ETSI TS 101 271 V1.2.1 (2013-08)

Access, Terminals, Transmission and Multiplexing (ATTM); Access transmission systems on metallic access cables; Very High Speed digital subscriber line system (VDSL2) [Recommendation ITU-T G.993.2 modified]

RTS/ATTM-06012

General Information

• Status: Published
• Publication Date: 07-Aug-2013
• Technical Committee: ATTM TM6 - Wireline Access Network Systems
• Current Stage: 12 - Completion
• Due Date: 15-Sep-2013
• Completion Date: 08-Aug-2013

Standards Content (Sample)

Technical Specification
Access, Terminals, Transmission and Multiplexing (ATTM);
Access transmission systems on metallic access cables;
Very High Speed digital subscriber line system (VDSL2)
[Recommendation ITU-T G.993.2 modified]

2 ETSI TS 101 271 V1.2.1 (2013-08)

Reference
RTS/ATTM-06012
Keywords
access, modem, transmission, VDSL2
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3 ETSI TS 101 271 V1.2.1 (2013-08)
Contents
Intellectual Property Rights . 4
Foreword . 4
1 Scope . 5
2 References . 5
2.1 Normative references . 5
2.2 Informative references . 5
3 Definitions, symbols and abbreviations . 5
3.1 Definitions . 5
3.2 Symbols . 6
3.3 Abbreviations . 6
4 Endorsement notice . 8
5 Longitudinal Conversion Loss . 8
6 Vectoring Requirements for the VTU-R . 8
7 Test Procedures . 8
7.1 Test set-up definition . 8
7.1.1 Signal and noise level definitions . 10
7.2 Test loops . 10
7.2.1 Functional description. 10
7.2.2 Test loop accuracy . 12
7.3 Impairment generators . 13
7.3.1 Functional description. 13
7.3.2 Cable crosstalk models . 14
7.3.3 Individual impairment generators . 15
7.3.3.1 NEXT noise generator [G1] . 15
7.3.3.2 FEXT noise generator [G2] . 16
7.3.3.3 Background noise generator [G3] . 16
7.3.3.4 White noise generator [G4] . 16
7.3.3.5 Broadcast RF noise generator [G5] . 16
7.3.3.6 Amateur RF noise generator [G6] . 17
7.3.3.6.1 Specification of Amateur RF noise generator . 18
7.3.3.7 Impulse noise generator [G7] . 18
7.3.4 Profile of the individual impairment generators . 19
7.3.4.1 Frequency domain profiles of generators G1 and G2 . 19
7.3.4.2 Crosstalk Scenarios . 19
7.3.4.2.1 Self crosstalk profiles . 19
7.3.4.2.2 Alien crosstalk profiles . 20
7.3.4.3 Time domain profiles of generators G1-G4 . 26
7.3.5 Upstream Power Back-Off testing . 28
8 Line Constants for Test Loop Set . 28
Annex A (informative): Cable Information. 31
Annex B (informative): External Systems in the frequency band 0 MHz to 30 MHz . 32
B.1 Amateur radio bands . 32
B.2 Other external radio systems . 32
B.3 Citizens Band (CB) frequencies in Europe . 33
Annex C (informative): Change History . 35
History . 36
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4 ETSI TS 101 271 V1.2.1 (2013-08)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Access, Terminals, Transmission
and Multiplexing (ATTM).
The present document contains information on the European requirements for Very High Speed Digital Subscriber Line
Systems (VDSL2). Unless specifically stated in the present document, the requirements are given in the
Recommendation ITU-T G.993.2 [1] (Very high speed digital subscriber line transceivers 2).
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5 ETSI TS 101 271 V1.2.1 (2013-08)
1 Scope
The present document provides the necessary adaptions to Recommendation ITU-T G.993.2 [1] for European
applications and other information relevant to the European environment.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
[1] Recommendation ITU-T G.993.2: "Very high speed digital subscriber line transceivers 2
(VDSL2)".
[2] ETSI TS 101 388 (V1.4.1): "Access Terminals Transmission and Multiplexing (ATTM); Access
transmission systems on metallic access cables; Asymmetric Digital Subscriber Line (ADSL) -
European specific requirements [ITU-T Recommendation G.992.1 modified]".
