Echo MIMO: a method for optimal multiple input multiple output channel estimation and matched cooperative beamforming

• US 20070099571A1
• Filed: 10/31/2005
• Published: 05/03/2007
• Est. Priority Date: 10/31/2005
• Status: Active Grant

• Current Assignee: Mitre Corporation
• Original Assignee: Mitre Corporation
• Inventors: Taylor, Robert, Withers, Langhorne
• Granted Patent: US 7,778,607 B2
• Time in Patent Office: Days
• US Class Current: 455/67.11
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• 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 5/14 Two-way operation using the same type of signal, i.e. duplex

Abstract

A method for estimating a communication channel comprising one or more sub-channels between at least a first transceiver and at least a second transceiver is provided. The method comprises transmitting a first set of training data from the first transceiver to the second transceiver, receiving observed signals at the second transceiver, re-transmitting said observed signal back to the first transceiver, and calculating a roundtrip channel estimate at the first transceiver. The method further comprises transmitting a second set of training data from the second transceiver to the first transceiver, receiving observed signals at the first transceiver, and calculating a reverse link channel estimate. From the roundtrip channel estimate and the reverse link channel estimate, a forward link channel estimate is computed at the first transceiver.

Claims

1. A method of estimating a communication channel comprising one or more sub-channels between at least a first transceiver and at least a second transceiver, the method comprising:

(a) transmitting a first set of training data from the first transceiver to the second transceiver;

(b) receiving first observed signals from the transmitted first set of training data at the second transceiver, and re-transmitting said first observed signals to the first transceiver;

(c) receiving the re-transmitted first observed signals at the first transceiver, and calculating a roundtrip channel estimate at the first transceiver;

(d) transmitting a second set of training data from the second transceiver to the first transceiver;

(e) receiving second observed signals from the transmitted second set of training data at the first transceiver, and calculating a reverse channel estimate at the first transceiver based on the received second observed signals; and

(f) calculating a forward channel estimate at the first transceiver based on the calculated first round-trip channel estimate and the calculated incoming channel estimate.

2. The method of claim 1, wherein the first transceiver comprises a first set of a plurality of transmit and receive antennas and wherein the second transceiver comprises a second set of a plurality of transmit and receive antennas.

3. The method of claim 2, wherein the forward channel estimate is optimized by having the roundtrip channel estimate and the reverse channel estimate jointly minimize a weighted least-square error.

4. The method of claim 2, wherein the first and second transceivers comprise electromagnetic transceivers.

5. The method of claim 2, wherein the first and second transceivers comprise acoustic transceivers.

6. The method of claim 1, further comprising:

(g) calculating a reverse channel estimate at the second transceiver based on the received first observed signals.

7. The method of claim 2, further comprising:

(g) calculating a transmit beamforming vector at the first transceiver based on the calculated forward channel estimate, wherein said transmit beamforming vector defines a transmit weight for each transmit antenna of the first transceiver.

8. The method of claim 7, wherein step (g) comprises:

(i) calculating a singular value decomposition (SVD) of a matrix of the forward channel estimate;

(ii) selecting the maximum singular value of the matrix; and

(iii) selecting the right-singular vector corresponding to said maximum singular value as the transmit beamforming vector.

9. The method of claim 7, further comprising:

(h) calculating a receive beamforming vector at the second transceiver based on the calculated reverse channel estimate at the second transceiver, wherein said receive beamforming vector defines receive weights for each receive antenna of the second transceiver.

10. The method of claim 7, wherein the communication channel is a frequency-selective channel, and wherein step (g) further comprises:

(i) estimating a set of finite-impulse response (FIR) channel response coefficients for each subchannel of the communication channel;

(ii) determining a frequency domain representation of the forward channel estimate;

(iii) calculating singular value decompositions (SVDs) of the forward channel estimate for discrete frequency values of a frequency communication band; and

(iv) calculating the inverse Fast Fourier Transforms (FFT) of the SVDs of the forward channel estimate to obtain a time-sequence of optimum transmit beamforming vectors.

