digital tv atv, freeview, freesat and all that… noel matthews g8gtz
TRANSCRIPT
Digital TVATV, Freeview, Freesat and all
that…
Noel Matthews G8GTZ
Agenda
• Digital TV basics– Why compress?– Compression and modulation standards– HD and SD– Multiplexing
• Services– SKY– FreeView– FreeSat
• Digital ATV– Why and How
Why digital?
• Analogue signals have been around since day 1 of broadcasting• The signals are very fragile and degrade very easily – poor “signal
to noise ratio”– Scratchy records– Medium and long wave radio– FM radio hiss– Ghosting on the TV pictures
• So we digitise it
• Once the signal is digital we can modify and transmit it without degrading it
• We can also copy and store it like computer data• CD were first real consumer digital products• But the problem is audio and pictures are very BIG
Digital video – how big?
PAL
270 Mbit/s
SDI
AnalogueA to D converter
1100101001010
HD – an even bigger problem!
1.3 Gbit/s
High
DefinitionA to D converter
1100101001010
Why compress video?
• Serial Digital Interface (SDI) is the uncompressed digital studio standard
• High quality loss-less digital video– 270 Mbit/sec is a lot of data!– approximately 33.3Mbytes per second
• Not practical to transmit 270Mbit/s - except on optical fibre
• Even worse with High Definition– Studio standard is 1.3 Gbit/s– Approximately 150M Bytes per second
Compression• In the broadcast world we compress using industry standard
techniques– MPEG-2– MPEG-4
• MPEG-2 Standard definition compresses video at 270Mbit/s down to 2Mbit/s
• MPEG-4 High definition compresses HD video at 1.3Gbit/s to 8 Mbit/s– In less than 1 second
• 99% reduction in bit rate but still better than VHS quality?– watch the background and grass!– And you get delay
• Both standard use similar techniques– Interframe– Intraframe
Inter frame compression
Macro block
Intra frame compression
I non-refB
ref B non-refB
P P
Inter frame compression – 1
Source Frame A
Inter frame compression – 2
Source Frame A
Inter frame compression – 3
Source Frame A
Inter frame compression – 4
Source Frame A
MPEG-2 and MPEG-4• Standards are crucial to the success of the broadcasting industry
– Ensures interoperability between the transmission head end and the set top box
• 2 main standards affect what we do– Motion Pictures Expert Group (MPEG)
• Video compression
– Digital video broadcasting (DVB)• Transmission standards
• MPEG-2 has been the major standard for the last 15 years– 100 million STBs!
• But we needed something better• MPEG-4 is a completely new algorithm
– 50% more efficient– Standard Definition used for “green field”
• DTV and IPTV
– High Definition used everywhere• SKY• FreeSat
8
7
6
5
4
3
2
1
Bit-rate for BroadcastQuality Television*
First BroadcastMPEG-2 Encoder
Enhanced MotionEstimation
Advanced Pre-processing
ReflexTM StatisticalMultiplexerEnhancements
TTV NoiseReduction
MPEG-2 Future
Advanced EncodingFuture
Year
Bit
Rate
(M
bit
s per
seco
nd)
MPEG-2 - improvements
1994
1996
1995
1997
1998
1999
2000
2001
2002
2004
2003
2005
How good is MPEG-4?
0.0
2.0
4.0
6.0
8.0
10.0
12.0
1.0 1.5 2.0 2.5 3.0
Bit rate (Mbit/s)
PS
NR
(d
B r
ela
tiv
e)
MPEG-4 AVC/m
WMV9 (beta)
MPEG-2
Encoders Multiplexers ModulatorsReceivers
Typical System Architecture
Don’t forget the audio!
