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Cumulative Radiated Emissions From Metallic Broadband Data Distribution Systems

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### Cumulative Radiated Emissions From Metallic Broadband Data Distribution Systems

Dr I D Flintoft

Dr A D Papatsoris

Dr D Welsh

Prof A C Marvin

York EMC Services Ltd.

University of York

Scope

ionosphere

Sky Wave

3-30 MHz

Space Wave

0.1-30 MHz

Ground Wave

0.1-3 MHz

London

Rome

Near Field

suburban

rural

average UK ground

0 km

5 km

200 km

1500 km

Contents

- Overview of PLT and xDSL technologies
- Modelling methodology
- RF launch models and measurements
- Sky wave propagation of PLT & VDSL
- Ground wave propagation of ADSL &VDSL
- Spectrum management
- Conclusions

Spectrum and Technologies

30 kHz

300 kHz

3 MHz

30 MHz

Low Frequency (LF)

Medium Frequency (MF)

High Frequency (HF)

Ground Wave

Sky Wave

Space Wave

ADSL (25 kHz-1.1 MHz)

VDSL (1.1-30 MHz)

DPL (2.9 & 5.1 MHz)

Power Line Telecommunication (PLT)

- Propriety systems
- PowerNET: 9-95 kHz (EN50065)
- Digital Power Line (DPL)
- Frequencies: 2.2-3.5 & 4.2-5.8 MHz
- 2 Mbit/s channels demonstrated
- Uses low voltage (LV) network

Mains Network Topology

DPL Cell

= Data Terminal

Medium Voltage (MV) Network

Low Voltage (LV) Network

Secondary

Substation

Transformer

50 single phase services off each distributor

Primary

Substation

Transformer

To High Voltage (HV) Network

250 m

Physical Structure Of LV Network

Armoured Cable

- Underground and overhead distribution
- Armoured cable
- Conditioning units (CU) may be used

Conditioning Unit (CU)

LV network

Network

internal mains network

MV network

CU

LV network

substation

data port

data network

Input Power For A DPL Cell

- DPL cell – coherently excited segment of network
- Physical channel shared by all users in cell
- Multi-user access scheme: TDMA
- Power spectral density from terminal = –40 dBm/Hz = 1 mW in 10 kHz bandwidth
- 10 kHz = typical HF AM radio bandwidth

Digital Subscriber Line (xDSL)

- Overlay technology enabling broadband services on telephony metallic local loop
- Symmetric and asymmetric upstream/downstream data rates
- Data rates up to 50 Mbit/s (VDSL)
- CAP, QAM, DMT modulation techniques

Telecommunications Network

overhead distribution

overhead drop

MDF

underground distribution

cross connect

cross connect

50 m

1.5 km

footway junction box

exchange

4 km

300 m

= Data Terminal

underground drop

xDSL Varieties

FTTEx = Fibre To The Exchange, FTTCab = Fibre To The Cabinet

Physical Structure

Balance of UTP

- Bundles of unshielded twisted pair (UTP)
- Designed for POTS – up to a few kHz
- Cable balance – degrades with frequency
- Network balance – interfaces
- Splitters
- Three wire internal cabling

(New cable under controlled conditions)

Modelling Methodology

- Identify coherently excited network elements
- Determine the radiative characteristics of these network elements
- Construct an effective single source for cumulative emissions – pattern & power
- Use these effective sources in propagation calculations

RF Launch Models

- Numerical Electromagnetics Code
- Sommerfeld-Norton lossy ground model
- Common-mode current model
- Predict antenna gain and radiation efficiency of the network elements
- Underground cables not considered these will be conservative estimates

Network Elements

PLT

House Main Ring

Street Lamp

10 m

3N m

xDSL

6 m

Overhead Drop (Splitter)

Overhead Drop (No Splitter)

N Storey Building (N=1,2,…, 10)

Antenna Patterns For xDSL

- At low frequencies (ADSL) patterns are omni-directional
- Model using an effective short vertical monopole

Normalised gains at 1 MHz

Validation Measurements

- Measurements on UTP aerial drop cable
- Balanced and unbalanced connections
- Results used to calibrate the NEC launch models

Cumulative Radiated Power

- Digital data transmission is a random process which can be modelled as a noise source
- Cumulative field from incoherently excited network elements calculated by noise power addition (REC. ITU-R PI.372-6)
- Phase effects ignored

Sky Wave Propagation

- Time of day
- Time of year
- Transmitter antenna power
- Transmitter antenna pattern
- Transmitter antenna position
- We have considered transmission on a February evening

ITS (Institute For Telecommunication Sciences) HF Propagation Software

- Package caters for area coverage or point to point predictions
- Allows choice of several propagation models: ICEPAC, VOACAP, REC533
- We chose to use REC533 model based on advice from RAL and the ITU
- Launch power and antenna pattern