11. The method of claim 7, further comprising:

(h) transmitting a third set of training data beamformed according to the calculated transmit beamforming vector from the first transceiver to the second transceiver; and

(i) receiving observed signals from the transmitted beamformed third set of training data, and calculating an optimum matching receive beamforming vector at the second transceiver.

12. The method of claim 6, wherein full duplex channel estimation can be achieved by repeating steps (a)-(c) starting from the second transceiver, and by calculating a forward channel estimate at the second transceiver based on a roundtrip channel estimate calculated at the second transceiver and the reverse channel estimate calculated at the second transceiver.

13. The method of claim 12, further comprising:

(h) calculating a transmit beamforming vector based on the calculated forward channel estimate at the second transceiver; and

(i) transmitting a fourth set of training data beamformed according to the calculated transmit beamforming vector from the second transceiver to the first transceiver; and

(j) receiving observed signals from the transmitted fourth set of training data, and calculating an optimum matching receive beamforming vector at the first transceiver.

14. The method of claim 9, wherein the transmit and receive beamforming vectors represent matched pairs of maximum ratio transmission/maximum ratio combining (MRT/MRC) weight vectors.

15. The method of claim 12, wherein full-duplex channel estimation between the first and second transceivers is achieved according to a time-division-duplexing (TDD) scheme using a single frequency band for communication between the first and second transceivers.

16. The method of claim 12, wherein full-duplex channel estimation between the first and second transceivers is achieved according to a frequency-division-duplexing (FDD) scheme using separate frequency bands for communication between the first and second transceivers.

17. A method for performing matched cooperative beamforming over a communication channel comprising one or more sub-channels between at least a first transceiver and at least a second transceiver, comprising:

(a) transmitting a set of training data beamformed according to a transmit beamforming vector from a first transceiver to a second transceiver; and

(b) receiving observed signals from the transmitted set of training data at a second transceiver, and calculating an optimum matching receive beamforming vector at the second transceiver.

18. The method of claim 17, wherein the communication channel is a frequency-selective channel, and wherein calculating the transmit beamforming vector further comprises:

(i) estimating a set of finite-impulse response (FIR) channel response coefficients for each subchannel of the communication channel;

(ii) determining a frequency domain representation of the forward channel estimate;

(iii) calculating singular value decompositions (SVDs) of the forward channel estimate for discrete frequency values of a frequency communication band; and

(iv) calculating the inverse Fast Fourier Transforms (FFT) of the SVDs of the forward channel estimate to obtain a time-sequence of optimum transmit beamforming vectors.

19. A method of estimating a quasi-symmetric communication channel comprising one or more sub-channels between at least a first transceiver and at least a second transceiver, the method comprising:

(a) transmitting a first set of training data from the first transceiver to the second transceiver;

(b) receiving observed signals from the transmitted first set of training data at the second transceiver, and re-transmitted the observed signals back to the first transceiver;

(c) receiving the re-transmitted observed signals at the first transceiver, and calculating a roundtrip channel estimate at the first transceiver based on the re-transmitted observed signals; and

(d) calculating a forward channel estimate at the first transceiver based on the calculated roundtrip channel estimate and by channel reciprocity exploitation.

20. The method of claim 19, wherein the first transceiver comprises a first set of a plurality of transmit and receive antennas and wherein the second transceiver comprises a second set of a plurality of transmit and receive antennas.

21. The method of claim 19, further comprising:

(e) calculating a transmit beamforming vector according to the calculated forward channel estimate at the first transceiver.

22. The method of claim 21, further comprising:

(f) transmitting a second set of training data beamformed according to the calculated transmit beamforming vector from the first transceiver to the second transceiver; and

(g) receiving observed signals from the transmitted beamformed second set of training data at the second transceiver, and calculating a matching receive beamforming vector at the second transceiver, wherein said beamforming vector defines a receive weight for each receive antenna of the second transceiver.