Download Proposed Test Procedure for VDSL/VDSL2 Signal Power

Telecommunications Industry Association
TR41.9-10-02-012
Document Cover Sheet
Project Number
PN-3-3602-RV4
Document Title
Proposed Test Procedure for VDSL/VDSL2
Source
Cisco Systems, Inc.
Contact
Tim Lawler
170 West Tasman Dr.
San Jose, CA 95134
Distribution
TR-41.9, at the February 2010 meeting
Intended Purpose
of Document
(Select one)
X
Phone: (408) 527-0681
Fax: (408) 526-4184
Email: [email protected]
For Incorporation Into TIA Publication
For Information
Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
This contribution provides test procedures for measuring VDSL/VDSL2 total power, power spectral
density, transverse balance and longitudinal output voltage. These test procedures are intended for the
revised TSB-31-C (TSB-31-D).
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14.4
14.4.1
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Conditioning VDSL/VDSL2 EUT to Transmit Continuously
General
This subclause provides a suggested test procedure to measure aggregate signal
power, power spectral density (PSD), and longitudinal output voltage (LOV) for
VDSL/VDSL2 modems (VTU-R) against the applicable requirements specified in
ANSI/TIA-968-B.
14.4.2
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 as allowed by the respective
PSD masks without a sustained connection to companion equipment. The method of
testing with a companion device is impractical for VDSL/VDSL2 equipment since the
companion (VTU-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 signal power levels. This is because VDSL/VDSL2 equipment automatically
reduces the line rate and power levels over long loops to maintain an acceptable level
of performance. VDSL2 modems that support extended upstream operation must be
tested against all of the spectral masks for all the operational modes that they support.
There are two possible methods to achieve the required state for the VDSL/VDSL2
modem. One method involves a test mode via software whereby the EUT’s transmitter
is forced to enter the showtime state without going through a training sequence.
Showtime refers to the state where the VDSL/VDSL2 modem is transmitting a pseudorandom data pattern continuously.
The other technique first involves bringing the VDSL/VDSL2 modem’s link up over an
artificial line (see Figure 14.4-1) whose characteristics effectively force the EUT into its
maximum signal power allowed by the PSD masks. Next, the EUT is strapped or
conditioned to disable retrains so that once the showtime state has been achieved, the
EUT may be disconnected from the artificial line and connected to a 100 ohm
measurement termination. Using the artificial line technique, the EUT may need to be
trained up with the VTU-C over various line loops to produce all of the EUT’s PSD
upstream signals (US0, US1 & US2). For example for profile 12a: when the EUT is
trained up over a 1000 ft loop it may only produce US1 and US2 PSD signals at their
maximum level. When the EUT is trained up over a 3000 ft loop it may only produce
US0 and US1 signals (US0 may not be at its maximum level). When the EUT is trained
up over a 9000 ft loop it may only produce US0 PSD signal at its maximum level. The
amount of line loops 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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Figure 14.4-1. VDSL/VDSL2 conditioning setup
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14.5
Signal Power Limitations, VDSL/VDSL2 Terminal Equipment
968-B, 5.3.1.1
14.5.1
ANSI/TIA-
Background
The aggregate signal power, or total power, of the VDSL/VDSL2 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.
14.5.2 Purpose
To verify that the signal power level transmitted to the network is properly limited.
14.5.3
Equipment
(1)
RF power meter SEL#71.
(2)
100 ohm, 1 %, non-inductive resistor.
Note: Refer to subclause 5.5 for equipment details.
14.5.4 Equipment States Subject to Test
Transmitting continuously at its highest signal power allowed by the PSD mask. For
VDSL2 modems that support extended upstream operation, each EU mask number
must be considered.
14.5.5
Procedure
(1)
Condition the EUT to transmit its upstream signals at the highest power level as
described in 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.5-1.
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(3)
Measure and record the signal power level in dBm. The level should be averaged
over a time span of at least 10 seconds if shorter term variations are observed.
(4)
Repeat steps 1 to 3 for other upstream signals and different Profiles.
14.5.6 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.
14.5.7 Suggested Test Data
(1)
Signal power level.
(2)
Upstream signals (US0, US1 & US2) that were measured.
(3)
Line loops length that were used to obtain the total power measurement.
