Digital TV ATV, Freeview, Freesat and all that… Noel Matthews G8GTZ.

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