DPL Source Power For London

- Power in 10 kHz bandwidth: 1 mW
- Area: 2500 km2
- Size of DPL cell: 0.28 km2 (diameter 600 m)
- Total number of cell: 2500/0.28 8925
- Total input power: 8925 1 mW = 8.9 W 40 dBm
- Antenna gain: –15 dB
- Total radiated power: 40 – 15 = 25 dBm

Coverage Of London At 5.1 MHz

0

Subtract 15 dB to read true dBmV/m, .i.e. for 15 dBmV/m read 0 dBmV/m

London cumulative antenna

Isotropic antenna

Cumulative DPL Sky Wave From Many Urban Areas

- Since the coverage from each urban area is Europe wide we need to sum the field from many urban areas
- Major sources over UK would be the Ruhr area of Germany, London, Birmingham and Manchester
- Total field over UK due to these major sources plus other major UK cities is predicted to be between 5 and 11 dBV/m
- Established ITU noise floor is 8 dBmV/m (rural area)

- Drop model without internal cables
- Average of 1000 homes per km2
- 25 % technology penetration
- Antenna gain of –25 dB (corresponds to 20 dB cable balance parameter)
- Terminal input power –60 dBm/Hz or –20 dBm/10kHz
- Total radiated power 13 dBm (20 mW)

Coverage Of London At 8 MHz

Subtract 27 dB to read true dBmV/m, .i.e. for 15 dBmV/m read -12 dBmV/m

Cumulative VDSL Sky Wave From Many Urban Areas

- Sum powers from major UK cities and Ruhr area of Germany
- Cumulative field over UK at 8 MHz is –6 dBmV/m in 10 kHz bandwidth
- Established ITU noise floor is 8 dBmV/m (rural area)
- 10 dB lower than DPL

Groundwave Propagation Theory (1)

- Sommerfeld (1909), Norton (1936, 1937)
- (V) fields >> (H) fields
- A(d,f,,) for (V) polarised fields
- Attenuation factor calculated according to ITU-R P.368, originally developed by GEC

Groundwave Propagation Theory (2)

- The E-field formula applies to a linear short (h<<) radiative element
- NEC used to determine the equivalent FMPt of radiative structures associated with xDSL
- Calculations done for upstream and downstream mode of transmission
- Radiation patterns omnidirectional for ADSL
- Balance, attenuation of UTPs

Calculation strategy of cumulative emissions (1)

- Electric fields Ei from uncorrelated individual sources add incoherently, i.e.,
- A: area enclosing all radiating sources in m2
- pi: percentage of building type associated with ith radiating source
- Di: density of installations per unit area
- Mpi: fraction of market penetration
- Li: fraction of installed lines used concurrently

Calculation strategy of cumulative emissions (2)

- Step 1. Definition of radiating medium, A=25km2
- The RSS summation, lends itself to an active spreadsheet implementation

Calculation strategy of cumulative emissions (3)

- Step 2. Definition of makeup of city buildings

Calculation strategy of cumulative emissions (4)

- Step 3. Specify reference radiating efficiencies, balance and attenuation at frequencies of interest for upstream and downstream transmission

Calculation strategy of cumulative emissions (5)

- Step 4. Define the appropriate transmission spectral mask, i.e., for ADSL PSD=-34.5dBm/Hz (upstream 138-276 kHz), PSD=-36.5dBm/Hz (downstream 138-1104 kHz).
- Step 5. Calculate the unattenuated electric field for each radiative element, i.e.,

Calculation strategy of cumulative emissions (6)

- Step 6. Calculate the appropriate electric field correction factor for each radiative element.
- Step 7. Evaluate the total electric field by performing the RSS summation over all xDSL installations.

Test cases and results ADSL(1)

- Case 1. A=25 km2, bal=40dB, Mpi=20%, Lui=10%

Test cases and results ADSL(2)

- Case 2. A=25 km2, bal=30dB, Mpi=50%, Lui=10%

Balance

Radiation levels increase by a margin equal to the balance difference in dB.

E(bal2)=E(bal1)+bal, bal= bal1 - bal2

Market Penetration

E(M2)=E(M1)+M, M=10log(M2/M1)

Distance

-20 dB/decade for f(100kHz - 400kHz)

-25 dB/decade for f(600kHz - 800kHz)

-30 dB/decade for f(1000kHz)

Test cases and results ADSL(3)Summary of results for ADSL

- Emission electric fields resulting from cumulative ATU-R upstream and MDF downstream transmissions at distance 1km away from the effective emission centre.(M=20%, L=10%, Typical bal=30 dB)

Graph of current noise floor, ITU-R P.372

- Median noise electric field at a receiver with bandwidth 10kHz at 12 noon in a residential location in the central UK.

