ETSI TR 102 930 V1.1.1 (2010-09)

Technical Report
PowerLine Telecommunications (PLT);
Study on signal processing
improving the coexistence of VDSL2 and PLT

2 ETSI TR 102 930 V1.1.1 (2010-09)

Reference
DTR/PLT-00030
Keywords
emission, powerline
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ETSI
3 ETSI TR 102 930 V1.1.1 (2010-09)
Contents
Intellectual Property Rights . 4
Foreword . 4
Introduction . 4
1 Scope . 5
2 References . 5
2.1 Normative references . 5
2.2 Informative references . 5
3 Abbreviations . 6
4 Analysis of the electromagnetic coupling between PLC and VDSL2 links . 6
4.1 Executive summary about the analysis . 6
4.2 First consideration . 7
4.3 Reference configuration . 7
4.4 Power Injected between two PLT modems . 7
4.5 Theoretical approach . 8
4.5.1 Coupling to aerial cables . 8
4.5.2 Synthesis processing . 10
4.6 Summary of the results . 10
4.6.1 Untwisted Telecom wires . 10
4.6.2 Twisted wires (CAT3) . 11
4.6.3 Twisted wires (CAT5) . 12
4.7 Examples of theoretical results . 12
5 Algorithms to allow the coexistence of PLT with VDSL2 . 15
5.1 Executive summary about the algorithms . 15
5.2 Problem statement . 15
5.3 Analysis of the PHY layers of PLT and VDSL2 . 15
5.4 Channel Coupling Model for Signal Processing . 16
5.5 Method 1: Adaptive interference cancelling filter . 17
5.6 Method 2: Spectral management . 18
6 PLT implementation of coexistence algorithms . 19
6.1 Executive summary . 19
6.2 Operating Principle. 20
6.3 End-user Coexistence Tool. 20
6.4 Installer Tool . 21
6.5 Service Provider Tool . 23
7 Crosstalk measurements in real houses . 24
7.1 Executive summary . 24
7.2 Measurements . 24
8 Effect of the mitigation on a VDSL2 system . 28
8.1 Executive summary . 28
8.2 Measurements . 28
9 Conclusions . 30
Annex A: Bibliography . 32
History . 35

ETSI
4 ETSI TR 102 930 V1.1.1 (2010-09)
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://webapp.etsi.org/IPR/home.asp).
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 Report (TR) has been produced by ETSI Technical Committee Powerline Telecommunications (PLT).
Introduction
The current solution for the IPTV market is based on ADSL link from the TELCO office to the customer premises, an
ADSL gateway at the customer premise to decode the signal, and a home network to distribute the signal within the
house. The next generation of broadband access, currently being deployed by European TELCOs, is based on VDSL2
technology. On the other hand, powerline technology is becoming the preferred solution for home networking when
applications, such as IPTV, requiring high throughput and QoS are provided. However, both technologies, VDSL2 and
PLT, use the same frequency band (2 MHz to 30 MHz), and several studies ([i.6] and [i.7]) predict the interference of
PLT modems over VDSL2 systems. To confirm these predictions the ETSI PLT group conducted a Plugtest where the
level of interference between both technologies was measured, and set up a Specialist Task Force with the following
assignments:
1) to analyze the severity of the interference; and
2) to propose solutions to mitigate it.
The present document presents the result of the STF.
ETSI
5 ETSI TR 102 930 V1.1.1 (2010-09)
1 Scope
The present document presents the result of the work of the STF and suggests the methods and practices to reduce or
mitigate the crosstalk between electricity and telephone cables. The present document also includes the results of a
small measurement campaign in real housed aimed at confirming the results of the Plugtest and validating the
mitigation methods.
The work was organised in three phases assigned to different STF members:
• Phase 1: Modelling the coupling channel between VDSL2 and PLT (clause 4).
• Phase 2: Simulations of signal processing algorithms for coexistence (clause 5).
• Phase 3: Implementation of the algorithms in PLT devices (clause 6); field measurements (clause 7) and
laboratory validation (clause 8).
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.
Not applicable.
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] "Analysis of Multiconductor Transmission Lines", C.R. Paul. John Wiley & Sons, 1994.
[i.2] "Coupling of External Electromagnetic Fields to transmission Lines", A.A Smith John. Wiley &
Sons, 1977.
[i.3] "Principes and applications of EM field coupling to transmission lines", F.M. Tesch. Proc. Int'l
Symp. Electromagn. Compat. (EMC'95), Zurich, Switzerland, pp.21-31 (Supplement), 1995.
[i.4] "Compatibilité Electromagnétique 1 - des concepts de base aux applications", P. Degauque,
A. Zeddam. Hermes Science. Get et Lavoisier, Paris 2007.
[i.5] "Coupling to Shielded Cables", E.F. Vance. John Wiley & Sons, 1977.
[i.6] "Analyse du rayonnement et des couplages électromagnétiques provoqués par des signaux hautes
fréquences interférant avec des câbles d'énergie basse tension", R.Razafferson. Thèse de doctorat,
Université des sciences et Technologies de Lille, 31 October 2002.
[i.7] "PowerLine effects over VDL2 performances", A.Bergaglio, U.Eula, M.Giunta, A.Gnazzo. IEEE
international Symposium on Power Line, ISPLC 2008.
ETSI
6 ETSI TR 102 930 V1.1.1 (2010-09)
[i.8] ETSI TR Plugtest Report on Coexistence VDSL2 and PLT (LANPARK).
[i.9] PLC-VDSL Crosstalk Measurements (DS2). Description of the test kit, installer tool and
measurement procedure for field and laboratory test.
[i.10] Broadband Forum TR-069. CPE WAN Management Protocol v1.1.
NOTE: See http://www.broadband-forum.org/technical/download/TR-069_Amendment-2.pdf.
3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ACS Auto Configuration Server
AFE Analog Front-End
AGC Automatic Gain Control
CAT3 Category-3 twisted-pair cable
CAT5 Category-5 twisted-pair cable
CPE Customer Premises Equipment
NOTE: DSL modem installed in the customer premises.
CSV Comma-Separated Value
DMT Discrete Multi Tone modulation
DSL Differential Subscriber Line
DSLAM Digital Subscriber Line Access Multiplexer
FDD Frequency Division Diplexing
MTL Multiconductor Transmission Lines
OFDM Orthogonal Frequency Division Multiplex
PHY Physical Layer
PLC Power Line Communications
PLT Power Line Telecommunications
POTS Plain Old Telephone Service (legacy telephone network)
PSD Power Spectral Density
RPC Remote Procedure Call
TEM Transversal Electromagnetic Mode
TLT Transmission Line Theory
UPA Universal Powerline Association
VDSL2 Very High-speed DSL 2
4 Analysis of the electromagnetic coupling between
PLC and VDSL2 links
4.1 Executive summary about the analysis
VDSL2 access technology will be used in Next generation networks as final drop for residential customer. Within
customer premises and in certain circumstances we can have coexistence between VDSL2 and Powerline technology
(PLT or PLC). The problem of coexistence between Powerline and VDSL2 depends on the fact that these technologies
share the same frequency band up to 30 MHz, and sometimes the power line can be located near the VDSL2 cable. It is
well known that cables constituting the power line network are not balanced and consequently at these frequencies some
radiated emissions may occur. The aim of this paper is to theoretically study the coupling between Powerline and
VDSL2 links. In order to validate the proposed model a comparison with experimental results is also given.
ETSI
7 ETSI TR 102 930 V1.1.1 (2010-09)
The simulation tool based on the transmission line theory allows us to have a good knowledge about the mechanisms of
coupling between a VDSL2 cable and PLT link located both in the customer premises. The differences observed
between theoretical and experimental results are mainly due to the difficulties to define with enough precision the per
unit length parameters of the lines and the parallelism between the wires. However we can consider as sufficient the
agreement between the theoretical results and the measurements obtained by LANPark Lab or given in [i.7] in order to
carry out a complementary study taking into account all the main parameters involved in the coupling.
4.2 First consideration
VDSL2 access technology will be used in next generation networks as final drop for residential customer. Within
customer premises and in certain circumstances we can have coexistence between VDSL2 and Powerline technology
(PLT or PLC). As both technologies use the same frequency bandwidth we are thus interested in this paper in the
theoretical study of the coupling between Powerline and VDSL2 links. In order to validate the proposed model a
comparison with experimental results is also given.
4.3 Reference configuration
Figure 1 shows a uniform multiconductor transmission line (unshielded VDSL2 multipair cable and unshielded 3-wires
powerline) above an ideal ground-plane. The conductors are assumed to be infinitely long and the ground-plane is
infinitely extended.
Power line
Pair 1
Variable separation
distance
Pair 3
VDSL2 cable
hj
Reference
Figure 1: Reference configuration
4.4 Power Injected between two PLT modems
Figure 2 shows a wanted signal differential Power Spectral Density (PSD) measured between the two PLT modems
using different coupling network. The obtained mean value is around -55 dBm/Hz (QuasiPeak). This value has been
used during the simulation.
ETSI
8 ETSI TR 102 930 V1.1.1 (2010-09)
Power injected
-55dBm/Hz
-40
-50
-60
-70
-80
-90
CDN
AMN
-100
TISN
Without Network
-110
1 6 11 16 21 26
Frequency (MHz)
Figure 2: PSD measured between 2 PLT modems
4.5 Theoretical approach
To resolve this problem, we have chosen to use modelling tools based on the transmission-line theory (TLT). This
choice is basically justified by the mathematical and computational simplicity of the model, together with the good
accuracy it has proven over more than one hundred years of extensive validations in many different contexts [i.1], [i.2],
[i.3], [i.4] and [i.5].
The formulation and analysis method employed is the quasi-TEM (transverse electromagnetic) approach, i.e. the
principal propagation mode of the line is TEM. Taylor and al. applied this approach to study the field coupling to a
two-wire line and later generalized to Multiconductor Transmission Lines (MTL), and the line is considered a uniform
line in that the (n+1) conductors are parallel to each other and the axis of a rectangular coordinate system.
4.5.1 Coupling to aerial cables
The process is first to consider the incident electric field in the absence of the cable then to transform this incident field
like an equivalent source term (Figure 3) in the model of the transmission-line theory (TLT). In practice, it is the
approach known as of Agrawal which primarily has the most advantages because the incident field useful for the model
is limited to the component of the incident electric field tangential to the cable [i.4].
r
incident
[]E (x, z) = ε ⋅ dl Equation (1)
T i
∫
C
i
The quantity []E (x, z) is the integral of the component of the incident electric field vector that is in the transverse
T i
plane and tangent to the contour c along that contour.
i
ETSI
DSP(dBm/Hz)
9 ETSI TR 102 930 V1.1.1 (2010-09)
Et
Et
+
-
+
- +
-
Et
+
-
+
- +
-
Et
+
-
+
- +
-
Et
Figure 3: Equivalent source term
The differential equations for the voltage and current along the transmission line in the presence of distributed
excitations are:
h
⎧ dV
⎛ ⎞
i i
⎛ ⎞
− =()Z ⋅(I)− E (x) − j ⋅ w⋅ B (x, z) ⋅ dz
⎜ ⎟
⎜ ⎟
x y
⎪
∫
⎝ ⎠
dz
⎪⎝ ⎠
Equation (2)
⎨
h
dI
⎛ ⎞
i
⎛ ⎞
⎪
− =()Y ⋅(V)+ j ⋅(C)⋅ w ⋅⎜ E (x, z) ⋅ dz⎟
⎜ ⎟
z
∫
⎪
⎝ ⎠
dz
⎝ ⎠
⎩
Where :
Z = impedance per unit length.
Y = admittance per unit length.
i
E (x) = tangential electric field at the surface of the ground and in the absence of the cable.
z
i
−
B (x, z) = the y component of the magnetic field in the absence of the cable.
y
i
−
E (x, z) = the z component of the electric field in the absence of the cable.
z
h h
⎛ ⎞ ⎛ ⎞
i i i
⎜ ⎟ ⎜ ⎟
The right hand terms E (x) , j ⋅ w⋅ B(ax, z)⋅ dznd j ⋅()C ⋅ w⋅ E (x, z)⋅ dz represent the distributed line
z y z
⎜ ⎟ ⎜ ⎟
∫ ∫
0 0
⎝ ⎠
⎝ ⎠
excitations of the common impedance, inductance and capacitive coupling modes, respectively. The impedance and
admittance per unit length ()Z and ()Y are defined as:
()Z = R + j ⋅(L)⋅ω
Equation (3)
()Y = G + j ⋅(C)⋅ω
In this section, we will consider an MTL line with perfect conductors surrounded by a homogeneous and lossless
medium. In this case matrices R and G are equal to zero. Due to the TEM assumption, the matrices of inductance and
capacitance are related to the static solution of Laplace's equation.
In particular, ()C and ()L are related by:
−1
()C = μ ⋅ε ⋅(L) Equation (3a)
where μ and ε are respectively the magnetic permeability and the dielectric permittivity of the surrounding medium.
nd
The differential equation current (4) of the 2 order is obtained by the combination of the equations (2) and (2) in
which ()S is a term related to excitation.
ETSI
10 ETSI TR 102 930 V1.1.1 (2010-09)
⎛ ⎞
d I
⎜ ⎟
−()Z ⋅(Y)⋅(I) =(S) Equation (4)
⎜ ⎟
dz
⎝ ⎠
The voltages and currents are virtual quantities, related to the physical ones by equation (1). Actually, the propagation
along each line corresponds to the N TEM modes allowed by a MTL, as introduced in clause 4.5. For this reason, this
solution of equation (4) is referred to as a modal approach. Hereafter, the quantities voltages and currents will be
referred to, respectively, as modal voltages, currents and excitation terms.
4.5.2 Synthesis processing
TM
Data processing and calculations were done using Fortran 90 Software (already developed in [i.6] for similar
TM
studies). Of course, we envisaged using the CRIPTE software for simulation, but it is not currently available. Since
the calculation process is the same. We think that the results will lively be the same.
Input Data Output
processing
Data Data
Transmission-Line
[]L [C]
[]V [I]
Theory (TLT)
Figure 4: Calculation process
4.6 Summary of the results
4.6.1 Untwisted Telecom wires
Table 2 shows the coupling noise PSD (dBm/Hz) on the telephone wires positioned at different distance according to
the simulation (Wire diameter, dw = 0,5 mm).
Table 1: Experimental results for untwisted telecom wires

The experimental results indicated in Table 1 (obtained by LanPark) show the variation of the level of coupling noise
between -121 dBm/Hz and -140,5 dBm/Hz.
ETSI
11 ETSI TR 102 930 V1.1.1 (2010-09)
Table 2: Summary of theoretical results for untwisted telecom wires
Length
1 m 5 m 20 m 40 m
20 cm -147,1 -145,3 -144,7 -143.5
6 cm -137,2 -132,4 -132,6 -131,3
1 cm -130,2 -127,6 -127,4 -127,1
0 cm -127,8 -126,2 -126,1 -125.7

The simulation results are shown in Table 2. These results show that the level of the coupled noise on the telephone
wires in presence of the PLC can reach -125,7 dBm/Hz to -147,1 dBm/Hz.
4.6.2 Twisted wires (CAT3)
Table 3 shows the coupling noise PSD (dBm/Hz) on the twisted telephone wires positioned at different distance
according to the simulation.
Table 3: Experimental results for twisted telecom wires (CAT 3)

The experimental results for the same cable are indicated in Table 3 (obtained by LanPark). They show the variation of
the level of coupling noise between -121 dBm/Hz and -140,7 dBm/Hz.
Table 4: Summary of theoretical results for twisted telecom wires (CAT3)
Length
1 m 5 m 20 m 40 m
20 cm -147,8 -147,3 -145,7 -144,7
6 cm -141,1 -139,7 -138,5 -137,6
1 cm -134,6 -133,3 -133,1 -132,7
0 cm
-131,6 -130,3 -129,8 -129,2
The simulation results are presented in Table 4. These results show that the level of the coupled noise on the telephone
wires (CAT3) in presence of the PLC can reach -129 dBm/Hz to -147,8 dBm/Hz.
ETSI
Spacing
Spacing
12 ETSI TR 102 930 V1.1.1 (2010-09)
4.6.3 Twisted wires (CAT5)
Table 5 shows the coupling noise PSD (dBm/Hz) on the twisted telephone wires positioned at different distance
according to the simulation.
Table 5:Experimental results for twisted telecom wires (CAT 5)

The experimental results for the same cable are indicated in Table 5 (obtained by LanPark). They show that the
variation of the level of coupling noise is between -136,8 dBm/Hz and -140,4 dBm/Hz.
Table 6:Summary of theoretical results for twisted telecom wires (cat5)
Length
1 m 5 m 20 m 40 m
20 cm -149,2 -147,3 -147,2 -146,8
6 cm -142,3 -140,3 -140,1 -140,1
1 cm -135,6 -134,4 -134,5 -134,3
0 cm
-132,5 -130,8 -130,9 -130,6
The simulation results are presented in Table 6. These results show that the level of the coupled noise on the telephone
wires (CAT5) in presence of the PLC can reach from -130,6 dBm/Hz to -149,2 dBm/Hz.
