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					November/2006                                                                                                                 doc.: IEEE 802.11-06/799r2

                         Addressing Multipath Fading in the TGT Draft
                                                                     Date: 2006-11-09
Authors:

 Pertti Visuri                Airgain, Inc          1930 Palomar Point Way, ste 107, Carlsbad, CA                           + 1 760 579              pvisuri@airgain.com
                                                    92028, USA                                                              0200

 Uriel Lemberger                   Intel            PO Box 1659, Matam Industrial Park, Haifa 31015                         +972-4-865-              uriel.lemberger@intel.com
                                                    Israel                                                                  5701

 Neeraj Sharma                     Intel            13290 Evening Creek Drive, San Diego, CA 92128                          (858)-385-4112           neeraj.k.sharma@intel.com


 Sasha Tolpin                      Intel            PO Box 1659, Matam Industrial Park, Haifa 31015                         +972-4-865-              alexander.tolpin@intel.com
                                                    Israel                                                                  5430
                                                    Other authors added later




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Submission                                                                                                                                                  Pertti Visuri, Airgain, Inc.
November/2006                            doc.: IEEE 802.11-06/799r2
    Changes to the Text in the Draft and their justification

• The text in the document 802.11-06/0160r1 “Multipath
  Fading in OTA Tests” forms the basis and justification
  for the changes proposed here for the Normative section
  of the Standard.
• It is not proposed that all of the text would be included as
  an addendum to become an integral part of the
  recommended practices. It is just the justification
  presentation.
• The following slides present proposals for changes in the
  draft text that will be appropriate to include for using
  sampling and statistical methods to manage uncertainty
  caused by multipath fading as a test modifier when it is
  needed


Submission                                          Pertti Visuri, Airgain, Inc.
November/2006                                              doc.: IEEE 802.11-06/799r2
                 Proposed changes and Justifications

1. Lower the rotating speed:
Current rotating speed is 1-10 RPM, 10 RPM is too fast,
proposed to use 1 RPM only as the test parameter.

2. Add stationary measurement:
Adding stop-motion rotating turntable as modifier enables slow algorithms to stabilize and
provide repeatable measurement in case of devices that have very slow or no tracking of the
device movement. In some cases this reduces the variation of results.
This modifier can be used to measure the effect of slow motion of the DUT on the test
result. The test result of a stop motion turntable is obtained by averaging the measured
data points comprising a complete turn. A further benefit of having additional data points
is that they can be used to estimate the uncertainty of the test result

3. Averaging over multiple locations of the WLCP:
Current draft uses WLCP in static position and DUT rotating.
Averaging over multiple locations and orientations of WLCP using a Cartesian mapping or
polar mapping reduces the overall measurement uncertainty caused by multipath fading
and the variance of results will be lower. Introducing a turntable or XY table at the WLCP
end of the link, as specified in the Test Environment modifiers, will effectively reduce the
uncertainty.

Submission                                                               Pertti Visuri, Airgain, Inc.
November/2006                                     doc.: IEEE 802.11-06/799r2
                     Changes for the draft text
• In sections 5.4, 5.5 and 5.6 there is a section in the tables about using
  a turntable that reads:
• “At all test locations at which the DUT is more than 3 meters distance
  from the WLCP, the DUT shall be spun clockwise about its geometric
  center point at a fixed rate of 1 - 10 RPM, within a run accuracy of ±
  10%.
  This requirement is intended to track any fading or antenna angle effects
  “
• Proposed to replace with the following text:
• “At all test locations, the DUT shall be spun. The rate of rotation shall be
  1 RPM clockwise and each test shall consist of a number of complete
  turns of the DUT.
  Large devices can be spun around their geometric center point, as long as
  the antenna is not at the center point. Small devices shall be placed on
  the edge of a turntable.
  The radius of the arc that the antenna of the DUT travels while on the
  turntable shall be at least 15 cm.”

Submission                                                    Pertti Visuri, Airgain, Inc.
    November/2006                                                doc.: IEEE 802.11-06/799r2

                              Changes for the draft text
•     In sections 5.4, 5.5 and 5.6 there is a section for modifiers 5.X. X.4 that reads:
•     “5.X.X.4 Modifiers and variations
•     No modifiers or variations of test conditions are associated with this environment.“
•     Proposed to replace with the following text:
•     add a modifier: “modifier 1 - A stop-motion turntable can be used so that the table turns to a
      new position, stops to perform a measurement, which is recorded as a data point, and will then
      move to a new position , stop again for a measurement of a data point and so on. Full test
      should complete a full circle with a minimal stops every 10 degrees (36 stops). The turning
      characteristics and the values of each data point shall be reported. The test result will be
      obtained by calculating the average of the data points measured at each stop.”
•     add a modifier: “modifier 2- A continuously rotating turntable can be used both at the WLCP
      and at the DUT end of the link. In case both tables are rotating continuously the WLCP
      rotation time should be at least 10 times slower than the DUT rotation time. The direction of
      rotation should be opposite for the two tables. The turning characteristics shall be reported.
      Using a turn table in both ends is especially important when making comparison measurements
      between DUTs that have different antenna systems
•     add a modifier: “modifier 3 – A stop motion turntable can be used in both ends of the link. In
      this case the turntable at both ends of the link shall be turned at the same time between each
      measurement of a data point. The direction of rotation should be opposite for the two tables.
      The turning characteristics and the values of each data point shall be reported. The test result
      will be obtained by calculating the average of the data points measured at each stop”




Submission                                                                      Pertti Visuri, Airgain, Inc.
November/2006                                    doc.: IEEE 802.11-06/799r2
                     Changes for the draft text
• Section 6.6.2.4 “Permissible error margins and reliability of test
• Prior to beginning the test, the test equipment described above should be
  calibrated, and all test software verified. The test setup may be
  monitored during the test to ensure that the test conditions do not change.
  The expected error margin for the test results is ±5% of the throughput
  measured at the shortest range, and ±15%of the throughput measured at
  the longest range.”
• Replace the text with:
• “Prior to beginning the test, the test equipment described above should
  be calibrated, and all test software verified. The test setup may be
  monitored during the test to ensure that the test conditions do not change.
  Error margins of ±5% of the throughput measured at the shortest range,
  and ±15%of the throughput measured at the longest range should be
  considered normal.



Submission                                                   Pertti Visuri, Airgain, Inc.

				
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