[3] Recommendation ITU-T G.227: "Conventional Telephone Signal".
[4] Recommendation ITU-T G.993.5: "Self-FEXT cancellation (vectoring) for use with VDSL2
transceivers".
[5] Broadband Forum TR-114: "VDSL2 Performance Test Plan".
[6] Broadband Forum TR-115: "VDSL2 Functionality Test Plan".
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI ATTM TM6 Permanent Document TM6(97) 02, June 1998: "Cable reference models for
simulating metallic access networks".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
crest factor (CF): peak to rms voltage ratio
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6 ETSI TS 101 271 V1.2.1 (2013-08)
design impedance (RV): target input and output impedance of the VDSL2 modem
NOTE: This is set at 100 Ω in [1].
downstream: transmission in the direction of LT towards NT (network to customer premise)
FTTCab: used to define when VDSL2 LT transceivers are located physically at a node (normally the Cabinet or PCP)
in the periphery of the access network
FTTEx: used to define when VDSL2 LT transceivers are located physically at the serving Local Exchange
network side: central office in Recommendation ITU-T G.993.2 [1]
reference impedance (R ): chosen impedance used for specifying transmission and reflection characteristics of cables
N
and test loops
NOTE: ETSI has normalized this value at 135 Ω for a wide range of xDSL performance and conformance tests,
including ADSL tests. This value is considered as being a reasonable average of characteristic
impedances (Z ) observed for a wide range of commonly used European distribution cables.
r.m.s: root mean square value
upstream: transmission in the direction of NT towards LT (customer premise to network)
vectoring: coordinated transmission and/or coordinated reception of signals of multiple DSL transceivers using
techniques to mitigate the adverse effects of crosstalk to improve performance
xDSL: generic term covering the family of all DSL technologies, e.g., SDSL, ADSL2, ADSL2plus, VDSL2
3.2 Symbols
For the purposes of the present document, the following symbols apply:
f Test loop calibration frequency for setting the insertion loss of the loop
T
kbps kilo-bits per second
NOTE: 1 kbps = 1 000 bits per second.
Mbps Mega bits per second
NOTE: 1 Mbps = 1 000 kbps.
R Reference Impedance
N
NOTE: Used for specifying transmission and reflection characteristics of cables and test loops.
R VDSL2 source/load design impedance (purely resistive)
V
Z Characteristic impedance of the test loop
Z Compromise reference impedance for the VDSL2 splitter (usually complex)
M
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ADSL Asymmetric Digital Subscriber Line
ADSL2 Asymmetric Digital Subscriber Line Transceivers 2
ADSL2plus Asymmetric Digital Subscriber Line Transceivers 2 with extended bandwidth
AM Amplitude Modulation
BER Bit Error Ratio
CF Crest Factor
CO Central Office
CP Customer Premises
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7 ETSI TS 101 271 V1.2.1 (2013-08)
DC Direct Current
DN Downstream
DRM Digital Radio Mondiale
DSL Digital Subscriber Line (or Loop)
FEC Forward Error Correction
FEXT Far End Cross Talk
FSAN Full Services Access Network organization
FTTCab Fibre To The Cabinet (see definitions)
FTTEx Fibre To The Exchange (see definitions)
HAM interference Amateur Radio interference
HD High Density
HF High Frequency
LAN Local Area Network
LCL Longitudinal Conversion Loss
LT Line Termination
NOTE: VTU-O or VTU at the Central Office in Recommendation ITU-T G.993.2 [1].
LW Long Wave
MD Medium Density
MW Medium Wave
NEXT Near-end crosstalk
NT Network Termination
NOTE: At the customer premise end of the line. VTU-R or VTU at the Remote End in Recommendation
ITU-T G.993.2 [1].
PCP Primary Cross-connection Point
NOTE: Also known as the cabinet.
PDF Probability Density Function
PE Polyethylene
PEP Psophometric Electrical Power
PRBS Pseudo Random Bit Sequence
PSD Power Spectral Density
PVC Poly Vinyl Chloride
RF Radio Frequency
RFI Radio Frequency Interference
RMS Root Mean Square
RS Red-Solomon
SDSL Symmetric single pair high bitrate Digital Subscriber Line
SW Short Wave
TBD To Be Decided
UP Upstream
UPBO Upstream Power Back-Off
VDSL2 Very high speed Digital Subscriber Line Transceivers 2
NOTE: Specified in Recommendation ITU-T G.993.2 [1].
