Pilot transmission schemes for a multi-antenna system

• US 7,145,940 B2
• Filed: 07/13/2004
• Issued: 12/05/2006
• Est. Priority Date: 12/05/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gore, Dhananjay Ashok, Agrawal, Avneesh, Kadous, Tamer
• Primary Examiner(s): Tran, Khai
• Application Number:
  US10/890,718
• Publication Number:
  US 20060034163A1
• Time in Patent Office: 875 Days
• Field of Search: 375/147, 375/267, 375/347, 375/316, 375/278, 370/204, 370/252, 370/235, 370/335, 370/267
• US Class Current: 375/147
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain

Abstract

Efficient pilot transmission schemes for multi-antenna communication systems are described. In general, MISO receivers prefer a pilot transmitted in one spatial direction, and MIMO receivers typically require a pilot transmitted in different spatial directions. In one pilot transmission scheme, a first set of T scaled pilot symbols is generated with a first training vector and transmitted (e.g., continuously) from T transmit antennas, where T>1. If MIMO receiver(s) are to be supported by the system, then at least T−1 additional sets of T scaled pilot symbols are generated with at least T−1 additional training vectors and transmitted from the T transmit antennas. The training vectors are for different (e.g., orthogonal) spatial directions. Each MISO receiver can estimate its MISO channel based on the first set of scaled pilot symbols. Each MIMO receiver can estimate its MIMO channel based on the first and additional sets of scaled pilot symbols.

Claims

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

generating a first set of T scaled pilot symbols with a first vector of T coefficients, where T is an integer greater than one, and wherein the first set of scaled pilot symbols is suitable for use for channel estimation by receivers with a single antenna;

selectively generating at least T−

1 additional sets of T scaled pilot symbols with at least T−

1 additional vectors if at least one receiver with multiple antennas is to be supported by the system, each additional vector including T coefficients, wherein the first and at least T−

1 additional vectors are different vectors in a matrix, and wherein the first and at least T−

1 additional sets of scaled pilot symbols are suitable for use for channel estimation by the at least one receiver with multiple antennas; and

transmitting each set of T scaled pilot symbols via T transmit antennas, one scaled pilot symbol on each transmit antenna.

2. The method of claim 1, wherein the first and at least T−

1 additional vectors are orthogonal to one another.

3. The method of claim 1, wherein T−

1 additional sets of T scaled pilot symbols are generated with T−

1 additional vectors.

4. The method of claim 3, wherein the first vector and T−

1 additional vectors are T vectors of a Walsh matrix.

5. The method of claim 1, wherein each set of T scaled pilot symbols is transmitted in one symbol period.

6. The method of claim 1, wherein the multi-antenna communication system utilizes orthogonal frequency division multiplexing (OFDM), and wherein each of the T scaled pilot symbols in each set is transmitted from a respective one of the T transmit antennas on a group of P subbands, where P is an integer greater than one.

7. The method of claim 6, wherein the P subbands are uniformly distributed across N total subbands and are spaced apart by N/P subbands.

8. The method of claim 6, wherein the first set of scaled pilot symbols is transmitted on a first group of subbands, and wherein the at least T−

1 additional sets of scaled pilot symbols are transmitted on a second group of subbands that is disjoint from the first group of subbands.

9. The method of claim 8, wherein the subbands in each of the first and second groups are uniformly distributed across N total subbands.

10. The method of claim 8, wherein the first set of scaled pilot symbols is transmitted continuously on the first group of subbands.

11. The method of claim 8, wherein the at least T−

1 additional sets of scaled pilot symbols are cycled through and each additional set of scaled pilot symbols is transmitted on the second group of subbands in a respective time interval.

12. The method of claim 8, wherein the first and second groups include same number of subbands.

13. An apparatus in a wireless multi-antenna communication system, comprising:

a pilot processor operative to

generate a first set of T scaled pilot symbols with a first vector of T coefficients, where T is an integer greater than one, and wherein the first set of scaled pilot symbols is suitable for use for channel estimation by receivers with a single antenna, and

selectively generate at least T−

1 additional sets of T scaled pilot symbols with at least T−

1 additional vectors if at least one receiver with multiple antennas is to be supported by the system, each additional vector including T coefficients, wherein the first and at least T−

1 additional vectors are different vectors in a matrix, and wherein the first and at least T−

1 additional sets of scaled pilot symbols are suitable for use for channel estimation by the at least one receiver with multiple antennas; and

a plurality of transmitter units operative to condition and transmit each set of T scaled pilot symbols via T transmit antennas, one scaled pilot symbol on each transmit antenna.

