Pilot transmission schemes for wireless multi-carrier communication systems

• US 20040131007A1
• Filed: 02/07/2003
• Published: 07/08/2004
• Est. Priority Date: 01/07/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Malladi, Durga Prasad, Walton, Jay Rod, Smee, John
• Granted Patent: US 7,280,467 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04L 1/0017 where the mode-switching is based on Quality of Service requirement
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 25/03866 using scrambling
• CPC Class Codes: H04L 27/26035 Maintenance of orthogonality, e.g. for signals exchanged between cells or users, or by using covering codes or sequences using different training sequence per antenna H04B7/0684; code allocation H04J13/16
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0039 Frequency-contiguous, i.e. with no allocation of frequencies for one user or terminal between the frequencies allocated to another
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

Pilot transmission schemes suitable for use in wireless multi-carrier (e.g., OFDM) communication systems. These pilot transmission schemes may utilize frequency, time, or both frequency and time orthogonality to achieve orthogonality among the pilots transmitted by multiple base stations on the downlink. Frequency orthogonality is achieved by transmitting pilots on disjoint sets of subbands. Time orthogonality is achieved by transmitting pilots using different orthogonal codes (e.g., Walsh codes). The pilots may also be scrambled with different scrambling codes, which are used to randomize pilot interference and to enable identification of the transmitters of these pilots. Pilot interference cancellation may be performed to improve performance since subbands used for data transmission by one transmitter may also be used for pilot transmission by another transmitter. Pilot interference is estimated and then subtracted from received symbols to obtain pilot-canceled symbols having improved quality.

Claims

1. A method of transmitting a pilot on a downlink in a wireless multi-carrier communication system, comprising:

generating pilot symbols for transmission on a first set of subbands, wherein the first set of subbands is used for pilot transmission by a first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity;

processing the pilot symbols to obtain a pilot signal having the pilot symbols included in the first set of subbands; and

transmitting the pilot signal from the first transmitting entity.

2. The method of claim 1, further comprising:

processing the pilot symbols with an orthogonal code to obtain covered pilot symbols, and wherein the covered pilot symbols are further processed to obtain the pilot signal.

3. The method of claim 1, further comprising:

processing the pilot symbols with a scrambling code to obtain scrambled pilot symbols, and wherein the scrambled pilot symbols are further processed to obtain the pilot signal.

4. The method of claim 1, wherein the subbands in the first set are evenly distributed across a plurality of subbands usable for pilot and data transmission by the first transmitting entity.

5. The method of claim 1, wherein pilot signals are transmitted in bursts from the first and second transmitting entities.

6. The method of claim 1, wherein pilot signals are transmitted with synchronous timing from the first and second transmitting entities.

7. The method of claim 1, wherein the multi-carrier communication system implements orthogonal frequency division multiplexing (OFDM).

8. An apparatus in a wireless multi-carrier communication system, comprising:

means for generating pilot symbols for transmission on a first set of subbands, wherein the first set of subbands is used for pilot transmission by a first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity;

means for processing the pilot symbols to obtain a pilot signal having the pilot symbols included in the first set of subbands; and

means for transmitting the pilot signal from the first transmitting entity.

9. The apparatus of claim 8, further comprising:

means for processing the pilot symbols with an orthogonal code to obtain covered pilot symbols, and wherein the covered pilot symbols are further processed to obtain the pilot signal.

10. The apparatus of claim 8, further comprising:

means for processing the pilot symbols with a scrambling code to obtain scrambled pilot symbols, and wherein the scrambled pilot symbols are further processed to obtain the pilot signal.

11. A base station in a wireless multi-carrier communication system, comprising:

at least one pilot processor operative to receive and process pilot symbols designated for transmission on a first set of subbands, wherein the first set of subbands is used for pilot transmission by the base station and is disjoint from a second set of subbands used for pilot transmission by another base station in the system;

a transform unit operative to derive time-domain samples having the covered pilot symbols included in the first set of subbands; and

a transmitter unit operative to process the time-domain samples to obtain a pilot signal for transmission on a downlink.

12. A computer-readable medium for transmitting a pilot on a downlink in a wireless multi-carrier communication system, the computer-readable medium comprising instructions which, when executed by a processor, cause said processor to perform the steps of:

generating pilot symbols for transmission from a first transmitting entity on a first set of subbands that is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity; and

processing the pilot symbols to obtain time-domain samples having the pilot symbols included in the first set of subbands.