VTU-R VTU at the Remote site
ETSI
8 ETSI TS 101 271 V1.2.1 (2013-08)
4 Endorsement notice
All elements of the ITU Recommendation G.993.2 [1] apply. The European specific requirements are given in
Recommendation ITU-T G.993.2 annex B [1].
5 Longitudinal Conversion Loss
Longitudinal conversion loss (LCL) is a measure of the degree of unwanted transversal signal produced at the input of
the VDSL2 transceiver due to the presence of a longitudinal signal on the connecting leads. The LCL requirements,
below and above 12 MHz, shall be identical to the requirements defined in clause 7.4. of Recommendation
ITU-T G.993.2 [1].
6 Vectoring Requirements for the VTU-R
This clause defines the self-FEXT (far-end crosstalk) cancellation (vectoring) requirements for the VTU-R:
1) When deploying vectoring technology, it is essential that the VTU-R transceiver implements the requirements
defined in Recommendation ITU-T G.993.5 [4].
2) VTU-R transceivers shall implement the vectoring requirements defined in Recommendation
ITU-T G.993.5 [4].
7 Test Procedures
This clause provides a specification of the test set-up, the insertion path and the definition of signal and noise levels.
The tests focus on the noise margin when VDSL2 signals under test are attenuated by standard test-loops and suffer
interference from standard crosstalk noise or impulse noise. This noise margin indicates what increase of crosstalk noise
or impulse noise level can be tolerated by the VDSL2 system under test before the bit error ratio exceeds the design
target.
7.1 Test set-up definition
Figure 7.1 illustrates the functional description of the test set-up. It includes:
• A data source capable of generating a Pseudo Random Bit Sequence (PRBS) with a minimum length of 2 -1
to the transmitter in the direction under test at the bitrate required. The transmitter in the opposite direction
shall be fed with a similar PRBS signal, although there is no need to monitor the receiver output in this path.
• The test loops, as specified in clause 7.2.
• An adding element to add the common mode and differential mode impairment noise (a mix of random,
impulsive and harmonic noise), as specified in clause 7.3.
• An impairment generator, as specified in clause 7.3, to generate both the differential mode and common mode
impairment noise to be fed to the adding element.
• A high impedance and well balanced differential voltage probe (e.g. better than 60 dB across the whole
VDSL2 bandwidth) connected with level detectors such as a spectrum analyzer or a true rms voltmeter.
• A high impedance and well balanced common mode voltage probe (e.g. better than 60 dB across the whole
VDSL2 bandwidth) connected with level detectors such as a spectrum analyzer or a true rms voltmeter.
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9 ETSI TS 101 271 V1.2.1 (2013-08)
application
application
interface
interface
test loop
[A1] [A2]
modem adding modem
PRBS PRBS
Tx test "cable" Rx
+ splitter element + splitter
[B1] [B2]
differential voltage voltage
voltage probe probe
probe U U
1 2
impairment
level level level
detector detector detector
generator
GND GND
Figure 7.1: Functional description of the set-up of the performance tests
The two-port characteristics (transfer function, impedance) of the test-loop, as specified in clause 7.2, is defined
between port Tx (node pairs A1, B1) and port Rx (node pair A2, B2). The consequence is that the two-port
characteristics of the test "cable" in figure 7.1 shall be properly adjusted to take full account of non-zero insertion loss
and non-infinite shunt impedance of the adding element and impairment generator. This is to ensure that the insertion of
the generated impairment signals does not appreciably load the line.
The balance about earth, observed at both ports and at the tips of the voltage probe shall exhibit a value that is 10 dB
greater than the transceiver under test. This is to ensure that the impairment generator and monitor function does not
appreciably deteriorate the balance about earth of the transceiver under test.
The signal flow through the test set-up is from port Tx to port Rx, which means that measuring upstream and
downstream performance requires an interchange of transceiver position and test "cable" ends.
The received signal level at port Rx is the level, measured between node A2 and B2, when port Tx as well as port Rx
are terminated with the VDSL2 transceivers under test. The impairment generator is switched off during this
measurement.
