Method of frequency offset compensation

• US 7,782,967 B2
• Filed: 08/21/2007
• Issued: 08/24/2010
• Est. Priority Date: 03/19/2007
• Status: Active Grant

• Current Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Original Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Inventors: Cheng, Fang-Chen, Song, Lei, Soni, Robert
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US11/842,398
• Publication Number:
  US 20080232516A1
• Time in Patent Office: 1,099 Days
• Field of Search: 375/260, 375/346, 375/349, 375/350
• US Class Current: 375/260
• CPC Class Codes: H04L 2027/0034 using hypothesis testing
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

The present invention provides a method of processing a baseband signal including user signals transmitted by a plurality of users. The method includes applying frequency offset compensations to the baseband signal, thereby to form respective frequency-shifted baseband signals. Each frequency compensation shifts the baseband signal by a multiple of a selected frequency offset and each resulting frequency-shifted baseband signal includes frequency-shifted user signals. The method also includes assigning at least some of the frequency-shifted user signals to groups. Each group corresponds to one of the frequency compensations and the assignment is carried out so that each group includes frequency-shifted user signals that have an estimated frequency offset that lies within a range determined by the corresponding frequency compensation. The method further includes estimating a frequency offset of each of the user signals based on the frequency-shifted user signal and the frequency compensation of the group including the frequency-shifted user signal.

Claims

1. A method of processing a baseband signal comprising user signals transmitted by a plurality of users, comprising:

applying frequency offset compensations to the baseband signal, thereby to form respective frequency-shifted baseband signals, wherein each frequency compensation shifts the baseband signal by a multiple of a selected frequency offset and each resulting frequency-shifted baseband signal comprises frequency-shifted user signals;

assigning at least some of the frequency-shifted user signals to groups, wherein each group corresponds to one of the frequency compensations and the assignment is carried out so that each group includes frequency-shifted user signals that have an estimated frequency offset that lies within a range determined by the corresponding frequency compensation; and

estimating a frequency offset of each of the user signals based on the frequency-shifted user signal and the frequency compensation of the group including the frequency-shifted user signal.

2. The method of claim 1, comprising selecting the frequency compensations and the frequency offset.

3. The method of claim 2, wherein selecting the frequency compensations comprises selecting a zero frequency compensation, at least one positive frequency compensation having a magnitude that is an integer multiple of the selected frequency offset, and at least one negative frequency compensation having a magnitude that is an integer multiple of the selected frequency offset.

4. The method of claim 2, wherein selecting the frequency compensations and the frequency offset comprises selecting the frequency compensations and the frequency offset based upon at least one of a previously determined frequency offset of a user signal and a pre-configured tolerable range of the frequency offset.

5. The method of claim 1, wherein assigning at least some of the frequency-shifted user signals to groups comprises assigning each of the frequency-shifted user signals to one of the groups based upon previously determined frequency offsets associated with each of the users.

6. The method of claim 5, wherein assigning each of the frequency-shifted user signals to one of the groups comprises assigning each of the frequency-shifted user signals to one of the groups based upon at least one of a frequency offset determined using a pilot signal or a frequency offset previously determined using a previous frequency-shifted user signal and a frequency compensation of a group including the previous frequency-shifted user signal.

7. The method of claim 5, wherein assigning at least some of the frequency-shifted user signals to groups comprises assigning each of the frequency-shifted user signals to one of the groups following fast Fourier transform processing of the frequency-shifted baseband signal.

8. The method of claim 1, comprising estimating frequency offsets for each of the users using the pilot signals provided by each of the plurality of users.

9. The method of claim 8, wherein estimating the frequency offsets for each of the users comprises applying the frequency compensations to the pilot signal to form a corresponding plurality of frequency-shifted pilot signals.

10. The method of claim 9, comprising determining a peak time for each of the frequency-shifted pilot signals.

11. The method of claim 10, wherein estimating the frequency offset for each of the users comprises combining the peak time for each of the frequency-shifted pilot signals and the frequency compensation for each of the pilot signals.

12. The method of claim 1, wherein estimating the frequency offset of each of the user signals comprises applying a single tap filter to the frequency-shifted user signal to determine a relative frequency offset that indicates the frequency offset relative to the frequency compensation of the corresponding group.

13. The method of claim 12, wherein estimating the frequency offset of each of the user signals comprises combining the relative frequency offset and the frequency compensation of the group including the frequency-shifted user signal.