Download TR41.9.2-03-05-017-ADSLSignalPower

TR41.9.2-03-05-017
Title: Proposed TSB-31C Test Procedure for Testing
Signal Power Limitations for ADSL Equipment
Distribution to: TIA TR41.9.2
Meeting Lake Buena Vista, Florida
Location: May 5, 2003
Submitting
Organization:
Contact Peter Walsh, NCE
Information: Paradyne Corporation:
8545 126th Ave. No.
Largo, FL 33773
Phone Tel: (727) 530-8381
Fax: (727) 530-2428
E-mail: [email protected]
Keywords: Part 68, TIA/TSB-31-C, ANSI/TIA-968-A
Abstract: This contribution presents a draft proposal to update text in
Sections 8.22 and 4.3 from the draft 4i version of TSB31C. The
text has been revised to align with the current technical
requirements in ANSI/TIA-968-A for ADSL modems; specifically
those for signal power, power spectral density, and longitudinal
output voltage.
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this contribution.
This document has been prepared by Paradyne Corporation to assist the TIA Engineering Committee. It
is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal
on Paradyne Corporation. Paradyne Corporation specifically reserves the right to amend or modify the
material contained herein and nothing herein shall be construed as conferring or offering licenses or
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copyright statement above.
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TR41.9.2-03-05-017
1.0 Contribution Overview
This contribution builds upon the test procedure set out in TR41.9-01-05-021R1 as
accepted by Committee TR41.9 to facilitate testing of ADSL terminal equipment against
the technical requirements of TIA/EIA/IS-883. With the adoption of ANSI/TIA-968-A by
the ACTA, changes have been made with respect to the signal power limitations for
ADSL modems. The most notable changes include an extension of the upper limit to
which PSD is measured (now 30 MHz) and new limitations for longitudinal output
voltage (LOV), based upon limits specified in ANSI T1.417-2001. This contribution
presents a proposal to revise the Revision 4i draft of TSB-31C as follows.
2.0 List of Significant Changes

Added a new test procedure to measure longitudinal output voltage.

Eliminated references to the Alcatel Order, TIA/EIA/IS-883 and some references
to ANSI T1.413.

Added references to ANSI/TIA-968-A.

Eliminated the list of commercially available equipment, which meets the
specifications of the suggested equipment list referenced throughout the
procedure.

Eliminated the section containing sample PSD plots.

Embedded sample plots showing an ADSL ATU-R’s PSD in each procedure that
details the measurement for each segment of the mask. Previously, the sample
plots were presented in a separate section and also, these were taken on a
RADSL unit. ANSI T1.413 compliant equipment was used to generate these
sample plots and they have been included with the procedure so that the user
has some reference of the expected result.

Extended the highest frequency to which PSD is measured to 30 MHz consistent
with the current ANSI/TIA-968-A requirement.

Changed the term, “total signal power” to “aggregate signal power” to be
consistent with ANSI/TIA-968-A terminology.

Moved the new SEL items to Section 4.3 since the procedure is no longer styled
as a standalone appendix.

