Satellite Comunication (Recent One)

8/3/2019 Satellite Comunication (Recent One)

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Misr Universityfor Science & Technology

Electronics & CommunicationEngineering Department


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SatelliteCommunications

BYProf.Dr. Saber H. Zainud-Deen


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Overview

Satellite is a microwave repeater in thespace.

There are about 750 satellite in thespace, most of them are used forcommunication.


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Satellite Frequencies

There are specific frequency ranges used by commercial satellites.

VHF-band 100 MHz- 300 MHz

UHF-band 300 MHz- 1GHz

L-band 1.0 2.0 GHz

S-band 1.55 3.9 GHz

C-band 3.7 6.2 GHz

X-band 8.0 12.0 GHz

Ku-band 12 18 GHz

K-band 18-27 GHz

Ka-band 27-40 GHz


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VHF and UHF is used for mobile and navigationalservices and for data transfer from weathersatellites.

L-band is used for mobile satellite services andnavigation systems.

C-band is used for fixed satellite services (FSS)

Ku-band is used for direct broadcast satellitesservices (BSS) and for fixed satellite services astelephone networks.


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base stationor gateway

Classical satellite systems

Inter Satellite Link

(ISL)Mobile UserLink (MUL) Gateway Link

(GWL)

footprint

small cells(spotbeams)

User data

PSTNISDN GSM

GWL

MUL

PSTN: Public SwitchedTelephone Network


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2.1. Satellite Orbits :-

Satellite

By inclinationangle By Altitude

InclinedEllipticalOrbits

40-80o

PolarOrbits

90o

EquatorialOrbits

0o

LEO MEO GEO


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Satellite orbits in term of their inclination angle,as in the following figure;


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Satellite Orbits in term of theiraltitudes :-

1.

Altitude from 500 to 1500 km .

Systems that deal with it, for

example, are IRIDIUM andGLOBALSTAR .

Low Earth Orbit Satellite LEO:


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1.2.Advantages of LEO :-

1. The satellites are orbited near theearth, thus minimizing the time delay

effects .

2. The low orbit altitude allows considerably

reducing the power requirementsonboard and the ground .

3. Low cost of launching satellite in LEO .


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1.3. Disadvantages of LEO :-

1. Have large number of satellites .

2. The visibility period of each satellite requiresfrequent hand over activities .

3. The very high orbital velocity results in

large Doppler offsets .

4. The satellite constellation can requirecomplex orbital design .


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2.

Altitude between 9,000 and 15,000 km .

Systems that deal with it, for example,

is ICO .

Medium Earth Orbit Satellite MEO:


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2.1.Advantages of MEO :-

1. Relatively large coverage area .

2. The lower delay than the GEO allow moreflexibility of system design for voice

communications .

3. Handover may be less frequent than that of theLEO .


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2.2. Disadvantages of MEO :-

1. The Doppler frequency offsets arelarger than GEO due to the higher

relative satellite motion .

2. A larger constellation is required to provide

continuous global converge .


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3.

Altitude is 35800 Km .

Systems that deal with it, for example,are, INMARSAT and THURAYA .

Geosynchronous satellite GEO:


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Advantages of GEO :-

1. Wide coverage .

5. The synchronization with the rotation ofthe earth makes the tracking process

more simple .

2. Wide-band communication .

4. Economic efficiency .

3. Availability for mobile communication .


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Disadvantages of GEO :-3.2.

1. Long propagation delay, because of thegreat distance between the earth andthe satellite .

2. Large propagation loss, because of thegreat distance between the earth and thesatellite so we need four times of powerto receive the transmitted signal withsame power level at transmitter .


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4. High cost of launching a satellite into aGEO .

3. The geostationary satellite is lacking ofcoverage at far northern and southernlatitudes


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Comparison of different orbits :-


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Orbital Mechanics


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Newtons Laws

s = ut + (1/2)at2

v2= u2+ 2at

v = u + at

F = ma

s= Distance traveled in time, t

u= Initial Velocity at t= 0

v= Final Velocity at time = t

a= Acceleration

F= Force acting on the object

Newtons

Second Law


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FORCE ON A SATELLITE : 1

Force = Mass AccelerationUnit of Force is a Newton

A Newton is the force required toaccelerate 1 kg by 1 m/s2

Units of a Newtonare kg m/s2


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ACCELERATION FORMULA a = acceleration due to gravity = / r2 km/s2

r=radius from center of earth = universal gravitational constant G multipliedby the mass of the earth ME

is Keplers constant and

= 3.9861352 105 km3/s2

G= 6.672 10-11 Nm2/kg2


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FORCE ON A SATELLITE : 2

Inward (i.e. centripetal force)

