Pilots for MIMO communication systems

• US 20040179627A1
• Filed: 06/30/2003
• Published: 09/16/2004
• Est. Priority Date: 10/25/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Howard, Steven J., Ketchum, John W., Walton, J. Rodney, Wallace, Mark S.
• Granted Patent: US 7,986,742 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0421 utilizing implicit feedback, e.g. steered pilot signals
• CPC Class Codes: H04B 7/043 using best eigenmode, e.g. beam forming or beam steering
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• 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 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• 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 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 2027/0089 In-band signals
• CPC Class Codes: H04L 25/0204 of multiple channels
• 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 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 5/0023 : Time-frequency-space
• CPC Class Codes: H04L 5/0026 : Division using four or more dimensions
• CPC Class Codes: H04L 5/0048 : Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/005 : of common pilots, i.e. pilots destined for multiple users or terminals
• CPC Class Codes: H04L 5/006 : Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04W 16/28 : using beam steering
• CPC Class Codes: H04W 28/20 : Negotiating bandwidth
• CPC Class Codes: H04W 52/50 : at the moment of starting communication in a multiple access environment

Abstract

Pilots suitable for use in MIMO systems and capable of supporting various functions are described. The various types of pilot include—a beacon pilot, a MIMO pilot, a steered reference or steered pilot, and a carrier pilot. The beacon pilot is transmitted from all transmit antennas and may be used for timing and frequency acquisition. The MIMO pilot is transmitted from all transmit antennas but is covered with different orthogonal codes assigned to the transmit antennas. The MIMO pilot may be used for channel estimation. The steered reference is transmitted on specific eigenmodes of a MIMO channel and is user terminal specific. The steered reference may be used for channel estimation. The carrier pilot may be transmitted on designated subbands/antennas and may be used for phase tracking of a carrier signal. Various pilot transmission schemes may be devised based on different combinations of these various types of pilot.

Claims

1. A method of generating pilots in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

obtaining a pilot symbol for each antenna in a plurality of antennas;

obtaining an orthogonal sequence for each antenna in the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences; and

covering the pilot symbol for each antenna with the orthogonal sequence for the antenna to obtain a sequence of covered pilot symbols for the antenna, wherein a plurality of sequences of covered pilot symbols for a plurality of orthogonal pilots are obtained for the plurality of antennas.

2. The method of claim 1, further comprising:

transmitting the plurality of orthogonal pilots from the plurality of antennas.

3. The method of claim 1, wherein the orthogonal sequences are Walsh sequences.

4. The method of claim 1, wherein one pilot symbol is obtained and used for the plurality of antennas.

5. The method of claim 1, wherein a set of pilot symbols is obtained for each antenna and designated for transmission on a set of subbands.

6. The method of claim 5, wherein the pilot symbols in the set are selected to have small peak-to-average variation in a waveform generated based on the pilot symbols.

7. An apparatus in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

means for obtaining a pilot symbol for each antenna in a plurality of antennas;

means for obtaining an orthogonal sequence for each antenna in the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences; and

means for covering the pilot symbol for each antenna with the orthogonal sequence for the antenna to obtain a sequence of covered pilot symbols for the antenna, wherein a plurality of sequences of covered pilot symbols for a plurality of orthogonal pilots are obtained for the plurality of antennas.

8. The apparatus of claim 7, further comprising:

means for transmitting the plurality of orthogonal pilots from the plurality of antennas.

9. In a wireless multiple-input multiple-output (MIMO) communication system utilizing orthogonal frequency division multiplexing (OFDM), a method of generating a MIMO pilot comprised of a plurality of orthogonal pilots suitable for transmission from a plurality of antennas, the method comprising:

obtaining a set of pilot symbols for each antenna in the plurality of antennas, wherein the set of pilot symbols is designated for transmission on a set of subbands;

obtaining an orthogonal sequence for each antenna in the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences; and

covering the set of pilot symbols for each antenna with the orthogonal sequence for the antenna to obtain a set of sequences of covered pilot symbols for the antenna; and

processing the set of sequences of covered pilot symbols for each antenna to obtain a sequence of OFDM symbols for the antenna, wherein a plurality of sequences of OFDM symbols for the plurality of orthogonal pilots are obtained for the plurality of antennas.

10. The method of claim 9, wherein the pilot symbols in the set are selected to have small peak-to-average variation in a waveform generated based on the pilot symbols.

