METHOD AND APPARATUS FOR CALIBRATION AND CHANNEL STATE FEEDBACK TO SUPPORT TRANSMIT BEAMFORMING IN A MIMO SYSTEM

• US 20070206504A1
• Filed: 03/01/2007
• Published: 09/06/2007
• Est. Priority Date: 03/01/2006
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Chandra, Arty, Wang, Jin, Koo, Chang-Soo, Olesen, Robert, Yen, Chia-Pang, Voltz, Peter
• Granted Patent: US 7,920,533 B2
• Time in Patent Office: Days
• US Class Current: 370/245
• CPC Class Codes: H04B 17/0085 using test signal generators
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/24 with feedback of measurements to the transmitter
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0643 Feedback on request
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03611 Iterative algorithms
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 25/0398 Restoration of channel reciprocity

Abstract

A method and apparatus for calibration and channel state feedback to support transmit beamforming in a multiple-input multiple-output (MIMO) system are disclosed. For radio frequency (RF) calibration, a first station (STA) sends a calibration request to a second STA, and the second STA sends a sounding packet to the first STA. The first STA receives the sounding packet, performs at least one channel measurement and performs calibration based on the channel measurement. For channel state feedback, the first STA sends a channel state feedback request to the second STA. The second STA sends a sounding packet to the first STA. The first STA receives the sounding packet and performs at least one channel measurement with the sounding packet. The first STA then calculates a steering matrix for transmit beamforming based on the channel measurement.

Claims

1. In a multiple-input multiple-output (MIMO) wireless communication system including a plurality of stations (STAs), a method for calibration to support transmit beamforming, the method comprising:

a first STA sending a calibration request to a second STA;

the second STA sending a sounding packet to the first STA;

the first STA receiving the sounding packet and performing at least one channel measurement to generate a channel estimate;

the first STA generating a correction vector based on the channel estimate; and

the first STA applying the correction vector for calibration.

2. The method of claim 1 wherein the calibration request is transmitted as one of a higher layer message and a medium access control (MAC) layer message.

3. The method of claim 1 wherein the calibration request is transmitted as a physical layer control message.

4. The method of claim 3 wherein the calibration request is included in a shared control part.

5. The method of claim 3 wherein the calibration request is included in a dedicated control part.

6. The method of claim 1 wherein the sounding packet is a packet dedicated for sounding purposes.

7. The method of claim 1 wherein the sounding packet is a data packet.

8. The method of claim 1 further comprising:

the first STA sending a second sounding packet along with a second calibration request to the second STA;

the second STA receiving the second sounding packet and performing at least one channel measurement to generate a second channel estimate; and

the second STA sending the second channel estimate to the first STA, wherein the first STA generates the first correction vector based on the first channel estimate and the second channel estimate.

9. The method of claim 8 further comprising:

the second STA generating a correction vector based on the second channel estimate; and

the second STA applying the correction vector for calibration.

10. The method of claim 8 further comprising:

the first STA generating a second correction vector for the second STA based on the first channel estimate and the second channel estimate;

the first STA sending the second correction vector to the second STA; and

the second STA applying the second correction vector for calibration.

11. In a multiple-input multiple-output (MIMO) wireless communication system including a plurality of stations (STAs), a method for channel state feedback to support transmit beamforming, the method comprising:

a first STA sending a channel state feedback request to a second STA;

the second STA sending a sounding packet to the first STA;

the first STA receiving the sounding packet and performing a channel measurement with the sounding packet; and

the first STA calculating a steering matrix for transmit beamforming based on the channel measurement.

12. The method of claim 11 wherein the channel state feedback request is transmitted as one of a higher layer message and a medium access control (MAC) layer message.

13. The method of claim 11 wherein the channel state feedback request is transmitted as a physical layer control message.

14. The method of claim 13 wherein the channel state feedback request is included in a shared control part.

15. The method of claim 13 wherein the channel state feedback request is included in a dedicated control part.

16. The method of claim 11 wherein the sounding packet is a packet dedicated for sounding purposes.

17. The method of claim 11 wherein the sounding packet is a data packet.

18. The method of claim 11 wherein the channel state feedback request is signaled implicitly.

19. The method of claim 11 wherein the second STA sends a channel state feedback response message along with the sounding packet.

20. The method of claim 19 wherein the channel state feedback response message is combined with the sounding packet.

21. The method of claim 19 wherein the channel state feedback response message is separated from the sounding packet.

22. The method of claim 21 wherein the channel state feedback response message and the sounding packet are transmitted using different mechanisms.

