unit-5: satellite applications

UNIT-5: SATELLITE APPLICATIONS ADC-15EC53T

MALLIKARJUN S H, LECTURER, GPT KAMPLI 1

INTRODUCTION TO SATELLITE APPLICATIONS

The conventional applications of satellites are radio telephony and long-distance

audio/video communications. The benefits of satellite technology have extended to newer

communication services such as fax, data communications, cellular phones, timely and

accurate weather forecasts navigational aids, remote sensing to unearth the hidden mineral

resources etc. The application areas are increasing.

SATELLITE APPLICATIONS IN DIFFERENT AREAS Satellites find applications in the following areas:

1. Communications

2. Military and surveillance

3. Meteorological, remote sensing and earth observation

4. Navigation

5. Scientific and technological

Communications

Satellites act as relay stations in the sky and permit reliable long-distance

communications worldwide. In the field of satellite communication applications, satellite

television, telephone and data communication are the major application areas. TV signals

can be transmitted easily from one place to another. All the major TV Networks and cable

TV companies rely on communications satellites for TV signal distribution.

Military and Surveillance

Military applications include providing strategic communication links between

border forc6 and headquarters, spying, providing navigational aids to ships, aircrafts etc.

Military satellites used to perform reconnaissance. Television cameras can take pictures

and send them back to earth infrared sensors detect heat sources. Intelligence satellites

collect information about enemies

Meteorological, Remote Sensing and Earth Observation

The meteorological applications include weather forecasting and flood forecast,

melting glaciers etc. Meteorological or weather satellites photograph cloud cover for the

purpose of predicting the weather. Geodetic satellites photograph the earth for the

purpose of creating more accurate and more detailed maps. In the category of remote

sensing and earth observation applications, the typical ones are the discovery of hidden

mineral resources, terrain mapping etc. satellites can observe crops, forests, lakes and



rivers. Satellites can spot diseased crop areas, sources of pollution and other

characteristics that are difficult to detect in other ways.

Navigation

One of the newest and most useful satellite systems is the Global Positioning

System (GPS). Its primary application is navigation. Navigation is the art of guiding a

vehicle in the proper path.

Scientific and Technological

In the category of satellites for science and technology, the applications include

use of satellites for astronomical research, monitoring of different layers of atmosphere

etc.

GLOBAL POSITIONING SYSTEM

Fig. 5.1 : GPS configuration

User Segment



GPS is an acronym for Global Positioning Systems. It is a navigation tool which

allows users to determine their location anywhere in the world at any time of the day.

GPS systems use a network of 24 low-earth-orbit satellites to establish the position of

individual users. Originally developed by the military, GPS is now widely utilized by

commercial users and private citizens. The military system error is less than 40 m whereas

the civilian system accuracy is less than 100 m from the actual location. All GPS positions

are based on measuring the distance from the satellites to the GPS receiver on the earth.

This distance to each satellite can be determined by the GPS receiver. The GPS

configuration shown in fig 5.1, is comprised of the following three segments:

1. Space segment

2. Control segment

3. User segment

Space Segment

It consists of the satellites themselves, transmitting time codes and orbital position

information to the users.

Control Segment

It ensures the overall system performance and accuracy. The control segment

consists of stations positioned on the earth's equator to control the satellites. The control

segment tracks the GPS satellites, updates their orbiting position and calibrates and

synchronizes their clocks. It determines the orbit of each satellite and predicts its path for

the following 24 hours. This information is uploaded to each satellite and subsequently

broadcast from it.

User Segment

The user segment consists of the actual GPS receivers which receive signals from

the four satellites, compute the time differences and determine position. There is no limit

to the number of receivers that can use the system simultaneously.

Limitations

GPS is unusable where it is impossible to receive the signal such as inside most

buildings, caves and subterranean locations as well as underwater.