11. The method of claim 9, wherein one set of pilot symbols is obtained and used for the plurality of antennas.

12. In a wireless multiple-input multiple-output (MIMO) communication system, a method of receiving a MIMO pilot comprised of a set of orthogonal pilots transmitted from a set of transmit antennas, the method comprising:

obtaining a first set of sequences of symbols from a set of receive antennas, one sequence of symbols for each of the receive antennas, wherein the first set of sequences of symbols is for the MIMO pilot, and wherein the set of orthogonal pilots for the MIMO pilot is generated based on a pilot symbol and a set of orthogonal sequences assigned to the set of transmit antennas, one orthogonal pilot for each of the transmit antennas;

processing each of the sequences of symbols in the first set with the pilot symbol to obtain a corresponding sequence of symbols in a second set; and

decovering each sequence of symbols in the second set with the set of orthogonal sequences to obtain channel response estimates between the set of transmit antennas and a receive antenna associated with the sequence of symbols in the second set.

13. The method of claim 12, wherein the channel response estimates for each receive antenna include a channel gain estimate for each of the transmit antennas and the receive antenna.

14. The method of claim 12, further comprising:

averaging the channel response estimates over a plurality of frames in which the MIMO pilot is received.

15. A method of generating a steered pilot in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

obtaining a first pilot symbol to be transmitted from a plurality of antennas;

obtaining a first steering vector for a first spatial channel of a MIMO channel in the MIMO system; and

processing the first pilot symbol with the first steering vector to obtain a first group of transmit symbols, one transmit symbol for each of the plurality of antennas, wherein the first group of transmit symbols is for the steered pilot for the first spatial channel.

16. The method of claim 15, further comprising:

obtaining a second pilot symbol to be transmitted from the plurality of antennas;

obtaining a second steering vector for a second spatial channel of the MIMO channel; and

processing the second pilot symbol with the second steering vector to obtain a second group of transmit symbols for the steered pilot for the second spatial channel.

17. The method of claim 16, further comprising:

transmitting the first group of transmit symbols from the plurality of antennas in a first symbol period; and

transmitting the second group of transmit symbols from the plurality of antennas in a second symbol period.

18. The method of claim 16, further comprising:

transmitting the first group of transmit symbols from the plurality of antennas on a first subband; and

transmitting the second group of transmit symbols from the plurality of antennas on a second subband.

19. The method of claim 18, wherein the first and second groups of transmit symbols are transmitted in one symbol period.

20. The method of claim 16, wherein the first and second steering vectors are associated with first and second eigenmodes, respectively, of a channel response matrix for the MIMO channel, and wherein the first and second spatial channels correspond to the first and second eigenmodes, respectively.

21. The method of claim 16, wherein the first and second steering vectors are orthogonal to one another.

22. The method of claim 15, wherein the first steering vector is obtained based on an eigenvector in a unitary matrix for a channel response matrix for the MIMO channel.

23. The method of claim 15, wherein the first steering vector includes a plurality of elements having equal magnitude, one element for each of the plurality of antennas.

24. The method of claim 15, wherein the first steering vector is associated with a principal eigenmode of a channel response matrix for the MIMO channel.

25. An apparatus in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

means for obtaining a first pilot symbol to be transmitted from a plurality of antennas;

means for obtaining a first steering vector for a first spatial channel of a MIMO channel in the MIMO system; and

means for processing the first pilot symbol with the first steering vector to obtain a first group of transmit symbols, one transmit symbol for each of the plurality of antennas, wherein the first group of transmit symbols is for a steered pilot for the first spatial channel.

26. The apparatus of claim 25, further comprising:

means for obtaining a second pilot symbol to be transmitted from the plurality of antennas; and

means for obtaining a second steering vector for a second spatial channel of the MIMO channel; and

means for processing the second pilot symbol with the second steering vector to obtain a second group of transmit symbols for a steered pilot for the second spatial channel.

27. A method of generating a steered pilot in a wireless multiple-input multiple-output (MIMO) communication system utilizing orthogonal frequency division multiplexing (OFDM), the method comprising:

obtaining a first set of pilot symbols to be transmitted from a plurality of antennas on a first set of subbands;

obtaining a first set of steering vectors for a first spatial channel of the first set of subbands; and

processing the first set of pilot symbols with the first set of steering vectors to obtain a first set of symbol vectors, one symbol vector in the first set of symbol vectors for each subband in the first set of subbands, wherein each symbol vector in the first set of symbol vectors includes a plurality of transmit symbols for the plurality of antennas and corresponds to the steered pilot for the first spatial channel of the subband associated with the symbol vector.

28. The method of claim 27, further comprising:

obtaining a second set of steering vectors for a second spatial channel of the first set of subbands; and

processing the first set of pilot symbols with the second set of steering vectors to obtain a second set of symbol vectors, wherein each symbol vector in the second set of symbol vectors corresponds to a steered pilot for the second spatial channel of the subband associated with the symbol vector.

