Satellite Communications

SATELLITE SATELLITE COMMUNICATIONSCOMMUNICATIONS

DEFINITIONSDEFINITIONS SATELLITESATELLITE: -a spacecraft placed in orbit around the earth : -a spacecraft placed in orbit around the earth

which carries on-board microwave receiving and transmitting which carries on-board microwave receiving and transmitting equipment capable of relaying signals from one point on earth equipment capable of relaying signals from one point on earth to other pointsto other points

SATELLITE SYSTEM: -SATELLITE SYSTEM: - a radio repeater in the sky a radio repeater in the sky consisting of a transponder, a ground based station to control consisting of a transponder, a ground based station to control its operation, and a user network of earth station that provides its operation, and a user network of earth station that provides the facilities for transmission and reception of the facilities for transmission and reception of communications traffic through the satellite systemcommunications traffic through the satellite system

SATELLITE SYSTEMSATELLITE SYSTEM

Elements of Satellite Elements of Satellite Communication SystemCommunication System

Earth StationEarth Station

Earth StationEarth Station

Earth station is the common name for every Earth station is the common name for every installation located on the Earth's surface and installation located on the Earth's surface and intended for communication (transmission and/or intended for communication (transmission and/or reception) with one or more satellites. reception) with one or more satellites.

refers to the collection of equipment that is needed to refers to the collection of equipment that is needed to perform communications via satellite: the antenna perform communications via satellite: the antenna (often a dish) and the associated equipment (often a dish) and the associated equipment (receiver/decoder, transmitter).(receiver/decoder, transmitter).

Elements of Satellite Elements of Satellite Communication SystemCommunication System

Communication SatelliteCommunication Satellite


Payload Payload - represents all equipment a satellite needs - represents all equipment a satellite needs to do its job. This can include transponder, antennas, to do its job. This can include transponder, antennas, cameras, radar and electronics.cameras, radar and electronics. TransponderTransponder - it is the part of the payload that takes the - it is the part of the payload that takes the

signals received from the transmitting Earth station, filters signals received from the transmitting Earth station, filters and translates these signals and then redirects them to the and translates these signals and then redirects them to the transmitting antenna on board. transmitting antenna on board.


BusBus - The bus is the part of the satellite that - The bus is the part of the satellite that carries the payload and all its equipment into carries the payload and all its equipment into space. It is the physical platform that holds all space. It is the physical platform that holds all the satellite's parts together and that provides the satellite's parts together and that provides electrical power, navigation, and control to the electrical power, navigation, and control to the spacecraft spacecraft

SATELLITE SYSTEMSATELLITE SYSTEM SATELLITE LINK:SATELLITE LINK: a communication path formed a communication path formed

between two or more ground stations transmitting and between two or more ground stations transmitting and receiving radio communications traffic via a satellitereceiving radio communications traffic via a satellite

UPLINK:UPLINK: that portion of the satellite that portion of the satellite communications link involving the transmission of communications link involving the transmission of traffic from the ground station up to the satellitetraffic from the ground station up to the satellite

DOWNLINK:DOWNLINK: that portion of a satellite that portion of a satellite communications link involving the transmission of communications link involving the transmission of traffic from the satellite to the earth terminaltraffic from the satellite to the earth terminal

Components of Uplink EquipmentComponents of Uplink Equipment

IF ModulatorIF Modulator - converts input baseband signal to - converts input baseband signal to FM, PSK, QAM IF.FM, PSK, QAM IF.

IF – RF microwave Up ConverterIF – RF microwave Up Converter – converts IF – converts IF to RF carrier frequencies.to RF carrier frequencies.

High Power Amplifier (HPA)High Power Amplifier (HPA) - provides - provides adequate input sensitivity and output power to adequate input sensitivity and output power to propagate signal to transponder.propagate signal to transponder.

Output Bandpass FilterOutput Bandpass Filter - limits bandwidth - limits bandwidth

Components of Downlink Components of Downlink EquipmentEquipment

Bandpass FilterBandpass Filter - limits input noise power - limits input noise power to LNA.to LNA.

Low Noise Amplifier (LNA)Low Noise Amplifier (LNA) - highly - highly sensitive, low noise device usually a tunnel sensitive, low noise device usually a tunnel diode or parametric amplifierdiode or parametric amplifier

RF – IF Down ConverterRF – IF Down Converter - - mixer/bandpass filter combination which mixer/bandpass filter combination which converts the received RF signal to an IF converts the received RF signal to an IF frequency.frequency.