Since Force = MassAcceleration

If the Force inwards due to gravity = FIN then

FIN= m (/ r2

)

= m (GME/ r2)


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Balancing the Forces - 2

Inward Force

r

mGME

F 3r

F

G= Gravitational constant = 6.672 10-11 Nm2/kg2

ME= Mass of the earth (and GME= = Keplers constant)

m= mass of satellite

r= satellite orbit radius from center of earth

r= unit vector in the rdirection (positive ris away from earth)


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Balancing the Forces - 3

Outward Force F

2

2

dt

d

mF

r


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Keplers Three Laws

Orbit is an ellipse with the larger body (earth) atone focus

The satellite sweeps out equal arcs (area) inequal time (NOTE: for an ellipse, this meansthat the orbital velocity varies around the orbit)

The square of the period of revolution equals aCONSTANT the THIRD POWER of SEMI-MAJOR AXIS of the ellipse

Well look at each of these in turn


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Review: Ellipse analysis

Points (-c,0) and (c,0) are the foci.

Points (-a,0) and (a,0) are the vertices.

Line between vertices is the major axis.

ais the length of the semimajor axis.

Line between (0,b) and (0,-b) is the minor axis.

bis the length of the semiminor axis.

12

2

2

2

b

y

a

x

222cba

Standard Equation:

y

V(-a,0)

P(x,y)

F(c,0)F(-c,0) V(a,0)

(0,b)

x

(0,-b)

abA

Area of ellipse:


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KEPLER 1: Elliptical Orbits

Law 1

The orbit is an ellipse

e = ellipses eccentricity

O = center of the earth (onefocus of the ellipse)

C = center of the ellipse

a = (Apogee + Perigee)/2


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KEPLER 1: Elliptical Orbits

(cont.)Equation 2.17 in text:

(describes a conic section,

which is an ellipse if e < 1)

)cos(10

0e

pr

e = eccentricity

e


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KEPLER 2: Equal Arc-Sweeps

Law 2

If t2 - t1 = t4 - t3

then A12 = A34

Velocity of satellite is

SLOWESTat

APOGEE; FASTESTat

PERIGEE


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KEPLER 3: Orbital Period

Orbital period and the Ellipse are related by

T2= (42a3) / (Equation 2.21)

That is the square of the period of revolution is equal to a

constant the cube of the semi-major axis.

IMPORTANT: Period of revolution is referenced to inertial space, i.e., to

the galactic background, NOT to an observer on the surface of one of the

bodies (earth).

= Keplers Constant = GME

i l l 1


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Numerical Example 1The Geostationary Orbit:

Sidereal Day = 23 hrs 56 min 4.1 sec

Calculate radius and height of GEO orbit: T2 = (4 2 a3) / (eq. 2.21) Rearrange to a3 = T2 /(4 2) T = 86,164.1 sec a3 = (86,164.1) 2 x 3.986004418 x 105/(4 2) a = 42,164.172 km = orbit radius h = orbit radius earth radius = 42,164.172 6378.14

= 35,786.03 km


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2.2. Orbital dynamics of satellitesystems :-

2.3.1. Kepler`s first law :-

Determine the shape of the pathof the satellite in the space .

ra rp

e=ra

ra : is the semi major axis of the ellipse.

rb : is the semi minor axis of the ellipse.

At e = 0 , ra = rb the ellipse will be a

circle.


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2.3.2. Kepler`s second law :-

Shows that there is a non-linear relationshipbetween (the distance between satellite andearth) and (the velocity of the satellite'srotation around the earth) .


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2.3.3. Kepler`s third law :-

It states the relation between the periodic time

of orbit ( po) and the mean distance between

the earth and the satellite (ra).

ra=A ( po )2/3

ra : It is the mean distance between the earth and satellite .

po : is the periodic time of orbit .

A : is a constant which can be determined according to ra & po .


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Satellite Network Configurations


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2.3. Selection ofMultiple accessscheme :-

Multiple AccessTechniques

TDMA FDMA CDMA


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1. TDMA

2. FDMA

3. CDMA


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Multiple Access System

Applications employ multiple-access systems to allow two ormore Earth stations to simultaneously share the resourcesof the same transponder or frequency channel.