29. The method of claim 28, further comprising:

transmitting the first set of symbol vectors from the plurality of antennas on the first set of subbands in a first symbol period; and

transmitting the second set of symbol vectors from the plurality of antennas on the first set of subbands in a second symbol period.

30. The method of claim 27, further comprising:

obtaining a second set of pilot symbols to be transmitted from the plurality of antennas on a second set of subbands;

obtaining a second set of steering vectors for a first spatial channel of the second set of subbands; and

processing the second set of pilot symbols with the second set of steering vectors to obtain a second set of symbol vectors, one symbol vector in the second set of symbol vectors for each subband in the second set of subbands, wherein each symbol vector in the second set of symbol vectors corresponds to a steered pilot for the first spatial channel of the subband associated with the symbol vector.

31. The method of claim 30, further comprising:

transmitting the first set of symbol vectors from the plurality of antennas on the first set of subbands; and

transmitting the second set of symbol vectors from the plurality of antennas on the second set of subbands.

32. The method of claim 31, wherein the first set of symbol vectors and the second set of symbol vectors are transmitted in one symbol period.

33. The method of claim 27, wherein the pilot symbols in the first set are selected to have small peak-to-average variation in a waveform generated based on the pilot symbols.

34. A method of receiving a steered pilot in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

receiving a first group of symbols from a plurality of antennas for a first steered pilot received via a first spatial channel of a MIMO channel in the MIMO system, wherein the first steered pilot is generated based on a pilot symbol and a first steering vector for the first spatial channel;

processing the first group of symbols with the pilot symbol to obtain a second group of symbols;

determining a first scaling factor based on an estimated power of the symbols in the first group; and

scaling the symbols in the second group with the first scaling factor to obtain a second steering vector for the first spatial channel.

35. The method of claim 34, wherein the first steered pilot is transmitted in a plurality of symbol periods, the method further comprising:

accumulating the symbols in the second group for the plurality of symbol periods.

36. The method of claim 34, further comprising:

deriving a matched filter for the first spatial channel based on the second steering vector.

37. The method of claim 34, wherein the second steering vector is used for spatial processing of a data transmission sent via the MIMO channel.

38. The method of claim 34, further comprising:

deriving a time-domain matched filter for the first spatial channel based on the second steering vector for the first spatial channel.

39. The method of claim 38, wherein the time-domain matched filter comprises a matched filter pulse for each of the plurality of antennas.

40. The method of claim 34, further comprising:

receiving a third group of symbols from the plurality of antennas for a second steered pilot received via a second spatial channel of the MIMO channel, wherein the second steered pilot is generated based on the pilot symbol and a first steering vector for the second spatial channel;

processing the third group of symbols with the pilot symbol to obtain a fourth group of symbols;

determining a second scaling factor based on an estimated power of the symbols in the third group; and

scaling the symbols in the fourth group with the second scaling factor to obtain a second steering vector for the second spatial channel.

41. A method for processing pilots at a first entity in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

generating a plurality of orthogonal pilots for a MIMO pilot based on a first pilot symbol and a plurality of orthogonal sequences for a plurality of antennas, wherein the plurality of orthogonal pilots are designated for transmission from the plurality of antennas on a first link; and

processing a steered pilot received from a second entity via a spatial channel on a second link, wherein the steered pilot is generated based on a second pilot symbol and a steering vector for the spatial channel, and wherein the steering vector is obtained based on the MIMO pilot.

42. The method of claim 41, wherein the first link is a downlink and the second link is an uplink in the MIMO system.

43. The method of claim 41, wherein the first and second links are time division duplexed on a single frequency band.

44. The method of claim 43, wherein the first and second links are calibrated and the first link is estimated to be reciprocal of the second link.

45. The method of claim 41, further comprising:

generating a beacon pilot based on a third pilot symbol, wherein the beacon pilot comprises a common pilot suitable for transmission from each of the plurality of antennas on the first link.

46. The method of claim 41, further comprising:

generating a carrier pilot suitable for transmission on the first link and used for phase tracking by the second entity.

47. The method of claim 41, wherein the generating the MIMO pilot includes

obtaining the plurality of orthogonal sequences for the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences, and

covering the first pilot symbol with each of the plurality of orthogonal sequences to obtain a respective one of the plurality of orthogonal pilots.

48. The method of claim 47, wherein the plurality of orthogonal sequences are Walsh sequences.

49. The method of claim 41, wherein the steered pilot received from the second entity is processed to obtain an estimate of at least one steering vector for the first link.

