Pilot transmission and channel estimation for MISO and MIMO receivers in a multi-antenna system

• US 20050195763A1
• Filed: 12/22/2004
• Published: 09/08/2005
• Est. Priority Date: 03/05/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gore, Dhananjay Ashok, Agrawal, Avneesh, Kadous, Tamer
• Granted Patent: US 8,077,691 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04L 25/0226 sounding signals per se

Abstract

A transmitter generates multiple composite pilots with a training matrix and a gain matrix. Each composite pilot includes multiple training pilots generated with multiple columns of the training matrix and scaled with multiple gain elements in a column of the gain matrix. The transmitter transmits each composite pilot via multiple transmit antennas. A MISO receiver obtains received symbols for the multiple composite pilots and derives an estimate of a composite MISO channel. For OFDM, the MISO receiver derives an initial impulse response estimate for each composite pilot, filters the initial impulse response estimates for all composite pilots, and derives a frequency response estimate for the composite MISO channel. A MIMO receiver obtains and processes received symbols for the multiple composite pilots based on the training and gain matrices and derives channel estimates for individual SISO channels between the multiple transmit antennas and multiple receive antennas.

Claims

1. A method of transmitting a pilot in a wireless communication system, comprising:

generating a plurality of composite pilots with a first matrix and a second matrix, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of the first matrix and scaled with a plurality of gain elements in a column of the second matrix; and

transmitting each of the plurality of composite pilots via a plurality of transmit antennas.

2. The method of claim 1, wherein the generating the plurality of composite pilots comprises, for each composite pilot,

generating the plurality of training pilots with the plurality of columns of the first matrix,

scaling the plurality of training pilots with the plurality of gain elements in one column of the second matrix, and

combining the plurality of scaled training pilots to generate the composite pilot.

3. The method of claim 1, wherein the generating the plurality of composite pilots comprises

generating the plurality of composite pilots such that, for each composite pilot, one training pilot among the plurality of training pilots is transmitted at unit power and each remaining training pilot is transmitted at less than unit power.

4. The method of claim 1, further comprising:

forming the first matrix with an orthonormal matrix having a plurality of orthogonal columns.

5. The method of claim 1, further comprising:

forming the first matrix with a Walsh matrix or a Fourier matrix.

6. The method of claim 1, further comprising:

forming the second matrix based on a gain value and an orthonormal matrix having a plurality of orthogonal columns.

7. The method of claim 1, further comprising:

forming the second matrix based on a gain value and a Walsh matrix or a Fourier matrix.

8. The method of claim 1, further comprising:

delaying pilot transmission from each of the plurality of transmit antennas by a delay selected for the transmit antenna.

9. The method of claim 1, wherein the generating the plurality of composite pilots comprises

generating the plurality of composite pilots with the first matrix, the second matrix, and a plurality of third matrices for a plurality of frequency subbands, the plurality of third matrices providing diversity for the plurality of composite pilots.

10. The method of claim 1, wherein the transmitting each of the plurality of composite pilots comprises

transmitting each composite pilot in a different symbol period and via the plurality of transmit antennas.

11. The method of claim 1, wherein the transmitting each of the plurality of composite pilots comprises

transmitting each composite pilot on a plurality of frequency subbands and via the plurality of transmit antennas.

12. A method of transmitting a pilot in a wireless communication system, comprising:

generating a first composite pilot with a training matrix and a first gain vector, the first composite pilot comprising a plurality of training pilots generated with a plurality of columns of the training matrix and scaled with a plurality of gain elements in the first gain vector;

selectively generating at least one additional composite pilot with the training matrix and at least one additional gain vector; and

transmitting the first composite pilot and the at least one additional composite pilot, if generated, via a plurality of transmit antennas.

13. The method of claim 12, wherein the selectively generating at least one additional composite pilot comprises

generating the at least one additional composite pilot if at least one receiver with multiple antennas is receiving the pilot.

14. An apparatus in a wireless communication system, comprising:

a pilot generator operative to generate a plurality of composite pilots with a first matrix and a second matrix, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of the first matrix and scaled with a plurality of gain elements in a column of the second matrix; and

a plurality of transmitter units operative to transmit each of the plurality of composite pilots via a plurality of transmit antennas.

