R V COLLEGE OF ENGINEERING, Bangalore

SATELLITE TELEVISION

Seminar report for Multimedia Communication

Compiled by

Pratheek Manjunath6th semester, Telecommunication Engineering

INTRODUCTION

Satellite television is television programming delivered by means of communication satellites. For receiving the transmission, usually a combination of a parabolic reflector, referred to as a satellite dish, and a satellite receiver either in the form of an external set-top box or a built-in satellite tuner module is employed. Satellite TV tuners are also available as a USB peripheral which can be attached to a personal computer.

In many areas of the world satellite television provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.

Direct-broadcast satellite television comes to the general public in two distinct flavours - analog and digital. This necessitates either having an analog satellite receiver or a digital satellite receiver. Analog satellite television is being replaced by digital satellite television and the latter is becoming available in a better quality known as high-definition television.

OVERVIEW OF THE SATELLITES EMPLOYED

Satellites used for television signals are generally in either very high elliptical orbit or geostationary orbit at 37,000 km above the earth’s equator.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility or the ground station. Uplink satellite dishes are very large, as much as 30 to 40 feet in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'retransmits' the signals back to Earth but at a different frequency band, a process known as translation which is used to avoid interference with the uplink signal. Currently used bands are the C-band (4–8 GHz) or Ku-band (12–18 GHz). Each transponder has a bandwidth of 27MHz to 50MHz. A typical satellite has up to 32 transponders for Ku-band and up to 24 for C-band.

The downlinked satellite signal, quite weak after traveling the great distance, can be collected by using a parabolic receiving dish.

SATELLITE TV BROADCAST STANDARDS

Currently, there are two standards for Digital Video Broadcast of Satellite television. DVB-S3 is still in experimental stages.

1. DVB-S DVB-S is an abbreviation for Digital Video Broadcasting — Satellite. It is the original Digital Video Broadcasting Forward error correction and

demodulation standard for Satellite Television. It dates back to1994, where it was first commercially available in France. It is used via satellites serving every continent of the world. DVB-S is used in both Multiple Channel per Carrier (MCPC) and Single channel per

carrier modes for Broadcast Network feeds as well as for Direct Broadcast Satellite services.

While the actual DVB-S standard only specifies physical link characteristics and framing, the overlaid transport stream delivered by DVB-S is mandated as MPEG-2 Transport Stream.

2. DVB-S2 Emerged in 2003 as a successor to DVB-S DVB-S2 incorporated provision for transmission of HDTV signals and Interactive

programs. Important new feature which was added is the powerful forward error correction

scheme- LDPC concatenated with BCH/RS coding The Variable Coding Modulation / Adaptive Coding Modulation, which allow

optimizing bandwidth utilization by dynamically changing transmission parameters.

Other features include enhanced modulation schemes of up to 32APSK and backward compatibility for MPEG-4 Comparison between the 2 standards:

DVB –S DVB-S2

Input Interface Single Transport Stream (TS) Multiple Transport Stream and Generic Stream Encapsulation (GSE)

Modes Constant Coding & Modulation Variable Coding & Modulation and Adaptive Coding & Modulation

FEC Reed Solomon (RS) 1/2, 2/3, 3/4, 5/6, 7/8

LDPC + BCH 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10

Modulation Single Carrier QPSK Single Carrier QPSK with Multiple Streams

Modulation Schemes

QPSK, 8PSK, 16QAM QPSK, 8PSK, 16APSK, 32APSK

Interleaving Bit-Interleaving Bit-InterleavingComparison with Terrestrial and Cable standards of transmission

DVB-S2 DVB-T2 DVB-C2

Input Interface Multiple Transport Stream and Generic Stream

Encapsulation (GSE)

Multiple Transport Stream and Generic Stream Encapsulation

(GSE)

Multiple Transport Stream and Generic Stream Encapsulation

(GSE)

Modes Variable Coding & Modulation Variable Coding & Modulation Variable Coding & Modulation

and Adaptive Coding & Modulation and Adaptive Coding & Modulation

FEC LDPC + BCH 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10

LDPC + BCH 1/2, 3/5, 2/3, 3/4, 4/5, 5/6

LDPC + BCH 1/2, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10[5]

Modulation Single Carrier QPSK with Multiple Streams

OFDM absolute OFDM[6]

Modulation Schemes

QPSK, 8PSK, 16APSK, 32APSK QPSK, 16QAM, 64QAM, 256QAM

16- to 4096-QAM

Guard Interval Not Applicable 1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/128

1/64 or 1/128

Fourier transform size

Not Applicable 1k, 2k, 4k, 8k, 16k, 32k DFT 4k Inverse FFT[7]

Interleaving Bit-Interleaving Bit- Time- and Frequency-Interleaving

Bit- Time- and Frequency-Interleaving

Pilots Pilot symbols Scattered and Continual Pilots Scattered and Continual Pilots

DIRECT-TO-HOME

Direct broadcast satellite (DBS) is a term used to refer to satellite television broadcasts intended for home reception. A designation broader than DBS would be direct-to-home signals, or DTH. As defined by the ITU, the frequency bands allocated for transmission to different regions of the globe are:

REGION COUNTRIES FREQUENCY BAND1 Europe, Russia, Africa 10.7 to 12.75 GHz2 North America, South

America12.2 to 12.7 GHz

3 Asia, Australia 11.7 to 12.2 GHz

CONDITIONAL ACCESS

Almost all DTH channels/programs are encrypted. They can be viewed only by authorized subscribers.

Conditional access is granted using scrambling and encryption for the transmitted signal

These standards define a method by which one can obfuscate a digital-television stream, with access provided only to those with valid decryption smart-cards. The data stream is

scrambled with an 48-bit secret key, called the control word. Knowing the value of the control word at a given moment is of relatively little value, as under normal conditions, content providers will change the control word several times per minute. The control word is generated automatically in such a way that successive values are not usually predictable.

In order for the receiver to unscramble the data stream, it must be permanently informed about the current value of the control word. In practise, it must be informed slightly in advance, so that no viewing interruption occurs. Encryption is used to protect the control word during transmission to the receiver: the control word is encrypted as an ‘Entitlement Control Message’ (ECM). The CA subsystem in the receiver will decrypt the control word only when authorised to do so; that authority is sent to the receiver in the form of an ‘Entitlement Management Message’ (EMM). The EMMs are specific to each subscriber, as identified by the smart card in his receiver, or to groups of subscribers, and are issued much less frequently than ECMs, usually at monthly intervals.

Apart from SD/HDTV signals, the protected content also includes the Interactive Services and Movie-on demand

SERVICE PROVIDERS / VENDORS

Renowned DTH service providers in India are 1. Tata Sky (uses INSAT 4A), 2. Airtel Digital TV (via SES-7), 3. Dish TV (via AsiaSat 5), 4. Videocon D2H(via ST 2), 5. Reliance Big TV (MEASAT 3)

Manufacturers of Set Top Boxes:1. PACE 4. Cisco2. D-link 5. Nokia3. Western Digital 6. Coship

Few renowned providers of CA technology are – NDS, Safe Access, Conax, Nagravision, Videoguard.

REFERENCES

The information presented in this report was sourced from various websites.

1. Wikipedia en.wikipedia.org/wiki/Satellite_televisionen.wikipedia.org/wiki/DVB-S2

2. ‘How stuff Works’ www.howstuffworks.com/satellite-tv.htm 3. www.indiatelevision.com 4. Project DVB www.dvb.org/technology/fact_sheets/DVB-S2