Remark: According to other results given in [i.7], the level of coupling noise PSD on the telephone lines
positioned at different distance can reach from -95 dBm/Hz to -110 dBm/Hz in the presence of
PLC.
4.7 Examples of theoretical results
Figure 5, Figure 6 and Figure 7 show the examples of theoretical results of the coupling noise PSD on the VDSL2 lines
at three different cables and different lengths, as the PLC signals is carried by the power line situated at a separating
distance of 0 cm.
ETSI
Spacing
13 ETSI TR 102 930 V1.1.1 (2010-09)
Untwisted Space 0cm
-100
-110
-120
20 m
-130
40 m
1 m
-140
5 m
-150
-160
-170
1 10 100
Frequency (MHz)
Figure 5: Coupling noise PSD on the VDSL2 lines positioned at different distance
(Untwisted, space = 0 cm and wire diameter (dw) = 0,5 mm)
CAT3 Space 0cm
-120
-130
-140
20 m
40 m
-150
5 m
1 m
-160
-170
-180
1 10 100
Frequency (MHz)
Figure 6: Coupling noise PSD on the VDSL2 lines positioned at different distance
(Cat3, space = 0 cm and wire diameter (dw) = 0,5 mm)
ETSI
DSP (dBm/Hz)
DSP (dBm/Hz)
14 ETSI TR 102 930 V1.1.1 (2010-09)
CAT5 Space 0cm
-120
-130
-140
20 m
40 m
-150
1 m
5 m
-160
-170
-180
110 100
Frequency (MHz)
Figure 7: Coupling noise PSD on the VDSL2 lines positioned at different distance
(Cat 5, space = 0 cm and wire diameter (dw) = 0,5 mm)
Cable untwisted ( length 5m)
-120
-130
-140
Space 6 cm
Space 20 cm
-150
Space 0 cm
Space 1 cm
-160
-170
-180
110 100
Frequency (MHz)
Figure 8: Coupling noise PSD on the VDSL2 lines positioned at different distance
(Cable untwisted length = 5m, space (variable) and wire diameter (dw = 0,5 mm)
Figure 8 shows the impact of the space for cable untwisted (length 5 m). We can see that we obtained a variation about
19 dB.
Figure 9: Experimental set up
ETSI
DSP (dBm/Hz)
DSP (dBm/Hz)
15 ETSI TR 102 930 V1.1.1 (2010-09)
The differences between the theoretical and the experiments results are mainly due to the non-respect of parallelism
between the wires (see the picture in Figure 9).
5 Algorithms to allow the coexistence of PLT with
VDSL2
5.1 Executive summary about the algorithms
We focus our effort on the spectral management as the occupation of each carrier . To ensure a better coexistence of
PLT and VDSL2 services, we propose two solutions for this purpose: an approach based on detection and an approach
based on avoidance.
1) In case of mild interference of PLT on VDSL2, an adaptive filter at the input of the VDSL2 transceiver is a
mitigation solution.
2) In case of severe interference of PLT on VDSL2, a spectral management based on listing PLT carriers close to
VDSL2 carriers and reducing their power level and modifying the bit loading should be implemented in PLT
modem.
5.2 Problem statement
A recent survey of literature on this coexistence problem shows the interest of other members not involved in this
STF384 and other publications motivating to solve this problem of coexistence.
This motivation is aiming our investigation on signal processing solutions by examining in detail both the VDSL2 and
PLT signals on the telephone and electrical channels.
The coupling of PLT on VDSL2 is a wide band signal and therefore traditional methods of coexistence (such as
notching) are not applicable.
The data exchange between the PHY layers of existing VDSL2 CPE and PLT modems is not possible, therefore the
DSM methods applied to DSL are not exploitable. The only feature we can exploit is the fact that the residential
gateway based on VDSL2 technology is connected to at least one PLT modem in the same outlet.
The constraint on this investigation is related to present PLT and VDSL2 equipments and not forthcoming products.
The solutions to be implemented should be simple and viable with existing technology.
VDSL2 and PLT technologies are based on ITU and ETSI standards respectively, both operating with OFDM
transmission on different wires at home.
Both PLT and VDSL2 modems operate in the frequency range from 2 MHz to 30 MHz, although on different cables.
