1. Addressing Multipath Fading in the TGT Draft
IEEE TO be obtained
November 2005
November/2006
Addressing Multipath Fading in the TGT Draft
Date:
Authors:
Pertti Visuri
Airgain, Inc
1930 Palomar Point Way, ste 107, Carlsbad, CA 92028, USA
Uriel Lemberger
Intel
PO Box 1659, Matam Industrial Park, Haifa Israel
Neeraj Sharma
13290 Evening Creek Drive, San Diego, CA 92128
(858)
Sasha Tolpin
Other authors added later
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Pertti Visuri, Airgain, Inc.
Pertti Visuri, AIrgain, Inc.

2. Changes to the Text in the Draft and their justification
November/2006
Changes to the Text in the Draft and their justification
The text in the document /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
Pertti Visuri, Airgain, Inc.

3. Proposed changes and Justifications
November/2006
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.
Pertti Visuri, Airgain, Inc.

4. Changes for the draft text
November/2006
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 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.”
Pertti Visuri, Airgain, Inc.

5. Changes for the draft text
November/2006
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”
Pertti Visuri, Airgain, Inc.

6. Changes for the draft text
November/2006
Changes for the draft text
Section “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.
Pertti Visuri, Airgain, Inc.