Satellit & Mobile Communication

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SatelliteSatellite

CommunicationsCommunications


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i) Introductioni) Introduction

In 1962, the AmericanIn 1962, the American

telecommunications gianttelecommunications giantAT&T launched the world'sAT&T launched the world's

first true communicationsfirst true communications

Satellite, called Telstar. SinceSatellite, called Telstar. Since

then, countlessthen, countlesscommunications satellitescommunications satellites

have been placed into earthhave been placed into earth

orbit, and the technologyorbit, and the technology

being applied to them isbeing applied to them isforever growing inforever growing in

sophistication.sophistication.


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ii) Various Uses ofii) Various Uses of

SatelliteSatelliteCommunicationsCommunications

TraditionalTraditional

TelecommunicationsTelecommunications Global PositioningGlobal Positioning

ServicesServices

CellularCellular Television SignalsTelevision Signals

Fixed Satellite ServiceFixed Satellite Service

(FSS)(FSS) Broadcasting SatelliteBroadcasting Satellite

Service (BSS)Service (BSS)


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1.Traditional1.Traditional

TelecommunicationsTelecommunications

Since the beginnings of the long distanceSince the beginnings of the long distancetelephone network, there has been a needtelephone network, there has been a need

to connect the telecommunicationsto connect the telecommunicationsnetworks of one country to another. Thisnetworks of one country to another. Thishas been accomplished in several ways.has been accomplished in several ways.Submarine cables have been used mostSubmarine cables have been used mostfrequently. However, there are manyfrequently. However, there are manyoccasions where a largeoccasions where a large

long distance carrier will choose tolong distance carrier will choose toestablish a satellite based link to connectestablish a satellite based link to connectto transoceanic points, geographicallyto transoceanic points, geographicallyremote areas or poor countries that haveremote areas or poor countries that havelittle communications infrastructure.little communications infrastructure.Groups like the international satelliteGroups like the international satellite

consortium Intelsat have fulfilled much ofconsortium Intelsat have fulfilled much ofthe world's need for this type of service.the world's need for this type of service.


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2.Global Positioning2.Global Positioning

ServicesServices

Another VSAT orientedAnother VSAT oriented

service, in which a smallservice, in which a smallapparatus containing theapparatus containing the

ability to determineability to determine

navigational coordinatesnavigational coordinates

by calculating aby calculating a

triangulating of the signalstriangulating of the signals

from multiplefrom multiple

geosynchronous.geosynchronous.


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3. Cellular3. Cellular

Various schemes have been devised toVarious schemes have been devised toallow satellites to increase the bandwidthallow satellites to increase the bandwidth

available to ground based cellularavailable to ground based cellularnetworks. Every cell in a cellular networknetworks. Every cell in a cellular networkdivides up a fixed range of channels whichdivides up a fixed range of channels whichconsist of either frequencies . Since aconsist of either frequencies . Since aparticular cell can only operate within thoseparticular cell can only operate within thosechannels allocated to it, overloading canchannels allocated to it, overloading canoccur. By using satellites which operate atoccur. By using satellites which operate at

a frequency outside those of the cell, wea frequency outside those of the cell, wecan provide extra satellite channels oncan provide extra satellite channels ondemand to an overloaded cell. These extrademand to an overloaded cell. These extrachannels can just as easily be, once free,channels can just as easily be, once free,used by any other overloaded cell in theused by any other overloaded cell in thenetwork, and are not bound by bandwidthnetwork, and are not bound by bandwidthrestrictions like those used by the cell. Inrestrictions like those used by the cell. Inother words, a satellite that providesother words, a satellite that providesservice for a network of cells can allow itsservice for a network of cells can allow itsown bandwidth to be used by any cell thatown bandwidth to be used by any cell thatneeds it without being bound by terrestrialneeds it without being bound by terrestrialbandwidth and location restrictions.bandwidth and location restrictions.