Satellite Communications Spectrum Satellite Communications Spectrum

C-bandC-band is the oldest allocation and operates in the is the oldest allocation and operates in the frequency range around 6 GHz for transmission frequency range around 6 GHz for transmission (uplink) and between 3.7 and 4.2 GHz for reception (uplink) and between 3.7 and 4.2 GHz for reception (downlink).(downlink).

Ku-bandKu-band is the most common transmission format in is the most common transmission format in Europe for satellite TV and uses around 14 GHz for Europe for satellite TV and uses around 14 GHz for uplink and between 10.9 and 12.75 GHz for uplink and between 10.9 and 12.75 GHz for downlink.downlink.

Ka-bandKa-band uses around 30 GHz up- and between 18 uses around 30 GHz up- and between 18 and 20 GHz downlink frequency.and 20 GHz downlink frequency.

Satellite Communications SpectrumSatellite Communications Spectrum

General Frequency Assignments for General Frequency Assignments for Satellite SystemsSatellite Systems

Uplink Frequencies Downlink Frequencies

5.925–6.425GHz 3.700–4.200GHz

7.900–8.400GHz 7.250–7.750GHz

14.00–14.50GHz 11.70–12.20GHz

27.50–30.00GHz 17.70–20.20GHz

Space Communications Band and Space Communications Band and their Frequency Rangetheir Frequency Range

L 1.0–2.0GHz

S 2.01–4.0GHz

C 4.01–8.0GHz

X 8.01–12.0GHz

Ku 12.01–18.0GHz

K 18.01–27.0GHz

Ka 27.01–40.0 GHz

APPLICATIONS OF SATELLITEAPPLICATIONS OF SATELLITE

REMOTE SENSING:REMOTE SENSING: monitoring of ecological situation monitoring of ecological situation (ocean contamination, deforestation…)(ocean contamination, deforestation…)

WEATHER FORECASTING/HAZARD DETECTION:WEATHER FORECASTING/HAZARD DETECTION: disaster prediction and early warningdisaster prediction and early warning

AGRICULTURAL PRODUCTION FORECASTING:AGRICULTURAL PRODUCTION FORECASTING: forecasting of meteorological effects of climate on agricultural forecasting of meteorological effects of climate on agricultural productionproduction

INTELLIGENCE/SURVEILLANCE OPERATION:INTELLIGENCE/SURVEILLANCE OPERATION: surveillance operations by remote satellite monitoringsurveillance operations by remote satellite monitoring

NAVIGATION:NAVIGATION: (GPS,GLONASS) – satellite-based (GPS,GLONASS) – satellite-based electronic navigationelectronic navigation


SEARCH AND RESCUE COMMUNICATIONSSEARCH AND RESCUE COMMUNICATIONS: highly : highly flexible search and rescue networks during emergencies and flexible search and rescue networks during emergencies and disasters.disasters.

INTER-ACTIVE EDUCATION:INTER-ACTIVE EDUCATION: interactive educational interactive educational broadcast for simultaneous instruction among several broadcast for simultaneous instruction among several classrooms throughout the globeclassrooms throughout the globe

SPACE RESEARCH/SCIENTIFIC EXPLORATIONSSPACE RESEARCH/SCIENTIFIC EXPLORATIONS: : astrophysics, biological experiments…astrophysics, biological experiments…


TELECOMMUNICATIONS/TELECOMMUNICATIONS/TELEBROADCASTING:TELEBROADCASTING: international TV international TV broadcasting, telepaging, cellular telephony, broadcasting, telepaging, cellular telephony, video conferencingvideo conferencing

Categories of SATELLITE as to Categories of SATELLITE as to FunctionFunction

PASSIVE SATELLITE:PASSIVE SATELLITE: communication communication satellite not equipped with electronic devices satellite not equipped with electronic devices to retransmit communications.to retransmit communications.

ACTIVE SATELLITE:ACTIVE SATELLITE: a satellite equipped a satellite equipped with electronic devices to receive, amplify, with electronic devices to receive, amplify, convert, and retransmit signals.convert, and retransmit signals.