• As many channels as you like – it’s only bits
• Mono, dual Mono
• Stereo, joint Stereo
• Multiple languages
• 5 Channel surround sound– Dolby & DTS
• Sample rates from 32 – 256 Kbit/s
Not just pictures - EPG and CA
• The EPG is the user interface• Transmitted at same time as
TV and radio services• Contains program info plus
forward looking data• Also available as XML files on
the internet
• Condition Access prevents illegal viewing of pay TV channels
• None encrypted channels are known as Free To Air (FTA)
Putting it all together - Multiplexing
• Alongside pictures we have stereo audio, conditional access EPG data etc
• Can even multiplex SD & HD together• Also many programs are combined in to one big bit stream
– Sky = 10 channels +
– Freeview = 6 channels
– to get many channels in a single radio channel
• Can multiplex SD & HD together
• Even greater gains using statistical multiplexing!– But that’s another story
• SPTS used by IPTV and amateurs
Modulators
• Now we have a data stream (or multiplex) containing all our programs we transmit it– Using DVB standards
• Over terrestrial channels– Using DVB-T (OFDM)– From transmitter towers
• Over satellite– Using DVB-S (QPSK, 8PSK or DVB-S2)
• Over cable– Using DVB-C = QAM – Modulator at edge for VoD – hence “edge QAM”
• Over IPTV– No standard adopted!– Not web TV
Multi vs single carrier
• All use error correction– Transmitted rate is not useable video rate
• Single carrier QPSK– Bandwidth varies with Bit rateBandwidth varies with Bit rate– Gives DX mode– Half the symbol rate = 3dB
• Multi-carrier OFDM– Fixed bandwidth– Freeview = PAL replacement = 8 MHz– Uses “guard interval” to protect against frequency
selective fading
QPSK
O
F
D
M
Multi-carrier vs single
OFDM on air
QPSK on air
Typical System
MULTIPLEXER
MPEG-2Encoding
ENCODER
ENCODER
ENCODER
MASTERCONTROL
COMPUTER
CONSUMER IRD
500
Studio
Home
ENCODER
ENCODER
ENCODER
Satellite Uplink
MODULATOR
Satellite
Satellite Dish
SICOMPILER
EPGCOMPILER
STREAM SERVERMANAGEMENT
SYSTEM
TSP
I/F I/F
Hampshire technology = 2,000+ customers
Agenda
• Digital TV basics– Why compress?– Compression and modulation standards– HD and SD– Multiplexing
• Services– SKY– FreeView– FreeSat
• Digital ATV– Why and How
The UK market
• Probably the most advanced market in the world– 22million TV households
• 5 major platforms providing a variety of services over different delivery systems:– Sky = DTH pay TV satellite– Freeview = Terrestrial– Virgin = cable– FreeSat = Free to air satellite– BTVision = “Hybrid IPTV”
FreeView• Digital terrestrial service
– Transmitted from TV masts around the country• Will become the main service after Analogue Switch Off in 2012
– Government funded through Free To View Ltd• Very tight on bandwidth – a channel costs £12m pa• 6 frequencies transmitted from each station
– 6 services per channel– Approximately 30 TV channels and 30 radio stations– 4 pay to view channels
• Currently 16m STBs (not homes!)– Available via a STB or integrated TV
• Currently uses MPEG2 Standard Definition and DVB-T– Experiments with MPEG4 HD and DVB-T2
• Large amount of TTV equipment – and growing;-0)
SKY
• Satellite based pay to view service– 8.5m subs
• Virtually unlimited bandwidth– 300 programs approximately
• Mixture of pay to view, FTA and national TV services• SKY services are encrypted
– Need a Sky Box to view
– SKY boxes can view free to air
– The SKY EPG joins it all up
• Most channels are MPEG-2 Standard definition• 20+ MPEG-4 High definition channels
• All TANDBERG TV technology ;-0)
BT Vision – 300k subs• BTVision is a “hybrid” service• Uses FreeView to deliver TV - free• Uses phone line to deliver on demand assets
– Hybrid PVR set top box with hard disk
• Is NOT a true IPTV service!• Why Hybrid?
– Needed to have a TV offering to stop customers leaving– BT network cannot support live TV– Movies are trickle fed to the STB
• Uses Microsoft MSTV system
• Great way to get a free Freeview PVR and powerline adaptors!
Virgin Media – 3m subs
• Consolidation of all UK cable companies (except IOW!)• Only available where the streets have been dug up!• Very controlled environment so high bit rates
– 36 Mbit/s & 54 Mbit/s
• MPEG2 SD and HD– Plenty of bandwidth
• USP is a 2 way system with return path– High speed internet– VoD services
FreeSat – 100k subs
• The BIG secret!• Is just an EPG!!• Uses same transmissions as SKY at 28 degrees east• FreeSat boxes have a new EPG to only list FTA
channels• Will have MPEG2 SD and MPEG4 HD• Note ITV HD is encrypted at moment
– Issues with SKY contract!
• Designed to compliment FreeView– Gives 99.5% coverage– But could end up being the winner!
Internet or Web TV
• Internet or web TV is watching video from a website– Not IPTV as quality is not guaranteed
• 28% of Europeans currently watch short or full-length videos on-line– an increase of 150% since 2006.
• Biggest sites are “catch up TV”– BBC iPlayer, Ch4 on demand
• BBC iPlayer is the outstanding success– 271m plays in 2008– 41m plays in December
• AND BATC.TV!
Agenda
• Digital TV basics– Why compress?– Compression and modulation standards– HD and SD– Multiplexing
• Services– SKY– FreeView– FreeSat
• Digital ATV– Why and How
ATV
• Most ATV is on 23cms or 1300MHz– Analogue FM
• GB3IV = 1316 output
• Some DATV activity using QPSK– 2 or 4 MHz bandwidth– Cheap receivers!– Expensive transmitters– Got gain but you can’t tweak!
Analogue P2
Digital P5
Switch/ splitter/ amp
Pre-amp
FM rxr
Digital rxr
In the shack
MPEG encoder
QPSK modulatorPower AmpSSB transverter
DATV transmit
WWW.BATC.TV
• Internet web site with loads of video clips!
• The easy way to get on ATV
• Most UK repeaters stream in real time– Including GB3IV from the IOW
• Video & repeater audio plus 144.750 MHz talkback– GB3IW streamed on IV site
• Real time chat room for talkback
Summary
• It’s a digital world– Every picture you watch has been digitzed at some
point!• Pictures are not better
– You start at 270 Mbit/s and watch 2 Mbit/s!• Digital will happen
– Digital has gain over analogue– Spectrally efficient
• We should start to experiment now– Digital can save 70cms ATV
• Have a look at www.batc.tv