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4.Television4.Television

SignalsSignals

Satellites have been used for since theSatellites have been used for since the1960's to transmit broadcast television1960's to transmit broadcast television

signals between the network hubs ofsignals between the network hubs oftelevision companies and their networktelevision companies and their networkaffiliates. In some cases, an entire series ofaffiliates. In some cases, an entire series ofprogramming is transmitted at once andprogramming is transmitted at once andrecorded at the affiliate, with each segmentrecorded at the affiliate, with each segmentthen being broadcast at appropriate timesthen being broadcast at appropriate timesto the local viewing populace. In the 1970's,to the local viewing populace. In the 1970's,

it became possible for private individuals toit became possible for private individuals todownload the same signal that thedownload the same signal that thenetworks and cable companies werenetworks and cable companies weretransmitting, using c-band reception dishes.transmitting, using c-band reception dishes.This free viewing of corporate content byThis free viewing of corporate content byindividuals led to scrambling andindividuals led to scrambling andsubsequent resale of the descramblingsubsequent resale of the descramblingcodes to individual customers, whichcodes to individual customers, whichstarted the direct-to-home industry. Thestarted the direct-to-home industry. Thedirect-to-home industry has gathered evendirect-to-home industry has gathered evengreater momentum since the introductiongreater momentum since the introductionof digital direct broadcast service.of digital direct broadcast service.


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iii) Characteristicsiii) CharacteristicsIncorporating satellites into terrestrialIncorporating satellites into terrestrial

networks is often hindered by threenetworks is often hindered by three

characteristics possessed by satellitecharacteristics possessed by satellitecommunication.communication.


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LatencyLatency

(propagation(propagation

delay):delay):

Due to the high altitudes of satelliteDue to the high altitudes of satellite

orbits, the time required for aorbits, the time required for a

transmission to navigate a satellite linktransmission to navigate a satellite link

(more than 2/10ths of a second from(more than 2/10ths of a second from

earth station to earth station) couldearth station to earth station) could

cause a variety of problems on a highcause a variety of problems on a high

speed terrestrial network that is waitingspeed terrestrial network that is waiting

for the packets.for the packets.


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Poor Bandwidth:Poor Bandwidth:

Due to radio spectrum limitations,Due to radio spectrum limitations,

there is a fixed amount of bandwidththere is a fixed amount of bandwidth

allocable to satellite transmission.allocable to satellite transmission.

Noise:Noise:

Radio signals strength is in proportionRadio signals strength is in proportion

to the square of the distance traveled.to the square of the distance traveled.

Due to the distance between groundDue to the distance between ground

station and satellite, the signalstation and satellite, the signal

ultimately gets very weak. Thisultimately gets very weak. Thisproblem can be solved by usingproblem can be solved by using

appropriate error correctionappropriate error correction

techniques.techniques.


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Error Correction :Error Correction :

Due to the high noise present on aDue to the high noise present on a

satellite link, numerous errorsatellite link, numerous error

correction techniques have beencorrection techniques have beentested in on such links. They fall intotested in on such links. They fall into

the two categories of forward-error-the two categories of forward-error-

correction (FEC) and automatic-repeat-correction (FEC) and automatic-repeat-

request (ARQ):request (ARQ):


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n s me o a cer a n num er o n orma onn s me o a cer a n num er o n orma onsymbols are mapped to new informationsymbols are mapped to new information

symbols, but in such a way as to get moresymbols, but in such a way as to get more

symbols than were original had. When thesesymbols than were original had. When these

new symbols are checked on the receiving end,new symbols are checked on the receiving end,

the redundant symbols are used to decipher thethe redundant symbols are used to decipher theoriginal symbols, as well as to check for dataoriginal symbols, as well as to check for data

integrity. The more redundant symbols that areintegrity. The more redundant symbols that are

included in the mapping, the better theincluded in the mapping, the better the

reliability of the error correction. However itreliability of the error correction. However it

should be noted that the more redundantshould be noted that the more redundant

symbols that are used to achieve bettersymbols that are used to achieve betterintegrity, the more bandwidth that is wasted.integrity, the more bandwidth that is wasted.

Since this method uses relatively a largeSince this method uses relatively a large

amount redundant data, it may not be the mostamount redundant data, it may not be the most

efficient choice on a clear channel. Howeverefficient choice on a clear channel. However

when noise levels are high, FEC can morewhen noise levels are high, FEC can more

reliably ensure the integrity of the data.reliably ensure the integrity of the data.

Automatic-repeat-request (ARR)Automatic-repeat-request (ARR)

In this method, data is broken into packets.In this method, data is broken into packets.

