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” –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 Analogue A to D converter

HD – an even bigger problem! 1.3 Gbit/s High Definition 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! 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 for Broadcast Quality Television* First Broadcast MPEG-2 Encoder Enhanced Motion Estimation Advanced Pre- processing Reflex TM Statistical Multiplexer Enhancements TTV Noise Reduction MPEG-2 Future Advanced Encoding Future Year Bit Rate (Mbits per second) MPEG-2 - improvements

How good is MPEG-4?

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 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

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 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-ampFM rxr Digital rxr In the shack

MPEG encoder QPSK modulator Power Amp SSB transverter DATV transmit

70cms case study Tests between G8GKQ and G8GTZ –70 Km obstructed path DVB-S QPSK –2 Msymbols ½ FEC –2 MHz 436 MHz Full PAL plus audio! See CQTV 200

Received spectrum – no signal

Received spectrum – what signal!

Received pictures - P5!

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 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