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8/6/2019 11 05 1198-00-000t TX Evm Metric in Conductive Setup
1/27
doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
TGT Power and EVM measurements
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 inthis 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 IEEEStandards publication; to copyright in the IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs sole discretion to permit
others to reproduce in whole or in pa rt 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 , including the statement"IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives ass urance 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
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Date: Sept 20, 2005Name Company Address Phone email
Uriel Lemberger Intel PO Box 1659, MatamIndustrial Park, Haifa 31015
Israel+972-4-865-5701
Alexander Tolpin Intel PO Box 1659, MatamIndustrial Park, Haifa 31015
Israel
Neeraj Sharma Intel 13290 Evening Creek Dr, SanDiego CA 92128
(858) 385-4112 [email protected]
Nir Alon IntelPO Box 1659, Matam
Industrial Park, Haifa 31015Israel
+972-4-865-6621 [email protected]
Authors:
8/6/2019 11 05 1198-00-000t TX Evm Metric in Conductive Setup
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 2
Abstract
This document introduces the description of transmit power
measurement and Transmit EVM measurements in
Conductive Test Environment as a part of RecommendedPractice for the Evaluation of 802.11 Wireless Performance.
We are seeking to get feedback from TGT group on work
under progress in this direction.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide
Summary
Purpose
Test Equipment Transmit power measurement
Transmit EVM measurement
Conclusion
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doc.: IEEE 802.11-05/1198r0
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Nov 2005
Uriel Lemberger, IntelSlide
Purpose of Power and EVM measurements
Provide calibrated Tx level which is required for manytests.
for e ample, TPT vs. ttenuation requires the knowledge of T
power to correctly correlate the TPT to the R signal level. Provide TX EVM which can effect TPT performance
tests.
for e ample, TPT can degrade when TX EV is low.
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doc.: IEEE 802.11-05/1198r0
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Nov 2005
Uriel Lemberger, IntelSlide 5
Main Test Equipment
DUT any wireless 802.11 device (AP or Client) that includes relevantSW running on the specific platform
WLCP (WireLess CounterPart) - reference AP or a reference Client.
Optional Shielded enclosure for DUTs and WLCPs in order to isolate
from extraneous signals Usually not required since the measured signal is much stronger than any possible
interferer. It is commonly used with other tests that requires shielding.
Cables RF-cables connected to antenna connectors.
Wired L cables
Control cables
Attenuators to close the RF link.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide
Main Test Equipment (cont.)
Power Meter Device to measure RF signal power per packet.Alternative options will be presented in this document.
Calibrated combiners, splitters and couplers to handle different RFpath, including antennas entries.
Wired Traffic Generator to generate data traffic from DUT to WLCP ontop of layer 2.
Optional - Wired Traffic Analyzer to gather delivered data payload overtime through wired interface on top of layer 2.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide
Main Test Equipment (cont.)
Test controller
Includes the following capabilities, likely automated and controlledby dedicated SW:
The ability to control TX rates and TX power of UT The ability to control power meter.
The ability to control Wired Traffic Generator.
ptional - The ability to control Wired Traffic nalyzer
ptional - The ability to control attenuators
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 8
Important Notes
The power measurement and EVM can be performed on any
output port of any 802.11 component in the network.
It is not required to have continuous transmission. The power
measuring techniques presented later should have triggeringmechanism that starts measuring the power only when the signal
ramps and stops when there is no signal, so that duty cycle
averaging wont effect the measurement.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide
TX Power measurement techniques for
WLAN
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 10
TX Power measurement techniques for WLAN
Power meter approach
Spectrum Analyzer approach
e tracted from doc doc.: IEEE 802.11-04/0935r4
VSA (Receiver) approach
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 11
Spectrum Analyzer approachextracted from doc doc.: IEEE 802.11-0 /0 5r
-
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 12
VSA approach
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
TX Power Test setup
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
VSA approach
What is measured.
How it is measured.
Freq domain measurement Integration of spectral density over W recommended.
Time domain measurement
not recommended, sensitive to window size errors.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 15
Test procedure example Set the spectrum window in the VSA at the center of the channel. With
span wider than the channel BW.
Set the power measurement boundaries +/-BW/2 around the center.
Set the Receiver range to be linear (for the expected TX power).
