TRANSMITTER AND RECEIVER CALIBRATION FOR OBTAINING THE CHANNEL RECIPROCITY FOR TIME DIVISION DUPLEX MIMO SYSTEMS

• US 20150139046A1
• Filed: 11/17/2014
• Published: 05/21/2015
• Est. Priority Date: 11/19/2013
• Status: Active Grant

• Current Assignee: Magnolia Broadband Incorporated
• Original Assignee: Magnolia Broadband Incorporated
• Inventors: WANG, Sherwin J., CHEN, Phil F., HAREL, Haim
• Granted Patent: US 9,236,998 B2
• Time in Patent Office: Days
• US Class Current: 370/278
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 17/14 of the whole transmission and reception path, e.g. self-test loop-back
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/08 at the receiving station
• CPC Class Codes: H04L 25/0398 Restoration of channel reciprocity
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic

Abstract

A communication device operating in time division duplex (TDD) mode using multiple antennas is provided herein. The communication device uses receive channel estimation measurements to perform transmit beamforming and multiple input multiple output (MIMO) transmission, based on self-calibration of the various up/down paths via a method of transmission and reception between its own antennas, thus achieving reciprocity mapping between up and down links. Either user equipment (UE) or a base station may routinely perform this self-calibration to obtain the most current correction factor for the channel reciprocity to reflect the most current operating conditions present during TDD MIMO operation.

Claims

1. A communication device having a receive path comprising:

a number M antennas and respective radio modules, wherein the M antennas and respective radio modules support N×

N multiple-input multiple-output (MIMO) transmissions and receptions, wherein M≧

N;

a processor operable in a baseband domain and configured to perform a self-calibration procedure by which a correction factor is computed for a channel reciprocity level, determined by said self-calibration procedure;

a plurality of switches and receive paths in each one of said radio modules, said switches configured to select a receive path for regular MIMO operation or a plurality of receive paths during said self-calibration procedure, wherein at least one of said receive paths includes a path loss element between the respective antenna and a low noise amplifier (LNA); and

a digital attenuator configured to adjust calibration signals in the baseband domain,

wherein the M antennas are configured to alternate transmitting and receiving periods on a single channel according to a time division duplex (TDD) communication protocol, wherein the M antennas are configured to define phases employed in MIMO transmission and selected using information measured at the communication device during receiving periods based on the channel reciprocity level,

wherein the digital attenuator is further configured to digitally attenuate the calibration signal by an amount that is sufficient to prevent the LNA in the path undergoing calibration from saturating,

wherein the communication device is further operable to perform the self-calibration procedure in which one antenna/radio (i) acts as a transmitter and the other antenna/radio (j) acts as the receiver during the self-calibration procedure, the self-calibration procedure comprising;

performing the following for each of two antennas/radios (i and j);

emitting a first calibration signal with a signal strength equivalent to a signal strength used during regular MIMO operation, the receiver using one receive path with some path loss to prevent the LNA from saturation and recording a received calibration signal R<sub>a—

ji</sub>;

transmitting a second calibration signal that is digitally attenuated, the receiver continually employing the same one receive path used in said emitting step and recording a received calibration signal R<sub>b—

ji</sub>;

transmitting a third calibration signal that is digitally attenuated, the receiver switch selecting the receive path used for regular MIMO operation and recording a received calibration signal R<sub>c—

ji</sub>; and

reversing roles of transmitter and receiver for the two selected antennas/radios to repeat said self-calibration procedure and recording the measured calibrated signals;

R<sub>a—

ij</sub>, R<sub>b—

ij</sub>, and R<sub>c—

ij</sub>.

2. The communication device of claim 1, wherein the processor is configured to perform the self-calibration procedure, in order to adjust for the differences in the transmit path and receive path for all the antenna/radios used in MIMO operation, wherein the correction factor is expressed by ρ

_ij, which is the weight ratio of antenna i to antenna j for the channel reciprocity level.

3. The communication device of claim 1, further operable to compute the correction factor for the channel reciprocity level by:

performing the following for a calibrated antenna/radio and un-calibrated antenna/radio pair;

selecting a calibrated and un-calibrated antenna/radio pair to perform the self-calibration procedure after completing the self-calibration for the first antenna/radio pair; and

repeating the self-calibration procedure until all the antennas/radios to be used for MIMO operations are calibrated.

4. The communication device of claim 3, further operable to compute the correction factor for the channel reciprocity level by:

determining the correction factor for the channel reciprocity level obtained with calibration data for antenna/radio elements i and j, wherein said correction factor is expressed by ρ

_ij=(R<sub>a—

ji</sub>*R<sub>c—

ji</sub>*R<sub>b—

ij</sub>)/(R<sub>b—

ji</sub>*R<sub>a—

ij</sub>*R<sub>c—

ij</sub>).

