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R&D White Paper
WHP 109
March 2005
Digital Radio Mondiale: DRM, digital radio on long, medium and short waves
– another radio revolution?
J.H. Stott
Research & Development BRITISH BROADCASTING CORPORATION
© BBC 2005. All rights reserved.
BBC Research & Development White Paper WHP 109
Digital Radio Mondiale: DRM, digital radio on long, medium and short waves – another radio revolution?
Abstract
This document publishes the slides used in a lecture given to the IEE Surrey Branch on 17 November 2004.
It gives an overview of DRM: what it is, why it is needed, and who has done it. It goes on to explain some details of the system and how it works (both audio source coding and the COFDM modulation scheme) with, in the case of the lecture itself, some demonstrations not reproducible here.
This is followed by a description of receiver architectures, including some examples of receivers designed or part-designed by the BBC R&D team, and the necessary transmission infrastructure needed by a broadcaster.
Finally an account is given of a range of field trial experiments, with examples drawn from BBC R&D experience.
© BBC 2005. All rights reserved. Except as provided below, no part of this document may be reproduced in any material form (including photocopying or storing it in any medium by electronic means) without the prior written permission of BBC Research & Development except in accordance with the provisions of the (UK) Copyright, Designs and Patents Act 1988.
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Authorisation of the Chief Scientist is required for publication.
Research & Development
Kingswood Warren
Welcome to
1
Research & Development
Jonathan Stott
17 November 2004
Kingswood Warren
IEE Surrey Branch
Digital Radio Mondiale
DRM, digital radio on long, medium and
short waves – another radio revolution?
2
Research & Development 3
Contents
DRM: what, who, when & whySome system details – the ‘how’
audio coding; COFDMand how it sounds in practice
ReceiversTransmission infrastructureField trialsConclusions
3
Research & Development 4
DRM = Digital Radio Mondiale
A consortium with the mission:
“to create a universal, digital system for the AM broadcasting bands below 30MHz”
The digital broadcasting system they have created to fulfil this mission
DRM™ – what is it?
4
Research & Development 5
Commercial Radio Australia (Australia); Nautel Ltd., Radio Canada International/CBC (Canada); Academy of Broadcasting Science of China, Communications University of China (China); RIZ Transmitters (Croatia); HFCC (Czech Republic); ESPOL, HCJB World Radio (Ecuador); Digita Oy, Kymenlaakso Polytechnik (Finland); CCETT, DRF, Radio France, Radio France Internationale, TDF, Thales Broadcast & Multimedia (France); ADDX, Ahead Software AG, APR, Atmel Germany GmbH, Coding Technologies GmbH, Deutsche Welle, DeutschlandRadio, DLM, Sender Europa 1, Fraunhofer IIS, Georg-Simon-Ohm – University of Applied Sciences Nuremberg, IZT, IRT, Medienanstalt Sachsen-Anhalt/Digitaler Rundfunk Sachsen-Anhalt, Micronas GmbH, Robert Bosch GmbH,Sony International Europe, SWR Südwestrundfunk, TELEFUNKEN SenderSysteme Berlin AG, T-Systems International GmbH, University of Applied Sciences - FH Merseburg, University of Hannover, University of Ulm, VPRT (Germany); Antenna Hungaria, National Communications Authority Hungary (Hungary); Basamad College,Tehran (Iran); Hitachi Kokusai Electric Ltd., NHK (Japan); Libyan Jamahiriya Broadcasting (Libya); Broadcasting Centre Europe, RTL Group (Luxembourg); Asia Pacific Broadcasting Union (Malaysia); Agentschap Telecom, Nozema, Radio Netherlands, Technical University Delft (Netherlands); Radio New Zealand International (New Zealand);Telenor/Norkring (Norway); Radiodifusao Portuguesa (Portugal); RTRN/Voice of Russia (Russia); Government of Catalonia, Universidad del Pais Vasco, (Spain); Swedish Radio International (Sweden); EBU, International Committee of the Red Cross, ITU (Switzerland); Arab States Broadcasting Union (Tunisia); BBC, Christian Vision, Digital One Ltd., Imagination Technologies Ltd., QinetiQ, RadioScape Ltd., VT Communications, WRN (U.K.); Broadcast Electronics, Inc., Dolby Laboratories Incorporated, Dolby LaboratoriesLicensing Corporation, DRS Broadcast Technology (formerly Continental Electronics), Harris Corporation, Broadcast Communications Division, IBB/VOA, Kintronic Laboratories, Inc., National Association of Short-waveBroadcasters, Sangean America, Inc.,TCI, a Dielectric Company, Via Licensing Corporation (U.S.A.); and Radio Vaticana (Vatican City).
