July 2005 doc.: IEEE 802.11-05/0703r1 July 2005 Methodology for Employing Variable Attenuators in a Conducted Test Environment Authors: Date: 2005-07-16 Name Company Address Phone email Marc Emmelmann Technical University Berlin Einsteinufer 25 10587 Berlin, Germany +49 (0)30/314-24580 emmelmann@ieee.org Tim Langgärtner +49 (0)30/314-23823 langgaertner@tkn.tu-berlin.de Berthold Rathke +49 (0)30/314-23832 rathke@tkn.tu-berlin.de Peter Egner Telefunken Racoms Eberhard-Finck-Str. 55 89075 Ulm-Boefingen, Germany +49 (0)731/1553 - 219 Peter.Egner@tfk-racoms.com 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 <stuart.kerry@philips.com> 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 <patcom@ieee.org>. Marc Emmelmann, Technical University Berlin Marc Emmelmann, Technical University Berlin

July 2005 doc.: IEEE 802.11-05/0703r1 Abstract July 2005 This presentation is in support of draft text in IEEE 802.11-05/0702r0. The draft text for the recommended practice follows the approved template as outlined in 802.11-05/1641r01, “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

July 2005 doc.: IEEE 802.11-05/0703r1 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

Where this Methodology does apply 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

Where this Methodology does not apply 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] Atten. 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

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

Involved Test Equipment July 2005 doc.: IEEE 802.11-05/0703r1 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 & “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

July 2005 doc.: IEEE 802.11-05/0703r1 Example Set-Ups July 2005 TPT vs. Attenuation conductive setup (taken from [8]), depends on how experiments are performed Focus of this methodology: How to scope with variable attenuator. Everything else is subject to a specific metric proposal! Roaming conductive setup (taken from [9]) Marc Emmelmann, Technical University Berlin Marc Emmelmann, Technical University Berlin

Changing Attenuation during the Measurement July 2005 doc.: IEEE 802.11-05/0703r1 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

Baseline Configuration & Modifiers July 2005 doc.: IEEE 802.11-05/0703r1 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

Special Reporting Requirements July 2005 doc.: IEEE 802.11-05/0703r1 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

July 2005 doc.: IEEE 802.11-05/0703r1 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 802.11-05/0702r0 Methodology for Employing Variable Attenuators in a Conducted Test Environment and include it into the P802.11.2 draft with necessary editorial changes Marc Emmelmann, Technical University Berlin Marc Emmelmann, Technical University Berlin

References July 2005 [1] Range vs. Rate (doc. 04/1397r00) doc.: IEEE 802.11-05/0703r1 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 802.11(doc. 05-0194r00) [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) P802.11.2-D0.1 - Draft Recommended Practice for the Evaluation of 802.11 Wireless Performance Marc Emmelmann, Technical University Berlin Marc Emmelmann, Technical University Berlin