doc.: ieee 802.11-05/0944r0 submission september 2005 dr. michael d. foegelle, ets-lindgrenslide 1...

September 2005

Dr. Michael D. Foegelle, ETS-Lindgren

Slide 1

Doc.: IEEE 802.11-05/0944r0

Submission

OTA TRP and TIS Testing

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <[email protected]> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <[email protected]>.

Date: 2005-9-21

Name Company Address Phone email Dr. Michael D. Foegelle ETS-Lindgren 1301 Arrow Point Drive

Cedar Park, TX 78613 (512) 531-6444 [email protected]

Authors:

September 2005


Slide 2

Doc.: IEEE 802.11-05/0944r0

Submission

Abstract

This presentation expands on the techniques for measuring transmit power and receiver sensitivity demonstrated in 11-05/0943 to define techniques for measuring the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) of individual DUTs using off-the-shelf test equipment with traceable calibrations.

The requirements for an over-the-air (OTA) test system necessary to produce accurate results are discussed.

Results of some TRP tests are shown to illustrate some issues to be addressed in the process.

September 2005


Slide 3

Doc.: IEEE 802.11-05/0944r0

Submission

Overview

• Introduction

• Basic Test Methodology

• Test Environment

• TRP Configuration

• TIS Configuration

• Some TRP Results– Issues to resolve

• Conclusions

September 2005


Slide 4

Doc.: IEEE 802.11-05/0944r0

Submission

Introduction

• It has been demonstrated that it is possible to perform conducted measurements of transmit power and receiver sensitivity of individual DUTs.

• The next piece of the wireless link budget is given by the radiation pattern(s) of the DUT including antenna, DUT body, etc., for both transmit power and receive sensitivity.

• From these patterns, useful metrics such as TRP and TIS may be determined.

September 2005


Slide 5

Doc.: IEEE 802.11-05/0944r0

Submission

Basic Test Methodology

• The basis of both TRP and TIS measurements is the measurement of a radiation pattern.

• Measure magnitude & direction of radiating energy using spherical coordinate system to represent location of each data point.

September 2005


Slide 6

Doc.: IEEE 802.11-05/0944r0

Submission


• At each point on the surface, we must be able to measure a randomly polarized signal– Measure two orthogonal polarizations and calculate the vector sum

of the two field values (assuming linear polarization), or total power.

E-Plane

x

y

E x

E y E = E + E yx

2 2

P = P + P yx

September 2005


Slide 7

Doc.: IEEE 802.11-05/0944r0

Submission


• To cover each point on the surface of the sphere requires a spherical positioning system to move either the DUT and/or the Measurement Antenna (MA).

Combined Axis System Distributed Axis System

September 2005


Slide 8

Doc.: IEEE 802.11-05/0944r0

Submission


• Measurement antenna is positioned relative to the DUT at even angular positions on the spherical surface and the quantity of interest (radiated power or sensitivity) is measured for each polarization.

September 2005


Slide 9

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• In order to measure a valid pattern that only represents the magnitude and direction of rays radiated directly from the DUT, a free-space test environment is required.

• Any reflections in the environment will cause energy that was already measured from other angles in the pattern to be re-measured at the current point on the surface.– Tends to fill in pattern nulls and produces erroneous readings.

Test Signal Path

September 2005


Slide 10

Doc.: IEEE 802.11-05/0944r0

Submission

Fully Anechoic Chamber

DUT

Positioner

MeasurementAntenna

RF AbsorberMaterial

Test Environment

• A Fully Anechoic Chamber is used to simulate free-space conditions.

September 2005


Slide 11

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• A Fully Anechoic Chamber is a shielded room lined with RF/microwave absorber on all walls, ceiling, and floor.

• The quality of the shielding effectiveness is normally determined using IEEE Std 299-1997, “IEEE Standard Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures”

• RF/microwave absorber reduces reflections from the inner walls of the shield. Absorber performance depends on the depth and design of the absorber and the angle of incidence of the field.– Normal incidence is best, shallower angles are worse.

September 2005


Slide 12

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• Limitations in RF absorber performance, etc. impose limitations on the performance of the chamber.