15. The apparatus of claim 14, wherein for each composite pilot the pilot generator is operative to generate the plurality of training pilots with the plurality of columns of the first matrix, to scale the plurality of training pilots with the plurality of gain elements in one column of the second matrix, and to combine the plurality of scaled training pilots to generate the composite pilot.

16. The apparatus of claim 14, wherein the pilot generator is operative to generate the plurality of composite pilots such that, for each composite pilot, one training pilot among the plurality of training pilots is transmitted at unit power and each remaining training pilot is transmitted at less than unit power.

17. The apparatus of claim 14, wherein the plurality of transmitter units are operative to delay pilot transmission from each of the plurality of transmit antennas by a delay selected for the transmit antenna.

18. The apparatus of claim 14, wherein the first and second matrices are each formed based on an orthonormal matrix having a plurality of orthogonal columns.

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

means for generating a plurality of composite pilots with a first matrix and a second matrix, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of the first matrix and scaled with a plurality of gain elements in a column of the second matrix; and

means for transmitting each of the plurality of composite pilots via a plurality of transmit antennas.

20. The apparatus of claim 19, wherein the means for generating the plurality of composite pilots comprises, for each composite pilot,

means for generating the plurality of training pilots with the plurality of columns of the first matrix,

means for scaling the plurality of training pilots with the plurality of gain elements in one column of the second matrix, and

means for combining the plurality of scaled training pilots to generate the composite pilot.

21. The apparatus of claim 19, wherein the means for generating the plurality of composite pilots comprises,

means for generating the plurality of composite pilots such that, for each composite pilot, one training pilot among the plurality of training pilots is transmitted at unit power and each remaining training pilot is transmitted at less than unit power.

22. A method of performing channel estimation in a wireless communication system, comprising:

obtaining, via a single receive antenna, received symbols for a plurality of composite pilots transmitted via a plurality of transmit antennas, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

processing the received symbols to obtain an estimate of a multiple-input single-output (MISO) channel between the plurality of transmit antennas and the single receive antenna.

23. The method of claim 22, wherein the processing the received symbols comprises

filtering the received symbols to obtain the estimate of the MISO channel.

24. The method of claim 22, wherein the processing the received symbols comprises

deriving a plurality of initial impulse response estimates for the plurality of composite pilots based on the received symbols, and

filtering the plurality of initial impulse response estimates to obtain an impulse response estimate for the MISO channel.

25. The method of claim 24, wherein the processing the received symbols further comprises

retaining first L channel taps in the impulse response estimate for the MISO channel, where L is an integer greater than one, and

setting remaining channel taps in the impulse response estimate for the MISO channel to zeros.

26. The method of claim 24, wherein the processing the received symbols further comprises

setting channel taps in the impulse response estimate for the MISO channel with magnitudes below a predetermined threshold to zeros.

27. The method of claim 24, wherein the processing the received symbols further comprises

deriving a frequency response estimate for the MISO channel based on the impulse response estimate for the MISO channel.

28. An apparatus in a wireless communication system, comprising:

a receiver unit operative to provide received symbols for a plurality of composite pilots transmitted from a plurality of transmit antennas to a single receive antenna, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

a channel estimator operative to process the received symbols to obtain an estimate of a multiple-input single-output (MISO) channel between the plurality of transmit antennas and the single receive antenna.

29. The apparatus of claim 28, wherein the channel estimator is operative to filter the received symbols to obtain the estimate of the MISO channel.

30. The apparatus of claim 28, wherein the channel estimator is operative to derive a plurality of initial impulse response estimates for the plurality of composite pilots based on the received symbols and to filter the plurality of initial impulse response estimates to obtain an impulse response estimate for the MISO channel.

31. An apparatus in a wireless communication system, comprising:

means for obtaining, via a single receive antenna, received symbols for a plurality of composite pilots transmitted via a plurality of transmit antennas, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

means for processing the received symbols to obtain an estimate of a multiple-input single-output (MISO) channel between the plurality of transmit antennas and the single receive antenna.

32. The apparatus of claim 31, wherein the means for processing the received symbols comprises

means for filtering the received symbols to obtain the estimate of the MISO channel.