TRILATERATION

Fig.5.2: Trilateration

GPS satellites circle the earth twice a day in a very precise orbit and transmit

information signal to earth. GPS receivers take this information and use trilateration

(triangulation) to calculate the user's exact location as shown in Fig. 5.2. The GPS

receiver is located at point X, where three spheres with radii R1, R2 and R3 intersect. The

centers of the spheres are the three GPS satellites s1,s2, and s3. If the distances RI, R2

and R3 are measured, the location of the point X can be uniquely &fined. The GPS

receiver compares the time a signal was transmitted by a satellite with the time it was

received. The range to the satellite is the product of the time difference and the speed of

light. Three satellites are needed since there are three position coordinates x, y and z. The

fourth satellite is used for cancelling out the error in the user clock. The user position is

determined by extensive numeric calculations based on signals received from the four

satellites. The GPS receiver requires between I and 3 minutes to acquire the initial time

stamp, perform all calculations and display the location information on the unit's

electronic map; subsequent updates are quicker.

s:



APPLICATIONS OF GPS

The most common applications of GPS are as listed below:

✓ Timing

✓ Roads and highways

✓ Space

✓ Aviation

✓ Agriculture

✓ Marine

✓ Rail

✓ Environment

✓ Public safety and disaster relief

✓ Surveying and mapping

✓ Recreation

✓ Tracking and locating

Timing

In addition to longitude, latitude and altitude, the GPS provides precise time data.

Each GPS satellite contains multiple atomic clocks. GPS receivers decode these signals,

effectively synchronizing each receiver to the atomic clocks. This enables users to

determine the time to within 100 billionths of a second, without the cost of owning and

operating atomic clocks.

Roads and Highways

The GPS offers increased efficiencies and safety for vehicles using highways, streets

and mass transit systems. Many problems associated with the routing and dispatch of

commercial vehicles, management of mass transit systems, road maintenance crews and

emergency vehicles are Significantly reduced with the help of GPS. GPS enables

automatic vehicles location and in vehicle navigation systems.

A geographic information system (GIS) stores, analyzes and displays geographically

referenced Information provided by GPS. GIS is used to monitor vehicle location, keep

transit vehicles on schedule and inform passengers of precise arrival times. Mass transit

systems use this capability to track rail, bus and other services to improve their

performance. GPS technology can be used to track and forecast the movement of

freight. Many nations use GPS to help survey their road and highway networks.



Space

The GPS is used in guidance systems for crewed vehicles, management, tracking and

control Communication satellite constellations and monitoring the Earth from space.

Aviation

GPS is used in aviation to increase the safety and efficiency of flight. GPS offers

satellite navigation services for aviation users. GPS allows aircraft to fly user-preferred

routes irrespective of the availability of ground-based navigation aids or surveillance

equipment.

Agriculture

GPS rate is used applications for farm planning, and yield field mapping. mapping,

GPS soil allows sampling, farmers tractor to work guidance, during crop low scouting

visibility field conditions such as rain, dust, fog and darkness.

Marine

GPS provides the fastest and most accurate method for mariners to navigate, measure

speed and determine location. This enables increased levels of safety and efficiency for

mariners worldwide.

Rail

Rail systems in many parts of the world use the Global Positioning System (GPS) in

combination with various sensors, computers and communication systems to improve

safety, security and operational effectiveness.

Environment

GPS helps in gathering accurate and timely information to sustain the Earth's

environment while balancing human needs.

Public Safety and Disaster Relief

GPS serves as a facilitating technology in knowing the precise location of landmarks,

streets buildings, emergency service resources and disaster relief sites so that timely

rescue operation is carried out.

Surveying and Mapping:Using GPS, highly accurate surveying and mapping results

can be quickly obtained, thereby greatly reducing the amount of equipment and efforts

required as compared to other conventional surveying and mapping techniques.



Recreation

GPS is popular among recreational users such as hikers, hunters, mountain bikers and

cross-country skiers.

Tracking and Locating

GPS is used for tracking a vehicle’s movement by investigators. It is also used for

locating and recovering stolen items, defining locations of crimes, evidence and traffic

accidents.