These include the three familiar methods: FDMA,

TDMA, and CDMA.

Another multiple access system called space divisionmultiple access (SDMA) has been suggested in the past. Inpractice, SDMA is not really a multiple access method butrather a technique to reuse frequency spectrum throughmultiple spot beams on the satellite.


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TDMA and FDMA require a degree of coordination amongusers: FDMA users cannot transmit on the same frequency and TDMA users can transmit on the same frequency but not at the

same time.

Capacity in either case can be calculated based on the totalbandwidth and power available within the transponder orslice of a transponder.

CDMA is unique in that multiple users transmit on the samefrequency at the same time (and in the same beam orpolarization).

This is allowed because the transmissions use a differentcode either in terms of high-speed spreading sequence orfrequency hopping sequence.


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The capacity of a CDMA network is not unlimited,however, because at some point the channelbecomes overloaded by self-interference from themultiple users who occupy it.

Furthermore, power level control is critical becausea given CDMA carrier that is elevated in power willraise the noise level for all others carriers by a likeamount.


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FDMA

The satellite operator divides up the power andbandwidth of the transponder and sells off the capacityin attractively priced segments.

Users pay for only the amount that they need. If therequirements increase, additional FDMA channels can be

purchased. The big advantage, however, is that each Earth station

has its own independent frequency on which to operate. A bandwidth segment can be assigned to a particular

network of users, who subdivide the spectrum further

based on individual needs. Another feature, is to assign carrier frequencies when

they are needed to satisfy a traffic requirement. This isthe general class of demand assigned networks, alsocalled demand-assigned multiple access (DAMA).


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Time Division Multiple Access

TDMA is a truly digital technology, requiring thatall information be converted into bit streams ordata packets before transmission to the satellite.

Contrary to most other communicationtechnologies, TDMA started out as a high-speedsystem for large Earth stations.

As the cost and size of digital electronics came

down, it became practical to build a TDMA Earthstation into a compact package.


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TDMA signals are restricted to assigned timeslots and therefore must be transmitted inbursts.

The time frame is periodic, allowing stations to

transfer a continuous stream of information onaverage.


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At the receiving Earth station, bursts from Earthstations are received in sequence, selected forrecovery if addressed for this station, and thenspread back out in time in an output expansionbuffer.


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TDMA is a good fit for all forms of digitalcommunications and should be considered as one optionduring the design of a satellite application.

The complexity of maintaining synchronization and

control has been overcome through miniaturization ofthe electronics and by way of improvements in networkmanagement systems.

With the rapid introduction of TDMA in terrestrial radionetworks like the GSM standard, we will see greater

economies of scale and corresponding price reductions insatellite TDMA equipment.


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Code Division Multiple Access

CDMA, also called spread spectrum communication,differs from FDMA and TDMA because it allows users toliterally transmit on top of each other.

This feature has allowed CDMA to gain attention in

commercial satellite communication. It was originally developed for use in military satellitecommunication where its inherent anti-jam and securityfeatures are highly desirable.

CDMA was adopted in cellular mobile telephone as aninterference-tolerant communication technology thatincreases capacity above analog systems.


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Code Division Multiple Access

It has not been proven that CDMA is universallysuperior as this depends on the specificrequirements.

For example, an effective CDMA system requires

contiguous bandwidth equal to at least thespread bandwidth.


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2.1. Some systems which use

satellitecommunication system :-

1- IRIDIUM


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Orbits and IRIDIUM coverage :-


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Satellite cross-links :-

IRIDIUM has the following


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Inclination of orbital

plane

Satellite 66

100 minutes, 27 secondsSatellite period

204 KbpsTransmission rate

ISLsLink

5-8 years

780 KmOrbital height

6Orbital planes

Satellite weight 700 Kg

No. of spot beams

Life time

48 per-satellite

g

specifications :-

86.4 degree


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IRIDIUM frequencies :-

The service link between the phone andthe satellite operates in the L-band .

i. The down link frequency is 1616 1626 MHz .

ii. The uplink frequency is 1616 1626MHz .


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The feeder link between the satelliteand Gateway operates in Ka-band .

i. The downlink frequency is 18.8 20.2GHz .

ii. The uplink frequency is 27.5 30 GHz .