5. The communication device of claim 1, further comprising:

a timer operable to be preset using said processor to repeat the self-calibration procedure for all the antennas/radios used for MIMO operation by recomputing and updating the correction factors for the channel reciprocity level.

6. The communication device of claim 1, further operable to recompute said correction factor for the channel reciprocity level based on the threshold of a changing condition by:

presetting said processor or other baseband logic to recompute and update the correction factor for the channel reciprocity level when said threshold is met; and

repeating the self-calibration procedure for all the antennas/radios to be used for MIMO operation.

7. A method comprising:

deploying a number M antennas and respective radio modules, wherein the M antennas and respective radio modules support N×

N multiple-input multiple-output (MIMO) transmissions and receptions, wherein M≧

N;

using a processor to perform a self-calibration procedure;

selecting from a plurality of receive paths using at least one of a plurality of switches in each radio module a receive path for regular MIMO operation or a plurality of receive paths during said self-calibration method, and a path loss element included in at least one receive path between the respective antenna and a low noise amplifier (LNA);

adjusting calibration signals in the baseband domain using a digital attenuator, to compute a correction factor for a channel reciprocity level in a communication device;

alternatively transmitting and receiving with an antenna set for alternating periods on a single channel according to a TDD communication protocol;

defining phases employed in MIMO transmissions for selecting said antenna set based on information measured at the communication device during receiving periods and the channel reciprocity level;

digitally attenuating the calibration signal by an amount that is sufficient to prevent the LNA in the path undergoing calibration from saturating; and

performing the self-calibration procedure in which one antenna/radio (i) acts as a transmitter and the other antenna/radio (j) acts as the receiver during the self-calibration procedure, the self-calibration procedure comprising;

performing the following for each of two antennas/radios (i and j);

emitting a first calibration signal with a signal strength equivalent to a signal strength used during regular MIMO operation, the receiver using one receive path with some path loss to prevent the LNA from saturation and recording a received calibration signal R<sub>a—

ji</sub>;

transmitting a second calibration signal that is digitally attenuated, the receiver continually employing the same one receive path used in said emitting step and recording a received calibration signal R<sub>b—

ji</sub>;

transmitting a third calibration signal that is digitally attenuated, the receiver switch selecting the receive path used for regular MIMO operation and recording a received calibration signal R<sub>c—

ji</sub>; and

reversing roles of transmitter and receiver for the two selected antennas/radios to repeat said self-calibration procedure and recording the measured calibrated signals;

R<sub>a—

ij</sub>, R<sub>b—

ij</sub>, and R<sub>c—

ij</sub>.

8. The method of claim 7, further comprising:

performing a self-calibration procedure with a processor or other baseband logic to adjust for the differences in the transmit path and receive path accounting for all the antenna/radios used in MIMO operation, wherein the correction factor is expressed by ρ

_ij, which is the weight ratio of antenna i to antenna j for the channel reciprocity level.

9. The method of claim 7, wherein computing the correction factor for the channel reciprocity level further comprises:

performing the following for a calibrated antenna/radio and un-calibrated antenna/radio pair;

selecting a calibrated and un-calibrated antenna/radio pair to perform the self-calibration procedure after completing the self-calibration for the first pair; and

repeating the self-calibration procedure until all the antennas/radios to be used for MIMO operations are calibrated.

10. The method of claim 7, wherein computing the correction factor for the channel reciprocity level further comprises:

determining the correction factor for the channel reciprocity level obtained with calibration data for antenna/radio elements i and j, wherein said correction factor is expressed by ρ

_ij=(R<sub>a—

ji</sub>*R<sub>c—

ji</sub>*R<sub>b—

ij</sub>)/(R<sub>b—

ji</sub>*R<sub>a—

ij</sub>*R<sub>c—

ij</sub>).

11. The method of claim 7, wherein performing the self-calibration procedure further comprises:

presetting a timer using a processor or other baseband logic to repeat the self-calibration procedure for all the antennas/radios to be used for MIMO operation by recomputing and updating the correction factors for the channel reciprocity level.

12. The method of claim 7, wherein performing the self-calibration procedure is based on meeting a predefined threshold of a changing condition by:

presetting a processor or other baseband logic to recompute and update the correction factor for the channel reciprocity level when said threshold is met; and

repeating the self-calibration procedure for all the antennas/radios to be used for MIMO operation.