1. July 2005
doc.: IEEE /0703r2
July 2005
Methodology for Employing Variable Attenuators in a Conducted Test Environment
Authors:
Date:
Name
Company
Address
Phone
Marc Emmelmann
Technical University Berlin
Einsteinufer 25
10587 Berlin, Germany
+49 (0)30/
Tim Langgärtner
+49 (0)30/
Charles R. Wright
Azimuth Systems
31 Nagog Park Acton MA 0189
Fanny Mlinarsky
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Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

2. Additional Authors July 2005 Name Company Address Phone email
doc.: IEEE /0703r2
July 2005
Additional Authors
Name
Company
Address
Phone
Berthold Rathke
Technical University Berlin
Einsteinufer 25
10587 Berlin, Germany
+49 (0)30/
Peter Egner
Telefunken Racoms
Eberhard-Finck-Str Ulm-Boefingen, Germany
+49 (0)731/
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

3. July 2005
doc.: IEEE /0703r2
Abstract
July 2005
This presentation is in support of draft text in IEEE /0702r2.
The draft text for the recommended practice follows the approved template as outlined in /1641r01, “Metrics Template Example”.
Employing variable attenuators in a conducted test environment is one methodology for measuring various metrics and sub-metrics. As the the speed by which the imposed attenuation is changed has an effect on reported results, this document provides a methodology for employing variable attenuators in a conducted test environment. The purpose of this document is to define a procedure that will result in repeatable, reliable, and comparable results. This methodology shall be applied for tests using a conducted environment whenever the attenuation of the communication channel is varied while measuring metrics and sub-metrics.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

4. July 2005
doc.: IEEE /0703r2
July 2005
Motivation
Some metrics and sub-metrics discussed by TGt require changing the attenuation imposed on the communication test signal during the test if a conducted test environment is used. E.g.:
Rate vs. Range [1]
BSS Transition Time [2]
The speed at which the imposed attenuation is changed does have an influence on the reported results for certain metrics. [3,4]
The objective of TGT is to come up with a repeatable measurement methodology ensuring that reported results are comparable.
Thus, a methodology for using variable attenuators in a conducted test environment is required to achieve TGt’s objective to guarantee high repeatability of test results (over-time and location).
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

5. Where this Methodology does apply
July 2005
doc.: IEEE /0703r2
July 2005
Where this Methodology does apply
Obey this methodology whenever the attenuation imposed on the communication test signal is changed while measurements are being taken
Example: BSS Transition time [2,6]
MSDU
ACK
. . .
Old AP
New AP
Transition Period
Frame Interval = Observed BSS Tranition Time
Time
Atten A
Atten B
Dwell Time
Transition Time
Crossover
Power Level
Power
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

6. Where this Methodology does not apply
July 2005
doc.: IEEE /0703r2
July 2005
Where this Methodology does not apply
Not applicable if attenuation is kept constant while metric / sub-metric is measured
Example: Rate vs. Range / Attenuation [1,7,8]
Attn.
Power
Time
Time Interval used conduct measurements
∆ t1
∆ t2
∆ t3
Each result is based on measurements gained while imposed attenuation is constant.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

7. July 2005
doc.: IEEE /0703r2
July 2005
Clarification
The previous two slides were merely for illustration purposes
The proposed draft text is a measurement methodology and does not specify any specific metric.
The methodology shall be applied in every measurement of a metric using a conductive environment in which the experienced attenuation is changed while conducting the measurement.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

8. Involved Test Equipment
July 2005
doc.: IEEE /0703r2
July 2005
Involved Test Equipment
Does not claim to be a complete list of test equipment used to establish a conducted test environment
Does only focus on equipment directly involved for employing variable attenuators:
DUT
Reference AP
Shielded enclosure
Variable attenuator(s)
Attenuator controller & “sweep function”
Additional (calibrated) equipment to connect the DUT and Reference AP via the variable attenuator(s), e.g.: cables, splitters, combiner, etc.
Extend this list according to set-up appropriate to the tested metric / sub-metric.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

9. Methodology: Baseline Configuration
July 2005
doc.: IEEE /0703r2
July 2005
Methodology: Baseline Configuration
Sweep function: Linear in dB
Two velocities by which to change the imposed attenuation:
Sweep times:  t1 and  t1
 attn = Max.Attn. - Min.Attn
v1 =  attn /  t1
v2 =  attn /  t2
v1 << 2*v2
Time [s]
Attenuation [dB]
 t2
 t1
 attn
Min. Attn.
Max. Attn.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

10. Methodology: Baseline Configuration (cont.)
July 2005
doc.: IEEE /0703r2
July 2005
Methodology: Baseline Configuration (cont.)
Increase of imposed attenuation in discrete step sizes permissible
Attenuation step size shall be constant
Step interval ( t increase) shall be constant
Keep step interval as small as possible
Time [s]
Attenuation [dB]
 t increase
 t1
 attn
Min. Attn.
Max. Attn.
attn. step size
Interruption of the RF path due to the change of imposed attenuation shall be as short as possible according to used equipment.
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

11. Methodology: Modifiers
July 2005
doc.: IEEE /0703r2
July 2005
Methodology: Modifiers
Modifiers
Sweep function
Velocity by which to change imposed attenuation
Change only one modifier at a time
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

12. Methodology: Special Reporting Requirements
July 2005
doc.: IEEE /0703r2
July 2005
Methodology: Special Reporting Requirements
Min. attenuation
Max. attenuation
Sweep time
Sweep function
Time RF path is interrupted due to change of attenuation
For step-wise approximation of attenuation linear in dB:
attenuation step size
time over which attenuation is kept constant
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

13. July 2005
doc.: IEEE /0703r2
July 2005
Conclusion
The speed at which the imposed attenuation is changed influences measurement results for certain metrics
Presented methodology assures that
reported results will be more precise and repeatable
allows to incorporate “mobility” issues into measurements in a reproducible manner
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

14. Discussion July 2005 July 2005 doc.: IEEE 802.11-05/0703r2
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

15. July 2005
doc.: IEEE /0703r2
July 2005
Motion
Request the technical editor to include the draft text proposal “Methodology for Employing Variable Attenuators in a Conducted Test Environment” (doc. 05/702r2) into the Draft.
Proposed:
Seconded:
Result (for/against/abstain):
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

16. References July 2005 [1] Range vs. Rate (doc. 04/1397r00)
doc.: IEEE /0703r2
July 2005
References
[1] Range vs. Rate (doc. 04/1397r00)
[2] BSS Transition Time (doc. 04/0989r01)
[3] Velocity Effects on RSM-Based Handover Decision (doc. 05/233r03)
[4] Marc Emmelmann. "Influence of Velocity on the Handover Delay associated with a Radio-Signal-Measurement-based Handover Decision". In Proc. of IEEE Vehicular Technology Conference (VTC 2005 Fall), Dallas, TX, USA, September 2005.
[5] Performance Testing of Diversity for (doc r00)
[6] BSS Transition Time -- draft text proposal (doc. 05/0537r0)
[7] TGT Conductive Test Environment and Metrics, Draft Text Proposal (doc. 05/0660r0)
[8] TGT Conductive Test Environment and Metrics, Draft Presentation (doc. 05/0661r0)
[9] TGT Conductive Test Environment (doc. 05/419r1)
P D0.1 - Draft Recommended Practice for the Evaluation of Wireless Performance
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin