direct broadcast satellite (dbs) television systems

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International Journal of Research and Reviews in Wireless Communication

Vol. 1, No. 1, March 2011

Copyright Science Academy Publisher, United Kingdom

Direct Broadcast Satellite (DBS) Television Systems

Lukman Sharif1, Munir Ahmed

2, and Nauman Sharif

3

1School of Computing, London College of Research, Reading, United Kingdom2College of Computer Science and Engineering, Taibah University, Al-Madinah Al-Munawwarah, Saudi Arabia3 Department of Computer Science, Mohammad Ali Jinnah University, Islamabad, Pakistan

Correspondence should be addressed to Lukman [email protected]

Abstract - Consumers around the world enjoy digital television from a variety of sources including terrestrial, cable, satellite

and broadband Internet broadcast systems. However, it is satellite broadcast systems that have provided consumers real

widespread opportunity to enjoy digital television. This paper presents an overview of direct broadcast satellite (DBS)

systems used in the delivery of digital television. The key DBS system building blocks are identified including the

broadcaster as well as the consumer side of the communication link. This paper also discusses the key technology evolutions

that facilitated the introduction of DBS services, the most common services provided through DBS TV technology and the

future directions that this technology is likely to take.

Keywords: Digital TV, direct broadcast satellite (DBS), GEO satellite, DVB-S2, subscription-based TV, interactive TV

1. IntroductionDigital Television is one of the most prevalent broadcast

platforms around the world. The use of satellites to transmit

digital TV directly to homes is perhaps one of the most

successful commercial applications of this communications

technology. The history of this particular application of

satellite technology can be traced back to Arthur C. Clarkes

truly visionary idea first proposed in an article called Extra-

terrestrial Relays in Wireless World Magazine in 1945

[10]. Clarke proposed that special space platforms (now

commonly referred to as satellites) could be launched into

orbits at some 22,200 miles above the earths equator and

used as relay stations to achieve worldwide communication.

The Russians were the first to explore Clarkes idea and their

efforts culminated in the launch of the first man-made

satellite, called Sputnik, in 1957 [10]. The first commercial

application of direct broadcasts using a satellite came in

1976, when Home Box Office (HBO) started programme

delivery to cable using satellite technology [13].

Satellite TV is essentially a wireless system used to deliver

TV programs to viewers all over the world. The signals used

by broadcast TV satellites are typically digitally compressed

which allows multiple programs to be transmitted from a

single transponder onboard the satellite. The type of program

content delivered by satellite TV could include existing cable

services, movies, sports, Pay per View (PPV) and a variety of

other services. The term Direct to Home (DTH) services and

Direct Broadcast Satellite (DBS) services is often used to

describe this technology.

This paper provides an overview of DBS systems used in

the delivery of TV content to consumers. DBS is a relativelynew TV distribution technology. The term is often used to

describe the actual communications satellites themselves as

well as the TV service received by the consumers on earth.

This paper provides a technical overview of the technology

used in DBS TV delivery, on the broadcaster/operator side as

well as the consumer side of the communication link. This

paper also discusses the most common services provided

through DBS TV technology and the future directions that

this technology is likely to take.

2. Overview of DBS TV systemsThe signal containing the actual TV content originates on

earth from broadcast stations. Due to the fact that this signal

can only travel in straight lines, it is not possible for viewers

receiving equipment to be in the required Line of Sight (LoS)

to be able to capture and decode the signal. Satellite

technology provides the solution to this particular problem.

As first envisioned by Clarke, the DBS TV service involves

the use of satellites launched into orbit at 22,200 miles above

the earths equator. These satellites are said to be in

geostationary or geosynchronous orbits (called GEO -

geostationary earth orbit) around the earth because the speed

of their orbit is exactly the same as that of the earth itself. As

a result, these satellites appear to be stationary above the

earth. A GEO satellite orbits directly above the earth's

equator at 0 latitude. As such the location of GEO satellites

is described in terms of the longitude only, e.g. 28.2 East for

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International Journal of Research and Reviews in Wireless Communications 2

the SES Astra satellite used to broadcast Sky digital satellite

television and radio services [6]. This particular feature of

GEO satellites allows TV broadcast stations to direct the TV

program signals at the satellites from an uplinking facility.

The GEO satellites essentially relay the signal back to earth

which can then be picked up by the consumer receiving

equipment such as the parabolic shaped mini-dishes and

converted back to the original TV programs using IntegratedReceiver Decoder (IRD) devices.

