Transcript No Slide Title

Digital TV
ATV, 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”
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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?
1100101001010
Analogue
270 Mbit/s
A to D converter
PAL
SDI
HD – an even bigger problem!
1100101001010
High
Definition
1.3 Gbit/s
A to D converter
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-ref
B
ref B
non-ref
B
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!
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•
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
Bit Rate (Mbits per second)
MPEG-2 - improvements
8
7
6
5
Bit-rate for Broadcast
Quality Television*
First Broadcast
MPEG-2 Encoder
Reflex TM Statistical
Multiplexer
Enhancements
Enhanced Motion
Estimation
TTV Noise
Reduction
4
Advanced Preprocessing
3
2
MPEG-2 Future
Advanced Encoding
Future
1
Year
How good is MPEG-4?
12.0
PSNR (dB relative)
10.0
8.0
MPEG-4 AVC/m
6.0
WMV9 (beta)
MPEG-2
4.0
2.0
0.0
1.0
1.5
2.0
Bit rate (Mbit/s)
2.5
3.0
Typical System Architecture
Receivers
Encoders
Multiplexers
Modulators
Don’t forget the audio!
• As many channels as you like
– it’s only bits
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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
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– 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!
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– 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 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
Multi-carrier vs single
QPSK
O
F
D
M
OFDM on air
QPSK on air
Typical System
MP EG-2
Encoding
Satellite
Studio
ENCODER
Satellite Dish
ENCODER
CONSUMER IRD
Satellite Uplink
500
ENCODER
MULTIPLEXER
MODULATOR
TSP
ENCODER
Home
I/F
I/F
ENCODER
ENCODER
MASTER
CONTROL
COMP UTER
SI
COMP ILER
STREAM SERVER
EP G
COMP ILER MANAGEMENT
SYSTEM
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:
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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
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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
In the shack
FM rxr
Pre-amp
Switch/
splitter/
amp
Digital
rxr
DATV transmit
QPSK modulator
SSB transverter
MPEG encoder
Power Amp
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