The ETSI PLUGTEST on PLT-VDSL2 coexistence confirms the risk of potential interferences when the cables are
very close to each other.
The work of the PLUGTEST was followed by a modelling performed by France Telecom in phase 1 of this STF384.
The findings can be summarized as follows:
1) The dominating part of the interference above certain frequency is due to electromagnetic emission (radiation).
2) The interference (or the coupling) will increase with frequency up to a certain cut-off frequency.
3) The conducted field interference is not so strong as would generally be perceived.
5.3 Analysis of the PHY layers of PLT and VDSL2
The physical layer of PLT modem (PHY) is based on windowed Orthogonal Frequency Division Multiplexing (OFDM)
as the basic modulation technique. The physical layer of VDSL1/VDSL2 modem (PHY) is based on windowed
Orthogonal Frequency Division Multiplexing (OFDM) as the basic modulation technique, also called DMT (Discrete
Multitone Transmission).
ETSI
16 ETSI TR 102 930 V1.1.1 (2010-09)
VDSL2 transceivers use frequency division diplexing (FDD) to separate upstream and downstream transmissions. The
overlapping of the upstream and downstream passbands is not allowed. The allocation of the upstream and downstream
frequency bands is defined by the band plan, which is specified by band-separating frequencies.
The VDSL2 signal can potentially use the frequency range up to 30 MHz, although the maximum frequency used by a
modem to transmit data depends on the selected band plan and the conditions of telephone line.
The VDSL2 transceiver may select one or more sub-carriers to use for timing recovery, called Pilot Tones. Pilot tones
are selected separately for initialization and showtime.
For VDSL2 two sub-carrier spacing are available: 4,3125 kHz and 8,625 kHz.
Table 7: PHY parameters of the VDSL2 profiles
Profile Bandwidth Number of Carrier Power (dBm) Max.
(MHz) carriers bandwidth (kHz) Throughput
(Mbit/s,
downstream)
8a 8,832 2 048 4,3125 +17,5 50
8b 8,832 2 048 4,3125 +20,5 50
8c 8,5 1 972 4,3125 +11,5 50
8d 8,832 2 048 4,3125 +14,5 50
12a 12 2 783 4,3125 +14,5 68
12b 12 2 783 4,3125 +14,5 68
17a 17,664 4 096 4,3125 +14,5 100
30a 60 3 479 8,625 +14,5 100
5.4 Channel Coupling Model for Signal Processing
For the purpose of signal processing to improve the coexistence of PLT with VDSL2, we consider the following model.
Let h be the channel model for VDSL2 and h the model for the PLT channel. Let h be the coupling model from
1,1 2,2 2,1
PLT to VDSL2 and h the coupling model from VDSL2 to PLT. This complete model is described in Figure 10 as an
1,2
additive model of the coupling.

Figure 10: Channel coupling model
Following the simulation results produced by France Telecom (see clause 4), we consider only the baseband signals up
to 30 MHz and focus on the coupling in the range of 1MHz to 30 MHz.
The cross-channel coupling depends on the type of cables (twisted or untwisted) used for VDSL2 transmission as well
as the space between cables and their length.
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17 ETSI TR 102 930 V1.1.1 (2010-09)
We observe that the coupling factor is increasing as a function of frequency; this observation is correlated to the
coupling factor between DSL lines in a same cable.
In the following clause 5.5, H(f) is the transfer function, based on the PLT and VDSL2 channel coupling model
(Figure 10), expressed as a matrix.
The following equations describe the coupling process between VDSL2 signal X and PLT signal X as linear mixing
1 2
of signals with additive gaussian noise:
Y = h X + h X + n
1 11 1 12 2 1
Equation (5)
Y = h X + h X + n
2 21 1 22 2 2
The input signals are X for VDSL2 and X for PLT and output signals (the ones actually received by the modems) are
1 2
Y for VDSL2 modem and Y for PLT modem.
1 2
5.5 Method 1: Adaptive interference cancelling filter
The present method relates to a cancellation filter to suppress the interference of a PLT signal carried by a power
distribution network in the user premises to the VDSL signal carried by a telephone system that is located close to some
power cable.
The method is based on feeding the signal carried by the power network to the adaptive filter in order to obtain an
estimate of the PLT signal that couples on the telephone line. The estimated signal is then subtracted from the signal
carried by the telephone line.