Test Loop #0, as specified in clause 7.2, shall always be used for calibrating and verifying the correct settings of
generators G1-G7, as specified in clause 7.3, during performance testing.
The transmitted signal level at port Tx is the level, measured between node A1 and B1, under the same conditions.
The impairment noise shall be a mix of random, impulsive and harmonic noise, as defined in clause 7.3. The level that
is specified in clause 7.3 is the level at port Rx, measured between node A2 and B2, while port Tx as well as port Rx are
terminated with the design impedance RV. These impedances shall be passive when the transceiver impedance in the
switched-off mode is different from this value.
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10 ETSI TS 101 271 V1.2.1 (2013-08)
7.1.1 Signal and noise level definitions
The signal and noise levels are probed with a well balanced differential voltage probe (U -U ). The differential
2 1
impedance between the tips of that probe shall be higher than the shunt impedance of 100 kΩ in parallel with 10 pF.
Figure 7.1 shows the probe position when measuring the Rx signal level at the LT or NT receiver. Measuring the Tx
signal level requires the connection of the tips to node pair (A1, B1).
The common mode signal and noise levels are probed with a well balanced common mode voltage probe as the voltage
between nodes A2, B2 and ground. Figure 7.1 shows the position of the two voltage probes when measuring the
common mode signal. The common mode voltage is defined as 1/2(U +U ).
1 2
NOTE: The various levels (or spectral masks) of signal and noise that are specified in the present document are
defined at the Tx or Rx side of this set-up. The various levels are defined while the set-up is terminated,
as described above, with the design impedance R or with VDSL2 transceivers under test.
V
Probing an rms-voltage Urms (V) in this set-up, over the full signal band, means a power level of
P (dBm) that equals:
P = 10 × log (U /R × 1 000) dBm
10 rms V
Probing an rms-voltage Urms (V) in this set-up, within a small frequency band of Δf (in Hertz), means an
average spectral density level of P (dBm/Hz) within that filtered band that equals:
P = 10 × log (U /R × 1 000/Δf) (dBm/Hz)
10 rms V
The bandwidth Δf identifies the noise bandwidth of the filter, and not the -3 dB bandwidth.
7.2 Test loops
The purpose of the test loops shown in figure 7.2 is to stress VDSL2 transceivers under a wide range of different
conditions that can be expected when deploying VDSL2 in real networks.
7.2.1 Functional description
The test loops in this clause are an artificial mixture of cable sections. A number of different loops have been used to
represent a wide range of cable impedances, and to represent ripple in amplitude and phase characteristics of the test
loop transfer function.
• The physical length of the individual loops is to be chosen such that the transmission characteristics of all
loops are comparable. This is achieved by normalizing the electrical length of the loops (insertion loss at
300 kHz). The purpose of this is to stress the equaliser of the VDSL2 modem under test in a similar way over
all loops, when testing at a specific bitrate.
The loops are defined as a combination of cable sections. Each section is defined by means of two-port cable models of
the individual sections (see clause 8). Cable simulators as well as real cables can be used for these sections.
• Loop #0 is a symbolic name for a loop with zero (or near zero) length, to prove that the VDSL2 transceiver
under test can handle the potentially high signal levels when two transceivers are directly interconnected.
• The impedances of Loop #1 and #2 are nearly constant over a wide frequency interval. These two loops
represent uniform distribution cables, one having a relatively low characteristic impedance and another having
a relatively high impedance (low capacitance per unit length). These impedance values are chosen to be the
lowest and highest values of distribution cables that are commonly used in Europe.
• The impedances of Loop #3 and #4 follow frequency curves that are oscillating in nature. This represents the
mismatch effects in distribution cables caused by a short extent with a cable that differs significantly in
characteristic impedance. Loop #3 represents this at the LT side to stress downstream signals. Loop #4 does
the same at the NT side to stress upstream signals.
Test loops 1 to 4 in figure 7.2 have equal electrical length (insertion loss at 300 kHz), but differ in input impedance (see
figure 7.3). It is these values for insertion loss and impedance that define an actual test loop set. This clause only defines
the loop topology – the detailed loop lengths are out of scope for the present document.