SATELLLTE FOR TELEVISION APPLICATIONS

Fig. 5.3: Satellite television

Satellite

SATELLITE

TV receivers



Satellite television refers to the use of satellites for relaying TV programmes to a large

geographical area. It is based on single point to multipoint connectivity feature of the

satellite Communication. It is a broadcasting service which allows subscribers to

receive television signals directly through a dish-shaped receiving antenna. It is one of

the most popular application areas of communication satellites as it involves masses at

large. Satellite has become a household name largely due to its television broadcast

capability. It can bring live events to our drawing rooms from Places thousands of

kilometers away. As shown in Fig. 5.3, the satellite receives TV Programmes from a

source point using uplink and then reflects the same towards earth using downlink.

These TV programs can be received by all those who lie within its coverage area. The

following configurations are used to implement satellite television:

1. Direct Broadcast Satellite (DBS) system

2. Direct-To Home (DTH)

3. Cable TV

Benefits of Satellite TV

✓ Satellite TV provides a strong digital signal to subscribers' television sets and it is

wireless

✓ Digital signals provide better quality audio and video as compared to analog

signals.

✓ A single communication satellite remains in a steady orbit above the Earth,

allowing all subscribers to receive the signals using a small dish receiver.

✓ Modern satellite television providers allow the use of popular cable or broadcast

channels including pay-channels. The tuner descrambles selected programs sent out

on a specific frequency.

✓ Satellite TV services are popular in rural areas.

✓ Services can be provided at extremely low prices. Digital satellite systems offer

additional data about channels currently playing and a schedule of the future.

Viewers can scroll through a digital guide.

✓ DTH, in sharp contrast to Cable TV, lends itself to easy monitoring and control.

✓ DTH transmission offers immense opportunities to both broadcasters and viewers.

✓ Broadcasters can provide a number of channels over a single delivery platform

using DTH.

✓ The number of channels that can be broadcast using digital technology is

significantly higher than with analog technology.

✓ Because of the rapid development of digital technology, DTH broadcasters have

been able to introduce new interactive applications in the television market.



✓ DTH transmission eliminates local cable operator completely, since an individual

user is directly connected to the service providers.

✓ As the signals in DTH are digital - they provide higher resolution picture quality

and better audio than traditional analog signals.

Limitations of Satellite TV

✓ Grove of trees or mountainous terrain can be problematic.

✓ There can be reception problems during heavy rains or snowfall.

✓ Signals between an earth-bound receiver and a space-based satellite can be affected

by atmospheric conditions.

DIRECT-TO-HOME (DTH)

Direct-To-Home (DTH) service is the one in which a large number of channels are digitally

compressed, encrypted and beamed from very high-power satellites. The programs can be

received at homes. This mode of reception facilitates the use of small receive dish antennas

of 45 to 60 cm diameter installed at convenient location in individual buildings without

needing elaborate foundation / space etc. Also, DTH transmission eliminates local cable

operator completely' sine an individual user is directly connected to the service providers.

A digital receiver is needed receive the multiplexed signals and view them on a TV.

Transmission in Ku band is most appropriate and widely used for the purpose. Most of the

DTH systems provide paid-service. The encrypted TV signals are received from the

satellite on the dish antenna and transmitted to the digital decoder.

The customer is provided with a viewing card, which is inserted into a slot in the digital

decoder. The viewing card decrypts the TV signals chosen and paid for by the customer.

A viewing card is a credit card sized smart card, which contains information about the

channels that the customer has subscribed to. When inserted in the decoder it enables

viewing of the channels chosen by the Subscriber. The subscription charges for viewing

these channels are collected by the DTH operator.

The complete DTH process is depicted in Fig. 5.4. It involves the following four major

components:

1. Programming sources

2. Broadcast center

3. Satellite and satellite dish

4. Satellite receiver



Programming Broadcast Center

Sources

Fig. 5.4: DTH process

Programming Sources

Programming sources are the channels that provide programmes for broadcast. The DTH

service Provider pays other companies for the right to broadcast their content via satellite.