This estimation is based on minimization of mean square error and following equation are classical for estimation of
original signals (X , X ) from linear combination of corrupted data (Y , Y ).
1 2 1 2
&&
X Y
⎛ ⎞ −1 ⎛ ⎞
1 1
T T
⎜ ⎟ =()H H H ⎜ ⎟ Equation (6)
⎜ ⎟ ⎜ ⎟
&&
X Y
⎝ 2 ⎠ ⎝ 2 ⎠
The implementation of this system involves a VDSL gateway fed by a splitter filter modified in order to reject the
interference of the PLT signal. The interference cancelling device includes an adaptive filter with a differential input
and one output.
The adaptive filter receives the signal from the VDSL splitter and from an outlet of the electrical network where the
PLT modem is connected. The device includes a capacitive coupler that is connected to an electrical outlet preferably
located near the gateway integrating the VDSL2 modem to retrieve the signal carried by the power line.
POTS
Mains Outlet
coupler
VDSL2 modem ethernet PLT
cancellation
splitter
gateway Modem
filter
Figure 11: Block diagram of the interference cancellation system.
The process to cancel the interference involves picking-up the signal carried on the power line so that the adaptive filter
obtains an estimate of the signal that disrupts the VDSL communication and subtracts the estimated signal from that
carried by telephone line.
&&
Y − h X Equation (7)
1 12 2
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18 ETSI TR 102 930 V1.1.1 (2010-09)
We proceed in two steps: first we use the zero forcing method to determine the complex coefficients of channel
parameters:
&&
Y − h X
⎛ ⎞ ⎛0⎞
1 12 2
⎜ ⎟ = ⎜ ⎟ Equation (8)
⎜ ⎟ ⎜ ⎟
&&
Y − h X
2 22 2 ⎝ ⎠
⎝ ⎠
Secondly, we estimate the original signals by solving the following equations:
&& &&
Y − h X h X
⎛ ⎞ ⎛ ⎞
1 12 2 11 1
⎜ ⎟ ⎜ ⎟
= Equation (9)
⎜ ⎟ ⎜ ⎟
&& &&
Y − h X h X
⎝ 2 22 2 ⎠ ⎝ 21 1⎠
These two steps are repeated within a time interval to take into account the time variations of the PLT channel.
5.6 Method 2: Spectral management
We describe a method to reduce the interference from the PLT signal to the VDSL signal transmitted over a telephone
line located at near the power line.
Both signals convey data in bits which are assigned to many carriers distributed over the same frequency band. The
frequency plan for the VDSL2 upstream and downstream bands varies depending on the region.
A spectral management method to reduce the interference between a PLT signal and a VDSL2 signal transmitted on a
phone line that is located near the power line is described.
In a first step, we determine at least one carrier frequency, called VDSL frequency, of a frequency plan used for the
transmission whose level of spectral power density exceeds a predetermined threshold.
In a second step we determine at least one carrier frequency, called PLT frequency, of another frequency plan used for
signal transmission on powerline, which is shared with at least one VDSL frequency.
And in a third step we reduce the power and therefore the number of bits assigned to each PLT frequency determined
thereby.
The proposed method is based on the fact that a PLT carrier and a VDSL2 carrier overlap or they are separated by a
distance smaller than a predetermined maximum distance.
The method is also based on the fact that the maximum distance is either zero, strictly greater than zero or greater than
or equal to zero. This distance is defined as the magnitude of the difference between the VDSL2 windowed OFDM
carrier and the PLT windowed OFDM carrier. This distance measures how close are the carriers between VDSL and
PLT signals.
In Figure 12, the first graphs shows roughly the N VDSL carriers with frequencies Fk in the range and a threshold
relative to the maximum PSD level. The second graph shows the N PLT carriers in the same band but the carrier
spacing has a ratio of 1 to 4 from VDSL to PLT. According to the distance D, one VDSL carrier may be affected by 3
PLT carriers. For instance, VDSL carrier at Fk (k = 11) is interfered by PLT carriers at Fk (k = 10, k = 11, k = 12).
The third graph shows the result of the iterative bit loading algorithm decreasing the power level of these 2 PLT carriers
and the redistribution of their payload on carriers 14 and 15.
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19 ETSI TR 102 930 V1.1.1 (2010-09)

Figure 12: Spectral management and redistribution of the bit loading in a PLT signal
We make additional iterations according to steps 1 to 3, where the number of bits assigned to PLT carriers is decreased
until the interference on the VDSL signal is compensated by the error correcting codes.