Categories of SATELLITE as to Categories of SATELLITE as to OrbitOrbit

NON-SYNCHRONOUS OR ORBITAL:NON-SYNCHRONOUS OR ORBITAL: rotate rotate around the earth in low altitude elliptical or circular around the earth in low altitude elliptical or circular patternpattern

PROGRADE:PROGRADE: when satellite orbits in the when satellite orbits in the same direction as that of the earth’s rotation.same direction as that of the earth’s rotation.

RETROGRADE:RETROGRADE: when a satellite orbits in the when a satellite orbits in the opposite direction as the earth’s rotation but an opposite direction as the earth’s rotation but an angular velocity less than of the earth.angular velocity less than of the earth.


GEOSTATIONARY OR GEOSTATIONARY OR GEOSYNCHRONOUSGEOSYNCHRONOUS: orbit in a circular : orbit in a circular pattern with an angular velocity equivalent to pattern with an angular velocity equivalent to that of earth and remain in a fixed position in that of earth and remain in a fixed position in respect to a given point on earth with an respect to a given point on earth with an orbital time of about 24 hours (sidereal day = orbital time of about 24 hours (sidereal day = 23 hrs 56 min 4 sec) with an altitude of 35,784 23 hrs 56 min 4 sec) with an altitude of 35,784 to 35,863 kms.to 35,863 kms.

MEO ( Medium Earth Orbit)MEO ( Medium Earth Orbit) - satellite is - satellite is one with an orbit from 2,000 – 34,780 kmsone with an orbit from 2,000 – 34,780 kms

above the Earth's surface. Satellites of this type above the Earth's surface. Satellites of this type are in a higher orbit than low Earth orbit are in a higher orbit than low Earth orbit (LEO) satellites, but lower than geostationary (LEO) satellites, but lower than geostationary (GEO) satellites. The orbital periods (the time (GEO) satellites. The orbital periods (the time in between two successive passes over one in between two successive passes over one particular place on Earth) of MEO satellites particular place on Earth) of MEO satellites ranges from about 2 to 12 hours. ranges from about 2 to 12 hours.



Low Earth Orbit (LEO)Low Earth Orbit (LEO) - satellite system - satellite system consists of a large number of satellites each in consists of a large number of satellites each in a circular orbit at a constant altitude between a circular orbit at a constant altitude between 320 and 800 km. 320 and 800 km.



English MarkerDistance

above earth (km)

Distance from center of earth

(km)

EarthBlue/brown

image 0 6370

Low Earth Orbit (LEO) Cyan area 160 to 2,000 6,530 to 8,370

Medium Earth Orbit (MEO) Yellow area 2,000 to 34,780 8,370 to 41,150

International Space Station (ISS) Red dotted line 500 6,870

Global Positioning System (GPS)

satellitesGreen dash-dot

line 20,230 26,600

Geostationary Orbit (GEO) Black dashed line 35,794 42,164

SATELLITE ORBITAL SATELLITE ORBITAL PATTERNSPATTERNS

EQUATORIAL PATTERN:EQUATORIAL PATTERN: rotation about the rotation about the earth’s equator, usually for geosynchronous earth’s equator, usually for geosynchronous communications satellitescommunications satellites

POLAR ORBIT:POLAR ORBIT: rotation over the North and South rotation over the North and South Poles, used for non-communications mission such as Poles, used for non-communications mission such as weather and surveillance observations.weather and surveillance observations.

INCLINED ORBIT:INCLINED ORBIT: rotation creating an angle rotation creating an angle between the equatorial or polar plane. between the equatorial or polar plane.

Satellite OrbitSatellite Orbit

ORBITAL TERMINOLOGYORBITAL TERMINOLOGY

ORBIT:ORBIT: the path of a celestial body or the path of a celestial body or satellite in “unpowered flight”satellite in “unpowered flight”

ASCENDING NODE:ASCENDING NODE: point where the orbit point where the orbit crosses the equatorial plane going from south crosses the equatorial plane going from south to north.to north.

DESCENDING NODE:DESCENDING NODE: point where the point where the orbit crosses the equatorial plane going from orbit crosses the equatorial plane going from North to SouthNorth to South

Engr. Leonardo A. Samaniego Jr.Engr. Leonardo A. Samaniego Jr.

ORBITAL TERMINOLOGYORBITAL TERMINOLOGY APOGEE:APOGEE: highest point of the orbit or it is the point in the earth highest point of the orbit or it is the point in the earth

satellite orbit which is farthest away from the earth.satellite orbit which is farthest away from the earth.