14. The apparatus of claim 13, wherein the pilot processor is operative to generate T−

1 additional sets of T scaled pilot symbols with T−

1 additional vectors, and wherein the first vector and T−

1 additional vectors are T vectors of a Walsh matrix.

15. The apparatus of claim 13, wherein the multi-antenna communication system utilizes orthogonal frequency division multiplexing (OFDM).

16. The apparatus of claim 15, wherein each of the T scaled pilot symbols in each set is transmitted from a respective one of the T transmit antennas on a group of P subbands, where P is an integer greater than one, and wherein the P subbands are uniformly distributed across N total subbands and are spaced apart by N/P subbands.

17. The apparatus of claim 15, wherein the first set of scaled pilot symbols is transmitted continuously on a first group of subbands, and wherein the at least T−

1 additional sets of scaled pilot symbols are transmitted on a second group of subbands that is disjoint from the first group of subbands.

18. An apparatus in a wireless multi-antenna communication system, comprising:

means for generating a first set of T scaled pilot symbols with a first vector of T coefficients, where T is an integer greater than one, and wherein the first set of scaled pilot symbols is suitable for use for channel estimation by receivers with a single antenna;

means for selectively generating at least T−

1 additional sets of T scaled pilot symbols with at least T−

1 additional vectors if at least one receiver with multiple antennas is to be supported by the system, each additional vector including T coefficients, wherein the first and at least T−

1 additional vectors are different vectors in a matrix, and wherein the first and at least T−

1 additional sets of scaled pilot symbols are suitable for use for channel estimation by the at least one receiver with multiple antennas; and

means for transmitting each set of T scaled pilot symbols via T transmit antennas, one scaled pilot symbol on each transmit antenna.

19. The apparatus of claim 18, wherein T−

1 additional sets of T scaled pilot symbols are generated with T−

1 additional vectors, and wherein the first vector and T−

1 additional vectors are T vectors of a Walsh matrix.

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

generating M sets of T scaled pilot symbols with M different vectors of a matrix, where T is an integer greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients; and

transmitting each of the M sets of T scaled pilot symbols from T transmit antennas, wherein the M sets of T scaled pilot symbols are suitable for use for channel estimation by both receivers with a single antenna and receivers with multiple antennas.

21. The method of claim 20, wherein the M vectors are not orthogonal to one another.

22. The method of claim 20, wherein the M times T coefficients in the M vectors are selected to minimize channel estimation errors by both the receivers with single antenna and the receivers with multiple antennas.

23. The method of claim 20, wherein the M times T coefficients in the M vectors are selected based on a sum of weighted mean square channel estimation errors for the receivers with single antenna and the receivers with multiple antennas.

24. The method of claim 20, wherein the M sets of T scaled pilot symbols are cycled through and each set is transmitted from the T transmit antennas in a respective time interval.

25. The method of claim 20, wherein the multi-antenna communication system utilizes orthogonal frequency division multiplexing (OFDM), and wherein each of the T scaled pilot symbols in each set is transmitted from a respective one of the T transmit antennas on a group of P subbands, where P is an integer greater than one.

26. The method of claim 25, wherein the P subbands are uniformly distributed across N total subbands and are spaced apart by N/P subbands.

27. An apparatus in a wireless multi-antenna communication system, comprising:

a pilot processor operative to generate M sets of T scaled pilot symbols with M different vectors of a matrix, where T is an integer greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients; and

a plurality of transmitter units operative to condition and transmit each of the M sets of T scaled pilot symbols from T transmit antennas, wherein the M sets of T scaled pilot symbols are suitable for use for channel estimation by both receivers with a single antenna and receivers with multiple antennas.

28. The apparatus of claim 27, wherein the M vectors are not orthogonal to one another.

29. An apparatus in a wireless multi-antenna communication system, comprising:

means for generating M sets of T scaled pilot symbols with M different vectors of a matrix, where T is an integer greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients; and

means for transmitting each of the M sets of T scaled pilot symbols from T transmit antennas, wherein the M sets of T scaled pilot symbols are suitable for use for channel estimation by both receivers with a single antenna and receivers with multiple antennas.