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11 ETSI TS 101 271 V1.2.1 (2013-08)
LT side (ONU or CO) NT side (CP)
(L0 = 0 m)
Loop #0
100 Ω (L1)
Loop #1
150 Ω (L2)
Loop #2
100 Ω 150 Ω (L3 - Δ L3)
Loop #3
Δ L3
100 Ω (L4 - Δ L4) 180 Ω
Loop #4
Δ L4
Figure 7.2: Test loop topology
The physical composition of the various test loops is defined in table 7.1.
Table 7.1: Test loop composition
Test loop Distribution Extension Extension
cable (L) length
cable (ΔL)
LT or NT side ΔL [m]
#0 - - -
#1 TP100 - -
#2
TP150 - -
#3 TP150 TP100x 70
#4 TP100 TP180x 70
NOTE: The labels "TPxxx" refer to the two-port cable models
specified in clause 8.
The variation of input impedance for the various test loops is shown in figure 7.3. Some typical transfer functions of
loops #1 to #4 are illustrated in figure 7.4. The test loops in this example are normalized in electrical length (or
insertion loss) at an arbitrary chosen frequency. Five examples denoted by Q1 to Q5 are shown in figure 7.4. Loop-set
Q1 has an insertion loss of 55 dB at 2 MHz and loop-set Q5 has an insertion loss of 18,5 dB at 10 MHz. The physical
length of loop-set Q1 is in the range of 1 990 m to 2 100 m and for loop-set Q5 is in the range of 250 m to 300 m. The
plot demonstrates the similarity of the transfer function of all the different loops when they are normalized.

Figure 7.3: Calculated variation of input impedance at a normalized loop length of 5 000 m
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12 ETSI TS 101 271 V1.2.1 (2013-08)

Figure 7.4: Typical transfer function (in R =135 Ω)
N
of the test loops when normalized in electrical length
The sections of the loops are defined in clause 8 by means of two-port cable models of the individual sections. Cable
simulators as well as real cables can be used for these sections. To minimize the electrical differences between test loop
configurations, their length is specified as electrical lengths instead of the physical length of the sections in cascade
(meaningful only when real cables are used). The electrical length is equivalent to the insertion loss of the loop at a
given test frequency and termination impedance.
The relationship between electrical length (insertion loss) and total physical length (when real cables are used) can be
calculated from the two-port models given in clause 8.
7.2.2 Test loop accuracy
The different cable sections are specified by two-port cable models that serve as a representation for real twisted-pair
cables. Cable simulators as well as real cables can be used for these test loops. The associated models and line constants
are specified in clause 8. The composition of the test-loops is specified in table 7.1.
The characteristics of each test loop, with cascaded sections, shall approximate the models within a specified accuracy.
This accuracy specification does not hold for the individual sections:
• The magnitude of the test loop insertion loss shall approximate the insertion loss of the specified models
within 3 % on a dB scale, between f and the highest frequency of the VDSL2 system for each specific band
0L
plan as defined in table B.1 of Recommendation ITU-T G.993.2 [1].
• The magnitude of the test loop characteristic impedance shall approximate the characteristic impedance of the
specified models within 7 % on a linear scale, between f and the highest frequency of the VDSL2 system for
0L
each specific band plan as defined in table B.1 of Recommendation ITU-T G.993.2 [1].
• The group delay of the test loop shall approximate the group delay of the specified cascaded models within
3 % on a linear scale, between f and the highest frequency of the VDSL2 system for each specific band plan
0L
as defined in table B.1 of Recommendation ITU-T G.993.2 [1].
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13 ETSI TS 101 271 V1.2.1 (2013-08)
• The total length of each loop is to be specified in terms of physical length. The electrical length (insertion loss
at 300 kHz) is to be determined from simulation of VDSL2 performance over the test loops. If the
implementation tolerances of a test loop cause the electrical length to be out of specification, then its physical
length, L1 to L4 (see figure 7.2) shall be scaled accordingly to correct this error.
7.3 Impairment generators
The impairment generator produces the noise that is injected into the test set and includes the crosstalk noise, ingress
noise and impulse noise.
The crosstalk noise power level varies with frequency, length of the test loop and transmit direction (upstream or
downstream). Various crosstalk noise models are defined in the following clauses and they are applied, as appropriate,
to a particular test scenario. The definition of the impairment noise for VDSL2 performance testing is very complex and
for the purposes of the present document it has been broken down into smaller, more easily specified components.