Desired Signal Path

Un-desired Signal Paths

September 2005


Slide 13

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• There are a number of site validation methodologies for determining the magnitude of the contribution from un-desired reflections. Applicable ones include:– Free-Space VSWR – Traditional method used for microwave

chambers. Designed primarily for directional antenna test systems (radar, horn antennas, etc.)

– CTIA Ripple Test – Rigorous system/site validation for spherical APM systems used for testing low directivity antennas. Used for validating systems used for TRP and TIS testing of mobile phones.

• Site Validation methodologies qualify a test area or volume known as a “Quiet Zone” (QZ).– The DUT must not be larger than the QZ for accurate

measurements.

September 2005


Slide 14

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• Within the Quiet Zone:– An antenna located at any point in the QZ (with the same

orientation) produces essentially the same signal level at the measurement antenna.

– Conversely, the signal from the measurement antenna appears to be a uniform plane wave within the QZ.

– The actual level of uniformity is determined by the site validation measurement.

• In free-space, the size of the QZ is determined solely by the far-field distance equation, r > 2D2/ , so that for a given range length, r, the largest dimension of the DUT cannot be more than , where is the wavelength to be measured.

• QZ in an anechoic chamber is always less than ideal.

2/r

September 2005


Slide 15

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• There are three principal regions to be aware of:– The Reactive Near-Field region is typically within a few

wavelengths of the antenna/DUT. The fields in this region are a combination of propagating electromagnetic waves and energy stored in electric (capacitive) or magnetic (inductive) fields. Any object introduced in this region changes the stored energy and thus affects the physical properties of the antenna (impedance, etc.)

– The Radiating Near-Field (Fresnel) region consists primarily of propagating RF energy, but in non-uniform directions. Individual details of the radiating object are apparent.

– The far-field (Fraunhoffer) region consists of propagating RF energy in coherent plane waves (or spherical wavefront when viewed in 3-D). E-M waves appear to be coming from a single point source.

September 2005


Slide 16

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

Radiating Near-Field5 Sources, 1 Apart

D=5 => r=50

September 2005


Slide 17

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

Far-Field5 Sources, 1 Apart

D=5 => r=50

September 2005


Slide 18

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

Near-Field to Far-Field5 Sources, 0.2 Apart

D=1 => r=2

September 2005


Slide 19

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• Most antenna patterns represent the relative strength of the radiation normalized to the maximum or bore-sight direction.

• For the purposes of TRP and TIS testing, it is necessary to calibrate the test range to remove the total path loss including effects of the range distance, measurement antenna, cables, etc.

• In the calibration process, a reference antenna with well known (calibrated) gain is placed in the center of the quiet zone with polarization aligned to each MA polarization in turn and used to determine the path loss relative to a theoretical isotropic radiator.

September 2005


Slide 20

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• An isotropic radiator is an ideal (non-existent) radiator that divides the total radiated power evenly across the surface of a sphere and all polarizations.– I.E. It radiates the same signal strength in all directions.

– An isotropic radiator has no Gain (no Directivity or Loss)

• The radiation pattern of an isotropic radiator is a perfect sphere.

IsotropicRad iato r

September 2005


Slide 21

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• The total path loss, PL, is given by the difference between the total amount of power radiated by an isotropic radiator, PISO, and the power that would actually be measured at the test equipment port, PTE.

Test Equipment

G M A

P I S O

c lM A - T E

P M A

r

IsotropicRad iato r

P T E

Total P ath Loss

TEISO PPPL

September 2005


Slide 22

Doc.: IEEE 802.11-05/0944r0

Submission

Signa lG enerato r

Receiver

P S G

G R A

P R A

c lS G - R Ac lT E - R X P R X

G M A

c lM A - T E

P M A

rP T E

Total P ath Loss

P I S O

Test Environment

• To calibrate the range, the path loss between the input of a reference antenna and the test equipment port is measured.

• The known gain (over isotropic) of the reference antenna is then used to correct the path loss relative to an isotropic radiator.