13. A method of processing pilots received via a downlink in a wireless multi-carrier communication system, comprising:

receiving a first pilot signal on a first set of subbands from a first transmitting entity, wherein the first set of subbands is used for pilot transmission by the first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity; and

processing the first pilot signal to obtain a pilot estimate for each of the subbands in the first set.

14. The method of claim 13, further comprising:

deriving a channel estimate for each of the subbands in the first set based on the pilot estimate for the subband.

15. The method of claim 14, further comprising:

deriving a channel estimate for at least one subband not in the first set based on channel estimates for the subbands in the first set.

16. The method of claim 13, further comprising:

deriving a signal strength estimate for the first pilot signal based on pilot estimates for the first set of subbands.

17. The method of claim 13, further comprising:

receiving a second pilot signal on the second set of subbands from the second transmitting entity; and

processing the second pilot signal to obtain a pilot estimate for each of the subbands in the second set.

18. The method of claim 17, further comprising:

deriving a channel estimate for each of the subbands in the second set based on the pilot estimate for the subband.

19. An apparatus in a wireless multi-carrier communication system, comprising:

means for receiving a first pilot signal on a first set of subbands from a first transmitting entity, wherein the first set of subbands is used for pilot transmission by the first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity; and

means for processing the first pilot signal to obtain a pilot estimate for each of the subbands in the first set.

20. The apparatus of claim 19, further comprising:

means for deriving a channel estimate for each of the subbands in the first set based on the pilot estimate for the subband.

21. The apparatus of claim 19, further comprising:

means for receiving a second pilot signal on the second set of subbands from the second transmitting entity; and

means for processing the second pilot signal to obtain a pilot estimate for each of the subbands in the second set.

22. A terminal in a wireless multi-carrier communication system, comprising:

a receiver unit operative to process a pilot signal received on a first set of subbands, wherein the first set of subbands is used for pilot transmission by a first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity; and

at least one pilot processor operative to process the pilot signal to obtain a pilot estimate for each of the subbands in the first set.

23. A computer-readable medium for processing pilots received via a downlink in a wireless multi-carrier communication system, the computer-readable medium comprising instructions which, when executed by a processor, cause said processor to perform the steps of:

receiving a first pilot signal on a first set of subbands from a first transmitting entity, wherein the first set of subbands is used for pilot transmission by the first transmitting entity and is disjoint from a second set of subbands used for pilot transmission by a second transmitting entity; and

processing the first pilot signal to obtain a pilot estimate for each of the subbands in the first set.

24. A method of transmitting a pilot in a wireless multi-carrier communication system, comprising:

generating pilot symbols for transmission on a first set of subbands used for pilot transmission by a first transmitting entity;

processing the pilot symbols with a first code to obtain covered pilot symbols, wherein the first code is orthogonal to a second code used for pilot transmission by a second transmitting entity;

processing the covered pilot symbols to obtain a pilot signal having the pilot symbols included in the first set of subbands; and

transmitting the pilot signal from the first transmitting entity.

25. The method of claim 24, wherein the first code is a Walsh code.

26. The method of claim 24, wherein the first code is applied to each of the subbands in the first set.

27. The method of claim 24, further comprising:

processing the covered pilot symbols with a scrambling code to obtain scrambled pilot symbols, and wherein the scrambled pilot symbols are further processed to obtain the pilot signal.

28. The method of claim 27, wherein the scrambling code is a pseudo-random number (PN) code.

29. The method of claim 27, wherein the first code includes N_W chips, and wherein each chip of the scrambling code is applied to N_W pilot symbols.

30. The method of claim 27, wherein the scrambling code is divided into a plurality of scrambling code segments, one scrambling code segment for each of the subbands in the first set, and wherein pilot symbols for each of the subbands in the first set are multiplied with the scrambling code segment for the subband.

31. The method of claim 27, wherein each chip of the scrambling code is applied to one pilot symbol.

32. The method of claim 24, wherein the subbands in the first set are evenly distributed across a plurality of subbands usable for pilot and data transmission by the first transmitting entity.

33. The method of claim 24, wherein each pair of adjacent subbands in the first set encompasses a frequency span that is less than or equal to a coherence bandwidth of a wireless channel in the system.