Coupling AC 50ohm
Trigger on IF pos slop
Resolution Bandwidth = 23.87kHz
Windowing type Flat top.
Time 90% overlap with average off. Synchronize on channel estimation Sequence
Demodulation (DSSS/CCK/OFDM)
Subcarrier select all, spacing 312.5Khz, Symbol timing adjust -3.125%
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
Calibration
TBD
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
EVM measurements techniques for WLAN
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 18
EVM Overview Background
EV IEEE minimal performance specification F e ample.
EV Test setup lock diagram
EV test definition from IEEE 802.11 clause 1 . . .
EVM Test
EV test procedure
Calibration
Results E ample
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 1
EVM (OFDM)17.3.9.6.3 Transmitter constellation error
The relative constellation R S error, averaged over subcarriers, F frames, and packets, shall not
e ceed a data-rate dependent value according to Table 0.
Table 90Allowed relative constellation error versus data rate
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 20
TX EVM Test setup
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doc.: IEEE 802.11-05/1198r0
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Nov 2005
Uriel Lemberger, IntelSlide 21
17.3.9.7 Transmit modulation accuracy testThe sampled signal shall be processed in a manner similar to an actual receiver, according to the following
steps, or an equivalent procedure:
a) Start of frame shall be detected.
b) Transition from short sequences to channel estimation sequences shall be detected, and fine timing
(with one sample resolution) shall be established.
c) Coarse and fine frequency offsets shall be estimated.
d) The packet shall be derotated according to estimated frequency offset.
e) The comple channel response coefficients shall be estimated for each of the subcarriers.
f) For each of the data F symbols: transform the symbol into subcarrier received values, estimatethe phase from the pilot subcarriers, derotate the subcarrier values according to estimated phase, and
divide each subcarrier value with a comple estimated channel response coefficient.
g) For each data-carrying subcarrier, find the closest constellation point and compute the Euclidean distance
from it.
h) Compute the R S average of all errors in a packet. It is given by:
(28)
where
LPis the length of the packet;
Nfis the number of frames for the measurement;
(I0(i,j,k), Q0(i,j,k)) denotes the ideal symbol point of the ith frame, jth F symbol of the
frame, kth subcarrier of the F symbol in the comple plane;
(I(i,j,k), Q(i,j,k)) denotes the observed point of the ith frame, jth F symbol of the frame,
kth subcarrier of the F symbol in the comple plane (see Figure 121);
P0 is the average power of the constellation.
The vector error on a phase plane is shown in Figure 121.
The test shall be performed over at least 20 frames (Nf), and the R S average shall be taken. The packets
under test shall be at least 1 F symbols long. Random data shall be used for the symbols.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 22
Equation 28 and figure 121
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 2
EVM test procedure example Set the spectrum window in the VSA at the center of the channel. With
span wider than the channel BW.
Set the power measurement boundaries +/-BW/2 around the center.
Set the Receiver range to be linear (for the expected TX power).
Coupling AC 50ohm
Trigger on IF positive slop Resolution Bandwidth = 23.87kHz
Windowing type Flat top.
Time 90% overlap with average off.
Synchronize on channel estimation Sequence
Demodulation (DSSS/CCK/OFDM)
I/Q normalize Pilot Track Phase & Timing
Equalizer training on channel estimation sequence only
Subcarrier select all,
Spacing 312.5Khz,
Symbol timing adjust -3.125%
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 2
Calibration
TBD
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 25
VSA Approach Results Example
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 2
Conclusions
These are Important secondary metrics.
Tx power is required in most tests in order to get
correct Signal strength in different location in the Link. EVM results can help analyze TPT anomalies.
It is important to verify good TX EV when testing RX
performance of the counterpart.
The proposed methodology is applicable for testing in a
full system.
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doc.: IEEE 802.11-05/1198r0
Submission
Nov 2005
Uriel Lemberger, IntelSlide 2
References
[1] IEEE 802.11-1999, P802.11a -1999, P802.11b -1999
[2] IEEE 802.11-05/0661r0 TGT Conductive TestEnvironment and Metrics. Alexander Tolpin.
[3]P802.11.2-D0.4 - Draft Recommended Practice for
the Evaluation of 802.11 Wireless Performance