Within each packet is included an errorWithin each packet is included an error

checking key. This key is often of the cyclicchecking key. This key is often of the cyclic

redundancy check (CRC) sort. If the error coderedundancy check (CRC) sort. If the error codereflects a loss of integrity in a packet, thereflects a loss of integrity in a packet, the

receiver can request the sender to resend thatreceiver can request the sender to resend that

packet. ARR is not very good in a channel withpacket. ARR is not very good in a channel with

high noise, since many retransmissions will behigh noise, since many retransmissions will be

required, and the noise levels that corrupted therequired, and the noise levels that corrupted the

initial packet will be likely to cause corruption ininitial packet will be likely to cause corruption insubsequent packets. ARR is more suitable tosubsequent packets. ARR is more suitable to


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SATIN (SatelliteSATIN (Satellite

IntegratedIntegrated

TerrestrialTerrestrialNetwork):Network):

The goal of SATIN is to create a fullyThe goal of SATIN is to create a fully

integrated hybrid network in which theintegrated hybrid network in which themethod of communication, which canmethod of communication, which canincorporate networks of local,incorporate networks of local,metropolitan and wide area scope,metropolitan and wide area scope,Broadband ISDN, Integrated NetworkBroadband ISDN, Integrated Network

Management, AIN (Advanced IntelligentManagement, AIN (Advanced IntelligentNetworks) and PCS (PersonalNetworks) and PCS (PersonalCommunications Services), in addition toCommunications Services), in addition toATM (Asynchronous Transfer Mode) overATM (Asynchronous Transfer Mode) oversatellite, is totally transparent to thesatellite, is totally transparent to theuser. The difficulties inherent in this areuser. The difficulties inherent in this are

obvious. Differences in latency, noise,obvious. Differences in latency, noise,bandwidth and reliability must bebandwidth and reliability must beequalized in all the media that willequalized in all the media that willencompass the network.encompass the network.


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VSAT Networks:VSAT Networks:

VSAT stands for Very SmallVSAT stands for Very Small

Aperture Terminal. Although thisAperture Terminal. Although thisacronym has been used amongstacronym has been used amongst

telecom groups for some time nowtelecom groups for some time now

to describe small earth stations,to describe small earth stations,

the concepts of VSAT are beingthe concepts of VSAT are being

applied to modern hand heldapplied to modern hand heldsatellite communications units,satellite communications units,

such as GPS (Global Positioningsuch as GPS (Global Positioning

System), portable Inmarsat phonesSystem), portable Inmarsat phones

and other types of portableand other types of portablesatellite communication devices.satellite communication devices.


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MobileMobile

CommunicationsCommunications


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i ) Introductioni ) Introduction

The mobile is aThe mobile is acommonlycommonly

used electronic device inused electronic device innow a day it is a verynow a day it is a very

essential thing in day toessential thing in day to

day life here is briefday life here is brief

information about theinformation about the

mobile communication andmobile communication and

mobiles.mobiles.


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ii ) Types ofii ) Types ofCommunicationCommunication

accessaccess

1. GSM1. GSM (Global System for Mobile(Global System for MobileCommunications)Communications)

2. CDMA2. CDMA (Code Division Multiple(Code Division MultipleAccess)Access)


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iii ) Mobileiii ) Mobile

communicationcommunicationdetailsdetails

GSM is aGSM is a cellular networkcellular network,,

which means thatwhich means thatmobile phonesmobile phones connect toconnect to

it by searching for cells init by searching for cells in

the immediate vicinity.the immediate vicinity.

GSM networks operate inGSM networks operate in

four differentfour different

frequency rangesfrequency ranges. Most. Most

GSM networks operate inGSM networks operate inthe 900 MHz or 1800 MHzthe 900 MHz or 1800 MHz

bands.bands.
http://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/GSM_frequency_rangeshttp://en.wikipedia.org/wiki/GSM_frequency_rangeshttp://en.wikipedia.org/wiki/GSM_frequency_rangeshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Cellular_network


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The portable telephones areThe portable telephones arecomfortable manner of communicationcomfortable manner of communicationabove a distance. With obviousabove a distance. With obvioussuitability and with fast access to helpsuitability and with fast access to helpin the large and small urgencies, thein the large and small urgencies, the

portable telephones can be economicportable telephones can be economicand essential for travelers testing withand essential for travelers testing withthe stay connected. To Japan, thethe stay connected. To Japan, thecompanies of portable telephonecompanies of portable telephoneprovide the immediate opinion of theprovide the immediate opinion of the

normal disaster and earthquakesnormal disaster and earthquakesother to their customers free.other to their customers free.


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On the other part of mobileOn the other part of mobile

communication the Infra redcommunication the Infra red

technology and blue toothtechnology and blue tooth

technology have increased thetechnology have increased theadvantages of mobile phonesadvantages of mobile phones

even more. With theseeven more. With these

technologies you can send andtechnologies you can send and

receive data from other mobilereceive data from other mobilephones as well as computersphones as well as computers

that are equipped with thethat are equipped with the

similar technologies.similar technologies.

Satellit & Mobile Communication

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