DRM has 85 members from 27 countries– major international broadcasters– other broadcasters & network
operators– transmitter manufacturers– receiver manufacturers– research institutes
DRM ConsortiumMembers
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Research & Development 6
1997 discussions lead to formation
1998 Consortium officially founded
2001 ETSI Specification published
2003 achieved triple recognition
IEC Standard 62272-1, ETSI Standard ES201980,as well as ITU-R Recommendation BS1514-1
and held ‘official launch’ alongside WRC Geneva
DRM very brief history
6
Research & Development 7
Starting a new service
BBC faced challenges in 1932 starting Empire Service at HF using AM – plus ça change!
“London calling”
Lord Reith“… neither very interesting
nor very good.”
7
Research & Development 8
Historically, these bands were used first
they use AM – ‘Ancient Modulation’!
AM listening experience doesn’t match modern expectations – ample scope for improvement
LF, MF, and HF broadcasting bands share the unique & valuable property that signals go a long way
as useful now as it was to the Empire Service
DRM for LF/MF/HF – why?
8
Research & Development 9
Ground wave
Long wave and medium wave offer good coverage by ground wave
transmitter– works best at lower
frequencies, and with good ground conductivity
ground wave hugs Earth surface
– supports verticalpolarisation
9
Research & Development 10
Short wave (& MW at night) travels further
refraction in the ionosphere ‘reflects’ waves
Sky wave
transmitter
NB: NOT TO SCALE!
Properties of the ionosphere vary cyclically, on a daily, seasonal and 11-year basisreflection also occurs
at the ground
10
Research & Development 11
NVIS
Near-Vertical Incidence Sky-Wave
used for national broadcasting
important for large, sparsely populated countries, especially in Tropics
signal sent upwards from transmitter
If frequency is too high, the wave isn’t ‘reflected’. For this reason, certain low-HF bands are reserved for NVIS Tropical Broadcasting
11
Research & Development 12
Bands below 30MHz have unique long-range coverage – vital for international broadcasting
only way to reach many ‘closed’ countriescannot reach by Internet or local relays
majority of BBC World Service listeners use MF/HF
Vital for some countries’ internal broadcasting
developing, large or tropical countries, using NVIS
Spectrum below 30MHz
12
Research & Development 13
Bands below 30MHz have unique long-range coverage – vital for international broadcasting
only way to reach many ‘closed’ countriescannot reach by Internet or local relays
majority of BBC World Service listeners use MF/HF
Vital for some countries’ internal broadcasting
developing, large or tropical countries, using NVIS
Spectrum below 30MHz
There’s just one snag – analogue
AM doesn’t meet modern
expectations for quality!
That’s the challenge for DRM…
13
Research & Development 14
The DRM challenge
DRM had to provide audio quality that could bear comparison with FM stations
while being a drop-in replacement in the spectrum!
frequency{
…
channel pitch, 9 or 10 kHz
AM
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Research & Development 15
The DRM challenge
DRM had to provide audio quality that could bear comparison with FM stations
while being a drop-in replacement in the spectrum!
frequency{…
channel pitch, 9 or 10 kHz
AM
DRM
15
Research & Development 16
DRM: how?
We have to fit a digital signal in a restricted RF bandwidth (9 or 10 kHz), which can adequately describe the audio signal
reduce the bit rate needed to describe the audiousing source coding
squeeze as much data as we can in the limited RF bandwidth (and difficult propagation channel) using advanced modulation & error coding
16
Research & Development 17
DRM source coding
Two general types are specified, with options
waveform coding (for any programme, incl. music)
speech coding (for speech only, not music)
Waveform coding is AAC plus optional SBR
Speech coding, two options
HVXC (with option of SBR)
CELP
17
Research & Development 18
Waveform coding
AAC (Advanced Audio Coding)
latest development MPEG 1 layer 2 MP3 AAC
achieves lower bit rate at same qualitybut ideally needs reduced bandwidth (say 7 kHz) in order to keep coding artefacts to acceptable limits
SBR (Spectral Band Replication)
restores the top octave by synthesis in the receiver,transmitting a small amount of helper data
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Research & Development 19
Spectral Band Replication
Sounds in the top octave are
high overtones of musical notes in first 7 kHz
noiselike (sibilants, cymbals, wire brush on snare)
Can synthesise this spectral content
‘helper’ flags noiselike/overtone, & spectral shape
receiver reconstructs a sufficient replica
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Research & Development 20
Why have speech coders?
General radio programme material has music, street ambience etc as well as speech
AAC waveform coding will normally be used
Some niche applications justify speech codecs
speech codecs require less bit rate, transmit one spoken service very ruggedly?
use for multilingual news within one 9/10kHz slot?
additional spoken service alongside main audio?
20
Research & Development 21
Modulation & error coding
AAC audio typically in range 15 ~ 25 kbit/s
Need modulation/FEC which fits in 9/10 kHz
has to cope with multipath, Doppler and fading …
Use Coded Orthogonal Frequency-Division Multiplex (COFDM) with Multi-Level Coding
provide ‘knobs’ to adapt to broadcasters’ requirements (trade ruggedness v. capacity)
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Research & Development 22
Why COFDM?
… …n+1 n+2 n+3 n+4nn–1n–2n–3n–4
… …n+1nn–1n–2n–3n–4n–5n–6n–7
… …n–2n–3n–4n–5n–6n–7n–8n–9{delayed paths
Multipath causes Inter-Symbol Interference (ISI) between successive data symbols
in principle can handle with an equaliser, but this is very difficult if multipath is long w.r.t. symbol1st path
t
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Research & Development 23
Why COFDM?
… …n+1 n+2 n+3 n+4nn–1n–2n–3n–4
… …n+1nn–1n–2n–3n–4n–5n–6n–7
… …n–2n–3n–4n–5n–6n–7n–8n–9{delayed paths
Multipath causes Inter-Symbol Interference (ISI) between successive data symbols
in principle can handle with an equaliser, but this is very difficult if multipath is long w.r.t. symbol
reception of nthsymbol disturbed by fragments of many
others
1st patht
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Research & Development 24
COFDM
We reduce the ISI by making symbols longbut reduces data rate
and occupied bandwidth
Get data rate back by using multiple carriersby making them orthogonal we avoidInter-Carrier Interference (ICI)
and adding a Guard Interval TG eliminates ISI
24
Research & Development 25
COFDM
We reduce the ISI by making symbols longbut reduces data rate
and occupied bandwidth
Get data rate back by using multiple carriersby making them orthogonal we avoidInter-Carrier Interference (ICI)
and adding a Guard Interval TG eliminates ISI
∫τ+TU
τ
ψm(t)ψ∗
n(t)dt = 0, m �= n,
= TU , m = n
Orthogonality
Pick
so carrier spacing
ψm(t) = ej m ωU t
ωU/2π
= 1active symbol period TU
Just use
FFT!
25
Research & Development 26
COFDM
We reduce the ISI by making symbols longbut reduces data rate
and occupied bandwidth
Get data rate back by using multiple carriersby making them orthogonal we avoidInter-Carrier Interference (ICI)
and adding a Guard Interval TG eliminates ISI
∫τ+TU
τ
ψm(t)ψ∗
n(t)dt = 0, m �= n,
= TU , m = n
Orthogonality
Pick
so carrier spacing
ψm(t) = ej m ωU t
ωU/2π
= 1active symbol period TU
Just use
FFT!
n+1n–1 symbol n
Use of guard interval
symbol n n+1n–1
symbol n n+1n–1
symbol n n+1n–1
symbol n n+1n–1 too early!
earliest
medium
latest
too late!
FFT window TU
total symbol lengthTS
TG
26
Research & Development 27
COFDM
We reduce the ISI by making symbols longbut reduces data rate
and occupied bandwidth
Get data rate back by using multiple carriersby making them orthogonal we avoidInter-Carrier Interference (ICI)
and adding a Guard Interval TG eliminates ISI
Finally add error-correction coding (the “C”)
too early!
earliest
medium
latest
too late!
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Research & Development 28
DRM is for all broadcasters, large & small
bandwidth options (4.5, 5, 9, 10, 18, 20kHz)
ruggedness against capacity trade-off
different constellations (16-QAM or 64-QAM)different code rates
options to match propagation requirements
degrees of multipath (& single-frequency networks)degrees of Dopplershort or long interleaver
DRM options
28
Research & Development 29
DRM is for all broadcasters, large & small
bandwidth options (4.5, 5, 9, 10, 18, 20kHz)
ruggedness against capacity trade-off
different constellations (16-QAM or 64-QAM)different code rates
options to match propagation requirements
degrees of multipath (& single-frequency networks)degrees of Dopplershort or long interleaver
mode use TU ,ms TG,ms TS ,ms fU ,Hz
AmostlyLF/MF
24 2 2
326 2
341 2
3
B‘workaday’
HF21 1
35 1
326 2
346 7
8
C ‘robust’ HF 14 2
35 1
320 68 2
11
D‘extreme’ HF
(NVIS)9 1
37 1
316 2
3107 1
7
DRM options
29
Research & Development 30
Let’s hear a real comparison
Broadcast from UK
medium-wave transmitter at Orfordness
Received at Erlangen in SE Germany
night-time, so skywave with fading, and co-channel interference
Alternate brief AM and DRM transmissions
So does it work?
30
Research & Development 31
Let’s hear a real comparison
Broadcast from UK
medium-wave transmitter at Orfordness
Received at Erlangen in SE Germany
night-time, so skywave with fading, and co-channel interference
Alternate brief AM and DRM transmissions
So does it work?
Analogue (AM):Low audio bandwidth, fading and co-channel interference
31
Research & Development 32
Let’s hear a real comparison
Broadcast from UK
medium-wave transmitter at Orfordness
Received at Erlangen in SE Germany
night-time, so skywave with fading, and co-channel interference
Alternate brief AM and DRM transmissions
So does it work?
Digital (DRM):Would you rather listen
to this or AM?
32
Research & Development 33
Receivers were needed for both system development and field trials
Present receivers of 2 main types
analogue front end, feeding a computer
with software demodulation and decoding
free-standing hardware
Real consumer receivers coming soon!
DRM receivers
33
Research & Development 34
Software receivers
conventional superhet radio
down-converter
IF, say 455kHz
soundcard
low IF, say 12kHz
f
computer, with demod/decoding
software
34
Research & Development 35
Fraunhofer produced PC software used by many DRM members, often with AOR 7030 receiver
Cut-down version made available cheaply to radio enthusiasts via website
FhG software receiver
35
Research & Development 36
Fraunhofer produced PC software used by many DRM members, often with AOR 7030 receiver
Cut-down version made available cheaply to radio enthusiasts via website
FhG software receiver
There’s also an open-source software-
receiver project called DREAM.It’s free!
36
Research & Development 37
Inspired by a paper at the IEE HF 2000 Conference, we made a ‘fully-digital’ design
BBC R&D ‘pro’ receiver
37
Research & Development 38
Inspired by a paper at the IEE HF 2000 Conference, we made a ‘fully-digital’ designA
D
27MHz LPF
digitaldown-
converter
DSP, with demod/decoding software
65Msample/s
BBC R&D ‘pro’ receiver
38
Research & Development 39
Coding Technologies brought partnerstogether to make small DRM receiver
BBC R&D: DSP card (based on ‘pro’ main board)
AFG: analogue front end
First consumer-size rx
BBC R&D DSP card
39
Research & Development 40
Coding Technologies brought partnerstogether to make small DRM receiver
BBC R&D: DSP card (based on ‘pro’ main board)
AFG: analogue front end
First consumer-size rx
BBC R&D DSP card
Secondgenerationis smaller
40
Research & Development 41
Future receivers for consumers must be cheap and low-power
technically possible
huge market ( 2.5 billion AM sets to replace)
Needs DRM ICs
several collaborations are working on this
User interface must be more user friendly
Future receivers
41
Research & Development 42
User friendliness
DRM has features built in to help this
conveys station name, text message, lists of other frequencies where same service is available, schedule of programmes and frequency changes…
listeners shouldn’t have to know or type frequency
signal structure supports alternative-frequency switching (AFS) or even full frequency diversity
42
Research & Development 43
User friendliness
DRM has features built in to help this
conveys station name, text message, lists of other frequencies where same service is available, schedule of programmes and frequency changes…
listeners shouldn’t have to know or type frequency
signal structure supports alternative-frequency switching (AFS) or even full frequency diversity
Basis of AFSSignal segmented in time,regular periods containing no audio data
frequency f1 audio data, etc audio data, etc t
receiver uses f1 initially… … then reverts to f1
… checks f2 in the ‘gap’… … if f2 better, switchesin next ‘gap’…
frequency f2 audio data, etc audio data, etcReceiver can use periods of non-audio to check second
frequency — note transmissions must be synchronised
43
Research & Development 44
User friendliness
DRM has features built in to help this
conveys station name, text message, lists of other frequencies where same service is available, schedule of programmes and frequency changes…
listeners shouldn’t have to know or type frequency
signal structure supports alternative-frequency switching (AFS) or even full frequency diversity
can use some capacity for other features, e.g. spoken news on demand, mini ‘web’ site
44
Research & Development 45
Added features
Here is a demonstration we gave this year at the International Broadcasting Convention in Amsterdam
Two low data-rate services were sent (from Orfordness) alongside the main audio
on-demand spoken news headlines
mini broadcast web site
Locally generated tonight!
45
Research & Development 46
We need broadcast infrastructuremany broadcasters have 2 or more transmittersin a network
single or multi-frequency (SFN or MFN)
DRM-DI Distribution Interface defined to distribute to transmitters and synchronise them
First synchronous MFN set up in June 2003by BBC R&D/VT Merlin
R&D receiver re-programmed as modulator
Broadcast chain
46
Research & Development 47
We need broadcast infrastructuremany broadcasters have 2 or more transmittersin a network
single or multi-frequency (SFN or MFN)
DRM-DI Distribution Interface defined to distribute to transmitters and synchronise them
First synchronous MFN set up in June 2003by BBC R&D/VT Merlin
R&D receiver re-programmed as modulator
Broadcast chainstudio centre
content(audio/data)
content server (makes DRM-DI)
GPSreceiver
GPS satellite network
DRM-DI
uplink station
distribution satellite network
DVB-Scarrying DRM-DI
DRM distribution for wide-spread transmitter network
transmitter site 1
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
transmitter site 2
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
coveragearea
DRM RF signal
DRM RF signal
47
Research & Development 48
We need broadcast infrastructuremany broadcasters have 2 or more transmittersin a network
single or multi-frequency (SFN or MFN)
DRM-DI Distribution Interface defined to distribute to transmitters and synchronise them
First synchronous MFN set up in June 2003by BBC R&D/VT Merlin
R&D receiver re-programmed as modulator
Broadcast chainstudio centre
content(audio/data)
content server (makes DRM-DI)
GPSreceiver
GPS satellite network
DRM-DI
uplink station
distribution satellite network
DVB-Scarrying DRM-DI
DRM distribution for wide-spread transmitter network
transmitter site 1
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
transmitter site 2
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
coveragearea
DRM RF signal
DRM RF signal
studio centre
content(audio/data)
content serverGPS
receiver
t & fref
GPS
DRM-DI
48
Research & Development 49
We need broadcast infrastructuremany broadcasters have 2 or more transmittersin a network
single or multi-frequency (SFN or MFN)
DRM-DI Distribution Interface defined to distribute to transmitters and synchronise them
First synchronous MFN set up in June 2003by BBC R&D/VT Merlin
R&D receiver re-programmed as modulator
Broadcast chainstudio centre
content(audio/data)
content server (makes DRM-DI)
GPSreceiver
GPS satellite network
DRM-DI
uplink station
distribution satellite network
DVB-Scarrying DRM-DI
DRM distribution for wide-spread transmitter network
transmitter site 1
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
transmitter site 2
GPSreceiver
satreceiver
modulator (acceptsDRM-DI)
transmitter
coveragearea
DRM RF signal
DRM RF signal
studio centre
content(audio/data)
content serverGPS
receiver
t & fref
GPS
DRM-DI
transmitter site
GPS GPSreceiver
satreceiver
satellitedistribution
modulator
t & f reference
DRM-DI
transmitterDRM
DRM RFsignal
49
Research & Development 50
Field Trials
BBC engineers took their field-trial brief seriously!
50
Research & Development 51
Field trials performed throughout project
both channel-sounding and system-testing
short- and long-term, all sorts of paths
long-term tests automatically gathered data from widespread receivers on members’ sites
some work EC-funded in the Radiate project
Ecuador NVIS tests led to extra modes
DRM Field Trials
51
Research & Development 52
Demonstrations at DRM Launch June 2003
included synchronous 2-frequency transmissions
had to drive kit there anyway, so…
Grasped chance to measure frequency-diversity reception
mobile measurement on journey
static measurement in Geneva
Recent BBC R&D tests (1)
52
Research & Development 53
Demonstrations at DRM Launch June 2003
included synchronous 2-frequency transmissions
had to drive kit there anyway, so…
Grasped chance to measure frequency-diversity reception
mobile measurement on journey
static measurement in GenevaA pause in France on the way to Geneva
Recent BBC R&D tests (1)
Three BBC R&D receivers logging MFN and frequency-diversity reception
53
Research & Development 54
Frequency-diversityFrequency 1
Frequency 2
Single-frequencyreception suffers some drop-outs
(poor SNR)
But solid reception using
diversity!
54
Research & Development 55
Sorting the synchronisation of separated transmitters enabled us to try a big SFN
long-distance HF
2 transmitters
Rampisham in UK (VT Merlin Communications)Bonaire in Netherlands Antilles (R Nederlands W)
Reception in Portugal
It worked!
Recent BBC R&D tests (2)
55
Research & Development 56
Sorting the synchronisation of separated transmitters enabled us to try a big SFN
long-distance HF
2 transmitters
Rampisham in UK (VT Merlin Communications)Bonaire in Netherlands Antilles (R Nederlands W)
Reception in Portugal
It worked!
Recent BBC R&D tests (2)Rampishamtransmitter
Bonairetransmitter
Portugalreceiver
56
Research & Development 57
Sorting the synchronisation of separated transmitters enabled us to try a big SFN
long-distance HF
2 transmitters
Rampisham in UK (VT Merlin Communications)Bonaire in Netherlands Antilles (R Nederlands W)
Reception in Portugal
It worked!
Recent BBC R&D tests (2)Rampishamtransmitter
Bonairetransmitter
Portugalreceiver
Impulse response as received in
Portugal
2ms
note logarithmic vertical scale Bonaire
Rampisham
57
Research & Development 58
Recent BBC R&D tests (3)
Possible benefits of polarisation diversitywere rediscovered when calibrating antennas
So investigated here and in staff homes
58
Research & Development 59
Recent BBC R&D tests (3)
Possible benefits of polarisation diversitywere rediscovered when calibrating antennas
So investigated here and in staff homes
59
Research & Development 60
Polarisation diversity
Each component of the received skywave has dominant polarisation that often rotates
Antennas normally respond to one polarisation only
vertical whip responds to vertical polarisation
thus get polarisation fading
Use crossed loops to get polarisation diversity
60
Research & Development 61
Polarisation diversity
Each component of the received skywave has dominant polarisation that often rotates
Antennas normally respond to one polarisation only
vertical whip responds to vertical polarisation
thus get polarisation fading
Use crossed loops to get polarisation diversity
Polarisation fading on crossed loops
Voice of Russia received at KW
61
Research & Development 62
Every silver lining…
Interference
… has a cloud!
other HF radio users
62
Research & Development 63
Interference remains a worry
especially from systems using the mains wiring
PLT/PLC – Power Line (Tele) Communications
some concern about VDSL on phone wiring
Strong political pressure for PLT
EC and UK in favour (‘Broadband for all’)
happy to turn EMC regulation on its head!
even the IEE position was toned down…
Interference
63
Research & Development 64
Future of DRM
Broadcasters looking to launch serious services into W Europe in a year’s time
several broadcasters (including BBC World Service) co-ordinating efforts
target France, Germany & Benelux countries
aim to have several services and receivers allavailable at the same time
… then The World!
64
Research & Development 65
DRM is now ready for introduction
so at last we can have good quality audio andthe long-distance reach of the ‘AM’ bands
DRM uses audio coding & COFDM to squeeze a digital signal into space of one AMtransmission
BBC R&D has played a significant rôle
but there’s plenty more to do!
Conclusions
65
Research & Development 66
The End
Thanks for listening!
and thanks also to:IEE for inviting me to give presentation,BBC colleagues for help with preparation,Catering staff for refreshments
66
Research & Development
Contact detailsJonathan Stott
BBC Research and Development,Kingswood Warren, TADWORTH,Surrey KT20 6NP, United Kingdom
Jonathan.Stott@rd.bbc.co.uk
More papers: www.bbc.co.uk/rdwww.drm.orgIEE Electronics & Communication,February 2002
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