Revised the new SEL items to reflect the need to test PSD out to 30 MHz.
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TR41.9.2-03-05-017
8.22 SIGNAL POWER LIMITATIONS FOR ADSL TERMINAL EQUIPMENT
8.22.1 General
This subclause provides a suggested test procedure to measure aggregate signal
power, power spectral density (PSD), and longitudinal output voltage (LOV) for ADSL
modems (ADSL ATU-R or similar CPE) against the applicable requirements specified in
ANSI Standard ANSI/TIA-968-A-2002.
8.22.2 Conditioning the EUT to Transmit Continuously
To properly measure aggregate signal power, PSD, and LOV, the EUT must be
conditioned to transmit at its highest signal power level and line rate without a sustained
connection to companion equipment. The method of testing with a companion device is
impractical for ADSL equipment since the companion (ATU-C) equipment may present
excessively high signal levels at frequencies at which the upstream PSD mask
demands very low PSD levels. The amount of attenuation required to reduce the
companion equipment’s signals below the upstream mask would be excessive to permit
the link to come up at the maximum upstream line rate. This is because ADSL
equipment automatically reduces the line rate over long loops to maintain an acceptable
level of performance.
There are two possible methods to achieve the required state for the ADSL modem.
One method involves a test mode whereby the EUT’s transmitter is forced to enter the
show time state without going through a training sequence. Show time refers to the
state where the ADSL modem is transmitting a pseudo-random data pattern
continuously. The other technique first involves bringing the link up over an artificial line
whose characteristics effectively force the EUT into its maximum signal power and line
rate and thus highest bandwidth state. Next, the EUT is strapped or conditioned to
disable retrains so that once the show time state has been achieved, the EUT may be
disconnected from the artificial line and connected to a 100  measurement
termination. The artificial line may be either a commercial telephone line simulator or a
simple 100  O-pad. In either case, the amount of through transmission attenuation
must be set to maximize the EUT’s transmit power and bandwidth. This is necessary as
most ATU-R’s utilize an adaptive transmit power scheme where power is cut back under
short loop conditions. By the same token, if the line attenuation is excessive, then the
link will not have sufficient margin to come up at its highest rate. The amount of line
attenuation will vary from one vendor’s CPE to another and even with the same CPE if
the start up margin is changed.
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TR41.9.2-03-05-017
8.22.3 Aggregate Signal Power – ANSI/TIA-968-A Section 4.5.9.1
8.22.3.1 Background
The aggregate signal power, or total power, of the ADSL modem must be limited to
minimize near end crosstalk (NEXT) with other DSL systems that share the same cable
binder. Crosstalk is widely recognized as a form of third party harm and represents the
principal impairment to many DSL systems.
8.22.3.2 Purpose
To verify that the signal power level transmitted to the network is properly limited.
8.22.3.3 Equipment
True rms ac voltmeter SEL#41.
100 , 1 %, non-inductive resistor.
NOTE: Refer to Section 4.3 for equipment details.
8.22.3.4 Equipment States Subject to Test
Transmitting continuously at its highest signal power and upstream line data rate.
8.22.3.5 Procedure
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.3.5-1.
Measure and record the signal power level in dBm.
If the ac voltmeter has its dBm scale referenced to 600 , then a correction factor of
+7.8 dB must be added to the displayed reading to account for the measurement
impedance of 100 .
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TR41.9.2-03-05-017
FIGURE 8.22.3.5-1. AVERAGE SIGNAL POWER
8.22.3.6 Alternative Methods
The total signal power may also be calculated by integrating the PSD over the operating
band. This task consists of measuring the PSD over the operating band using a 10 kHz
resolution bandwidth at discrete frequencies with a stepped interval of 10 kHz. The
individual PSD readings are then converted to power readings by multiplying the PSD
(in terms of watts/Hz) by the 10 kHz resolution bandwidth. This results in a power level
for each 10 kHz window. These are then summed over the operating band to give the
total power. The PSD measurement procedure is given in 8.22.4.
8.22.3.7 Suggested Test Data
Signal Power Level.
Line Data Rate and Baud Rate if applicable.
8.22.3.8 Comments
It is recommended that the voltmeter provide a high-impedance balanced input
particularly if the EUT has intentional paths to ground. The resistor value in the above
figure is in ohms.
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8.22.4 Power Spectral Density – ANSI/TIA-968-A Section 4.5.9.2
8.22.4.1 Background
As is the case for the ADSL modem’s total power, its PSD must be limited to minimize
crosstalk. PSD is limited by the imposition of a PSD mask, which specifies a limit as a
function of frequency. The mask permits a reasonable level in the operating band while
restricting the ADSL modem’s PSD below the operating band to protect POTS and
above the operating band both to minimize interference both with the downstream
spectrum as well as other DSL systems potentially affected by crosstalk. The mask
presents measurement challenges because it specifies such a broad range of signal
