Time synchronization using spectral estimation in a communication system

• US 20050282568A1
• 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: Keerthi, Arvind Vijay
• Granted Patent: US 7,492,828 B2
• Time in Patent Office: Days
• US Class Current: 455/502
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal
• CPC Class Codes: H04W 56/0005 synchronizing of arrival of multiple uplinks
• CPC Class Codes: H04W 56/0075 based on arrival time vs. expected arrival time

Abstract

To perform time synchronization using spectral estimation, a receiver obtains a frequency response estimate for pilot symbols received on each set of frequency subbands used for pilot transmission. The receiver performs spectral estimation on frequency response estimates for different sets of subbands to obtain a measured arrival time for a transmission from a transmitter. The spectral estimation determines a dominant frequency component in the frequency response estimates and derives the measured arrival time based on this dominant frequency component. A time error between the measured arrival time and a desired arrival time is computed and possibly filtered. The filtered or unfiltered time error is scaled with a fixed or adjustable gain. A time adjustment is then generated based on the scaled time error and using linear and/or non-linear functions. The time adjustment is sent to the transmitter and used to adjust the transmit timing at the transmitter.

Claims

1. A method of performing time synchronization in a communication system, comprising:

measuring an arrival time of a transmission received via a communication channel using spectral estimation;

determining a time error between the measured arrival time and a desired arrival time for the transmission; and

generating a time adjustment based on the time error.

2. The method of claim 1, wherein the measuring the arrival time of the transmission comprises

obtaining a channel estimate for the communication channel, and

performing spectral estimation on the channel estimate to obtain the measured arrival time for the transmission.

3. The method of claim 2, wherein the obtaining the channel estimate for the communication channel comprises

obtaining a plurality of frequency response estimates for a plurality of sets of frequency subbands, wherein the channel estimate comprises the plurality of frequency response estimates.

4. The method of claim 2, wherein the performing spectral estimation on the channel estimate comprises

determining a dominant frequency component in the channel estimate, and

deriving the measured arrival time based on the dominant frequency component.

5. The method of claim 1, further comprising:

scaling the time error with a gain, and wherein the time adjustment is generated based on the scaled time error.

6. The method of claim 5, further comprising:

adjusting the gain based on at least one condition of the communication channel.

7. The method of claim 5, further comprising:

adjusting the gain based on an operating mode selected from among a plurality of operating modes comprising an acquisition mode and a tracking mode.

8. The method of claim 5, further comprising:

determining a rate of shift in a channel profile obtained from the spectral estimation; and

adjusting the gain based on the rate of shift in the channel profile.

9. The method of claim 1, wherein the generating the time adjustment based on the time error comprises

filtering the time error, and

deriving the time adjustment based on the filtered time error.

10. The method of claim 1, further comprising:

limiting the time adjustment to be within a predetermined range of values.

11. The method of claim 1, wherein the generating the time adjustment based on the time error comprises

determining magnitude of the time error,

generating the time adjustment based on a first function if the magnitude of the time error is within a predetermined range, and

generating the time adjustment based on a second function if the magnitude of the time error is outside of the predetermined range.

12. An apparatus operative to perform time synchronization in a communication system, comprising:

a measurement unit operative to measure an arrival time of a transmission received via a communication channel using spectral estimation;

a summer operative to provide a time error between the measured arrival time and a desired arrival time for the transmission; and

a post processor operative to generate a time adjustment based on the time error.

13. The apparatus of claim 12, wherein the measurement unit comprises

a pilot processor operative to receive a pilot sent via the communication channel and to derive a channel estimate for the communication channel, and

a spectral estimator operative to perform spectral estimation on the channel estimate to obtain the measured arrival time for the transmission.

14. The apparatus of claim 13, wherein the pilot processor is operative to derive a plurality of frequency response estimates for a plurality of sets of frequency subbands, and wherein the channel estimate comprises the plurality of frequency response estimates.

15. The apparatus of claim 14, wherein the pilot processor is operative to receive pilot symbols on each of the plurality of sets of frequency subbands and to derive the frequency response estimate for each set of frequency subbands based on the received pilot symbols for the set of frequency subbands.

16. The apparatus of claim 14, wherein each set of subbands includes a subset of N total subbands in the system, where N is an integer greater than 1.

17. The apparatus of claim 14, wherein each set of subbands includes M consecutive subbands in the system, where M is an integer greater than 1.