23. A station (STA) configured to perform calibration to support transmit beamforming in a multiple-input multiple-output (MIMO) wireless communication system, the STA comprising:

a plurality of antennas;

a channel estimator for generating a channel estimate based on a sounding packet transmitted by a communication peer; and

a calibration unit configured to send a calibration request to the communication peer to request a transmission of the sounding packet and generate a correction vector for calibration based on the channel estimate.

24. The STA of claim 23 wherein the calibration request is transmitted as one of a higher layer message and a medium access control (MAC) layer message.

25. The STA of claim 23 wherein the calibration request is transmitted as a physical layer control message.

26. The STA of claim 25 wherein the calibration request is included in a shared control part.

27. The STA of claim 25 wherein the calibration request is included in a dedicated control part.

28. The STA of claim 23 wherein the sounding packet is a packet dedicated for sounding purposes.

29. The STA of claim 23 wherein the sounding packet is a data packet.

30. The STA of claim 23 wherein the calibration unit is configured to send a second sounding packet along with a second calibration request to the communication peer, and generates the first correction vector based on the first channel estimate and a second channel estimate generated based on a second sounding packet transmitted by the communication peer in response to the second calibration request.

31. The STA of claim 30 wherein the calibration unit is configured to generate a second correction vector for the communication peer based on the first channel estimate and the second channel estimate and send the second correction vector to the communication peer to be applied at the communication peer for calibration.

32. A station (STA) configured to obtain channel state feedback to support transmit beamforming in a multiple-input multiple-output (MIMO) wireless communication system, the STA comprising:

a plurality of antennas;

a channel estimator for generating a channel estimate based on a sounding packet transmitted by a communication peer; and

a processor configured to send a channel state feedback request to a communication peer and calculate a steering matrix for transmit beamforming based on the channel estimate.

33. The STA of claim 32 wherein the channel state feedback request is transmitted as one of a higher layer message and a medium access control (MAC) layer message.

34. The STA of claim 32 wherein the channel state feedback request is transmitted as a physical layer control message.

35. The STA of claim 34 wherein the channel state feedback request is included in a shared control part.

36. The STA of claim 34 wherein the channel state feedback request is included in a dedicated control part.

37. The STA of claim 32 wherein the sounding packet is a packet dedicated for sounding purposes.

38. The STA of claim 32 wherein the sounding packet is a data packet.

39. The STA of claim 32 wherein the channel state feedback request is signaled implicitly.

40. The STA of claim 32 wherein the communication peer sends a channel state feedback response message along with the sounding packet.

41. The STA of claim 40 wherein the channel state feedback response message is combined with the sounding packet.

42. The STA of claim 40 wherein the channel state feedback response message is separated from the sounding packet.

43. The STA of claim 42 wherein the channel state feedback response message and the sounding packet are transmitted using different mechanisms.

44. A method for calibrating radio frequency (RF) chains in stations (STAs) to insure channel reciprocity, the method comprising:

a first STA sending a first sounding packet to a second STA and the second STA sending a second sounding packet to the first STA;

the first STA estimating a channel matrix {tilde over (H)}_BA of a channel from the second STA to the first STA based on the second sounding packet;

the second STA estimating a channel matrix {tilde over (H)}_AB of a channel from the first STA to the second STA based on the first sounding packet;

the second STA sending the channel matrix {tilde over (H)}_AB to the first STA;

the first STA calculating calibration matrices K_A,tx and K_B,tx for the first STA and the second STA, respectively;

the first STA sending the calibration matrix K_B,tx to the second STA; and

the first STA and the second STA applying the calibration matrices, respectively.

45. The method of claim 44 wherein the calibration matrices K_A,tx and K_B,tx are calculated to minimize the sum of squares of all the elements of the matrix {tilde over (H)}_ABK_A,Tx−

K_B,Tx({tilde over (H)}_BA)^T.

46. The method of claim 45 wherein the first STA calculates the calibration matrices K_A,Tx and K_B,Tx by the steps of:

performing a vector operation to the matrix {tilde over (H)}_ABK_A,Tx−

K_B,Tx({tilde over (H)}_BA)^T to get (I{tilde over (H)}_AB)vec(K_A,Tx)−

({tilde over (H)}_BAI)vec(K_B,Tx);

defining a vector x=[(d_A)^T(d_B)^T]^T comprising diagonal elements of the calibration matrices such that vec(K_A,tx)=S_Ad_A and vec(K_B,tx)=S_Bd_B;

defining a matrix W=[(I{tilde over (H)}_AB)S_A−

({tilde over (H)}_BAI)S_B]; and

finding x which minimizes E=∥

Wx∥

subject to ∥

x∥

=1.

