Iterative interference cancellation

• US 8,351,532 B2
• Filed: 09/29/2008
• Issued: 01/08/2013
• Est. Priority Date: 10/01/2007
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Inventors: Cheng, Fang-Chen, Ye, Henry Hui, Song, Lei
• Primary Examiner(s): PATEL, DHAVAL V
• Application Number:
  US12/239,983
• Publication Number:
  US 20090196370A1
• Time in Patent Office: 1,562 Days
• Field of Search: 375/148, 375/267, 375/136, 375/147, 375/260, 375/316, 375/347, 375/348, 375/349, 370/203, 370/204, 370/205, 370/206, 370/208, 370/209, 370/210, 370/342, 455/130, 455/296, 455/306
• US Class Current: 375/267
• CPC Class Codes: H04L 1/0027 Scheduling of signalling, e.g. occurrence thereof
• CPC Class Codes: H04L 1/1671 the supervisory signal being transmitted together with control information
• CPC Class Codes: H04L 1/1692 Physical properties of the supervisory signal, e.g. acknowledgement by energy bursts
• CPC Class Codes: H04L 1/1893 Physical mapping arrangements physical resource mapping in general H04L5/00
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals

Abstract

An exemplary method of communicating includes determining a first user channel estimate from a communication comprising first and second user reference sequences. The first user reference sequence is reconstructed using the determined first user channel estimate. The communication is revised based upon the reconstructed first user reference sequence. Then determining a second user channel estimate is based on the revised communication.

Claims

1. A method of communicating, comprising the steps of:

(A) determining a first user channel estimate from a communication comprising first and second user constant amplitude zero autocorrelation (CAZAC) reference sequences by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the first user and filtering the product of the multiplying to thereby determine the first user channel estimate;

(B) reconstructing the first user reference sequence by multiplying the determined first user channel estimate by the CAZAC sequence assigned to the first user;

(C) revising the communication by subtracting the reconstructed first user reference sequence from the communication; and

(D) determining a second user channel estimate from the revised communication by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the second user and filtering the product of the multiplying to thereby determine the second user channel estimate.

2. The method of claim 1, comprising

(E) reconstructing the second user reference sequence by multiplying the determined second user channel estimate by the CAZAC sequence assigned to the second user;

(F) revising the communication by subtracting the reconstructed second user reference sequence from the communication; and

(G) revising the first user channel estimate from the revised communication.

3. The method of claim 2, comprising

(H) revising the reconstructed first user reference sequence using the revised first user channel estimate;

(I) revising the communication based upon the revised reconstructed first user reference sequence; and

(J) revising the second user channel estimate from the revised communication.

4. The method of claim 3 comprising

(K) revising the reconstructed second user reference sequence using the revised second user channel estimate;

and

iteratively, repeating steps (F) through (K).

5. The method of claim 4, comprising

iteratively repeatedly performing steps (F) through (K) a selected number of times.

6. The method of claim 5, comprising

determining the channel estimates using an averaging filter technique in a frequency domain.

7. The method of claim 1, wherein revising the communication comprises

adding a delay to each reconstructed reference sequence;

and

subsequently subtracting the reconstructed reference sequence from the communication to thereby revise the communication.

8. The method of claim 1, wherein revising the communication comprises cancelling an effect of the reconstructed reference sequence from the communication.

9. The method of claim 1, wherein the communication comprises a multi-user multiple input multiple output communication.

10. The method of claim 9, wherein the communication comprises at least one resource block and the first and second user reference sequences are both within the at least one resource block.

11. The method of claim 1, comprising

determining a first user reference signal or pilot a second user reference signal or pilot.

12. The method of claim 1, comprising

determining the channel estimates using an averaging filter technique in a frequency domain.

16. The method of claim 4, comprising

iteratively repeatedly performing steps (F) through (K) until a selected amount of convergence is achieved for the channel estimate of at least one of the user channels.

17. The method of claim 1, wherein the reference sequences each comprises a Zadoff-Chu sequence.

13. A receiver device comprising

a channel estimation module for at least estimating a channel of each of a plurality of users from which a communication is received simultaneously, the communication comprising first and second user constant amplitude zero autocorrelation (CAZAC) reference sequences, the channel estimation module being configured to

determine a first user channel estimate from the communication by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the first user and filtering the product of the multiplying to thereby determine the first user channel estimate;

reconstruct the first user reference sequence by multiplying the determined first user channel estimate by the CAZAC sequence assigned to the first user;

revise the communication by subtracting the reconstructed first user reference sequence from the communication; and

determine a second user channel estimate from the revised communication by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the second user and filtering the product of the multiplying to thereby determine the second user channel estimate.

14. The device of claim 13, wherein the channel estimation module is configured to

reconstruct the second user reference sequence by multiplying the determined second user channel estimate by the CAZAC sequence assigned to the second user;

revise the communication by subtracting the reconstructed second user reference sequence from the communication;

revise the first user channel estimate from the revised communication;

revise the reconstructed first user reference sequence using the revised first user channel estimate;

revise the communication based upon the revised reconstructed first user reference sequence;

revise the second user channel estimate from the revised communication;

revise the reconstructed second user reference sequence using the revised second user channel estimate; and

iteratively, repeatedly revise each channel estimate, the communication and each reconstructed reference sequence.