The inter-satellite link (satellite-to-satellite)operates in,

Ku-band 22.5 23.5 GHz .


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IRIDIUM ll t


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IRIDIUM call-setup :-Intersatellite Link , ISL

ISL requires the eatablishment of a networkbetween those satellites in order to interchangedifferent kinds as well as rout calls through a

netweok in space. Establishing the network network between

satellites is a complex and expensive taskbecause of large distance between satellites

For ISL, each satellite reqires an additionaltransmitter, receiver and antenna which increasethe payload, weight and cost of satellite.


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Advantages of ISL

Satellite do not have to see the earthgateway stations all the time.

The system is independent of theterrestrial facilities.


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Types of ISL

There are two types:1. The link between satellites in the same

orbital plane, called interiorityintersatellite links.

2. The link between satellites in a different

orbital planes called interorbitintersatellite links.


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2- if the subscriber's cellularsystem is unavailable, thephone will automaticallydirectly access with a satellite

overhead .


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IRIDIUM Transmission Access

Techniques :-

The multiplexing techniques are a combination ofFrequency Division Multiple Access (FDMA) andTime Division Multiple Access (TDMA).


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2- GLOBALSTAR


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Orbits and GLOBALSTARcoverage :-


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GLOBALSTAR satellite system :-

Globalstar is a consortium of leading international telecommunicationscompanies originally established in 1991 to provide voice, data, fax,and other telecommunication services to users

world-wide.

GLOBALSTAR f i


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GLOBALSTAR frequencies :-

Mobile-to-Satellite(L-band)

1610-1626.5 MHz (UL)

5091-5250 MHz (UL)Gateway-to-Satellite(C-band)

2483.5-2500 MHz (DL)Satellite-to-Mobile

(S-band)

Satellite-to-Gateway(C-band)

6700-7075 MHz (DL)


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GLOBALSTAR call-setup :-

1. A caller uses Globalstar mode to place a call viathe satellite to one or more Gateways.

2.The Gateway routes the call to the existingphone network, in the case indicated below, a

cellular Public Land Mobile Network (PLMN)network .


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Bent-pipe Tube :-

If the destination phone is

part of the PSTN, the callis routed from theoriginating satellite to thenearest gateway, which

turn connects the callthrough the PSTN .


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GLOBALSTAR Transmission

Access Techniques :-

It is using CDMA technique .

CDMA is based on the spreading

of the spectrum that making

several users share the same

frequency band.


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It consist of 3 or 4 dish antennas, andeach Gateway serving a specific zone upto 3000 km in diameter.

The gateway is located, receivestransmissions from orbiting satellites,processes calls, and switches them to theappropriate ground network.

Because all of the switches and complex

hardware are located on the ground, it iseasier for Globalstar to maintain andupgrade its system than it is for systemswhich handle switching in orbit.

GLOBALSTAR Gateways :-


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GLOBALSTAR Devices :-

Globalstar phones are multimode andfunction as cellular phones whereterrestrial cellular service is available andas satellite phones where cellular service

is not available. Globalstar phonesprovide multimode capabilities.

The same Globalstar phone will workanywhere in the world that is served by

a Globalstar gateway.

Three manufacturers produce Mobilephones for Globalstar Qualcomm,Ericsson and Telit.


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3- ICO


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Orbits and ICO coverage :-


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ICO satellite system :-

Boeing Satellite Systems, Inc. (BSS) establishedICO Global Communications, in January 1995 as

a private company to provide global Mobilepersonal communications services by satellite,including digital voice, data, fax, and messagingservices. MEO is called Intermediate Circular

Orbit (ICO).


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ICO Gateways :-

This will consist of 12 Earth stations or satellite accessnodes (SANs) located around the globe .

Six of ICO SANs have been equipped as telemetry,tracking and control stations .

They are expected to provide nearly continuousmonitoring of the satellites in orbit, which will be

controlled from the companys Satellite Control Centre inthe UK.


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ICO frequencies :-

User-to-Satellite(service)

1980-2010 MHz (DL)2170-2200 MHz (UL)

7 GHz (DL)5 GHz (UL)

Satellite-to-earth station(feeder)


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ICO devices :-

Most ICO user terminals are expected to be handheld,pocket- sized phones capable of dual -mode (satelliteand cellular) operation and very similar in size,

appearance and voice quality to today's handheld cellularphones. The price of ICO dual-mode phones is about$500.

Satellite Comunication (Recent One)

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