When compared with traditional TV delivery platforms

such as terrestrial and cable, DBS systems offer numerous

advantages. These include consistently high picture quality

and a very wide range of channels. The use of satellites as the

delivery mechanism ensures fast and comprehensive coverage

[9], making it possible to reach low density population areas

as well as parts of the world which may not yet have the basic

cable or terrestrial TV infrastructure [2]. The receiving and

decoding equipment required by consumers is readily

available which allows the DBS service to be deployed in a

very short period of time.The origins of DBS service could be traced back to 1975

when HBO first started to use satellite technology to deliver

program content to cable TV companies for broadcast. This

led to individuals, often those living in rural areas, installing

their own dishes in order to capture the signals intended for

distribution by cable companies [16]. These dishes became

known as Television Receive Only (TVROs) in order to

differentiate them from the commercial satellite TV systems

used at the time. The TVRO systems operated in the C-band

frequencies which typically range from 3.74.2 GHz for

downlinks and 5.9256.425 GHz for uplinks [1]. Due to these

lower frequencies, much larger dish sizes were required on

earth in order to adequately receive the signal. Typical TVRO

dishes were often in excess of 4m in diameter [16].

The GEO satellites are generally classified as either Fixed

Satellite Service (FSS) or Broadcasting Satellite Service

(BSS) [1]. FSS tends to use C band frequencies for open

satellite communications. This typically involves the use of

the service to relay raw feeds and program content from the

originating studios to cable head-ends and DBS uplink

facilities to be rebroadcast as DBS services to viewers [16].

In contrast BSS services tend to use Ku-band frequencies in a

closed system to deliver subscription based program content

directly to small dishes installed at the consumer premises.

The 11.7 to 12.5 GHz range is reserved for BSS [1].

Most modern DBS systems use the Ku-band frequencies.

The higher power used in Ku-band means that the signal from

satellite to receiver can be better directed allowing much

smaller dish sizes to be used [16]. Most modern domestic

dishes used for satellite TV services are between 43 cm to 80

cm (18in to 31in) in diameter. Before the advent of DBS,

viewers would typically have motorised C-band dishes in

order to capture the signal from different satellites [16].

Modern Ku-band dishes however, can be fixed in one

position and still receive the full signal provided there is a

clear LoS fix on the transmitting GEO satellite. Although

modern consumer DBS receiving dishes tend to be fixed in

one position, it is possible for them to be blown out of

alignment due to bad weather, e.g. thunderstorms, resulting in

degradation or loss of signal [16]. The presence of moisture

(in the form of rain) along the LoS is one of the main issues

for the smaller sized dishes. This generally results in signal

fades. In DBS systems, there is also the issue of interference

from other satellites at neighbouring orbits which could be

picked up by the consumer dishes. In general, close

coordination with the ITU and other operators can ensure that

such interference is minimised [1].

3. Technical overview of DBS TV systemsFrom a technical perspective, there are three main

components of a DBS service:

Broadcasting / uplink facility GEO broadcasting satellites Consumer premise equipment

Broadcasting / uplink facility

Like various other forms of satellite communication, the DBS

service signal originates on earth. The DBS subscriptionbased channels are typically sent over to the uplink facility

through fibre connections or other satellite backhaul links [1].

The latter are generally Fixed Satellite Service (FSS) systems

making use of the Ku-band and C-band uplink frequencies.

The backhaul signals may also be used to deliver program

content to other distributors (typically cable and satellite

companies) [5]. It is increasingly common for DBS service

providers to offer local off-the-air channels as part of their

service [6]. For example, in the UK the main DBS provider,

Sky, offers the digital public service channels such as BBC,

ITV, and Channel 4 as part of its service. This requires the

use of digital facilities to backhaul the public service channelsto Skys uplink facilities. The uplink satellite dishes are

generally quite large, typically around 9 to 12 meters in

diameter [16]. This plays an important role in aiming and

delivering higher signal strength to the relevant satellite. The

signals are uplinked at a particular frequency range and can

only be picked up by the satellite onboard transponder that is

correctly tuned to that frequency range [1]. Figure 1 provides

an overview of the process involved in the backhaul of

signals to the DBS uplink facility.

Figure 1 [1]: Backhaul of program signals to a DBS uplink facility

In general, the content received by the uplink facility is not

altered. However, the uplink facility does provide a number


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of important functions. This includes adjustment and

resynchronization of the incoming signal [1]. In the case of

pre-recorded content, this also involves quality control and

playback functions. The program content is also copied from

master tapes and stored on video servers to be broadcast on

the relevant satellite channel in accordance with the schedules

/ Electronic Program Guide (EPG). Conditional access forms

a very important part of the DBS service business model. Assuch, the DBS service provider needs to supply the necessary

equipment in order for the consumer to receive and pay for

the service (discussed later).