PERIGEE:PERIGEE: the point in the earth satellite orbit which is closest to the point in the earth satellite orbit which is closest to the earththe earth

ORBITAL TERMINOLOGYORBITAL TERMINOLOGY

EccentricityEccentricity - a number between zero and - a number between zero and one which describe the shape of an ellipse.one which describe the shape of an ellipse.

e = 1 – be = 1 – b22/a/a22

Where: Where: a – minor axis ( the shorter axis of the a – minor axis ( the shorter axis of the ellipse)ellipse)

b - major axis (the longer distance of the b - major axis (the longer distance of the ellipse)ellipse)

SATELLITE MULTIPLE ACCESS SATELLITE MULTIPLE ACCESS TECHNIQUESTECHNIQUES

FREQUENCY DIVISION MULTIPLEX FREQUENCY DIVISION MULTIPLEX ACCESSING (FDMA)ACCESSING (FDMA)

TIME DIVISION MULTIPLEX TIME DIVISION MULTIPLEX ACCESSING (TDMA)ACCESSING (TDMA)

CODE DIVISION MULTIPLE CODE DIVISION MULTIPLE ACCESSING (CDMA) orACCESSING (CDMA) or

SPREAD SPECTRUM MULTIPLE SPREAD SPECTRUM MULTIPLE ACCESSING (SSMA)ACCESSING (SSMA)

FREQUENCY DIVISION FREQUENCY DIVISION MULTIPLEX ACCESSING MULTIPLEX ACCESSING

(FDMA)(FDMA) A satellite transponder is divided into smaller A satellite transponder is divided into smaller

freqquency band segments where each freqquency band segments where each segment is assigned for his uplink or downlink segment is assigned for his uplink or downlink frequency.frequency.

1. Pre-assigned1. Pre-assigned - a given number of - a given number of available voice band channels from each available voice band channels from each station are assigned to dedicated destinations.station are assigned to dedicated destinations.

2. Demand Assigned2. Demand Assigned - voice band - voice band channels are assigned on “as-needed” basis.channels are assigned on “as-needed” basis.

TIME DIVISION MULTIPLEX TIME DIVISION MULTIPLEX ACCESSING (TDMA)ACCESSING (TDMA)

In this method, stations are restricted to precise time In this method, stations are restricted to precise time slot. It has no restriction on frequency or bandwidth.slot. It has no restriction on frequency or bandwidth.

Number of Voice Channel CalculationNumber of Voice Channel Calculation

n = ( 1/r )( R – NP/T )n = ( 1/r )( R – NP/T )

Where: Where: r – voice channel bit rater – voice channel bit rate

P – no. of digits in the preambleP – no. of digits in the preamble

R - satellite channel bit rateR - satellite channel bit rate

N – no. of burst in a frameN – no. of burst in a frame

T - frame periodT - frame period

CODE DIVISION MULTIPLE CODE DIVISION MULTIPLE ACCESSING (CDMA)ACCESSING (CDMA)

Also known as Also known as SPREAD SPECTRUM SPREAD SPECTRUM MULTIPLE ACCESSING (SSMA),MULTIPLE ACCESSING (SSMA),

has no restriction on time or bandwidth. Each has no restriction on time or bandwidth. Each station may transmit whenever it wishes and station may transmit whenever it wishes and can use any or all of the bandwidth allocated. can use any or all of the bandwidth allocated. Transmission are separated through envelope Transmission are separated through envelope encryption-decryption technique. It uses encryption-decryption technique. It uses unique binary words called “CHIP CODES”.unique binary words called “CHIP CODES”.


SATELLITE FOOTPRINTSATELLITE FOOTPRINT

FOOTPRINT:FOOTPRINT: a geographic representation of a satellite a geographic representation of a satellite radiation pattern, with contour lines representing limits of radiation pattern, with contour lines representing limits of equal receive power density.equal receive power density.