15. The device of claim 14, wherein the channel estimation module is configured to iteratively, repeatedly revise each channel estimate until a selected amount of convergence is achieved for the channel estimate of at least one of the user channels.

18. The device of claim 13, wherein the reference sequences each comprises a Zadoff-Chu sequence.

19. A communication device, comprising:

user channel estimate means for determining a first user channel estimate from a communication comprising first and second user constant amplitude zero autoconelation (CAZAC) reference sequences by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the first user and filtering the product of the multiplying to thereby determine the first user channel estimate;

reconstructing means for reconstructing the first user reference sequence by multiplying the determined first user channel estimate by the CAZAC sequence assigned to the first user; and

revising means for revising the communication by subtracting the reconstructed first user reference sequence from the communication; and

the user channel estimate means also being for determining a second user channel estimate from the revised communication by multiplying the communication by a complex conjugate of the CAZAC sequence assigned to the second user and filtering the product of the multiplying to thereby determine the second user channel estimate.

20. The device of claim 19, wherein

the reconstructing means is also for reconstructing the second user reference sequence by multiplying the determined second user channel estimate by the CAZAC sequence assigned to the second user;

the revising means is also for revising the communication by subtracting the reconstructed second user reference sequence from the communication; and

the user channel estimate means is also for revising the first user channel estimate from the revised communication.

21. The device of claim 20, wherein

the reconstructing means is also for revising the reconstructed first user reference sequence using the revised first user channel estimate;

the revising means is also for revising the communication based upon the revised reconstructed first user reference sequence; and

the user channel estimate means is also for revising the second user channel estimate from the revised communication.

22. The device of claim 21, wherein the reconstructing means is also for revising the reconstructed second user reference sequence using the revised second user channel estimate.

23. The device of claim 19, wherein the user channel estimate means determines the channel estimates using an averaging filter technique in a frequency domain.

24. The device of claim 19, wherein the revising means revises each communication by

adding a delay to each reconstructed reference sequence;

and

subsequently subtracting the reconstructed reference sequence from the communication to thereby revise the communication.

25. The device of claim 19, wherein the revising means cancels an effect of the reconstructed reference sequence from the communication.

26. The device of claim 19, wherein the communication comprises a multi-user multiple input multiple output communication.

27. The device of claim 19, wherein the communication comprises at least one resource block and the first and second user reference sequences are both within the at least one resource block.

28. The device of claim 19, comprising means for determining a first user reference signal or pilot and a second user reference signal or pilot.

29. The device of claim 19, wherein the reference sequences each comprise a Zadoff-Chu sequence.

30. A communication device, comprising:

a first multiplier configured to multiply a communication by a complex conjugate of a constant amplitude zero autocorrelation (CAZAC) reference sequence assigned to a user;

a filter configured to filter a product of the first multiplier;

a second multiplier configured to reconstruct a user reference signal by multiplying an output from the filter by the CAZAC sequence assigned to the user; and

a subtractor configured to revise a communication by subtracting a product of the second multiplier from the communication;

wherein

the first multiplier and the filter are configured to determine a first user channel estimate from a communication comprising first and second user CAZAC reference sequences by the first multiplier multiplying the communication by a complex conjugate of the first user CAZAC sequence assigned to a first user and the filter filtering the product of the first multiplier to determine the first user channel estimate;

the second multiplier is configured to reconstruct the first user CAZAC reference sequence by multiplying the determined first user channel estimate by the first user CAZAC sequence; and

the subtractor is configured to revise the communication by subtracting the reconstructed first user CAZAC reference sequence from the communication; and

the first multiplier and the filter are configured to determine a second user channel estimate by the first multiplier multiplying the communication, after its revision, by a complex conjugate of the second user CAZAC sequence assigned to a second user and the filter filtering the product of the first multiplier to determine the second user channel estimate.

31. The device of claim 30, wherein

the second multiplier is configured to reconstruct the second user CAZAC reference sequence by multiplying the determined second user channel estimate by the second user CAZAC sequence;

the subtractor is configured to revise the communication by subtracting the reconstructed second user CAZAC reference sequence from the communication; and

the first multiplier and the filter are configured to revise the first user channel estimate from the communication after revision by the subtractor.

32. The device of claim 31, wherein

the second multiplier is configured to revise the reconstructed first user CAZAC reference sequence using the revised first user channel estimate;

the subtractor is configured to revise the communication based upon the revised reconstructed first user CAZAC reference sequence; and

the first multiplier and the filter are configured to revise the second user channel estimate from the communication after revision by the subtractor.

33. The device of claim 32, wherein the subtractor is configured to revise the reconstructed second user CAZAC reference sequence using the revised second user channel estimate.

34. The device of claim 30, wherein the filter is configured to use an averaging filter technique in a frequency domain.

35. The device of claim 30, wherein the subtractor is configured to revise each communication by

adding a delay to each reconstructed reference sequence;

and

subsequently subtracting the reconstructed reference sequence from the communication to revise the communication.

36. The device of claim 30, wherein the subtractor is configured to cancel an effect of the reconstructed reference sequence from the communication.

37. The device of claim 30, wherein the communication comprises a multi-user multiple input multiple output communication.

38. The device of claim 30, wherein the communication comprises at least one resource block and the first and second user CAZAC reference sequences are both within the at least one resource block.

39. The device of claim 30, wherein the CAZAC reference sequences assigned to the first user and the second user each comprise a Zadoff-Chu sequence.