These components include equivalent disturbers and crosstalk coupling functions. These separate and uncorrelated
components can be isolated and summed to form the impairment generator for the VDSL2 system under test. The
detailed specifications of the components of the noise model(s) are given in the clauses below together with a brief
explanation.
7.3.1 Functional description
Figure 7.5 defines a functional diagram of the composite impairment noise. It defines a functional description of the
combined impairment noise, as it should appear at the test probes at the receiver input of the VDSL2 transceiver under
test. Details of the measurement technique are defined in clause 7.1.
The functional diagram has the following elements:
• The seven impairment generators G1 to G7 generate noise as defined in clause 7.3.3. Their noise
characteristics are independent of the test loops and bit-rates.
• The transfer function H (f,L) models the length and frequency dependency of the NEXT impairment, as
specified in clause 7.3.2. The transfer function is independent of the loop-set number, but changes with the
0,75
electrical length of the test loop. Its transfer function changes with the frequency f, roughly according to f .
• The transfer function H (f,L) models the length and frequency dependency of the FEXT impairment, as
specified in clause 7.3.2. Its transfer function is independent of the loop-set number, but changes with the
electrical length of the test loop. Its transfer function changes with the frequency f, roughly according to f
times the cable transfer function.
• Switches S1-S7 determine whether or not a specific impairment generator contributes to the total impairment
during a test.
• Amplifier A1 provides the facility to increase the level of generators G1, G2 and G3. A value of x dB means a
frequency independent increase of the level by x dB over the full VDSL2 band, from f to the highest
0L
frequency of the VDSL2 system for each specific band plan as defined in table B.1 of Recommendation
ITU-T G.993.2 [1]. Unless otherwise specified, its gain is fixed at 0 dB.
In a practical implementation of the test set-up, there is no need to give access to any of the internal signals of the
diagram in figure 7.5. These function blocks may be incorporated with the test-loop and the adding element as one
integrated construction.
ETSI
14 ETSI TS 101 271 V1.2.1 (2013-08)
independent crosstalk
noise generators transfer functions
G1
S1
H (f,L)
NEXT noise
G2
S2
H (f,L)
A1
FEXT noise
Σ
G3
S3
Background noise
Cable independent
G4 probe
S4
White noise level
Cable independent
Σ
differential
mode
G5
Broadcast RF noise
S5d
Cable independent
Fixed powers, fixed freq
Amateur RF noise G6
S6d
Cable independent
Fixed power, variable freq
G7
Impulsive noise
S7
Cable independent
bursty in nature
S5c
probe
level
Σ
S6c
common
mode
NOTE: Generator G7 is the only one that is symbolically shown in the time domain.

Figure 7.5: Functional diagram of the composition of the impairment noise
This functional diagram will be used for impairment tests in downstream and upstream directions.
Each test has its own impairment specification that is described in clause 7.3.3 The overall impairment noise shall be
characterized by the sum of the individual components as specified in the relevant clauses. The combined impairment

noise is applied to the receiver under test at either the LT (for upstream) or NT (for downstream) end of the test loop.
7.3.2 Cable crosstalk models
The purpose of the cable crosstalk models is to model both the length and frequency dependence of crosstalk measured
in real cables. These crosstalk transfer functions adjust the level of the noise generators in figure 7.5 when the electrical
length of the test-loops are changed. The frequency and length dependency of these functions is in accordance with
observations from real cables. The cable specification is based on the following constants, parameters and functions:
• Variable f identifies the frequency in Hz.
• Constant f identifies a chosen reference frequency, which was set to 1 MHz.
• Variable L identifies the physical length of the actual test loop in metres. This value is calculated from the
cable models in clause 8 for a given insertion loss and test frequency.
• Constant L identifies a chosen reference length, which was set to 1 km.
• The function s (f,L) represents the frequency and length dependent amplitude of the transmission function of
T
the actual test loops. This value equals s = |s |, where s is the transmission s-parameter of the loop
T 21 21
normalized to the reference impedance R =135 Ω as specified in clause 8.
N
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15 ETSI TS 101 271 V1.2.1 (2013-08)
• Constant K identifies an empirically obtained number that scales the NEXT transfer function H (f,L). The
xn 1
resulting transfer function represents a power summed crosstalk model ( [i.1]) of the NEXT as it was observed
in a test cable. Although several disturbers and wire pairs were used, this function H (f,L) is scaled down as if
it originates from a single disturber in a single wire pair.