47. The method of claim 46 wherein x is found to be an eigenvector of W*W corresponding to a smallest eigenvalue.

48. The method of claim 45 wherein the first STA calculates the calibration matrices K_A,tx and K_B,tx by the steps of:

performing a vector operation to the matrix {tilde over (H)}_ABK_A,Tx−

K_B,Tx({tilde over (H)}_BA)^T to get (I{tilde over (H)}_AB)vec(K_A,Tx)−

({tilde over (H)}_BAI)vec(K_B,Tx);

defining a vector x=[(d_A)^T(d_B)^T]^T comprising diagonal elements of the calibration matrices such that vec(K_A,tx)=S_Ad_A and vec(K_B,tx)=S_Bd_B; and

estimating d_A and d_B using a least square (LS) method.

49. The method of claim 48 wherein the LS method is applied iteratively.

50. The method of claim 49 wherein the calibration matrices K_A,tx and K_B,tx are obtained by equating some elements of the matrix equation {tilde over (H)}_ABK_A,Tx=K_B,Tx({tilde over (H)}_BA)^T.

51. A wireless communication system for calibrating radio frequency (RF) chains to insure channel reciprocity, the system comprising:

a first station (STA) comprising;

a first transceiver configured to send a first sounding packet to a second STA;

a first channel estimator configured to estimate a channel matrix {tilde over (H)}_BA of a channel from the second STA to the first STA based on a second sounding packet received from the second STA; and

a calibration matrix calculator configured to calculate calibration matrices K_A,Tx and K_B,tx for the first STA and the second STA, respectively, based on the channel matrix {tilde over (H)}_BA and a channel matrix {tilde over (H)}_AB received from the second STA, whereby the first STA sends the calibration matrix K_B,tx to the second STA and apply the calibration matrix K_A,tx; and

the second STA comprising;

a second transceiver configured to send the second sounding packet to the first STA; and

a second channel estimator configured to estimate a channel matrix {tilde over (H)}_AB of a channel from the first STA to the second STA based on the first sounding packet wherein the second STA sends the channel matrix {tilde over (H)}_AB to the first STA and apply the calibration matrix K_B,Tx received from the first STA.

52. The system of claim 51 wherein the calibration matrices K_A,Tx and K_B,tx are calculated to minimize the sum of squares of all the elements of the matrix {tilde over (H)}_ABK_A,tx−

K_B,Tx({tilde over (H)}_BA)^T.

53. The system of claim 52 wherein the calibration matrix calculator is configured to perform a vector operation to the matrix {tilde over (H)}_ABK_A,Tx−

K_B,Tx({tilde over (H)}_BA)^T to get (I{tilde over (H)}_AB)vec(K_A,Tx)−

({tilde over (H)}_BAI)vec(K_B,Tx);

define a vector x=[(d_A)^T(d_B)^T]^T comprising diagonal elements of the calibration matrices such that vec(K_A,tx)=S_Ad_A and vec(K_B,tx)=S_Bd_B;

define a matrix W=[(I{tilde over (H)}_AB)S_A−

({tilde over (H)}_BAI)S_B]; and

find x which minimizes E=∥

Wx∥

subject to ∥

x∥

=1.

54. The system of claim 53 wherein the calibration matrix calculator finds the x as an eigenvector of W*W corresponding to a smallest eigenvalue.

55. The system of claim 52 wherein the calibration matrix calculator is configured to perform a vector operation to the matrix {tilde over (H)}_ABK_A,Tx−

K_B,Tx({tilde over (H)}_BA)^T to get (I{tilde over (H)}_AB)vec(K_A,Tx)−

({tilde over (H)}_BAI)vec(K_B,Tx);

define a vector x=[(d_A)^T(d_B)^T]^T comprising diagonal elements of the calibration matrices such that vec(K_A,tx)=S_Ad_A and vec(K_B,tx)=S_Bd_B; and

estimate d_A and d_B using a least square (LS) method.

56. The system of claim 55 wherein the calibration matrix calculator applies the least square method iteratively.

57. The system of claim 55 wherein the calibration matrix calculator calculates the calibration matrices K_A,tx and K_B,tx by equating some elements of the matrix equation {tilde over (H)}_ABK_A,Tx=K_B,Tx({tilde over (H)}_BA)^T.