14.5.8 Comments
If the RF power meter has 50 ohms input impedance then a Balun may be necessary
(50 to 100 Balun).
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 ohm termination
Balun loss (if used)
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Figure 14.5-1. Average Signal Power
Note: If the RF power meter has 50 ohms input impedance, a 50 to 100 ohm Balun
(SEL#59) would be needed and the 100 ohm resistor would be remove.
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14.6
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Power Spectral Density, VDSL/VDSL2 Terminal Equipment ANSI/TIA-968B, 5.3.8.1.3, 5.3.8.1.4
14.6.1 Background
As is the case for the VDSL/VDSL2 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
bands while restricting the VDSL/VDSL2 modem’s PSD below the operating bands to
protect POTS and above the operating bands both to minimize interference both with
the downstream spectrum as well as other DSL systems potentially affected by
crosstalk. The masks 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 two segments.
14.6.2
Purpose
To verify that the PSD is below the mask.
14.6.3 Equipment
(1)
Spectrum analyzer SEL#57.
(2)
100:50 ohm balun transformer SEL#70
(3)
100:50 ohm balun transformer SEL#59.
Note: Refer to subclause 5.5 for equipment details.
14.6.4
Equipment States Subject to Test
Transmitting continuously its upstream signals at their highest signal power allowed by
the PSD mask. For VDSL2 modems that support extended upstream operation, each
EU mask number must be considered.
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14.6.5
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Procedure
In this section the criteria frequency range has been divided into two segments. The
number of segments chosen is dependent upon the capabilities of the test equipment.
Each frequency point in the operating bands (corresponding to a measurement in a
single resolution bandwidth) of a PSD should be measured by averaging the power in
the resolution bandwidth of that frequency point for a time period of at least 10 seconds.
14.6.5.1
Procedure for Segment 1
(1)
Condition the EUT to transmit US0 continuously as described in subclause 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.6-1 using balun transformer
SEL#70.
(3)
Set the spectrum analyzer as follows:
Resolution bandwidth (RBW): 100 Hz
Video bandwidth: 3 Hz
Attenuation: Set for minimum without overload
Reference level: (-20) dBm
dB/div: 10 dB
Marker Function: Noise dBm/Hz
Start frequency: 200 Hz
Stop frequency: 25.875 kHz
(4)
Measure and record the PSD over the first segment (200 Hz to 25.875 kHz) of the
mask, which covers the voice frequency band.
(5)
Repeat steps 1 to 4 for other Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
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14.6.5.2
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Procedure for Segment 2
(1)
Condition the EUT to transmit its upstream signals continuously as described in
14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.6-1 using balun transformer
SEL#59.
(3)
Set the spectrum analyzer as follows:
Resolution bandwidth: 10 kHz
Video bandwidth: 3 kHz
Attenuation: 40 dB
Reference level: (0) dBm
dB/div: 10 dB
Marker Function: Noise dBm/Hz
Start frequency: 25.875 kHz
Stop frequency: 30 MHz
(4)
Measure and record the PSD over the second segment (25.875 kHz to 30 MHz) of
the mask.
(5)
Repeat steps 1 to 4 for other upstream signals (US0, US1 & US2) and different
Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
14.6.6 Alternative Methods
None
14.6.7 Suggested Test Data
(1)
Plots of the PSD for each segment with the limit line shown on each graph.
(2)
Upstream signals (US0, US1 & US2) that were measured.
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(3)
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Line loops length that were used to obtain the PSD measurement for the upstream
signals.
14.6.8 Comments
(1)
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 ohm termination
Balun loss
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
(2)
Some spectrum analyzers may need a low-pass filter set to cut off frequency of 30
kHz for the Segment 1 measurement.
(3) Some spectrum analyzers may need a high-pass filter to cut off the US0 frequency
for the Segment 2 measurement.
Figure 14.6-1. PSD Connection Diagram For Segments 1 & 2
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14.7
Transverse Balance, VDSL/VDSL2 ANSI/TIA-968-B, 5.3.8.2
14.7.1
Background
See subclause 10.1.1.
14.7.2 Purpose
To determine transverse balance of VDSL/VDSL2 EUT.
14.7.3 Equipment
(1)
Spectrum analyzer SEL#34
(2)
Tracking generator SEL#39.
(3)
Transverse balance test fixture shown in Figure 14.7-1
Note: Refer to subclause 5.5 for equipment details.