The Powerline Modem should be modified so as to detect the VDSL signal in silent periods of the PLT transmission by
using an amplifier of VDSL signal when this signal is too weak to be detected by PLT modem.
6 PLT implementation of coexistence algorithms
6.1 Executive summary
The main requirement of this STF is to produce algorithms that can be implemented with the existing technologies. At
present there is no standardized way to exchange information between the VDSL2 and PLT systems that would allow a
coordinated action to detect and mitigate the interference. Therefore, it has been chosen to work exclusively on the PLT
technology as it is the expertise of the concerned experts.
From the algorithms presented in clause 5, the one that is suitable for implementation on PLT devices is the spectral
management (adjustment of the amplitude of the OFDM carriers). This clause presents three methods to manage the
PLT spectrum: one for End Users, one for Installers and one for Service Providers. Although the implementation has
been done for UPA modems, the methods described in this document are applicable to other power line technologies.
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20 ETSI TR 102 930 V1.1.1 (2010-09)
In addition to the tools, DS2 has developed a kit for installers that allows an easy measurement of the crosstalk in real
scenarios. This kit has been used to measure the crosstalk level in several locations in order to complement the results
obtained in the Plugtest. The results obtained in Spain and in France confirm that the coupling levels in real houses are
in line with the experimental values, and they are low enough to allow the simultaneous use of VDSL2 and PLT.
6.2 Operating Principle
The spectral management consists in modifying the amplitude of the OFDM carriers of the PLT modem in the
frequencies where the VDSL2 communication is affected.
Being the interference level very low as demonstrated in [i.8], it is likely that it will affect only the downstream bands
of the VDSL2 signal. Therefore, only these bands are regarded when it comes to analyzing the interference and
applying the spectral management.
The PLT system is tolerant to any variation in the PSD of the transmitted signal. If the spectrum is modified, the
modems negotiate a new bit-loading scheme and the communication continues with a lower physical speed. A reduction
of 10 dB to 20 dB in some parts of the PLT signal will still leave enough bandwidth to provide the required services
while protecting the VDSL2 communication.
Figure 13 explains how the spectrum management is used to mitigate the interference. The red line represents the
crosstalk of the PLT signal measured on the telephone line. Applying a different attenuation to each carrier that falls
within a downstream band will set the crosstalk level to a predefined value (blue line) that is low enough to allow the
correct demodulation of these bands in the CPE.
US1 US2 US3
DS1
DS2
DS3
f
Figure 13: PSD of the PLT crosstalk signal before (red) and
after (blue) the modification of the spectrum
6.3 End-user Coexistence Tool
This tool is designed for users that have bought a set of PLT modems in the retail market and have found that they
interfere with their VDSL2 communication. In this case the Service Provider may be able to diagnose the problem on
the VDSL2 system but he will not have the means to configure the PLT modems.
Knowing the VDSL2 profile being used, the end user can configure the PLT modems to reduce the power in the
downstream bands. The tool allows setting a variable attenuation of the PLT signal in these bands between 0 dB and
25 dB. If the Service Provider is not able to give a clue of the attenuation required on the PLT signal, the end user
should try out, through trial and error different values until the VDSL2 communication works smoothly.
A snapshot of the tool is presented in Figure 14. There are two controls that need to be configured by the user: the
VDSL2 profile and the percentage of the mitigation. Once the level is selected, it can be applied individually to each of
the modems shown in the list. There is an indicator that turns green if the operation has been successful.
The information regarding the frequencies of the upstream and downstream bands is contained in a configuration file
located in the same directory as the application.
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21 ETSI TR 102 930 V1.1.1 (2010-09)
This tool has one major shortcoming. The lack of information about the real coupling level and the frequencies where
this coupling is more intense does not allow an optimal adjustment of the PLT spectrum. The mitigation is applied
blindly on all the downstream bands and with the same intensity. Therefore, when the level is adjusted for the band
where the interference is strongest it might be excessive for the other bands, resulting in an unnecessary deterioration of
the PLT speed.
Figure 14: End-user tool for PLT spectral management
6.4 Installer Tool
This tool is designed for the crew in charge of installing the VDSL2 and PLT modems provided by the Service
Provider. The software application is complemented with a special PLT modem that connects to the telephone outlet in
order to measure the interference seen by the VD
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