In this Way' the DTH service provider is kind of mediator between the viewer and the

actual programming Sources.

Broadcast Centre

The broadcast center first converts all programs into a high-quality, uncompressed digital

stream at about 270 Mbps per channel. These programs are compressed and scrambled

so that an unauthorized person cannot view the transmission. The service providers use

the MPEG-2 (Motion Picture Experts Group-2) compressed video format. With MPEG-



2 compression, the provider can reduce the 270 Mbps stream to about 3 or 10 Mbps

depending on the type of programming. Encryption of the digital data is performed in

such a way that it can only be decrypted (converted back into usable data) if the receiver

has the correct decoding satellite receiver with decryption algorithm and security keys.

Satellite and Satellite Dish

The compressed and scrambled signal is beamed to the satellite using a satellite dish. The

satellite receives the signals from the broadcast station and rebroadcasts them to the

ground. With digital compression, a typical satellite can transmit about 200 channels.

Without digital compression it can transmit only about 30 channels.

The viewer's dish picks up the signal from the satellite. A satellite dish is a special kind

of antenna designed to focus on a specific broadcast source. The standard dish consists

of a parabolic surface and a central feed horn. The central element in the feed horn is the

low noise block (LNB). The LNB amplifies the signal bouncing off the dish and filters

out the noise. The LNB passes the amplified and filtered signal to the satellite receiver in

the viewer's house.

Satellite Receiver

The satellite receiver processes the signal received form satellite and passes it on to a

standard television set, where the viewer can watch and listen to the program.

CABLE TV (CATV)

The abbreviation CATV originally stood for Community Antenna Television

which meant single outdoor unit and common receiving antenna for the community. The

signal received by this common antenna is distributed to large number of houses through

a network of coaxial cables Such a system eliminates the need for each house to have its

own antenna dish on rooftop. Fig. 5.5 shows a typical set up.

Cable operator receives from a number of satellite telecasts by either having more than

one receiving dish antennas or even a single dish antenna with multiple feeds. All the

carriers are demodulated in a common receiver-filter system. The channels are then

combined into a standard multiplexed signal and transmitted over a distribution network

of coaxial cables. This is done on single point to multipoint connectivity basis to a large

number of subscribers who pay monthly fee for this service. With the CATV system,

local programming material also may be distributed to subscribers.



Cable distribution

Fig. 5. 5: Community Antenna TV (CATV) System



VOICE COMMUNICATION (TELEPHONE SERVICES) VIA

SATELLITE

Satellites play an important role in providing long distance trunk or point-to-point

telephone services. The satellite serves the purpose of a repeater station. The satellite link

is advantageous when the distance involved exceeds 1000 km or when the region to be

covered has less population density or has difficult geographical terrain.

Fig. 5.6: International telephone service via satellite

Fig. 5.6 shows a typical set up of international telephone service via satellite. The user is

connected to the earth station through terrestrial network. This terrestrial network may

various configurations including central office (telephone exchange), toll office and

leased links to the earth station. Signal generated by the user is processed and transmitted

from the earth station to the satellite. The satellite receives the modulated RF carriers at

the predetermined uplink (earth-to-satellite) frequencies from all the earth stations in the

network, amplifies these carriers and then retransmits them back to earth at down link

(satellite to earth) frequencies. The downlink frequencies are kept different from the

uplink frequencies in order to avoid interference. The modulated carrier received at

receiving earth station is processed and converted back to the original baseband signal.

This signal is then sent to the user through a terrestrial network.



DATA COMMUNICATION SERVICES

Data communication services are the result of developments made in the field of

computers and telecommunications. The purpose of data communication is to link

remotely located computers and data processing facilities by a communication channel.

The telecommunication channel could be terrestrial or satellite based. Terrestrial links

have lower data transfer speed, high cost, lesser reliability and throughput capability.