14.7.4 Equipment States Subject To Test
Active state with appropriate grounding applied and the EUT transmitter turned off.
Note: Terminal equipment may require special attention to ensure it is properly configured
for this test. For example, if the equipment would normally be connected to ac-power
ground, cold-water-pipe ground, or if it has a metallic or partially metallic exposed
surface, then these points are connected to the test ground plane. Similarly, if the
EUT provides connections to other equipment through which ground may be
introduced to the equipment, then these points are connected to the test ground plane.
Equipment that does not contain any of these potential connections to ground are
placed on a conductive plate that is connected to the test ground plane (see comment
1); this applies to both non-powered and ac-powered equipment.
14.7.5 Procedure
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(1)
Connect the 100 ohms calibration test resistor (RCAL) to the test circuit of Figure
14.7-1.
(2)
Set the spectrum analyzer and tracking generator to the appropriate frequency
ranges:
(a)
For VDSL over POTS - 13.6 kHz to 12,000 kHz
(b)
For VDSL2 over POTS profiles 8a, 8b, 8c, and 8d - 13.6 kHz to 8,500 kHz
(c)
For VDSL2 over POTS profiles 12a and 12b - 13.6 kHz to 12,000 kHz
(d)
For VDSL2 over POTS profiles 17a - 13.6 kHz to 20,000 kHz
(e)
For VDSL2 over POTS profiles 30a - 13.6 kHz to 30,000 kHz
(f)
For VDSL2 all digital mode profiles 8a, 8b, 8c, and 8d - 200 Hz to 8,500 kHz
(g)
For VDSL2 all digital mode profiles 12a and 12b - 200 Hz to 12,000 kHz
(h)
For VDSL2 all digital mode profiles 17a - 200 Hz to 20,500 kHz
(i)
For VDSL2 all digital mode profiles 30a - 200 Hz to 30,000 kHz
(3)
Adjust the tracking generator voltage to measure a VM of 0.316 Vrms across the
calibration test resistor of 100 ohms.
(4)
Connect the spectrum analyzer across the RL resistor (90 or 500 ohms as per
ANSI/TIA-968-B, Table 62).
(5)
Adjust capacitor C1 until a minimum voltage across the RL resistor is obtained.
This represents the highest degree to which the bridge can be balanced. The
result of this balance calibration should be at least 20 dB better than the
requirement for the applicable frequency band. If this degree of balance cannot be
attained, further attention should be given to component selection for the test
circuit and its construction.
(6)
Reverse the polarity of the tip-and-ring pair under test. If the transverse voltage
(VL) changes by less than 1 dB, the calibration is acceptable. If the transverse
voltage changes by more than 1 dB, it indicates that the bridge needs further
adjustment to accurately measure the balance of the EUT. Repeat the calibration
process until the measurements differ by less than 1 dB while maintaining the
balance noted in step (5) above.
(7)
Replace the calibration resistor with the tip-and-ring pair of the EUT.
(8)
Measure the voltage across the tip and ring of the EUT; this is the metallic
reference voltage (VM).
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(9)
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Measure the voltage across the RL resistor; this is the longitudinal voltage (VL).
(10)
Calculate the balance using the following formula:
TransverseBalance 20logV M
V
L
Note: If the readings are, for example, taken in dBV, then the equation may be simplified to:
Balance ( dB )  V
(11)
M
( dBV )  V L ( dBV )
Reverse the tip and ring connections of the EUT and repeat step (8) through step
(10). The lesser of the two results is the transverse balance of the EUT.
14.7.6 Alternative Methods
See Appendix C.
Note: The test method that is described in Appendix C may be more appropriate to use for
frequencies above 3 MHz.
14.7.7 Suggested Test Data
(1)
Frequencies tested.
(2)
Balance measured for the EUT.
(3)
Calibration balance measured.
14.7.8 Comments
(1)
EUT that is not normally grounded should be set in its normal position directly on a
conductive plate. It is recommended that the overall area of the conductive plate
be at least 50% greater than that of the base of the EUT. This represents the
closest proximity to ground that is likely to be encountered by the EUT.
(2)
Interference from power frequency harmonics can be minimized by using test
frequencies midway between multiples of 60 Hz.
(3)
In some cases, EUT may apply internally generated signals to the test set. Such
signals should not be construed as part of the transverse balance test.