ADSL and current noise floor

- No likely change to the established median electric noise field for the well balanced city (bal=50 dB) model at d>1km away from the MDF centre.
- For the typically balanced city model ADSL fields are predicted above the current noise floor (cnf)
- ATU-R field > cnf by 5dB - 10dB at d<2km
- MDF field > cnf by 10dB - 20dB at d<3km
- For distances > 10km, ADSL<cnf

Summary of results for VDSL

- Emission electric fields resulting from cumulative NT-LT upstream and LT-NT downstream transmissions at distance 1 km away from the effective emission centre. (M=20%, L=20%, Typical bal=20 dB.)

VDSL and current noise floor

- No likely change to the median electric noise field for the well balanced small city (bal=30 dB) model at d>1km away from the emission centre.
- For the typically balanced city model VDSL fields are predicted above the current noise floor (cnf):
- NT-LT field > cnf by 10dB - 20dB at d<1.5km
- LT-NT field > cnf by 5dB - 15dB at d<1.5km
- For distances > 5km, VDSL<cnf.
- Radiation diagrams of radiative elements give rise to significant space wave component.

Spectrum management issues

- AM broadcasting in band 6 (MF)
- For ‘good’ quality reception
- 88dBV/m, 74dBV/m, 60dBV/m for typical city/industrial, city/residential and rural/residential areas, respectively.
- AM transmitter serving designated metropolitan area enclosed by a 50km radius in UK.
- =15, =10mS/m, Pt=10kW
- PR=30dB, thus interfering field 44dBV/m
- xDSL(d>1km)< 44dBV/m, but Gaussian in nature
- For rural locations near xDSL fields important

Spectrum management issues

- Digital MF broadcasting
- DRM consortium preliminary specification
- Narrow bandwidth (max 10kHz), thus:
- very efficient source coding scheme [MPEG-4 AAC]
- multi-carrier modulation to overcome multipath, Doppler, [OFDM]
- high state linecode modulation scheme, [QPSQ, 16QAM, 64QAM depending on service requirements]
- Protection ratios:
- AM interfered with by DM, [f/kHz=0, PR=36dB]
- DM interfered with by AM, [f/kHz=0, PR=0dB]
- DM interfered with by DM, [f/kHz=0, PR=15dB]

Spectrum management issues

- Digital MF broadcasting
- DRM consortium preliminary specification
- Carrier-to-noise ratios:
- C/N of 24dB for BER=1x10-5 is at least required.

Spectrum management issues

- Power savings of 4-8dB can be made by DM transmitters, for same daytime coverage.
- xDSL(d<1km)>C/N, near xDSL ?
- assessment of xDSL mux and mod techniques

Spectrum management issues

- AM transmitters to be phased out by 2020
- Lower PR could be used, 10-15 dB less than the currently assumed for AM, thus:
- reduced radiation of digital transmitter power
- much quieter EM environment
- If xDSL>planned interference value:
- DM power must increase (financial implications?)
- concerted actions of broadcasting authorities to restore the service
- xDSL near fields at remote locations?

xDSL and aeronautical services

- Services likely to be affected are:
- Radiolocation & mobile communications
- NEC simulations show a significant space-wave propagation component for f>1MHz
- most radiation is directed towards elevation angles ranging between 30 and 60 degrees
- Space wave stronger than ground wave

xDSL and government services

- Services likely to be affected are:
- Military mobile communications in HF
- low data rate systems work even 8 dB below ambient noise in a 3 kHz receiver bandwidth
- 9.6 kbps and above data rates at 3 kHz bandwidth are standardized requiring a minimum 33 dB C/N ratio
- 3 - 5MHz, critically important for short/medium length communications paths at night when other HF frequencies do not work

Conclusions (1)

- Active spreadsheet tool for RA
- Preliminary calculations suggest:
- AM and DM broadcasting may be unfavourably affected
- xDSL(d<1km) & selected areas
- xDSL near fields need to be assessed
- lower PR for DM mean very low power Tx resulting to a much quieter EM environment, fossil fuel savings and reduction in greenhouse gases

Conclusions (2)

- Preliminary calculations suggest:
- Aeronautical services may be unfavourably affected
- xDSL(d<1km) & selected areas
- Further study is needed
- cumulative space wave emissions
- technical and operational characteristics of aeronautical NDBs, current and future mobile communications
- Government services may be unfavourably affected
- Mobile communications
- Further study is needed

Conclusions (3)

- It is therefore provisionally suggested that xDSL emissions should be contained at a maximum level of 20dB above the established radio noise floor near the effective radiation centres (d=1km). (For the UK lower values than those in the ITU-R P.372 can be used.)

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