34. The method of claim 24, wherein the pilot symbols transmitted from the first transmitting entity are different from pilot symbols transmitted from the second transmitting entity.

35. The method of claim 24, wherein the first set of subbands is disjoint from a second set of subbands used for pilot transmission by a third transmitting entity.

36. The method of claim 35, wherein pilot signals are transmitted in bursts from the first and second transmitting entities.

37. The method of claim 35, wherein pilot signals are transmitted continuously from the first and second transmitting entities.

38. The method of claim 24, wherein pilot signals are transmitted with synchronous timing from the first and second transmitting entities.

39. The method of claim 24, wherein pilot signals are transmitted with asynchronous timing from the first and second transmitting entities.

40. The method of claim 24, wherein the multi-carrier communication system implements orthogonal frequency division multiplexing (OFDM).

41. An apparatus in a wireless multi-carrier communication system, comprising:

means for generating pilot symbols for transmission on a set of subbands used for pilot transmission by a first transmitting entity;

means for processing the pilot symbols with a first code to obtain covered pilot symbols, wherein the first code is orthogonal to a second code used for pilot transmission by a second transmitting entity;

means for processing the covered pilot symbols to obtain a pilot signal having the pilot symbols included in the set of subbands; and

means for transmitting the pilot signal from the first transmitting entity.

42. The apparatus of claim 41, further comprising:

means for processing the pilot symbols with a scrambling code to obtain the scrambled pilot symbols, and wherein scrambled pilot symbols are processed to obtain the pilot signal.

43. A base station in a wireless multi-carrier communication system, comprising:

at least one pilot processor operative to receive and process pilot symbols with a first code to obtain covered pilot symbols, wherein the pilot symbols are designated for transmission on a set of subbands used for pilot transmission by the base station, and wherein the first code is orthogonal to a second code used for pilot transmission by another base station in the system;

a transform unit operative to derive time-domain samples having the covered pilot symbols included in the set of subbands; and

a transmitter unit operative to process the time-domain samples to obtain a pilot signal for transmission over a wireless link.

44. A computer-readable medium for transmitting a pilot in a wireless multi-carrier communication system, the computer-readable medium comprising instructions which, when executed by a processor, cause said processor to perform the steps of:

generating pilot symbols for transmission on a first set of subbands used for pilot transmission by a first transmitting entity;

processing the pilot symbols with a first code to obtain covered pilot symbols, wherein the first code is orthogonal to a second code used for pilot transmission by a second transmitting entity; and

processing the covered pilot symbols to obtain a pilot signal having the pilot symbols included in the first set of subbands.

45. A method of processing pilots received via a wireless link in a wireless multi-carrier communication system, comprising:

receiving a first pilot signal on a first set of subbands used for pilot transmission by a first transmitting entity;

processing the first pilot signal with a first code to obtain decovered symbols for the first transmitting entity, wherein the first code is used for pilot transmission by the first transmitting entity and is orthogonal to a second code used for pilot transmission by a second transmitting entity; and

processing the decovered symbols for the first transmitting entity to obtain a pilot estimate for each of the subbands in the first set.

46. The method of claim 45, further comprising:

deriving a channel estimate for each of the subbands in the first set based on the pilot estimate for the subband.

47. The method of claim 46, further comprising:

deriving a channel estimate for at least one subband not in the first set based on channel estimates for the subbands in the first set.

48. The method of claim 45, further comprising:

deriving a signal strength estimate for the first pilot signal based on pilot estimates for the subbands in the first set.

49. The method of claim 45, further comprising:

processing the decovered symbols for the first transmitting entity with a descrambling code for the first transmitting entity.

50. The method of claim 45, further comprising:

receiving a second pilot signal on a second set of subbands used for pilot transmission by the second transmitting entity;

processing the second pilot signal with the second code to obtain decovered symbols for the second transmitting entity; and

processing the decovered symbols for the second transmitting entity to obtain a pilot estimate for each of the subbands in the second set.

51. An apparatus in a wireless multi-carrier communication system, comprising:

means for receiving a pilot signal on a set of subbands used for pilot transmission by a first transmitting entity;

means for processing the pilot signal with a first code to obtain decovered symbols, wherein the first code is used for pilot transmission by the first transmitting entity and is orthogonal to a second code used for pilot transmission by a second transmitting entity; and

means for processing the decovered symbols to obtain a pilot estimate for each of the subbands in the set.

