Nov 200 5 Uriel Lemb erger Slide 1 doc.: IEEE 802.11-05/1198r0 Submission 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 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 < [email protected]> 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 Date: Sept 20, 2005 N am e C om pany A ddress Phone em ail U rielLem berger Intel PO Box 1659, M atam IndustrialPark, H aifa 31015 Israel +972-4-865-5701 [email protected]A lexanderTolpin Intel PO Box 1659, M atam IndustrialPark, H aifa 31015 Israel +972-4-865-5430 [email protected]N eerajSharm a Intel 13290 Evening C reek D r, San D iego C A 92128 (858)385-4112 [email protected]NirAlon Intel PO Box 1659, M atam IndustrialPark, H aifa 31015 Israel +972-4-865-6621 [email protected]Authors:
Transcript
Nov 2005
Uriel Lemberger, Intel
Slide 1
doc.: IEEE 802.11-05/1198r0
Submission
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 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 <[email protected]> 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 <[email protected]>.
Date: Sept 20, 2005Name Company Address Phone email
Uriel Lemberger Intel PO Box 1659, Matam Industrial Park, Haifa 31015 Israel
This document introduces the description of transmit power measurement and Transmit EVM measurements in Conductive Test Environment as a part of Recommended Practice for the Evaluation of 802.11 Wireless Performance. We are seeking to get feedback from TGT group on “work under progress” in this direction.
Nov 2005
Uriel Lemberger, Intel
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Summary
• Purpose
• Test Equipment
• Transmit power measurement
• Transmit EVM measurement
• Conclusion
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Uriel Lemberger, Intel
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Purpose of Power and EVM measurements
• Provide calibrated Tx level which is required for many tests.– for example, TPT vs. Attenuation requires the knowledge of Tx
power to correctly correlate the TPT to the Rx signal level.
• Provide TX EVM which can effect TPT performance tests.– for example, TPT can degrade when TX EVM is low.
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Uriel Lemberger, Intel
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Main Test Equipment
• DUT – any wireless 802.11 device (AP or Client) that includes relevant SW 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 LAN cables– Control cables
• Attenuators – to close the RF link.
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Uriel Lemberger, Intel
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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 RF path, including antennas entries.
• Wired Traffic Generator to generate data traffic from DUT to WLCP on top of layer 2.
• Optional - Wired Traffic Analyzer to gather delivered data payload over time through wired interface on top of layer 2.
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Uriel Lemberger, Intel
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Main Test Equipment (cont.)
Test controller Includes the following capabilities, likely automated and controlled by dedicated SW:– The ability to control TX rates and TX power of DUT– The ability to control power meter.– The ability to control Wired Traffic Generator.– Optional - The ability to control Wired Traffic Analyzer– Optional - The ability to control attenuators
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Uriel Lemberger, Intel
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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 triggering mechanism that starts measuring the power only when the signal ramps and stops when there is no signal, so that duty cycle averaging won’t effect the measurement.
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Uriel Lemberger, Intel
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TX Power measurement techniques for WLAN
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Uriel Lemberger, Intel
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TX Power measurement techniques for WLAN
• Power meter approach
• Spectrum Analyzer approach extracted from doc doc.: IEEE 802.11-04/0935r4
• VSA (Receiver) approach
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Uriel Lemberger, Intel
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Spectrum Analyzer approachextracted from doc doc.: IEEE 802.11-04/0935r4
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Uriel Lemberger, Intel
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VSA approach
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Uriel Lemberger, Intel
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TX Power Test setup
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Uriel Lemberger, Intel
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VSA approach
• What is measured.
• How it is measured.
• Freq domain measurement – Integration of spectral density over BW– recommended.
• Time domain measurement – not recommended, sensitive to window size errors.
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Uriel Lemberger, Intel
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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%
The relative constellation RMS error, averaged over subcarriers, OFDM frames, and packets, shall notexceed a data-rate dependent value according to Table 90.
Table 90—Allowed relative constellation error versus data rate
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Uriel Lemberger, Intel
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TX EVM Test setup
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Uriel Lemberger, Intel
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17.3.9.7 Transmit modulation accuracy testThe sampled signal shall be processed in a manner similar to an actual receiver, according to the followingsteps, 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 complex channel response coefficients shall be estimated for each of the subcarriers.f) For each of the data OFDM symbols: transform the symbol into subcarrier received values, estimatethe phase from the pilot subcarriers, derotate the subcarrier values according to estimated phase, anddivide each subcarrier value with a complex estimated channel response coefficient.g) For each data-carrying subcarrier, find the closest constellation point and compute the Euclidean distancefrom it.h) Compute the RMS average of all errors in a packet. It is given by:(28)whereLP is the length of the packet;Nf is 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 OFDM symbol of theframe, kth subcarrier of the OFDM symbol in the complex plane;(I(i,j,k), Q(i,j,k)) denotes the observed point of the ith frame, jth OFDM symbol of the frame,kth subcarrier of the OFDM symbol in the complex 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 RMS average shall be taken. The packetsunder test shall be at least 16 OFDM symbols long. Random data shall be used for the symbols.
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Uriel Lemberger, Intel
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Equation 28 and figure 121
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Uriel Lemberger, Intel
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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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Calibration
• TBD
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Uriel Lemberger, Intel
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VSA Approach Results Example
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Uriel Lemberger, Intel
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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 EVM when testing RX
performance of the counterpart.
• The proposed methodology is applicable for testing in a full system.
