CHANNEL ESTIMATION FOR A VERY LARGE-SCALE MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) SYSTEM

• US 20120288022A1
• Filed: 01/03/2012
• Published: 11/15/2012
• Est. Priority Date: 05/09/2011
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Guey, Jiann-Ching, Balachandran, Kumar, Hui, Dennis
• Granted Patent: US 8,837,621 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0691 using subgroups of transmit antennas
• CPC Class Codes: H04L 2025/03808 Transmission of equaliser coefficients
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A transmitter, receiver, and method for channel estimation for a Multiple-Input Multiple-Output (MIMO) communication system in which the transmitter includes a multiplicity of transmit antennas spaced such that spacing between adjacent antennas provides a spatial correlation coefficient greater than a threshold level. The transmitter selects a subset of the multiplicity of transmit antennas for transmitting the pilot reference signals. The pilot reference signals are transmitted only from the selected subset of transmit antennas to the receiver. The receiver includes a channel estimator configured to derive a channel estimation for all of the multiplicity of transmit antennas using the received pilot reference signals and known or estimated spatial correlation among the multiplicity of transmit antennas.

Claims

1. A method of transmitting pilot reference signals utilized by a receiver for channel estimation in a Multiple-Input Multiple-Output (MIMO) communication system in which a transmitter utilizes a plurality of transmit antennas, the method comprising the steps of:

spacing the plurality of transmit antennas such that spacing between adjacent antennas provides a spatial correlation coefficient greater than a threshold level;

selecting by the transmitter, a selected subset of the plurality of transmit antennas for transmitting the pilot reference signals; and

transmitting the pilot reference signals only from the selected subset of transmit antennas to a receiver.

2. The method as recited in claim 1, wherein the spacing between adjacent antennas is equal to or less than one-half wavelength of the transmitted pilot reference signals.

3. A method of channel estimation for a Multiple-Input Multiple-Output (MIMO) communication system in which a transmitter utilizes a plurality of transmit antennas, the method comprising the steps of:

receiving by a receiver, pilot reference signals transmitted only from a selected subset of the plurality of transmit antennas; and

deriving a channel estimation for all of the plurality of transmit antennas using spatial correlation among the plurality of transmit antennas.

4. The method as recited in claim 3, further comprising spacing the plurality of transmit antennas such that spacing between adjacent antennas provides a spatial correlation coefficient greater than a threshold level.

5. The method as recited in claim 3, wherein the step of deriving a channel estimation includes estimating a spatial correlation coefficient for the transmit antennas in the subset.

6. The method as recited in claim 3, wherein the step of deriving a channel estimation includes obtaining knowledge of a spatial correlation coefficient for the plurality of transmit antennas prior to the deriving step.

7. The method as recited in claim 3, wherein the step of deriving a channel estimation includes utilizing an estimator to interpolate the channel for transmit antennas that do not transmit the pilot reference signals.

8. The method as recited in claim 7, wherein the step of utilizing an estimator to interpolate the channel includes utilizing a Minimum Mean Square Estimator (MMSE) to interpolate the channel for transmit antennas that do not transmit the pilot reference signals.

9. The method as recited in claim 7, wherein the step of utilizing an estimator to interpolate the channel includes utilizing a Least Squares estimator to interpolate the channel for transmit antennas that do not transmit the pilot reference signals.

10. The method as recited in claim 7, further comprising the receiver utilizing the channel estimation to demodulate downlink transmissions.

11. The method as recited in claim 7, further comprising the receiver feeding back the channel estimation to the transmitter for downlink pre-coding.

12. The method as recited in claim 7, further comprising the receiver feeding back a compressed version of the MIMO channel by extracting representative features including delay-Doppler and angular response.

13. A transmitter for transmitting pilot reference signals utilized by a receiver for channel estimation in a Multiple-Input Multiple-Output (MIMO) communication system, the transmitter comprising:

a plurality of transmit antennas spaced such that spacing between adjacent antennas provides a spatial correlation coefficient greater than a threshold level;

an antenna subset selector configured to select a subset of the plurality of transmit antennas for transmitting the pilot reference signals; and

a radio frequency transmitter coupled to the selected subset of transmit antennas and configured to transmit the pilot reference signals only from the selected subset of transmit antennas to the receiver.

14. The transmitter as recited in claim 13, wherein the spacing between adjacent antennas is equal to or less than one-half wavelength of the transmitted pilot reference signals.

15. A receiver in a Multiple-Input Multiple-Output (MIMO) communication system in which a transmitter utilizes a plurality of transmit antennas, the receiver comprising:

a radio frequency receiver configured to receive pilot reference signals transmitted only from a selected subset of the plurality of transmit antennas; and

a channel estimator configured to derive a channel estimation for all of the plurality of transmit antennas using the received pilot reference signals and known or estimated spatial correlation among the plurality of transmit antennas.

16. The receiver as recited in claim 15, wherein the channel estimator is configured to derive the channel estimation by interpolating the channel for transmit antennas that do not transmit the pilot reference signals.

17. The receiver as recited in claim 16, wherein the channel estimator is a Minimum Mean Square Estimator (MMSE).

18. The receiver as recited in claim 16, wherein the channel estimator is a Least Squares estimator.

19. The receiver as recited in claim 15, further comprising a demodulator configured to utilize the channel estimation to demodulate downlink transmissions.

20. The receiver as recited in claim 15, further comprising a feedback transmitter configured to transmit the channel estimation to the transmitter for downlink pre-coding.

21. A method of transmitting pilot reference signals utilized by a receiver for channel estimation in a Multiple-Input Multiple-Output (MIMO) communication system in which a transmitter utilizes a plurality of transmit antennas, the method comprising the steps of:

selecting by the transmitter, a selected subset of the plurality of transmit antennas for transmitting the pilot reference signals; and

transmitting the pilot reference signals only from the selected subset of transmit antennas through a propagation environment to a receiver;

wherein the selecting step includes selecting transmit antennas at an interval in the spatial domain depending on scattering characteristics of the propagation environment such that the receiver can interpolate the channel over those antennas that do not transmit pilot reference signals.

22. The method as recited in claim 21, wherein the plurality of transmit antennas is arranged in an array having a vertical dimension and a horizontal dimension, and the selecting step reduces redundancy of the pilot reference signals in the array by:

selecting every T_m,v antennas in the vertical dimension; and

selecting every T_m,h antennas in the horizontal dimension;

where T_m,v is inversely proportional to a transmit elevation angular spread, and T_m,h is inversely proportional to a transmit azimuth angular spread.