Satellite links are attractive for data communication because of higher data transfer rate

capability, higher reliability and much higher performance to cost ratio particularly

achievable with VSAT networks (Very Small Aperture Terminal).

DATA BROADCASTING USING SATELLITE

Fig. 5.7 shows data broadcasting using a satellite. Data from a central database is routed

to the earth station via data packet assembler. The data packet assembler places headers

containing destination address at the beginning ofeach packet for routing purpose.

Fig. 5.7: Data broadcasting using satellite

Each data packet is encoded so that only authorized users can access it. The data beamed

up at the satellite is retransmitted towards Receive Only (RO) terminals on earth. The RO

terminals identify data packets addressed to them. The respective RO terminal receives

and delivers the data to the user terminal. In the example shown, data is delivered to user

terminal A. The user terminals are linked to the central facility via dial-up lines and

modems to request for broadcast of additional data.

INTERACTIVE DATA COMMUNICATION

Fig. 5.8 shows the typical arrangement in an interactive data communication network

Here, remotely located user terminals can exchange information with central computer.



Such a network is implemented using Very Small Aperture Terminals (VSATs). Each

VSAT supports large number of user terminals. The remote stations can transmit

information to the central facility that does the data broadcast.

Fig.5.8 Interactive data communication network

There is no need for terrestrial link. data concentrator multiplexes the data different user

terminals and sends a single stream of bits to the VSAT indoor electronic unit. also,

demultiplexes the data broadcast received from the satellite for delivery to user terminals.

Remote

Interactive



SATELLITES FOR EARTH OBSERVATION (REMOTE SENSING)

Satellites are used for a variety of earth observation applications listed below:

➢ Cartography

➢ Monitoring agriculture and forestry

➢ Oceanography

➢ Ice reconnaissance

➢ Monitoring oil pollution and air pollution

➢ Snow melt

➢ Mineral and oil exploration

Cartography

Cartography deals with map-making. Satellites equipped with high resolution cameras

have been used to correct and update maps in various countries. Satellite imagery has

been used to produce maps for construction of roads, railways and irrigation channels. It

has been used to map underwater features such as coral reefs which are dangerous for

shipping.

Monitoring Agriculture and Forestry

Satellite imagery has been used for better crop and forestry management. Remote sensing

data from the earth observation satellite is used for crop identification, crop yield, land

fertility, agricultural crop acreage and field estimation, drought monitoring and

assessment, flood mapping land use and land cover mapping, wasteland management,

forest resources survey and management monitoring optimum plantation and harvest

times and so on.

Oceanography

Satellite data can be used to determine sea conditions such as sea surface temperature,

wind speed, wind direction, local air temperature and moisture content etc. Satellites have

also been used to make pictures of ocean waves, ice fields, ice bergs, ice leads and sea

conditions along the coastal lines, coastal sedimentation and pollution, conservation and

use of fish stocks, ship routing. wave forces for use in the design of off-shore structures

and wave power generating systems mapping of polar ice caps, ocean temperatures and

winds for improved climate and weather forecasting. Fishermen can make use of satellite

information for fishing.



Ice Reconnaissance

Remote sensing satellite data can be used to gather information on the properties,

distributi0 variability and behavior of ice bergs for navigation of ships in cold waters.

Forecasts require knowledge of air and sea temperatures, precipitation, wind and currents.

Data on ice thickness be obtained by infrared sensors abroad satellites under cloud free

conditions.

Monitoring Oil Pollution and Air Pollution

Satellites can be used for monitoring oil slicks in the sea. To do so, the space borne

measure the amount of sunlight reflected from the sea surface.

Snow Melt

Satellites can monitor snow cover area, thickness, density etc. to make predictions of

snow melt. Accurate predictions of snowmelt are important for water management,

irrigation, controlling flood water etc.

Mineral and Oil Exploration

satellite data can be used for oil and mineral exploration. The data can be used by

geologists to get clues to mineral deposits and select sites for nuclear power stations and

routes for pipelines.

