaling symbol to be detected.

41. The apparatus of claim 39, wherein the demodulator is operative to derive at least one channel gain estimate for at least one signaling symbol based on the pilot estimates, to multiply the at least one signaling symbol with the at least one channel gain estimate to obtain at least one demodulated symbol, and to sum inphase and quadrature components of the at least one demodulated symbol to obtain a detected value for the signaling.

42. A method comprising:

waking up from sleep to receive signaling during discontinuous reception (DRX) operation;

filtering pilot symbols with a non-causal filter to obtain pilot estimates; and

performing detection for the signaling based on the pilot estimates.

43. The method of claim 42, wherein the filtering the pilot symbols comprises

filtering the pilot symbols with a non-causal finite impulse response (FIR) filter having equal number of taps on both sides of each signaling symbol to be detected.

44. The method of claim 42, wherein the performing detection comprises

deriving at least one channel gain estimate for at least one signaling symbol based on the pilot estimates,

multiplying the at least one signaling symbol with the at least one channel gain estimate to obtain at least one demodulated symbol, and

summing inphase and quadrature components of the at least one demodulated symbol to obtain a detected value for the signaling.

45. A method comprising:

filtering a first set of pilot symbols with a first non-causal filter for a first antenna to obtain a first set of at least one pilot estimate for the first antenna;

filtering a second set of pilot symbols with a second non-causal filter for a second antenna to obtain a second set of at least one pilot estimate for the second antenna; and

performing detection of signaling based on the first and second sets of at least one pilot estimate.

46. The method of claim 45, further comprising:

selecting the first set of pilot symbols to include equal number of sum and difference pilot symbols; and

selecting the second set of pilot symbols to include equal number of sum and difference pilot symbols.

47. The method of claim 45, wherein the performing detection of the signaling comprises

performing space-time transmit diversity (STTD) decoding of at least one pair of signaling symbols with the first and second sets of at least one pilot estimate to obtain a detected value for the signaling.

48. The method of claim 45, wherein the first set of pilot symbols is equal to the second set of pilot symbols.

49. The method of claim 45, wherein the first set of pilot symbols is non-symmetric with the signaling and includes unequal numbers of pilot symbols on left and right sides of the signaling.

50. The method of claim 45, wherein the second set of pilot symbols includes at least one pilot symbol not included in the first set of pilot symbols.

51. The method of claim 50, further comprising:

filtering the first set of pilot symbols with a third non-causal filter for the second antenna to obtain a third set of at least one pilot estimate for the second antenna; and

filtering the second set of pilot symbols with a fourth non-causal filter for the first antenna to obtain a fourth set of at least one pilot estimate for the first antenna, and wherein the detection of the signaling is performed further based on the third and fourth sets of at least one pilot estimate.

52. The method of claim 51, further comprising:

performing space-time transmit diversity (STTD) decoding of at least one pair of signaling symbols with the first, second, third, and fourth sets of at least one pilot estimate to obtain a detected value for the signaling.

53. The method of claim 51, further comprising:

averaging the first and fourth sets of at least one pilot estimate for the first antenna to obtain a first set of at least one averaged pilot estimate for the first antenna;

averaging the second and third sets of at least one pilot estimate for the second antenna to obtain a second set of at least one averaged pilot estimate for the second antenna; and

performing space-time transmit diversity (STTD) decoding of at least one pair of signaling symbols with the first and second sets of at least one averaged pilot estimate to obtain a detected value for the signaling.

54. An apparatus comprising:

a processor operative to perform quick frequency tracking to obtain at least one frequency error estimate for at least one finger processor and to perform quick time tracking to obtain at least one timing error estimate for the at least one finger processor; and

a demodulator operative to perform detection for signaling with the at least one frequency error estimate and the at least one timing error estimate for the at least one finger processor.

55. The apparatus of claim 54, wherein the processor is operative, for each finger processor, to perform coherent accumulation to obtain energies for a plurality of hypothesized frequency errors and to determine a frequency error estimate for the finger processor based on the energies for the plurality of hypothesized frequency errors.

56. The apparatus of claim 54, wherein the processor is operative, for each finger processor, to perform coherent accumulation, interpolation, and non-coherent accumulation to obtain energies for a plurality of time offsets and to determine a timing error estimate for the finger processor based on the energies for the plurality of time offsets.

57. The apparatus of claim 54, wherein the demodulator is operative to filter pilot symbols with a non-causal filter to obtain pilot estimates and to perform detection for the signaling based on the pilot estimates.

58. The apparatus of claim 54, wherein the processor is operative to perform quick frequency tracking and quick time tracking in parallel.

59. The apparatus of claim 54, wherein the controller is operative to determine an amount of time to perform quick frequency tracking and quick time tracking in a next awake interval based on expected channel conditions and to determine a sleep duration based on the amount of time to perform quick frequency tracking and quick time tracking in the next awake interval.

60. The apparatus of claim 54, wherein the processor is operative to perform detection for a paging indicator sent at a predetermined time interval.

61. A method comprising:

performing quick frequency tracking to obtain at least one frequency error estimate for at least one finger processor;

performing quick time tracking to obtain at least one timing error estimate for the at least one finger processor; and

performing detection of signaling with the at least one frequency error estimate and the at least one timing error estimate for the at least one finger processor.

62. The method of claim 61, wherein the performing quick frequency tracking comprises, for each finger processor,

performing coherent accumulation to obtain energies for a plurality of hypothesized frequency errors, and

determining a frequency error estimate for the finger processor based on the energies for the plurality of hypothesized frequency errors.

63. The method of claim 61, wherein the performing quick time tracking comprises, for each finger processor,

performing coherent accumulation, interpolation, and non-coherent accumulation to obtain energies for a plurality of time offsets, and

determining a timing error estimate for the finger processor based on the energies for the plurality of time offsets.

64. The method of claim 61, further comprising:

filtering pilot symbols with a non-causal filter to obtain pilot estimates, and wherein the detection of the signaling is performed based on the pilot estimates.

65. The method of claim 61, further comprising:

determining an amount of time to perform quick frequency tracking and quick time tracking in a next awake interval based on expected channel conditions; and

determining a sleep duration based on the amount of time to perform quick frequency tracking and quick time tracking in the next awake interval.

66. An apparatus comprising:

means for performing quick frequency tracking to obtain at least one frequency error estimate for at least one finger processor;

means for performing quick time tracking to obtain at least one timing error estimate for the at least one finger processor; and

means for performing detection of signaling with the at least one frequency error estimate and the at least one timing error estimate for the at least one finger processor.

67. The apparatus of claim 66, wherein the means for performing quick frequency tracking comprises, for each finger processor,

means for performing coherent accumulation to obtain energies for a plurality of hypothesized frequency errors, and

means for determining a frequency error estimate for the finger processor based on the energies for the plurality of hypothesized frequency errors.

68. The apparatus of claim 66, wherein the means for performing quick time tracking comprises, for each finger processor,

means for performing coherent accumulation, interpolation, and non-coherent accumulation to obtain energies for a plurality of time offsets, and

means for determining a timing error estimate for the finger processor based on the energies for the plurality of time offsets.

69. The apparatus of claim 66, further comprising:

means for filtering pilot symbols with a non-causal filter to obtain pilot estimates, and wherein the detection of the signaling is performed based on the pilot estimates.