30. In a wireless multi-antenna communication system utilizing orthogonal frequency division multiplexing (OFDM), a method of performing channel estimation at a receiver, comprising:

obtaining, via R receive antennas, R times M sets of P received pilot symbols for T times M sets of P scaled pilot symbols generated with T times M coefficients in a T by M matrix, where R, T and P are integers greater than one, M is an integer equal to or greater than T, M groups of R sets are formed for the R times M sets, and M groups of T sets are formed for the T times M sets, wherein one coefficient in the T by M matrix is used to generate each set of P scaled pilot symbols, and wherein each group of T sets of P scaled pilot symbols is transmitted from T transmit antennas on P subbands;

deriving an initial frequency-domain frequency response estimate for each set of P received pilot symbols, wherein R times M initial frequency response estimates are derived for the R times M sets of P received pilot symbols;

deriving an initial time-domain impulse response estimate for each initial frequency response estimate, wherein R times M initial impulse response estimates are derived for the R times M initial frequency response estimates;

deriving R times T final time-domain impulse response estimates based on the R times M initial impulse response estimates and the T by M matrix; and

deriving a final frequency-domain frequency response estimate for each final impulse response estimate, wherein R times T final frequency response estimates are derived for the R times T final impulse response estimates and represent an estimate of a multiple-input multiple-output (MIMO) channel between the T transmit antennas and the R receive antennas.

31. The method of claim 30, wherein M is equal to T and the T by M matrix is a Walsh matrix.

32. The method of claim 30, wherein the T times M coefficients in the T by M matrix are selected to minimize channel estimation errors by both receivers with a single antenna and receivers with multiple antennas.

33. The method of claim 30, wherein the T times M coefficients in the T vectors are selected based on a sum of weighted mean square channel estimation errors for receivers with a single antenna and receivers with multiple antennas.

34. The method of claim 30, wherein one group of T sets of P scaled pilot symbols is transmitted at all times and remaining M−

1 groups of T sets of P scaled pilot symbols are transmitted only if at least one receiver with multiple antennas is to be supported by the system.

35. The method of claim 30, wherein one group of R sets of P received pilot symbols is obtained via the R receive antennas on a first group of P subbands, and remaining M−

1 groups of R sets of P received pilot symbols are obtained via the R receive antennas on a second group of P subbands.

36. The method of claim 30, further comprising:

for each of the R times T final impulse response estimates, setting tap values below a particular threshold to zero.

37. The method of claim 30, further comprising:

for each of the R times T final impulse response estimates, setting last L-th through P-th taps to zero, where L is an expected delay spread for the system.

38. The method of claim 30, further comprising:

filtering sets of received pilot symbols corresponding to sets of scaled pilot symbols generated with same vector of T coefficients in the T by M matrix.

39. The method of claim 30, further comprising:

filtering initial frequency response estimates corresponding to sets of scaled pilot symbols generated with same vector of T coefficients in the T by M matrix.

40. The method of claim 30, further comprising:

filtering initial impulse response estimates corresponding to sets of scaled pilot symbols generated with same vector of T coefficients in the T by M matrix.

41. The method of claim 30, further comprising:

filtering the final impulse response estimates.

42. The method of claim 30, further comprising:

filtering the final frequency response estimates.

43. An apparatus in a wireless multi-antenna communication system utilizing orthogonal frequency division multiplexing (OFDM), comprising:

a plurality of receiver units operative to obtain, via R receive antennas, R times M sets of P received pilot symbols for T times M sets of P scaled pilot symbols generated with T times M coefficients in a T by M matrix, where R, T and P are integers greater than one, M is an integer equal to or greater than T, M groups of R sets are formed for the R times M sets, and M groups of T sets are formed for the T times M sets, wherein one coefficient in the T by M matrix is used to generate each set of P scaled pilot symbols, and wherein each group of T sets of P scaled pilot symbols is transmitted from T transmit antennas on P subbands; and

a channel estimator operative to

derive an initial frequency-domain frequency response estimate for each set of P received pilot symbols, wherein R times M initial frequency response estimates are derived for the R times M sets of P received pilot symbols,

derive an initial time-domain impulse response estimate for each initial frequency response estimate, wherein R times M initial impulse response estimates are derived for the R times M initial frequency response estimates,

derive R times T final time-domain impulse response estimates based on the R times M initial impulse response estimates and the T by M matrix, and

derive a final frequency-domain frequency response estimate for each final impulse response estimate, wherein R times T final frequency response estimates are derived for the R times T final impulse response estimates and represent an estimate of a multiple-input multiple-output (MIMO) channel between the T transmit antennas and the R receive antennas.