50. The method of claim 41, wherein the MIMO system utilizes orthogonal frequency division multiplexing (OFDM).

51. The method of claim 50, wherein the MIMO pilot is transmitted on a plurality of subbands.

52. The method of claim 50, wherein the steered pilot is received on a plurality of subbands.

53. A method of processing pilots at a first entity in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

generating a beacon pilot based on a first pilot symbol, wherein the beacon pilot comprises a common pilot suitable for transmission from each of a plurality of antennas on a downlink in the MIMO system;

generating a plurality of orthogonal pilots for a MIMO pilot based on a second pilot symbol and a plurality of orthogonal sequences for the plurality of antennas, wherein the plurality of orthogonal pilots are designated for transmission from the plurality of antennas on the downlink; and

processing a steered pilot received from a second entity via a spatial channel on an uplink in the MIMO system, wherein the steered pilot is generated based on a third pilot symbol and a steering vector for the spatial channel, and wherein the steering vector is obtained based on the MIMO pilot.

54. The method of claim 53, wherein the steered pilot received from the second entity is processed to obtain an estimate of at least one steering vector for the downlink.

55. The method of claim 53, wherein the MIMO system utilizes orthogonal frequency division multiplexing (OFDM), wherein the beacon pilot is generated based on a first set of pilot symbols and transmitted on a first set of subbands, and wherein the MIMO pilot is generated based on a second set of pilot symbols and transmitted on a second set of subbands.

56. A method of generating a steered pilot in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

estimating a channel response of a first link in the MIMO system;

obtaining a set of steering vectors for a second link in the MIMO system based on the estimated channel response of the first link; and

generating a steered pilot for a spatial channel of the second link based on a steering vector in the set of steering vectors.

57. The method of claim 56, further comprising:

transmitting the steered pilot on the second link.

58. The method of claim 56, further comprising:

receiving a MIMO pilot on the first link, wherein the MIMO pilot comprises a plurality of orthogonal pilots generated based on a plurality of orthogonal sequences and transmitted on the first link via a plurality of antennas, and wherein the channel response of the first link is estimated based on the received MIMO pilot.

59. The method of claim 56, wherein the set of steering vectors for the second link is obtained by performing decomposition of a channel response matrix for the estimated channel response of the first link.

60. The method of claim 56, wherein the first link is a downlink and the second link is an uplink in the MIMO system.

61. The method of claim 56, wherein the generating includes performing beam-forming on a pilot symbol with both amplitude and phase information for the steering vector to generate the steered pilot.

62. The method of claim 56, wherein the generating includes

performing beam-steering on a pilot symbol with phase information for the steering vector to generate the steered pilot.

63. An access point in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

a transmit spatial processor operative to generate a plurality of orthogonal pilots for a MIMO pilot based on a first pilot symbol and a plurality of orthogonal sequences for a plurality of antennas, wherein the plurality of orthogonal pilots are designated for transmission from the plurality of antennas on a downlink in the MIMO system; and

a receive spatial processor operative to process a steered pilot received from a terminal via a spatial channel on an uplink in the MIMO system, wherein the steered pilot is generated by the terminal based on a second pilot symbol and a steering vector for the spatial channel, and wherein the steering vector is obtained by the terminal based on the MIMO pilot received via the downlink.

64. The access point of claim 63, wherein the transmit spatial processor is further operative to generate a beacon pilot based on a third pilot symbol, wherein the beacon pilot comprises a common pilot suitable for transmission from each of the plurality of antennas on the downlink.

65. The access point of claim 63, wherein the plurality of orthogonal sequences are Walsh sequences.

66. The access point of claim 63, wherein the MIMO system utilizes orthogonal frequency division multiplexing (OFDM), wherein the MIMO pilot is generated for a first set of subbands, and wherein the steered pilot is received on a second set of subbands.

67. A terminal in a wireless multiple-input multiple-output (MIMO) communication system, comprising:

a receive spatial processor operative to process a MIMO pilot received from an access point on a downlink in the MIMO system to obtain channel response estimates for the downlink, wherein the MIMO pilot comprises a plurality of orthogonal pilots generated based on a pilot symbol and a plurality of orthogonal sequences assigned to a plurality of antennas at the access point, one orthogonal pilot for each of the plurality of antennas; and

a transmit spatial processor operative to generate a steered pilot based on a second pilot symbol and a steering vector for a spatial channel on an uplink in the MIMO system.

68. The terminal of claim 67, further comprising:

a controller operative to derive the steering vector for the spatial channel on the uplink based on the channel response estimates obtained for the downlink.

69. The terminal of claim 68, wherein the controller is operative to perform decomposition of a channel response matrix for the channel response estimates for the downlink to derive the steering vector for the spatial channel on the uplink.

70. The terminal of claim 67, wherein the MIMO system utilizes orthogonal frequency division multiplexing (OFDM), wherein the channel response estimates are obtained for each of a first plurality of subbands based on the MIMO pilot received on the subband, and wherein the steered pilot is generated for each of a second plurality of subbands.