• Constant K identifies an empirically obtained number that scales the FEXT transfer function H (f,L). The
xf 2
resulting transfer function represents a power summed crosstalk model ( [i.1]) of the FEXT as it was observed
in a test cable. Although several disturbers and wire pairs were used, this function H (f,L) is scaled down as if
it originates from a single disturber in a single wire pair.
The transfer function equations below shall be used as crosstalk transfer functions in the impairment generator:
0.75
H (f, L) = K × (f/f ) × 1 – |s (f, L)|
T
1 xn 0
H (f, L) = K × (f/f ) × (L/L ) × |s (f, L)|
2 xf 0 T
Where:
(-50/20)
K = 10 ≈ 0,0032, f = 1 MHz
xn 0
(-45/20)
K = 10 ≈ 0,0056, L = 1 km
xf 0
S (f, L) = |s | = test loop transfer function
T 21
7.3.3 Individual impairment generators
7.3.3.1 NEXT noise generator [G1]
The NEXT noise generator represents the equivalent disturbance of all impairments that are identified as crosstalk noise
from a predominantly Near End origin. The noise when filtered by the NEXT crosstalk coupling function of
clause 7.3.2 represents the contribution of all NEXT in the composite impairment noise of the test.
The PSD of the noise generator is a weighted sum of the self-crosstalk and alien crosstalk profiles as specified in
clause 7.3.4.1:
• G1.UP.# = (XS.LT.# ♦ XA.LT.#).
• G1.DN.# = (XS.NT.# ♦ XA.NT.#).
The symbols in the above expressions are defined below:
• "#" is a placeholder for noise model "HD_Ex", "HD_CAB_27" etc.;
• "XS.LT.#" and "XS.NT.#" refer to the self crosstalk profiles defined in clause 7.3.4.2.1;
• "XA.LT.#" and "XA.NT.#" refer to the alien crosstalk profiles defined in clause 7.3.4.2.2;
Kn Kn 1/Kn
• "♦" refers to the FSAN crosstalk sum of two PSDs which is defined as P = (P + P ) where P is
X XS XA
the PSD in W/Hz and Kn = 1/0,6.
The PSD of this generator is independent of the cable because this is modelled separately as transfer function H (f,L) as
specified in clause 7.3.2.
The noise from this generator shall be uncorrelated with all other noise sources in the impairment generator and
uncorrelated with the VDSL2 system under test. The noise shall be random in nature with a near Gaussian amplitude
distribution as specified in clause 7.3.4.3.
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16 ETSI TS 101 271 V1.2.1 (2013-08)
7.3.3.2 FEXT noise generator [G2]
The FEXT noise generator represents the equivalent disturbance of all the impairments that are identified as crosstalk
noise from a predominantly Far End origin. The noise when filtered by the FEXT crosstalk coupling function of
clause 7.3.2 represents the contribution of all FEXT in the composite impairment noise of the test.
The PSD of the noise generator is a weighted sum of the self-crosstalk and alien crosstalk profiles as specified in
clause 7.3.4.1.
• G2.UP.# = (XS.NT.# ♦ XA.NT.#).
• G2.DN.# = (XS.LT.# ♦ XA.LT.#).
The symbols in the above expressions are defined below:
• "#" is a placeholder for noise model "HD_Ex", "HD_CAB_27","etc.;
• "XS.LT.#" and "XS.NT.#" refer to the self crosstalk profiles defined in clause 7.3.4.2.1;
• "XA.LT.#" and "XA.NT.#" refer to the alien crosstalk profiles defined in clause 7.3.4.2.2;
Kn Kn 1/Kn
• "♦" refers to the FSAN crosstalk sum of two PSDs which is defined as P = (P + P ) where P is
X XS XA
the PSD in W/Hz and Kn = 1/0,6.
The PSD of this generator is independent of the cable because this is modelled separately as transfer function H (f,L) as
specified in clause 7.3.2.
The noise from this generator shall be uncorrelated with all other noise sources in the impairment generator and
uncorrelated with the VDSL2 system under test. The noise shall be random in nature with a near Gaussian amplitude
distribution as specified in clause 7.3.4.3.