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(4)
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Test leads between the test fixture and the EUT will affect the calibration and EUT
balance measurements. Such cables must be in place when making the
calibration balance adjustments.
T1
1:1 impedance ratio, 100 ohm wide-band transformer.
Optimally a dual-stator air-variable RF capacitor that maintains a constant
20pF
capacitance between stators while providing a variable capacitance from either
Differential
stator to ground.
3 pF
Composition RF capacitor
RCAL
100 ohms
RL
90/500 ohms: A non-inductive precision resistor
(chosen according to Table 62 of ANSI/TIA-968-B).
Note 1.
The 3 pF capacitor may be placed on either line of the test set, as required, to obtain
proper balancing of the bridge.
Note 2.
The effective output impedance of the tracking generator should match the 100 ohms test
impedance. The spectrum analyzer's input should be differentially balanced to measure
VM.
Figure 14.7-1 Transverse Balance, VDSL/VDSL2
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14.8
Longitudinal Output Voltage, VDSL/VDSL2 Terminal Equipment ANSI/TIA968-B, 5.3.8.3
14.8.1
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.
VDSL/VDSL2 over POTS modems must also meet certain LOV limits for voiceband
terminal equipment. These measurements can be done by using the procedure set out
in subclasses 9.15 and 9.17.
14.8.2 Purpose
To verify that the longitudinal output voltage is below the limit.
14.8.3
Equipment
(1)
Spectrum analyzer SEL#34.
(2)
LOV test fixture shown in Figure 14.8-1.
Note: Refer to subclause 5.5 for equipment details.
14.8.4
Equipment States Subject to Test
Transmitting continuously as described in subclause 14.4.2. For VDSL2 modems that
support extended upstream operation, each Extended Upstream (EU) mask number
must be considered.
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14.8.5 Procedure
In this section the criteria frequency range has been divided into two segments. The
number of segments chosen is dependent upon the capabilities of the test equipment.
14.8.5.1 Procedure for Segment 1
(1)
Condition the EUT to transmit continuously as described in subclause 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.8-1.
(3)
Set the spectrum analyzer as follows:
Resolution bandwidth: 3 kHz or 4 kHz, if supported by spectrum analyzer
Video bandwidth: 300 Hz
Attenuation or range: Set for minimum without overload
Reference level: (-30) dBV
dB/div: 10 dB
Start frequency: fa Hz (from Table 63 in TIA-968-B)
Stop frequency: 2.5 MHz
Marker Function: Voltage dBV
Limit test: On with limit line programmed with the LOV limit
(4)
Measure and record the LOV averaging the readings over several sweeps.
(5)
Repeat steps 1 to 4 for other Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
14.8.5.2 Procedure for Segment 2
(1)
Condition the EUT to transmit continuously as described in subclause 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.8-1.
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(3)
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Set the spectrum analyzer as follows:
Resolution bandwidth: 3 kHz or 4 kHz, if supported by spectrum analyzer
Video bandwidth: 1 kHz
Attenuation or range: Set for minimum without overload
Reference level: (-30) dBV
dB/div: 10 dB
Start frequency: 2.5 MHz
Stop frequency: See Table 63 of TIA-968-B
Marker Function: Voltage dBV
Limit test: On with limit line programmed with the LOV limit
(4)
Measure and record the LOV averaging the readings over several sweeps.
(5)
Repeat steps 1 to 4 for other Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
Note: A resolution bandwidth (RBW) of 3 kHz is typically used as most spectrum analyzers
support this RBW.
14.8.6
Alternative Methods
None
14.8.7
Suggested Test Data
(1)
Plot of the LOV with the limit line shown
(2)
Upstream signals (US0, US1 & US2) that were measured.
(3)
Line loop lengths that were used to obtain the LOV measurement for the
upstream signals.
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14.8.8
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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
of the EUT. For EUT’s without an earth ground, a ground plane should be used as
discussed in subclause 9.15.8.
T
50
EUT
50
R
0.15 µF
100
Spectrum
analyzer
NOTE - All resistor values are in ohms, and resistors are to be matched to better than 0.1%.
Use a spectrum analyzer with a high input (>10k) impedance.
Figure 14.8-1 LOV Test Fixture & Connection Diagram, VDSL/VDSL2
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