levels which can’t practically be made in a single sweep due to limitations in the
spectrum analyzer’s dynamic range. For this reason and resolution bandwidth
considerations, the mask is broken into segments. Either low pass or high pass filtering
techniques are employed, as necessary, to allow the spectrum analyzer to effectively
measure low PSD levels in the presence of high PSD level conditions associated with
the operating band.
8.22.4.2 Purpose
To verify that the PSD is below the mask.
8.22.4.3 Equipment
Spectrum analyzer SEL#57.
100 , 1 % non-inductive resistor.
Differential amplifier with 10X passive probe set and built in LPF SEL#58.
100:50  balun transformer SEL#59.
10 dB, 50  pad SEL#60
500 kHz High Pass Filter SEL#61
8.22.4.4 Equipment States Subject to Test
Transmitting continuously at its highest signal power and upstream line data rate.
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8.22.4.5 Procedure
The test procedure is broken down into four sections associated with making the PSD
measurements in a given frequency range segment.
8.22.4.5.1 Procedure for Segment 1
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.4.5.1-1.
Set the differential amplifier for unity gain and a low pass cut-off frequency of 10 kHz.
Set the spectrum analyzer as follows:
Resolution bandwidth: 100 Hz
Video bandwidth: 3 Hz
Attenuation or range: Set for minimum without overload
Reference level: -40 dBm
dB/div: 10 dB
Start frequency: 200 Hz
Stop frequency: 4000 Hz
Marker Function: Noise dBm/Hz
Limit test: On with limit line programmed with the mask’s peak limit
Measure and record the PSD over the first segment of the mask, which covers the voice
frequency band.
NOTES: The PSD readings must be adjusted by a net correction factor of 17 dB derived
from the 10X probe which introduces 20 dB of loss and the 100:50 ohm impedance
correction factor of –3 dB. The resistor value in Figure 8.22.4.5.1-1 is in ohms.
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TR41.9.2-03-05-017
FIGURE 8.22.4.5.1-1. PSD CONNECTION DIAGRAM FOR SEGMENTS 1 & 2
FIGURE 8.22.4.5.1-2. SAMPLE PSD PLOT FOR SEGMENT 1
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TR41.9.2-03-05-017
8.22.4.5.2 Procedure for Segment 2
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.4.5.1-1.
Set the differential amplifier for unity gain with no filtering
Set the spectrum analyzer as follows:
Resolution bandwidth: 1 kHz
Video bandwidth: 30 Hz
Attenuation or range: Set for minimum without overload
Reference level: -20 dBm
dB/div: 10 dB
Start frequency: 4 kHz
Stop frequency: 26 kHz
Marker Function: Noise dBm/Hz
Limit test: On with limit line programmed with the mask’s peak limit
Measure and record the PSD over the second segment of the mask, which covers the
frequencies between the voice band and the ADSL operating band.
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TR41.9.2-03-05-017
FIGURE 8.22.4.5.2-1. SAMPLE PSD PLOT FOR SEGMENT 2
8.22.4.5.2 Procedure for Segment 3
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.4.5.3-1.
Set the spectrum analyzer as follows:
Resolution bandwidth: 10 kHz
Video bandwidth: 300 Hz
Attenuation or range: Set for minimum without overload
Reference level: -20 dBm
dB/div: 10 dB
Start frequency: 25 kHz
Stop frequency: 525 kHz
Marker Function: Noise dBm/Hz
Limit test: On with limit line programmed with the mask’s peak limit
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TR41.9.2-03-05-017
Measure and record the PSD over the third segment of the mask, which covers the
ADSL operating band on up to 525 kHz.
FIGURE 8.22.4.5.3-1. PSD CONNECTION DIAGRAM FOR SEGMENT 3
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TR41.9.2-03-05-017
FIGURE 8.22.4.5.3-1. SAMPLE PSD PLOT FOR SEGMENT 3
8.22.4.5.4 Procedure for Segment 4
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.4.5.4-1.
Set the spectrum analyzer as follows:
Resolution bandwidth: 10 kHz
Video bandwidth: 300 Hz
Attenuation or range: Set for minimum without overload
Reference level: -70 dBm
dB/div: 10 dB
Start frequency: 525 kHz
Stop frequency: 30 MHz
Marker Function: Noise dBm/Hz
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Limit test: On with limit line programmed with the mask’s peak limit and above 1221 kHz
the dashed line mask limit from ANSI T1.413 which will ensure compliance with the –50
dBm total power in a 1 MHz sliding window.
Measure and record the PSD over the fourth segment of the mask, which covers the
high frequencies above the ADSL operating band.
NOTE: The 10 dB pad may be omitted if the high pass filter can withstand high input
levels without introducing distortion products. The PSD readings must be adjusted to
take into account losses introduced by the balun, pad and filter.
FIGURE 8.22.4.5.4-1. PSD CONNECTION DIAGRAM FOR SEGMENT 4
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FIGURE 8.22.4.5.4-2. SAMPLE PSD PLOT FOR SEGMENT 4
8.22.4.6 Alternative Methods
A balun transformer may be used instead of the differential amplifier as long as its
frequency response and return loss are acceptable. Also, more than one type of balun
may be used to cover the entire frequency range of interest.
If the PSD exceeds the dashed limit in the mask at any point above 1221 kHz,
measurements must be made to calculate the total power in a 1 MHz sliding window.
This concept was discussed in 8.22.3.6. The peak limit of –90 dBm/Hz, above 1221
kHz, must never be exceeded by any individual spectral component. However, noise
