1. July 2005
doc.: IEEE /0703r0
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/
Berthold Rathke
+49 (0)30/
Peter Egner
Telefunken Racoms
Eberhard-Finck-Str Ulm-Boefingen, Germany
+49 (0)731/
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Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

2. July 2005
doc.: IEEE /0703r0
Abstract
July 2005
This presentation is in support of draft text in IEEE /0702r0.
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

3. July 2005
doc.: IEEE /0703r0
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

4. July 2005
doc.: IEEE /0703r0
July 2005
Main 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 & “channel model”
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

5. Example Set-Up: (Rate vs.) Range
July 2005
doc.: IEEE /0703r0
Example Set-Up: (Rate vs.) Range
July 2005
ATT
Analyzer
shielded enclosure AP
DUT
Parameters
Channel
Model
Attenuator
Speed
Symmetric channel characteristic for up- and down-link
ATT
Analyzer
shielded enclosure AP
DUT
Parameters
Channel
Model
Attenuator
Speed
Asymmetric channel characteristic for up- and down-link
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

6. Example Set-Up: BSS Transition / Handover
July 2005
doc.: IEEE /0703r0
July 2005
Example Set-Up: BSS Transition / Handover
STA
AP1
AP2
ATT
Monitor
Generator /
Analysator
Symmetric channel characteristic for up- and down-link
AP1
Generator /
Analyzer
STA
ATT
Monitor
Asymmetric channel characteristic for up- and down-link
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

7. Changing Attenuation during the Measurement
July 2005
doc.: IEEE /0703r0
July 2005
Changing Attenuation during the Measurement
All scenarios change the attenuation imposed on the communication test signal while the measurement of a metric / sub-metric is running
Example (modified after [5]):
Atten A
Atten B
Dwell Time
Transition Time
Crossover
Power Level
Time
Power
Attenuation changed while test is running
change given in dB/s
Here: linear fading
Others are possible!
Focus of this methodology
Constant attenuation imposed
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

8. Baseline Configuration & Modifiers
July 2005
doc.: IEEE /0703r0
July 2005
Baseline Configuration & Modifiers
Baseline Configuration
Linear fading (channel model)
Two velocities by which to change the imposed attenuation:
v1 =  attn /  t1
v2 =  attn /  t2
v1 << 2*v2
Modifiers
Channel model (e.g.: log-normal fading, etc.)
Velocity by which to change imposed attenuation
Change only one modifier at a time
Time [s]
Attenuation [dB]
 t2
 t1
 attn
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

9. Special Reporting Requirements
July 2005
doc.: IEEE /0703r0
July 2005
Special Reporting Requirements
Reported measurement results of the considered metric / sub-metric shall be accompanied by a specification of
used channel model(s)
the attenuation imposed on the communication test signal between the DUT and “reference AP” at any given time during the experiment (speed by which the attenuation on changed)
in order to guarantee high repeatability of test results over-time and location
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

10. July 2005
doc.: IEEE /0703r0
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
Recommendation:
TGT should consider the draft recommended text included in /0702r0 Methodology for Employing Variable Attenuators in a Conducted Test Environment and include it into the P draft with necessary editorial changes
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin

11. References July 2005 [1] Range vs. Rate (doc. 04/1397r00)
doc.: IEEE /0703r0
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)
P D0.1 - Draft Recommended Practice for the Evaluation of Wireless Performance
Marc Emmelmann, Technical University Berlin
Marc Emmelmann, Technical University Berlin