TERARA PGPPL

RARAISO GPP so

September 2005


Slide 23

Doc.: IEEE 802.11-05/0944r0

Submission

Test Environment

• The range calibration must be repeated any time there is a change to the test system, such as:– Replacement of cable(s) or measurement antenna.

– Change in measurement antenna or quiet zone location or orientation.

– Other alterations of the measurement system affecting path loss.

• The site validation measurement must be repeated any time there is a change to the test environment, such as:– Replacement or re-arrangement of absorber.

– Change in measurement antenna or quiet zone location or orientation.

– Addition or removal of objects in the test environment.

• Both should be repeated at least annually.– More regular testing, especially for range calibration, is recommended to

ensure continued integrity of results.

– Regular use of a golden test object can also help ensure stability.

September 2005


Slide 24

Doc.: IEEE 802.11-05/0944r0

Submission

Total Radiated Power Configuration

CalibratedMeasurement Paths

(One for each polarization)

TrafficGenerator

Directional Coupler

CalibratedReceiver

Communication Path

Variable Attenuator


DUT

Positioner

Dual PolarizedMeasurement

Antenna

PolarizationControl

(RF Switch)

September 2005


Slide 25

Doc.: IEEE 802.11-05/0944r0

Submission

Total Isotropic Sensitivity Configuration

CalibratedPacket

Generator

Directional Coupler

ACKCounter Low-Loss

ACK Detection Path

Variable Attenuator

CalibratedMeasurement Paths

(One for each polarization)


DUT

Positioner

Dual PolarizedMeasurement

Antenna

PolarizationControl

(RF Switch)

September 2005


Slide 26

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

• The TRP test system used here consisted of an ETS-Lindgren wireless APM system with a 4.4 m (14.5 ft) range length, consisting of a rectangular fully anechoic chamber with multi-axis positioning system (MAPS) and dual polarized antenna connected to a Rohde & Schwarz FSQ vector signal analyzer with 50 MHz RBW as the calibrated receiver (same as used in 11-05/0943).– With all path loss included, and the noise floor of the VSA at -70

dBm for 50 MHz RBW, there remains only about 20 dB of dynamic range for performing TRP measurements. Barely enough.

• We ran TRP tests for a number of laptop configurations, including a built in 802.11b NIC and a PCMCIA plug-in card with diversity antennas.

September 2005


Slide 27

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

• View of dual-polarized measurement antenna in fully anechoic chamber.

September 2005


Slide 28

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

• Latitude D600 Laptop mounted on MAPS positioner in “Free-Space” configuration.

September 2005


Slide 29

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results• Relationship of DUT to Measurement Antenna

September 2005


Slide 30

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Front Face

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

Y X

Z

Azimuth = -90.0Elevation = 90.0Roll = 90.0

September 2005


Slide 31

Doc.: IEEE 802.11-05/0944r0

Submission

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Left Side

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

XY

Z


Some TRP Results

September 2005


Slide 32

Doc.: IEEE 802.11-05/0944r0

Submission

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Back Face

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

X

Z

Y

Azimuth = -90.0Elevation = -90.0Roll = 90.0

Some TRP Results

September 2005


Slide 33

Doc.: IEEE 802.11-05/0944r0

Submission

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Right Side

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

Y

Z

X


Some TRP Results

September 2005


Slide 34

Doc.: IEEE 802.11-05/0944r0

Submission

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Top View

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

X

Y

Z

Azimuth = 0.0Elevation = 0.0Roll = 0.0

Some TRP Results

September 2005


Slide 35

Doc.: IEEE 802.11-05/0944r0

Submission

Dell Latitude D600, 11 MBPS, 5 Degree Steps, Bottom View

Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

14

ZX

Y


Some TRP Results

September 2005


Slide 36

Doc.: IEEE 802.11-05/0944r0

Submission

• Some Useful Metrics:

• Peak EIRP = 14.4 dBm– Maximum received power in pattern, corrected for range path loss.

– “Best it ever gets” transmit link power.

• TRP = 8.4 dBm– Total power radiated by DUT.

– Determined by integrating total power surface• (weighted sum of measured EIRP data)

– Provides statistical representation of DUT radiated performance.

Some TRP Results

Y

Z

X

P eak E IRP

Y

Z

X

T R P

September 2005


Slide 37

Doc.: IEEE 802.11-05/0944r0

Submission

• Directivity = 5.9 dBi– Ratio of Peak EIRP to TRP (EIRP – TRP in dB).

– Indicates directionality of DUT relative to isotropic radiator.

Some TRP Results

X

Y

Z

Y

Z

X Y

Z

X

Isotrop ic S ourc eDirec tivity = 0 dB

Dipole L ike S ourc eDirec tivity = 2.5 dB

Direc tive S ourc eDirec tivity = 8.1 dB

September 2005


Slide 38

Doc.: IEEE 802.11-05/0944r0

Submission

• Efficiency = Unknown (no conducted power data)– Ratio of TRP to antenna port input power (APIP = conducted power)

(TRP – APIP in dB).

– Includes internal losses of antenna and VSWR of antenna as well.

– Assumes APIP is forward power, not net power.• Power reflected back from antenna does not radiate.

• Gain = Unknown (no conducted power data)– Product of Directivity and Efficiency (sum in dB).

– Equivalent to ratio of EIRP to APIP (EIRP – APIP in dB).

– Common term representing apparent amplification (gain) seen in bore sight (peak EIRP) direction over that from an equivalent lossless isotropic radiator.

Some TRP Results

September 2005


Slide 39

Doc.: IEEE 802.11-05/0944r0

Submission

• Near Horizon Partial Radiated Power; ±45° = 6.9 dBm, ±30° = 5.5 dBm, ±22.5° = 4.4 dBm – CTIA defined specification.

– Cell towers exist along the horizon.

– Energy radiated up into space or down to earth is lost to network.

– Similar situation exists in layout of an 802.11 network on one floor of a building.

Some TRP Results

Energy lost to the network

Network ce ll towerslie a long the horizon

September 2005


Slide 40

Doc.: IEEE 802.11-05/0944r0

Submission

• Near Horizon Partial Radiated Power– Numerically reduces the data integrated from that for TRP by

discarding data near the top and bottom of the pattern.

Some TRP Results

Y

Z

X

T R P26.3 dB m

Y

Z

X Y

Z

X

N H P R P +/-45° (P i/4)25.2 dB m

N H P R P +/-30° P i/ 6)23.7 dB m

(

September 2005


Slide 41

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

• Effect of reducing from 5 ° steps to 15 ° steps.– Significant loss in pattern resolution.

– TRP only goes from 8.44 dBm to 8.40 dBm.• Peaks tend to be broad and nulls don’t amount to much.

– Peak EIRP, however, goes from 14.4 dBm to 13.4 dBm.


Po

wer

(d

Bm

)

-4

16

-2

0

2

4

6

8

10

12

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Y X

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Po

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(d

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)-4

16

-2

0

2

4

6

8

10

12

14

Y X

Z

Azimuth = 90.0Elevation = 90.0Roll = -90.0

September 2005


Slide 42

Doc.: IEEE 802.11-05/0944r0

Submission

Some TRP Results

• Latitude D600 Laptop with D-Link DWL-AG660 PCMCIA NIC mounted on MAPS positioner in “Free-Space” configuration.

September 2005


Slide 43

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Front Face

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

Y X

Z


Some TRP Results

September 2005


Slide 44

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Left Side

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

XY

Z


Some TRP Results

September 2005


Slide 45

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Back Face

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

X

Z

Y

Azimuth = -90.0Elevation = -90.0Roll = 90.0

Some TRP Results

September 2005


Slide 46

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Right Side

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

Y

Z

X


Some TRP Results

September 2005


Slide 47

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Top View

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

X

Y

Z


Some TRP Results

September 2005


Slide 48

Doc.: IEEE 802.11-05/0944r0

Submission

DWL-AG660 in Latitude D600, 11 MBPS, 5 Degree Steps, Bottom View

Po

wer

(d

Bm

)

-5

25

0

5

10

15

20

ZX

Y


Some TRP Results

September 2005


Slide 49

Doc.: IEEE 802.11-05/0944r0

Submission

• Performance Metric Results:

TRP = 12.2 dBm, Peak EIRP = 20.3 dBm,

Directivity = 8.1 dBi, Efficiency = -2.8 dB†,

Gain = 5.3 dBi†, NHPRP ±45° = 11.2 dBm,

NHPRP ±30° = 10.1 dBm, NHPRP ±22.5° = 9.1 dBm

† Based on manufacturer’s spec of 15 dBm TX Power.

