11 05 1198-00-000t tx evm metric in conductive setup

8/6/2019 11 05 1198-00-000t TX Evm Metric in Conductive Setup

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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.

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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

[email protected]

Alexander Tolpin Intel PO Box 1659, MatamIndustrial Park, Haifa 31015

Israel

[email protected]

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:


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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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Uriel Lemberger, IntelSlide

Summary

Purpose

Test Equipment Transmit power measurement

Transmit EVM measurement

Conclusion


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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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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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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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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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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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TX Power measurement techniques for

WLAN


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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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Spectrum Analyzer approachextracted from doc doc.: IEEE 802.11-0 /0 5r

-


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VSA approach


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TX Power Test setup


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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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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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Calibration

TBD


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EVM measurements techniques for WLAN


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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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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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TX EVM Test setup


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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 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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Equation 28 and figure 121


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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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VSA Approach Results Example


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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 EV when testing RX

performance of the counterpart.

The proposed methodology is applicable for testing in a

full system.


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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

11 05 1198-00-000t tx evm metric in conductive setup

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