The broadcasting facility also provides important signal

processing functions such as compression of video and audio

content. The program content is typically compressed (from

around 270 Mbps) to between 1-10 Mbps before transmission

[1]. This also has the effect of dramatically increasing the

number of channels for a given bandwidth. MPEG-2 is the

most common encoding standard used [7] whilst Quadrature

Phase Shift Keying (QPSK) is the most common modulation

scheme used by DBS systems [8].

GEO broadcasting satellites

The signal broadcast from the DBS uplink facility is picked

up by the appropriate RF transponder (part of the frequency-

translating repeater) onboard the satellite. Most

communications satellites are simply microwave radio relay

stations and have dozens of onboard transponders. Each

transponder could have a bandwidth in the region of tens of

megahertz.

The typical operation of a transponder is often referred to

as bent-pipe because of the fact that the uplink signals are

simply amplified and shifted to different frequency (called

translation) in order to avoid interference with the uplink

signal before being sent back trough the downlink [1]. In

general, for a BSS Ku-band, the 11.7 to 12.5 GHz range is

used.

Figure 2 [1]: A typical GEO satellite deployed for DBS services

The GEO satellites used for DBS services tend to be verysimilar to those used for traditional communications (see

Figure 2). Since the mid 1990s, the satellites deployed for

DBS services have greatly increased in size and weight.

However this increase in size and weight offers many benefits

for DBS services. The large onboard solar panels allow more

DC power to be generated [1] and larger antennas facilitate

better shaping of the downlink microwave beams.

Figure 3 [1]: Repeater configuration for one RF carrier onboard a GEO

satellite

As shown in Figure 3, each DBS service satellite has a

frequency-translating repeater. There is a front-end broad-

band receiver which converts to downlink frequency. The

latter also drives multiple RF chains (transponders) with each

transponder having high-power Travelling Wave Tube

(TWT) transmitter [14]. Each TWT amplifier typically has a

maximum power rating of 240W [15].

Consumer premise equipment

The typical equipment used by the consumer to receive and

decode the DBS signal is illustrated in Figure 4. The

equipment consists of a parabolic shaped dish used to reflect

the satellite signal to the feed-horn. The latter is the dishs

focal point and front-end of a waveguide that is used to pass

the signal to a Low Noise Block (LNB) down-converter

where the signal is down-converted to L-band IF of 950

1450MHz [2].

Figure 4 [1]: A typical dish and Integrated Receiver Decoder (IRD) box at

consumer premises

The dish also receives low-voltage DC power through the

coaxial cable which is used to deliver the converted signal to


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the IRD box inside the consumer premises [6]. The IRD box

has a number of very important components required for a

DBS service. This includes a QPSK demodulator, TV signal

regenerator, an IF tuner, FEC decoder, stream de-multiplexer,

decryptor (for conditional access), and a MPEG decoder

(video/audio) [1].

In the UK, DBS receivers typically make use of smart

cards with embedded chips that can be used for generatingcryptographic keys in order to decrypt the program content

for consumer viewing. For the purpose of viewing the

program content, the IRD box decrypts and outputs the

content to a SD or HDTV. The use of a smart card and

encryption technology plays an important role in

implementing the conditional access system for DBS

providers. The conditional access system ensures that the

consumers account is up to date with payments and that the

consumer is in the correct geographical location in order to

receive the content [6].

4.

DBS consumer services and applicationsUnlike terrestrial broadcasting which is traditionally

supported through advertising revenues [3], the DBS industry

has successfully created and sustained a consumer

subscription based business model. Typically, in this type of

model, the DBS service provider designs and implements

subscription based services to be offered to consumers. The

main characteristics of this type of business model are that the

service offering has to be compelling and cost effective for

the consumer in order to achieve widespread take-up. Some

of the most commonly available DBS services and

application are discussed below.

Subscription-based TV

DBS TV providers typically offer tier based subscription

services. The vast majority of customers tend to subscribe to

the most basic package and perhaps one or two premium

packages. In the UK, Sky offers a basic starter package and

premium content such as sports and movies is marketed as

additional add-ons that consumers can opt for at additional

cost.

Pay per-view (PPV)

This type of service allows DBS TV consumers to choose and

pay for specific programs as one-off transactions. The chosenprogram is typically broadcast at the same time to everyone

and could include concerts, sports events such as boxing and

football matches.

Public service channel rebroadcasts

Most DBS TV providers offer packages that include the local

free-to-air channels. In the UK, Sky is the dominant DBS

service provider. Currently Sky offers around 240 free-to-air

digital channels included as part of any Sky TV package

chosen by consumers. This includes the major public service

channels such as BBC, ITV and Channel 4.