Some TRP Results

September 2005


Slide 50

Doc.: IEEE 802.11-05/0944r0

Submission

• So, what can we say about the difference in these results?

• On average, the Diversity NIC will offer at least 1.5 times the range of the built-in NIC (assuming equivalent sensitivities).

• In the “Best” direction of each NIC, the Diversity NIC will offer twice the range.

Some TRP Results

QuantityLaptop

NICDiversity

NIC DifferenceDistance

RatioTot. Rad. Pwr. (dBm) 8.4 12.2 3.8 1.5Peak EIRP (dBm) 14.4 20.3 6.0 2.0Directivity (dBi) 5.9 8.1 2.2 NAEfficiency (dB) ? -2.8 ? NAGain (dBi) ? 5.3 ? NANHPRP ±Pi/4 (dBm) 6.9 11.2 4.2 1.6NHPRP ±Pi/6 (dBm) 5.5 10.1 4.6 1.7NHPRP ±Pi/8 (dBm) 4.4 9.1 4.8 1.7

September 2005


Slide 51

Doc.: IEEE 802.11-05/0944r0

Submission

• Diversity antenna throws new complexity into measurement process.– Changing between polarizations causes oscillations in diversity

switching and un-desirable patterns

Some TRP Results

Theta

Po

wer

(d

Bm

)

Phi Angle (°)Scale: 2/divMin: 0Max: 16

0

180

30

210

60

240

90 270

120

300

150

330

Phi

Po

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(d

Bm

)


0

180

30

210

60

240

90 270

120

300

150

330

September 2005


Slide 52

Doc.: IEEE 802.11-05/0944r0

Submission

Phi

Po

wer

(d

Bm

)


0

180

30

210

60

240

90 270

120

300

150

330

• Diversity antenna throws new complexity into measurement process.– Sequentially measuring each polarization (full pattern or cut between

polarization change) improves results but slows test.

– Still evidence of less than optimal diversity selection at some points.

Some TRP Results

Theta

Po

wer

(d

Bm

)

Phi Angle (°)Scale: 2/divMin: -8Max: 14

0

180

30

210

60

240

90 270

120

300

150

330

September 2005


Slide 53

Doc.: IEEE 802.11-05/0944r0

Submission

• Ideally, diversity would be disabled and each separate path would be tested with the resulting maximum performance taken at each data point.

• If diversity switching is allowed, fixed polarization orientations of dual polarized antenna still bias results:– indeterminate alignment between MA polarization being tested and

DUT polarization may not select the diversity antenna that produces the highest EIRP in the current test direction.

– sum of components from different diversity antennas may overestimate “real” TRP.

– Use of circularly polarized measurement antenna may help resolve this issue.

– Measurement of TRP near sensitivity may force diversity algorithm to make “best” antenna choice.

Some TRP Results

September 2005


Slide 54

Doc.: IEEE 802.11-05/0944r0

Submission

Conclusions

• This presentation defines the system necessary for measuring over-the-air total radiated power and total isotropic sensitivity of wireless devices.

• Results of using such a system for TRP testing were demonstrated along with the most useful metrics obtained from the measurements.

• There are a number of issues to be resolved include dealing with diversity switching and increasing the available dynamic range of test equipment.

• A future presentation will present TIS data.• Future presentations will show how results from these

tests can be used to avoid the pitfalls inherent in some of the other proposed OTA methodologies.

doc.: ieee 802.11-05/0944r0 submission september 2005 dr. michael d. foegelle, ets-lindgrenslide 1...

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