44. The apparatus of claim 43, wherein the channel estimator is further operative to filter received pilot symbols, initial frequency response estimates, initial impulse response estimates, final impulse response estimates, or final frequency response estimates.

45. An apparatus in a wireless multi-antenna communication system utilizing orthogonal frequency division multiplexing (OFDM), comprising:

means for obtaining, via R receive antennas, R times M sets of P received pilot symbols for T times M sets of P scaled pilot symbols generated with T times M coefficients in a T by M matrix, where R, T and P are integers greater than one, M is an integer equal to or greater than T, M groups of R sets are formed for the R times M sets, and M groups of T sets are formed for the T times M sets, wherein one coefficient in the T by M matrix is used to generate each set of P scaled pilot symbols, and wherein each group of T sets of P scaled pilot symbols is transmitted from T transmit antennas on P subbands;

means for deriving an initial frequency-domain frequency response estimate for each set of P received pilot symbols, wherein R times M initial frequency response estimates are derived for the R times M sets of P received pilot symbols;

means for deriving an initial time-domain impulse response estimate for each initial frequency response estimate, wherein R times M initial impulse response estimates are derived for the R times M initial frequency response estimates;

means for deriving R times T final time-domain impulse response estimates based on the R times M initial impulse response estimates and the T by M matrix; and

means for deriving a final frequency-domain frequency response estimate for each final impulse response estimate, wherein R times T final frequency response estimates are derived for the R times T final impulse response estimates and represent an estimate of a multiple-input multiple-output (MIMO) channel between the T transmit antennas and the R receive antennas.

46. The apparatus of claim 45, further comprising:

means for filtering received pilot symbols, initial frequency response estimates, initial impulse response estimates, final impulse response estimates, or final frequency response estimates.

47. A method of performing channel estimation at a receiver in a wireless multi-antenna communication system, comprising:

obtaining, via R receive antennas, M sets of R received pilot symbols for M sets of T scaled pilot symbols generated with M different vectors of a matrix and transmitted via T transmit antennas, where R and T are integers greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients, and wherein the coefficients in the M vectors are selected to facilitate channel estimation by both receivers with a single antenna and receivers with multiple antennas; and

performing a matrix multiply of the M sets of R received pilot symbols with an inverse of the matrix to obtain estimates of R times T channel gains between the T transmit antennas and the R receive antennas.

48. The method of claim 47, wherein the M vectors are not orthogonal to one another.

49. The method of claim 47, wherein the coefficients in the M vectors are selected to minimize channel estimation errors by both the receivers with single antenna and the receivers with multiple antennas.

50. The method of claim 47, wherein the coefficients in the M vectors are selected based on a sum of weighted mean square channel estimation errors for the receivers with single antenna and the receivers with multiple antennas.

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

a plurality of receiver units operative to obtain, via R receive antennas, M sets of R received pilot symbols for M sets of T scaled pilot symbols generated with M different vectors of a matrix and transmitted via T transmit antennas, where R and T are integers greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients, and wherein the coefficients in the M vectors are selected to facilitate channel estimation by both receivers with a single antenna and receivers with multiple antennas; and

a channel estimator operative to perform a matrix multiply of the M sets of R received pilot symbols with an inverse of the matrix to obtain estimates of R times T channel gains between the T transmit antennas and the R receive antennas.

52. A method of performing channel estimation at a receiver in a wireless multi-antenna communication system, comprising:

obtaining, via a single receive antenna, M received pilot symbols for M sets of T scaled pilot symbols generated with M different vectors of a matrix and transmitted via T transmit antennas, where T is an integer greater than one and M is an integer equal to or greater than T, wherein each vector includes T coefficients, and wherein the coefficients in the M vectors are selected to facilitate channel estimation by both receivers with a single antenna and receivers with multiple antennas; and

filtering the M received pilot symbols to obtain an estimate of a composite multiple-input single-output (MISO) channel between the T transmit antennas and the single receive antenna.