18. The apparatus of claim 14, wherein each set of subbands includes M subbands uniformly distributed across N total subbands in the system, where M and N are integers greater than one, and M is less than N.

19. The apparatus of claim 14, wherein the plurality of sets of subbands are determined by a pseudo-random sequence used for frequency hopping.

20. The apparatus of claim 13, wherein the pilot processor is operative to receive a wideband pilot sent via the communication channel and to derive the channel estimate based on the wideband pilot.

21. The apparatus of claim 13, wherein the spectral estimator is operative to determine a dominant frequency component in the channel estimate and to derive the measured arrival time based on the dominant frequency component.

22. The apparatus of claim 13, wherein the spectral estimator is operative to perform spectral estimation on the channel estimate using a multiple signal classification (MUSIC) technique, a periodogram technique, a Prony estimator, or a Pisarenko harmonic decomposition technique.

23. The apparatus of claim 12, further comprising:

a multiplier operative to scale the time error with a gain, and wherein the post processor is operative to generate the time adjustment based on the scaled time error.

24. The apparatus of claim 23, wherein the gain is adjusted based on at least one condition of the communication channel.

25. The apparatus of claim 23, wherein the gain is adjusted based on a signal-to-noise ratio (SNR) of the transmission.

26. The apparatus of claim 23, further comprising:

a controller operative to select an operating mode from among a plurality of operating modes and to adjust the gain based on the selected operating mode.

27. The apparatus of claim 12, further comprising:

a filter operative to filter the time error.

28. The apparatus of claim 12, wherein the post processor is operative to limit the time adjustment to be within a predetermined range of values.

29. The apparatus of claim 12, wherein the post processor is operative to determine magnitude of the time error, to generate the time adjustment based on a first function if the magnitude of the time error is within a predetermined range, and to generate the time adjustment based on a second function if the magnitude of the time error is outside of the predetermined range.

30. The apparatus of claim 12, wherein the post processor is operative to generate the time adjustment based on the time error and in accordance with a first order loop for the time synchronization.

31. The apparatus of claim 12, wherein the post processor is operative to generate the time adjustment based on the time error and in accordance with a second order loop for the time synchronization.

32. The apparatus of claim 12, wherein the communication system utilizes orthogonal frequency division multiplexing (OFDM).

33. The apparatus of claim 12, wherein the communication system is an orthogonal frequency division multiple access (OFDMA) system.

34. An apparatus operable to perform time synchronization in a communication system, comprising:

means for measuring an arrival time of a transmission received via a communication channel using spectral estimation;

means for determining a time error between the measured arrival time and a desired arrival time for the transmission; and

means for generating a time adjustment based on the time error.

35. The apparatus of claim 34, wherein the means for measuring the arrival time of the transmission comprises

means for obtaining a channel estimate for the communication channel, and

means for performing spectral estimation on the channel estimate to obtain the measured arrival time for the transmission.

36. The apparatus of claim 35, wherein the means for obtaining the channel estimate for the communication channel comprises

means for obtaining a plurality of frequency response estimates for a plurality of sets of frequency subbands, wherein the channel estimate comprises the plurality of frequency response estimates.

37. The apparatus of claim 35, wherein the means for performing spectral estimation on the channel estimate comprises

means for determining a dominant frequency component in the channel estimate, and

means for deriving the measured arrival time based on the dominant frequency component.

38. The apparatus of claim 34, further comprising:

means for scaling the time error with a gain, and wherein the time adjustment is generated based on the scaled time error.

39. The apparatus of claim 34, further comprising:

means for limiting the time adjustment to be within a predetermined range of values.

40. A method of measuring arrival time in a communication system, comprising:

obtaining a channel estimate for a communication channel;

performing spectral estimation on the channel estimate to determine a dominant frequency component in the channel estimate; and

deriving a measured arrival time based on the dominant frequency component.

41. The method of claim 40, wherein the obtaining the channel estimate for the communication channel comprises

obtaining a plurality of frequency response estimates for a plurality of sets of frequency subbands, and wherein the channel estimate comprises the plurality of frequency response estimates.

42. An apparatus operative to measure arrival time in a communication system, comprising:

means for obtaining a channel estimate for a communication channel;

means for performing spectral estimation on the channel estimate to determine a dominant frequency component in the channel estimate; and

means for deriving a measured arrival time based on the dominant frequency component.