33. The apparatus of claim 31, wherein the means for processing the received symbols comprises

means for deriving a plurality of initial impulse response estimates for the plurality of composite pilots based on the received symbols, and

means for filtering the plurality of initial impulse response estimates to obtain an impulse response estimate for the MISO channel.

34. A method of performing channel estimation in a wireless communication system, comprising:

obtaining, via a plurality of receive antennas, received symbols for a plurality of composite pilots transmitted via a plurality of transmit antennas, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

processing the received symbols based on the first and second matrices to obtain estimates of a plurality of single-input single-output (SISO) channels between the plurality of transmit antennas and the plurality of receive antennas.

35. The method of claim 34, wherein the processing the received symbols comprises

performing matrix multiply on the received symbols based on the first and second matrices to obtain estimates of the plurality of SISO channels.

36. The method of claim 34, wherein the processing the received symbols comprises

deriving a plurality of initial impulse response estimates for a plurality of combinations of composite pilot and receive antenna based on the received symbols, and

processing the plurality of initial impulse response estimates based on the first and second matrices to obtain a plurality of intermediate impulse response estimates for the plurality of SISO channels.

37. The method of claim 36, wherein the processing the received symbols further comprises

retaining first L channel taps in each of the plurality of intermediate impulse response estimates, where L is an integer greater than one, and

setting remaining channel taps in each of the plurality of intermediate impulse response estimates to zeros.

38. The method of claim 36, wherein the processing the received symbols further comprises

setting channel taps in each of the plurality of intermediate impulse response estimates with magnitudes below a predetermined threshold to zeros.

39. The method of claim 36, wherein the processing the received symbols further comprises

delaying the plurality of intermediate impulse response estimates based on delays introduced at the plurality of transmit antennas.

40. The method of claim 36, wherein the processing the received symbols further comprises

deriving a plurality of frequency response estimates for the plurality of SISO channels based on the plurality of intermediate impulse response estimates.

41. The method of claim 34, wherein the processing the received symbols comprises

processing the received symbols based on the first and second matrices to obtain a plurality of initial frequency response estimates for the plurality of SISO channels,

deriving a plurality of impulse response estimates for the plurality of SISO pilots based on the plurality of initial frequency response estimates, and

deriving a plurality of final frequency response estimates for the plurality of SISO channels based on the plurality of impulse response estimates.

42. An apparatus in a wireless communication system, comprising:

a plurality of receiver units operative to provide received symbols for a plurality of composite pilots transmitted from a plurality of transmit antennas to a plurality of receive antennas, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

a channel estimator operative to process the received symbols based on the first and second matrices to obtain estimates of a plurality of single-input single-output (SISO) channels between the plurality of transmit antennas and the plurality of receive antennas.

43. The apparatus of claim 42, wherein the channel estimator is operative to perform matrix multiply on the received symbols based on the first and second matrices to obtain estimates of the plurality of SISO channels.

44. The apparatus of claim 42, wherein the channel estimator is operative to derive a plurality of initial impulse response estimates for a plurality of combinations of composite pilot and receive antenna based on the received symbols and to process the plurality of initial impulse response estimates based on the first and second matrices to obtain a plurality of intermediate impulse response estimates for the plurality of SISO channels.

45. An apparatus in a wireless communication system, comprising:

means for obtaining, via a plurality of receive antennas, received symbols for a plurality of composite pilots transmitted via a plurality of transmit antennas, each composite pilot comprising a plurality of training pilots generated with a plurality of columns of a first matrix and scaled with a plurality of gain elements in a column of a second matrix; and

means for processing the received symbols based on the first and second matrices to obtain estimates of a plurality of single-input single-output (SISO) channels between the plurality of transmit antennas and the plurality of receive antennas.

46. The apparatus of claim 45, wherein the means for processing the received symbols comprises

means for deriving a plurality of initial impulse response estimates for a plurality of combinations of composite pilot and receive antenna based on the received symbols, and

means for processing the plurality of initial impulse response estimates based on the first and second matrices to obtain a plurality of intermediate impulse response estimates for the plurality of SISO channels.