52. A terminal in a wireless multi-carrier communication system, comprising:

a receiver unit operative to process a pilot signal received on a set of subbands used for pilot transmission by a first transmitting entity; and

at least one pilot processor operative to process the pilot signal with a first code to obtain decovered symbols and to process the decovered symbols to obtain a pilot estimate for each of the subbands in the set, wherein the first code is used for pilot transmission by the first transmitting entity and is orthogonal to a second code used for pilot transmission by a second transmitting entity.

53. A computer-readable medium for processing pilots received via a wireless link in a wireless multi-carrier communication system, the computer-readable medium comprising instructions which, when executed by a processor, cause said processor to perform the steps of:

receiving a first pilot signal on a first set of subbands used for pilot transmission by a first transmitting entity;

processing the first pilot signal with a first code to obtain decovered symbols for the first transmitting entity, wherein the first code is used for pilot transmission by the first transmitting entity and is orthogonal to a second code used for pilot transmission by a second transmitting entity; and

processing the decovered symbols for the first transmitting entity to obtain a pilot estimate for each of the subbands in the first set.

54. A method of canceling pilot interference at a receiver in a wireless multi-carrier communication system, comprising:

obtaining received symbols for a plurality of subbands, wherein the received symbols include desired symbols received from a first transmitting entity and pilot symbols received from a second transmitting entity;

deriving pilot symbol estimates for the second transmitting entity based on the received symbols, wherein the pilot symbol estimates are estimates of pilot symbols received on the plurality of subbands from the second transmitting entity; and

subtracting the pilot symbol estimates for the second transmitting entity from the received symbols to obtain pilot-canceled symbols.

55. The method of claim 54, wherein the deriving and subtracting are performed separately for each of the plurality of subband.

56. The method of claim 54, wherein the deriving includes

obtaining channel estimates for the second transmitting entity, and wherein the pilot symbol estimates are derived using the channel estimates.

57. The method of claim 54, wherein the desired symbols for the first transmitting entity are pilot symbols.

58. The method of claim 54, wherein the desired symbols for the first transmitting entity are data symbols.

59. The method of claim 54, wherein the deriving includes

multiplying pilot symbols for each of the plurality of subbands with an orthogonal code to obtain covered pilot symbols for the subband, wherein the orthogonal code is used by the second transmitting entity for pilot transmission, and

multiplying the covered pilot symbols for each of the plurality of subbands with channel estimates for the subband to obtain pilot symbol estimates for the subband.

60. The method of claim 59, wherein the deriving further includes

multiplying the pilot symbols for each of the plurality of subbands with chips from a scrambling code to obtain scrambled pilot symbols for the subband, and wherein the scrambled pilot symbols are multiplied with the orthogonal code to obtain the covered pilot symbols.

61. The method of claim 54, wherein the received symbols further include pilot symbols received from a third transmitting entity, the method further comprising:

deriving pilot symbol estimates for the third transmitting entity based on the received symbols; and

subtracting the pilot symbol estimates for the third transmitting entity from the received symbols to obtain the pilot-canceled symbols.

62. An apparatus in a wireless multi-carrier communication system, comprising:

means for obtaining received symbols for a plurality of subbands, wherein the received symbols include desired symbols received from a first transmitting entity and pilot symbols received from a second transmitting entity;

means for deriving pilot symbol estimates for the second transmitting entity based on the received symbols, wherein the pilot symbol estimates are estimates of pilot symbols received on the plurality of subbands from the second transmitting entity; and

means for subtracting the pilot symbol estimates for the second transmitting entity from the received symbols to obtain pilot-canceled symbols.

63. A terminal in a wireless multi-carrier communication system, comprising:

at least one pilot interference estimator operative to process received symbols for a plurality of subbands to obtain pilot symbol estimates for the plurality of subbands, wherein the received symbols include desired symbols received from a first transmitting entity and pilot symbols received from a second transmitting entity, and wherein the pilot symbol estimates are estimates of pilot symbols received on the plurality of subbands from the second transmitting entity; and

a summer operative to subtract the pilot symbol estimates from the received symbols to obtain pilot-canceled symbols.