Transcript RRAC Presentation

Radio Technology & Compatibility Group
Whyteleafe Surrey
Leakage Emissions
from
ADSL & Power Line
Telecommunication
Networks
14 November 2003
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL & PLT Telecommunication Networks
• Modern ‘Local Loop’ broadband access systems
• Based on secondary use of existing cables
• ADSL utilises existing twisted pair telephone lines
• PLT utilises the low voltage electricity distribution
network
• Both compete with broadband coaxial cable systems
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL & PLT Leakage Issues
• Telephone & Power cables were not designed for
high frequency use
• Leakage emissions can occur on ADSL lines under
certain fault conditions but will occur inherently on
PLT networks.
• Leakage emissions may be at significant levels and
thus have the potential to cause serious interference
to local radio reception
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL & PLT Interference – RA’s obligations
ITU Radio Regulations – Chapter IV - Interference
15.12 § 8
Administrations shall take all practicable and
necessary steps to ensure that the operation of
electrical apparatus or installations of any kind,
including power and telecommunication distribution
networks, but excluding equipment used for
industrial, scientific and medical applications, does
not cause harmful interference to a radio
communication service and, in particular, to a radio
navigation or any other safety service operating in
accordance with the provisions of these Regulations.
RRAC Open Forum - Church House Westminster - 14 November 2003
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The ADSL Situation
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ADSL emissions & interference mechanism
• ADSL frequency spectrum encompasses the LW and
MW broadcast bands
• Leakage emissions can occur due to imbalance in
the unscreened twisted-pair telephone lines
• The resultant flow of common mode current
generates an electromagnetic field around the
telephone line
• Domestic AM broadcast receivers with integral ferrite
rod antennas couple into the electromagnetic field
• ADSL interference is audible as white noise, a
heterodyne whistle or a combination of both
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ADSL Spectrum
Discrete Multi-Tone ADSL - 256 carriers
Upstream 20 kHz to 130 kHz - Maximum data rate 256 kbit/s
Downstream 160 kHz to 1.1 MHz - Maximum data rate 512 kbit/s
50
Differential Mode Current (dBuA in 200 Hz)
40
30
20
10
0
-10
-20
-30
-40
0
200
400
600
800
1000
1200
Frequency in kHz
RRAC Open Forum - Church House Westminster - 14 November 2003
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Actions by RA to limit ADSL interference
• Accepted the positioning of a domestic portable radio
•
•
•
•
between 1 & 3 metres from internal telephone wiring
as the default operating condition requiring protection
Consulted with Broadcasters and Telcos during the
development of draft emission limits intended to
protect LW and MW broadcast reception
Issued the limits as a draft standard called MPT1570
& conducted a regulatory impact assessment
Studied the feedback received & recommended a set
of limits for ministerial approval
Published MPT1570 containing emission limits from 9
kHz to 1.6 MHz
RRAC Open Forum - Church House Westminster - 14 November 2003
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The MPT 1570 Standard – Points to note
• Not a compliance standard
• Limits to be applied only for adjudication purposes in
cases of reported interference
• A compromise between the need to offer some
protection to radio users whilst allowing Telcos to roll
out ADSL without fear of undue expenditure on
interference limiting measures
• So what protect does the MPT1570 limit offer ?
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL interference at the MPT1570 limit
• Best demonstrated subjectively with audio recordings
• These recordings were made at Whyteleafe using
BBC broadcast stat0ions adjusted to a ‘edge of
service area’ field strength of 66 dBuV/m in LW & 60
dBuV/m in MW
• The heterodyne case - unmodulated ADSL carriers
• The white noise case - modulated ADSL carriers
• Did RA get it right ?
RRAC Open Forum - Church House Westminster - 14 November 2003
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An ADSL Interference complaint
ADSL downstream levels at Telephone pole
MPT1570 1 metre measurement
120
Field Level dBuV/m (9 kHz - Peak)
110
100
90
80
70
60
50
40
30
100
300
500
700
900
1100
1300
1500
1700
Frequency kHz
ADSL on
ADSL off
MPT1570 limit line
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL Interference resolution
ADSL downstream levels at Telephone pole - (after remedial action )
MPT1570 1 metre measurement
120
110
Field Level dBuV/m (9 kHz - Peak)
100
90
80
70
60
50
40
30
100
300
500
700
900
1100
1300
1500
1700
Frequency in kHz
ADSL on
ADSL off
MPT1570 limit line
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL Interference – The Facts
• Approaching 1.5 million ADSL lines in the UK
• MPT1570 limit offers only minimal protection to LW &
MW broadcast reception
• RA aware of only 1 substantiated interference
complaint so far
• So how do we reconcile this situation ?