may exceed the dashed line limit provided that the power integrated over a 1 MHz
bandwidth is less than –50 dBm. As the procedure given in 8.22.4.5.4 suggest, the
sliding window calculation is not necessary if the PSD never exceeds the dashed line.
As an example, the dashed line in ANSI T1.413-1998 Figure 32 reaches a noise floor of
–110 dBm/Hz, which over a 1 MHz band is equivalent to –50 dBm.
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TR41.9.2-03-05-017
8.22.4.7 Suggested Test Data
Plots of the PSD for each segment with the limit line shown on each graph
Line Data Rate and Baud Rate if applicable.
8.22.4.8 Comments
Care must be taken to ensure that measurement errors are kept to a minimum.
Sources of error may include the following:
Impedance deviations from the ideal 100  termination
Differential amplifier loss or gain
Balun loss
Attenuator pad loss over the ideal loss
High pass or low pass filters’ frequency response
Limited dynamic range of the differential amplifier
Limited amplitude accuracy of the spectrum analyzer
PSD measurement errors caused by excessively fast sweep times or not averaging
enough samples when making a swept average measurement
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TR41.9.2-03-05-017
8.22.5 Longitudinal Output Voltage – ANSI/TIA-968-A Section 4.5.9.3
8.22.5.1 Background
Longitudinal output voltage (LOV) limits complement PSD limits by restricting the
amplitude of common mode signals much like the PSD limits restrict the amplitude of
the equipment’s differential mode signals. LOV limits are necessary as common mode
signals tend to couple more readily than differential mode signals in multi-line, twisted
pair cable plant. In other words, LOV limits are necessary to limit crosstalk. LOV limits
have been crafted to allow higher levels around the equipment’s operating band. This is
necessary as a common mode image of the desired differential mode signal results
through imbalance in the line interface, cabling and the measurement circuitry. A tighter
limit applies above the equipment’s operating band where the LOV source is usually not
associated with any signal intended to be applied to the line.
ADSL modems must also meet certain LOV limits for voiceband terminal equipment.
These measurements should be made using the procedure set out in Sections 8.15 and
8.17.
8.22.5.2 Purpose
To verify that the longitudinal output voltage is below the limit.
8.22.5.3 Equipment
Spectrum analyzer SEL#57.
LOV Test fixture shown in Figure 8.22.5.5-1
8.22.5.4 Equipment States Subject to Test
Transmitting continuously at its highest signal power and upstream line data rate.
8.22.5.5 Procedure
Condition the EUT to transmit at it highest upstream signal power level and line rate as
described in 8.22.2.
Connect the EUT to the test circuit of Figure 8.22.5.5.1-1.
Resolution bandwidth: 3 kHz
Video bandwidth: 300 Hz
Attenuation or range: Set for minimum without overload
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TR41.9.2-03-05-017
Reference level: -30 dBV
dB/div: 10 dB
Start frequency: 10 kHz
Stop frequency: 844 Hz
Marker Function: Voltage dBV
Limit test: On with limit line programmed with the LOV limit
Measure and record the LOV averaging the readings over several sweeps.
NOTES: The resistor values in Figure 8.22.5.5.1-1 are in ohms. A resolution bandwidth
(RBW) of 3 kHz is typically used as most spectrum analyzers support this RBW.
FIGURE 8.22.5.5.1-1. LOV TEST FIXTURE & CONNECTION DIAGRAM
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FIGURE 8.22.5.5.1-2. SAMPLE LOV PLOT
8.22.5.6 Alternative Methods
None
8.22.4.7 Suggested Test Data
Plot of the LOV with the limit line shown
Line Data Rate and Baud Rate if applicable.
8.22.4.8 Comments
Care must be taken in the construction of the LOV test fixture. Resistor values must be
matched as previously mentioned. Test leads from the fixture to the EUT should be
kept as short as possible to minimize RF ingress. The ground connection to the fixture
should be of a low inductance, kept short, and connected directly to the chassis ground
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TR41.9.2-03-05-017
of the EUT. For EUT’s without an earth ground, a ground plane should be used as
discussed in Section 9.1.8.
Amend Section 4.3 as follows:
(57) Spectrum analyzer: input impedance 50 ohms, frequency range from 20 Hz to at
least 30 MHz, sensitivity of –130 dBm/Hz or better, resolution < 1 Hz, absolute
amplitude accuracy +1.5 dB or better, RBW of 100 Hz, 1 kHz, 3 kHz, and 10 kHz.
(58) Differential amplifier with 10X passive probe set: amplifier gain 1,10, gain accuracy
+1%, bandwidth DC to 10 MHz, output impedance 50 ohms, input resistance 1
megohm, input capacitance 20 pF, bandwidth limit filter upper cutoff frequency 10
kHz, filter response 6 dB/octave, minimum common mode rejection ratio 10000.
(59) 100:50  balun transformer: frequency range 10 kHz to 30 MHz minimum.
(60) 10 dB 50  pad: frequency range DC to 30 MHz minimum.
(61) High Pass Filter: fc 3 dB cut off frequency 500 kHz, f/ fc ratio 0.40:1, stop band
attenuation –50 dBc.
Update the Table of Contents as follows:
8.22 SIGNAL POWER LIMITATIONS FOR ADSL TERMINAL EQUIPMENT
8.22.1
8.22.2
8.22.3
8.22.4
8.22.5
General
Conditioning the EUT to Transmit Continuously
Aggregate Signal Power – ANSI/TIA-968-A Section 4.5.9.1
Power Spectral Density – ANSI/TIA-968-A Section 4.5.9.2
Longitudinal Output Voltage – ANSI/TIA-968-A Section 4.5.9.3
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