High-definition television (HDTV)

HDTV is rapidly becoming the norm for television viewing.

HDTV offers a significantly enhanced viewing experience

with notably higher picture quality than standard definition

television (SDTV). DBS TV has been one of the earliest

adopters of HDTV technology [4]. Satellite receiving and

decoding equipment for HD content has been available since

1999 [2]. In the UK, the majority of HDTV services tend tobe HD simulcasts of subscription-based, PPV, and free-to-air

digital channels which are already available as Standard

Definition TV (SDTV). The components of a typical DBS

HDTV system are illustrated in Figure 5.

Figure 5 [1]: Components of a typical DBS HDTV system

In addition to the main services discussed above, DBS

providers also offer a number of very useful ancillary

applications.

Digital video recorders (DVR)

A DVR is essentially a device that allows the recording of

video content in a digital format. The content is typicallystored on a disk drive but USB memory drives, SD memory

cards and various other storage media could also be used.

There are two very important aspects of the DBS service that

make DVR devices an attractive ancillary application. The

first is the Electronic Program Guide (EPG) that provides the

consumers with comprehensive program schedules. The

second is the availability of program content in a digital

format. This allows consumers to select a program from

within the EPG and record it directly to the DVR onboard

hard disk in a digital format [1].

Support for IP-based home networkingModern DBS receiving and decoding equipment such as set-

top boxes provide integrated IP networking capabilities. This

typically involves support for an internet connection through

a broadband network such as cable or ADSL. The internet

connection provides consumers remote DVR scheduling

capabilities.


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Figure 6 [1]: Program content sharing between multiple set-top boxes over

an IP network

In a traditional DBS service setup, there is typically one

antenna dish installed at the consumer premises. This dish

may be connected through a multi-switch to numerous set-top

boxes in the consumers home. This would require multipleconnections (typically using coaxial cable) originating from

the dish (multi-switch) to various locations in the house [1].

However, the IP-based home networking feature allows

multiple set-top boxes to be connected through an IP network

and enables digital TV programs to be recorded on one main

set-top box and distributed to multiple boxes in the house

over a wired or wireless network.

Interactive services

Interactive television (also called iTV) is an increasingly

common feature allowing viewers to interact with the

television content. The interactivity level of the service variesdepending on the delivery platform being used, e.g. Digital

Terrestrial TV (DTT), cable, or satellite (DBS). At the low

end of the interactivity scale, this could involve simple

controls, e.g. on/off, volume, browsing channels, etc to more

moderate levels of interaction involving features such as

movies on demand, etc. However, in order to be truly

interactive, the viewer must be able to have some influence

over the viewing experience [1]. Some examples of this

include, being able to choose the angle to view a football

match from or participating in a live program through voting

in order to influence the outcome. This involves the use of

some kind of return path to send information back to thebroadcaster. With DBS services, this typically involves the

use of broadband connections such as cable or ADSL.

Sky offers one of the most advanced iTV services through

DBS in the UK [11]. There is an increasing trend with DBS

operators to offer more complex interactive features which

are integrated within the actual program content. To date,

most of the technologies used by DBS operators to offer

interactive services have been proprietary implementations.

There have been numerous efforts to standardise the delivery

of interactive services on various TV platforms. The

Advanced Common Application Platform (ACAP) standard

by the Advanced Television Systems Committee (ATSC) is awell known example of such efforts [12]. This standard aims

to provide the technical basis for the development of

interoperable interactive services and products and is

expected to play an important role in future DBS services.

5. Advances in DBS technology and futuredirections

Early efforts to create DBS services in the 1980s were not

particularly successful. Most of the early applicants of the

DBS service were forced to either postpone or completely

abandon their plans due to the high start up costs involved[16]. However, by the early 1990s, there had been significant

developments in the area of digital satellite communications.

In particular, progress in four important areas of the

technology paved the way for a more practical and

economically viable launch of the DBS service [1]:

Advances in video and audio encoding techniques The

development of the MPEG-2 standard for source coding

offered significant gains in compression.

Advances in modulation and error correction techniques

DBS technology provided the basis for the first mass-market

application of concatenated coding (FEC).Advances in consumer electronics Rapid improvements in

digital circuit design and decreasing cost of consumer

electronics equipment.

Advances in satellite platforms Increases in satellite size

and weight, higher power generation using more efficient

solar technology, support for up to 240W transponders and

subsequent increased signal strength.