MILITARY APPLICATIONS OF SATELLITE

Following are some of the common military applications of satellite:

❖ Reconnaissance and intelligence gathering functions

❖ Command and communications

❖ Navigation

❖ Early warning

❖ Meteorological functions

❖ Nuclear detection

Reconnaissance and Intelligence Gathering Functions

Military satellites are used to verify the extent and composition of military forces and the

monitoring of new military developments. This is achieved by a variety of electronic and

photographic means.

Command and Communications

Military satellites can provide instant communication between the operational forces and

their national command authorities irrespective of the distance or time of the day.



Navigation

The navigational satellites are capable of providing data to enable position fixing with an

accuracy of a few meters. Receivers fix position through a combination of Doppler Effect

and accurate orbital details transmitted by satellites.

Early Warning

Early warning satellites provide an advance warning to the owners of a missile attack.

Meteorological Functions

Satellite data is useful for accurate weather forecasts. The weather satellites provide long

range forecast for military planners and play a key role in reconnaissance satellites. They

provide advance information on whether the target area will be clear of cloud cover or

not.

Nuclear Detection

Satellites are used for detecting nuclear explosion at the distance and reporting its yield

and other characteristics.

VERY SMALL APERTURE TERMINAL (VSAT)

VSAT CONCEPT

A new development in the communication satellite world is the development of low-cost

micro stations, called VSATs. VSAT is an acronym for Very Small Aperture Terminal.

The earth station antennas used in commercial satellite communications systems were

very large and expensive, with typical aperture diameters of 30 m. These large antennas

operated in C band (614 GHz). With the rapid expansion of satellite telecommunications

worldwide, there was a need to make access to the satellite more affordable. This came

about in two ways: a significant increase in the transmit power capabilities of satellites

and the move to frequency bands above C band Both led to a rapid decrease in the size

and cost of the earth station antenna.

Most VSAT systems operate in Ku band, with earth station antenna diameters of 1 to 2

m and transmitter powers of 1 or 2 W. The earth stations are usually organized in a star

network, in which the earth stations connect to a central hub station via a Geostationary

(GEO) satellite. Data rates on the links are up to 256 kbps. VSAT systems are used to

link businesses and stores to a central computer system so that sales transactions can be

completed more rapidly than by using a telephone line and modem.

In many VSAT systems, the micro stations do not have enough power to communicate

directly with one another via the satellite. Instead, the hub is used to relay traffic between

VSATs. Hub is a special ground station with a large and high-gain antenna.



VSAT/WLL COMMUNICATIONS NETWORK

Conventionally, traffic from individual users is multiplexed and carried over trunk

lines via terrestrial microwave systems, satellite systems or optical fiber cables.

Redistribution of user traffic is done by the demultiplexing process at the

destination. This is still the most economical transmission architecture for point-to-

point communications. VSAT networks take advantage of the wide area broadcast

capabilities of geostationary (GEO) satellites to achieve the same goal One such

distribution architecture is Wireless Local Loop (WLL) coupled with VSAT. WLL

is a system that connects subscribers and the switch using radio signals instead of

copper cables Fig. 5.9 illustrates the concept schematically. The geostationary

satellite links a large number Of VSATs with the main switching center in a large

city. Each VSAT acts as the link to the local switching center in the village or rural

community over a WLL.



REVIEW QUESTIONS

5 Marks Questions

l . List satellite applications in different areas.

2. List the remote sensing applications of satellite.

3. List the components and applications of GPS.

4. Define VSAT concept.

5. Explain GPS.

6. Explain VSAT.

7. Explain earth observation application of satellite.

8. Describe cable TV application of satellite

10 Marks Questions

l. Explain DTH system with neat figure.

2. Explain GPS system with neat sketch.

3. Illustrate voice and data communication through satellite.

4. Explain satellite TV applications.

unit-5: satellite applications

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