7.3.3.3 Background noise generator [G3]
The background noise generator G3 is inactive and currently is set to zero.
7.3.3.4 White noise generator [G4]
The white noise generator has a fixed value of -140 dBm/Hz and is frequency independent.
The noise from this generator shall be uncorrelated with all other noise sources in the impairment generator and
uncorrelated with the VDSL2 system under test. The noise shall be random in nature with a near Gaussian amplitude
distribution as specified in clause 7.3.4.3.
7.3.3.5 Broadcast RF noise generator [G5]
The broadcast RF noise generator represents the discrete tone-line interference caused by amplitude modulated
broadcast transmissions in the SW, MW and LW bands which ingress into the cable. These interference sources have
more temporal stability than the amateur/HAM interference because their carrier is not suppressed. Ingress causes
differential mode as well as common mode interference.
Power levels of up to -40 dBm can occur on telephone lines in the distant vicinity of broadcast AM transmitters. The
closest ten transmitters to the victim wire-pair typically dominate the noise.
The ingress noise signal for differential mode impairment (or common mode impairment) shall be a superposition of
random modulated carriers (AM). The total voltage U(t) of this signal is defined as:
U (t) = Uk ×cos(2π • fk ×t +ϕk)×(1+ m×αk(t))
∑
k
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17 ETSI TS 101 271 V1.2.1 (2013-08)
The individual components of this ingress noise signal U(t) are defined as follows:
U The voltage U of each individual carrier is specified in table 7.2 as power level P (dBm). Note that a spectrum
k k
analyser will detect levels that are slightly higher than the value specified in table 7.2 when their resolution
bandwidth is set to 10 kHz or more since they will detect the modulation power as well.
f The frequency f of each individual carrier is specified in table 7.2. The values do not represent actual radio
k k
station broadcasts but they are chosen to cover the relevant frequency range of the VDSL2 modem under test.
There is no harmonic relationship implied between the carriers.
ϕ The phase offset ϕ of each individual carrier shall have a random value that is uncorrelated with the phase
k k
offset of each other carrier in the ingress noise signal.
m The modulation depth m of each individually modulated carrier shall be 0,32 to create a modulation index of at
least 80 % during the peak levels of the modulation signal mxα (t) having a crest factor of 2,5.
k
α (t) The normalized modulation noise α (t) of each individually modulated carrier shall be random in nature with a
k k
near Gaussian distribution and an RMS value of α = 1 and a crest factor of 2,5 or more. There shall be no
rms
correlation between the modulation noise of each modulated carrier in the noise signal.
Δ The modulation width Δ of each modulated carrier shall be at least 2 x 5 kHz. This is equivalent to creating
b b
α (t) from white noise that has passed through a low-pass filter with a cut-off frequency at 1/2Δ = 5 kHz. This
k b
modulation width covers the full band used by AM broadcast stations.
The ingress noise generator may have two distinct outputs, one contributing to the differential mode impairment and the
other contributing to the common mode impairment.
The RFI ingress is expected to vary depending on the network topology. The levels specified for generator G5 are given
in table 7.2. Generator G5.#.A represents a strong RFI environment and generator G5.#.B represents a weaker RFI
environment.
Table 7.2: Noise generator G5 carrier frequencies and average power
Carrier Differential mode power Common
Frequency (dBm) mode power
(kHz) (dBm)
[G5.UP.A] [G5.DN.A] [G5.UP.B] [G5.DN.B]
99 -70 -60 -80 -70 tbd
207 -70 -60 -80 -70 tbd
-70 -60 -80 -70 tbd
-70 -60 -80 -70 tbd
909 -70 -60 -80 -70 tbd
981 -50 -40 -60 -50 tbd
1 458 -50 -40 -60 -50 tbd
6 050 -50 -40 -60 -50 tbd
7 350 -50 -40 -60 -50 tbd
9 650 -50 -40 -60 -50 tbd
7.3.3.6 Amateur RF noise generator [G6]
The Amateur RF noise generator represents a large (almost impulse like) RF interference that has radically changing
temporal characteristics due to the single-sideband suppressed nature of the amateur radio transmission. The
interference exhibits severe temporal variations, can be high in amplitude (up to 0 dBm Peak Envelope Power, PEP),
can occur anywhere within the int
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