A second phase of the technology evolution is making it

possible for DBS providers to offer bigger and better services

to consumers. There havent been any major breakthroughs

and much of the basic DBS technology has remained thesame. However, much of the change has been in the way that

existing technology can be customised and deployed for

specific applications.

With regards to video and audio encoding techniques, the

advent of HDTV has given rise to the MPEG-4 AVC

standard which is expected to deliver even greater

performance. Similarly, DVB-S2 is being promoted as the

successor to the DVB-S standard and will also provide

improved modulation and coding. The existing trend of cost

vs performance is expected to continue and consumers are

likely to benefit from declining cost of electronics equipment.

Consumers are also expected to benefit from smallerparabolic dish sizes and improved signal reception. In

particular, the addition of multiple feed-horns and LNBs to

give consumers access to signals from multiple satellites is

also likely to continue and improve. Technical improvements

in satellite platforms are also expected to continue and there

is a trend of increasing number of onboard transponders and

greater bandwidth per satellite. The use of larger solar panel

area has also led to greater DC power levels.

6. ConclusionsDBS TV is an increasingly popular platform for television

viewing around the world. In comparison with other TV

delivery platforms such as terrestrial and cable, DBS systems

offer a number of advantages. The bandwidth available to

DBS providers is generally much higher than that available


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for cable TV. This allows a consistently higher picture quality

and a wide range of channels to be delivered. DBS offers fast

and comprehensive coverage for consumers all over the

world. Due to the wireless nature of the technology, there is

no need for physical infrastructure such as cable deployment

to the consumer premises. This makes DBS technology an

ideal candidate for low population density / rural areas as well

as developing countries where the traditional terrestrial andcable infrastructure may not be available.

The DBS industry has managed to create and sustain a

successful subscription based business model. Although early

efforts to create economically viable DBS services failed due

to high start-up costs, later advances in technology paved the

way for practical and economically feasible DBS services to

be deployed. Advances in four particular areas of satellite

technology have helped to transform DBS TV into one of the

fastest growing TV platforms: video and audio encoding

techniques, modulation and error correction techniques,

technical improvements in satellite platforms and cheaper and

more efficient consumer electronics. Most of the major DBSoperators are expected to increase their fleet of satellite

platforms and delivery capacity in the near future. There is

strong evidence of growing consumer demand for HD content

and with more and more local and free-to-air channels being

rebroadcast over satellite, DBS networks are expected to play

an increasingly important role.

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summit-1219/

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[14] Godwin, J.P. (1999). Direct satellite television broadcasting. In WileyEncyclopedia of Electrical and Electronics Engineering, J. G. Webster,

Wiley, pp. 590602

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Lukman Sharif is a professional member of the Institution of Engineering

and Technology (IET). He gained his Bachelors degree from London

Metropolitan University in Computer Networking. He has worked in the IP

communications industry for over a decade as a Network Architect and

Consultant. He is currently a Senior Lecturer in Computer Networking and

Information Security at London College of Research, UK. His research

interests include IP routing and security in Mobile Ad-Hoc Networks.

Professor Dr Munir Ahmed is a professional member of the Institution of

Engineering and Technology (MIET). He is currently pursuing his DProf

(Doctorate in Professional Studies) in Computer CommunicationsEngineering Specialisation in Information Security with Middlesex

University, London, UK. He earned his PhD in Digital Communications

Systems Engineering from London Institute of Technology, UK (in

collaboration with London South Bank University, UK) in 1997 and his

MSc in Information Systems Engineering from London South Bank

University, UK in 1994. Before joining Taibah University as Professor of

Computer Networks and Communications Engineering, he was a Professor

of Computing and Telecommunications at The American University,

London, UK. He has extensive experience in the commercial sector and has

held a variety of high-level positions in the industry, including Chief

Executive Officer (CEO), Chief Operations Officer (COO), Training

Director and Chief Network Architect in the UK. His current research

interests include Wireless Sensor Networks, Mobile Ad-Hoc Networks,

Routing Protocols, Network/Information Security and Digital Modulations.

Prof. Ahmed is author or co-author of 6 books and more than 25 papers.Nauman Sharif is a professional member of the British Computer Society

(BCS). He holds M.Sc. in Internet Engineering from University of East

London, PGCE from University of Greenwich and B.Sc. in Computing from

University of Westminster, UK. He is currently an Assistant Professor with

the Department of Computer Science at Mohammad Ali Jinnah University,

Islamabad, Pakistan. Before joining academia, he worked in the IT and

Computer Networking industry for many years in a variety of roles including

Systems Administrator, Consultant and Technical Author. His research

interests include wireless networks, ubiquitous computing and the semantic

web.

direct broadcast satellite (dbs) television systems

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