RRAC Open Forum - Church House Westminster - 14 November 2003
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ADSL Interference - Observations
• The majority of fault-free ADSL lines have leakage
radiation well below the MPT1570 limit
• Any faulty lines are usually repaired quickly & before
any interference being experienced has the potential
to become a ‘persistent interference’ complainant
• White noise & heterodyne whistles may not be
recognised as external interference by most listeners
• Most radio listeners do not know how to complain or
who to complain to
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Conclusions
• As the ADSL roll-out gathers pace and radio users
become aware of the technology further interference
complaints are deemed inevitable
• The situation is likely to be exacerbated by the
current use of self-install ADSL products having no
filter between the incoming telephone line and
customer premises wiring
• Interference resolution is likely to be more reliant on
the cooperation and goodwill of Telcos than the
effectiveness of the MPT1570 emission standard
• ADSL interference is not expected to become a
serious issue for Ofcom
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The PLT Situation
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Current status of PLT in the UK
• A recent competitor in the broadband local loop
• Scottish & Southern Energy plc is currently the only
PLT operator in the UK
• S&SE has commercial trials underway at Crieff
Campbeltown and Stonehaven in Scotland and most
recently in Winchester
• In comparison with other broadband systems the
current number of PLT users is still very small
• RA have received no interference complaints to date
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The PLT Network
• Comprises an electricity sub-station and those PLT
users served by it
• Typically up to 200 electricity users per sub-station
with a potential of up to 20 PLT users
• Typical sub-station network is 200 to 300 metres long
• PLT launch power is similar to ADSL at -40 dBm/Hz
but high attenuation means that repeaters may be
required for maximum reach
• Each sub-station requires a dedicated high capacity
link to service its PLT users
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PLT signals & spectrum
• PLT standards and equipment still evolving
• Several competing systems exist - built around:
Gaussian minimum shift keying
Direct sequence spread spectrum
Orthogonal frequency division multiplex
• PLT spectrum lies in the 2 – 30 MHz range
• Band can be split between access & in-house
Local Loop access from 2 to 10 MHz
In-house distribution from 15 to 30 MHz
RRAC Open Forum - Church House Westminster - 14 November 2003
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PLT leakage emissions
• Power cables are not designed for high frequency
use They are unscreened and unbalanced to RF
• Leakage emissions are therefore inherent and
unavoidable under normal PLT operating conditions
• Common mode PLT current generates an
electromagnetic field around all power cables
connected to a PLT enabled sub-station
• All properties fed by a PLT enabled sub-station will
have high frequency electromagnetic fields radiated
by their internal wiring whether they take the PLT
service or not
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Action by RA to investigate PLT emissions
• Field Strength measurement programme during the
original Nor.Web PLT trials in Manchester - 1998/9
• Field Strength measurement programme on an
electricity network using a Gaussian White Noise
‘generic PLT’ signal - 2001
• Field Strength measurement programme during the
current Scottish & Southern Energy PLT trials in
Crieff and Campbeltown - 2002/3
• Measurement programme planned for the S&SE PLT
trials at Winchester early in 2004
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‘PLT’ Emissions inside a user premises
Generic 'PLT' emissions measured at 1 metre from 'Customer Premises' wiring
Guassian white noise source - injection power -40 dBm/Hz
90
Equivalent E Field - dBuV/m in 9 kHz
(Peak Detector)
80
70
60
50
40
30
20
1
2
3
4
5
6
7
8
9
10
Frequency in MHz
PLT injection at Customer Premises
PLT injection at Sub-Station
Ambient levels without PLT
RRAC Open Forum - Church House Westminster - 14 November 2003
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‘PLT’ Emissions ‘next door’ to a ‘PLT’ user
Generic 'PLT' emission levels measured at 3 metres from 'PLT Customer Premises' wiring
Guassian white noise source - injection power -40 dBm/Hz
90
Equivalent E Field - dBuV/m in 9 kHz
(Peak Detector)
80
70
60
50
40
30
20
1
2
3
4
5
6
7
8
9
10
Frequency in MHz
Injection at PLT Customer Premises
PLT injection at Sub-Station
Ambient levels without PLT
German NB30 3 metre Limit
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PLT interference to SW Broadcast reception
• Relatively high emission levels are to be expected in
the general vicinity of a PLT network
• SW broadcast reception in the home using domestic
receivers having whip antennas will be particularly
susceptible to PLT interference which may also be
conducted into the receiver via the mains lead
• Typical near field strength regression levels of 1/r or
20 dB per decade indicate that external antennas
situated within or at the boundaries of normal size
domestic premises may also prove inadequate for the
interference free reception of SW broadcast signals
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PLT interference to Amateur Radio reception
• Potential to affect all 10 Amateur Radio allocations
between 1.8 & 30 MHz
• Likely to be particularly problematic due to the low
field strength levels involved
• Nature and extent of interference will depend on the
PLT signalling system in use
• Amateur radio operator may or may not be able to
avoid interference by changing frequency or band
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RA consultation on PLT and VDSL interference
• RA’s UK technical working group met during 2001/2
to study compatibility between Radio Services and
VDSL & PLT operation in the 1.6 to 30 MHz range
• The UKTWG comprised broadcasters radio users
and network operators A full and comprehensive
report on the study appears on the RA website
• The report concludes that neither VDSL or PLT
emissions can be reduced sufficiently to meet radio
users near-field protection requirements
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PLT Interference – Points to Ponder
• RA measurements and UKTWG studies have shown
that PLT deployment is likely to be incompatible with
1.6 to 30 MHz reception within the domestic
environment due to substantial near-field emission
levels
• Although Short Wave reception is generally
considered a minority interest enjoyed by the
technically aware this may change with the
introduction of Digital Radio Mondiale broadcasts
• As PLT networks continue to roll out any interference
complaints that do arise will be potentially
irresolvable Ofcom will therefore need to consider
their policy on this issue as a matter of urgency
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