SPOT COVERAGE:SPOT COVERAGE: beams concentrate the beams concentrate the radiated power in a very small geographic arearadiated power in a very small geographic area


EARTH COVERAGE:EARTH COVERAGE: covers approximately covers approximately one-third of earth’s surface using a 17 degrees one-third of earth’s surface using a 17 degrees beamwidthbeamwidth


ZONAL COVERAGE:ZONAL COVERAGE: covers less than one- covers less than one-third of earth’s surfacethird of earth’s surface

SATELLITE TYPES AS TO SATELLITE TYPES AS TO TERRITORIAL COVERAGETERRITORIAL COVERAGE

GLOBAL:GLOBAL: covers the whole world covers the whole world REGIONAL:REGIONAL: covers selected regions such as covers selected regions such as

Pacific, Atlantic, etc.Pacific, Atlantic, etc. NATIONAL/DOMESTIC:NATIONAL/DOMESTIC: covers domestic covers domestic

or national territoryor national territory

Satellite Design ParametersSatellite Design Parameters

Angle of ElevationAngle of Elevation ( (BB)- It is the angle )- It is the angle formed between the direction of travel of a formed between the direction of travel of a wave radiated from an earth station antenna wave radiated from an earth station antenna and the horizontal.and the horizontal.

BB = tan = tan-1-1 1 - R 1 - R

tano (R + h)sinotano (R + h)sino


Azimuth - defined as the horizontal pointing Azimuth - defined as the horizontal pointing angle of an antenna. It is measured in a angle of an antenna. It is measured in a clockwise direction in degrees from true north.clockwise direction in degrees from true north.

Az = cosAz = cos-1-1 _ tanu _ tanu

tanotano



Range Range - (also known as “slant distance”) - (also known as “slant distance”) refers to the distance of the satellite from an refers to the distance of the satellite from an earth station. It is also the LOS distance earth station. It is also the LOS distance between an earth station antenna and the between an earth station antenna and the satellite.satellite.

dd = = -Rsin-RsinBB + + (R + h)(R + h)22 – R – R22coscos22BB



Where: Where:

BB – angle of elevation in degrees – angle of elevation in degrees

o - coso - cos-1-1 cosu.cos \ cosu.cos \

u – latitude of earth station antennau – latitude of earth station antenna

\ - difference in longitude between an \ - difference in longitude between an earth station antenna and the sub-satellite pointearth station antenna and the sub-satellite point

h – satellite height (km) ; R – radius of h – satellite height (km) ; R – radius of earth (6378 km)earth (6378 km)



Orbital HeightOrbital Height (vertical height) - refers to (vertical height) - refers to the average distance of a satellite above the the average distance of a satellite above the surface of the earth.surface of the earth.

h = h = 33 gR gR22TT2 2 - R- R

4 4 22



Orbital PeriodOrbital Period - defines as the time a - defines as the time a satellite to rotate around the earth.satellite to rotate around the earth.

TT = = 22 (h + R)(h + R)33

g Rg R22



Orbital VelocityOrbital Velocity – the apparent velocity of a – the apparent velocity of a satellite as it rotates around the earthsatellite as it rotates around the earth

v = 2 (h + R)v = 2 (h + R)

TT



Propagation Time (one-way)Propagation Time (one-way) - amount - amount of time it takes a signal to reach the satellite of time it takes a signal to reach the satellite after it leaves the earth station antenna or vice-after it leaves the earth station antenna or vice-versa.versa.

PPTIMETIME = slant distance = d = slant distance = d

speed of light cspeed of light c



Propagation Delay (two-way)Propagation Delay (two-way) - amount - amount of time that elapsed after the signal reaches the of time that elapsed after the signal reaches the receiving earth station after it was transmitted receiving earth station after it was transmitted by an earth station.by an earth station.

PPdelaydelay = 2.P = 2.PTIMETIME



Free Space Loss (FSL) Free Space Loss (FSL)

FSL = 92.4 + 20log ( f x d)FSL = 92.4 + 20log ( f x d)

Where:Where:

f – frequency (GHz)f – frequency (GHz)

d – distance (km)d – distance (km)


Satellite System ParametersSatellite System Parameters

Bit Energy (EBit Energy (Ebb)) - the amount of energy - the amount of energy

carried by a single bit of information.carried by a single bit of information.

EEbb = Pt / f = Pt / fbb

Where;Where;

Pt - total transmit powerPt - total transmit power

ffbb - bit rate (bps) - bit rate (bps)



Noise Density (No)Noise Density (No) – is the noise power – is the noise power normalized in a 1-Hz bandwidth.normalized in a 1-Hz bandwidth.

No = N / BWNo = N / BW

Where:Where:

N – noise power (W)N – noise power (W)

BW – bandwidth (Hz)BW – bandwidth (Hz)



Gain –to- Equivalent Noise Gain –to- Equivalent Noise Temperature – Temperature – a figure of merit used to a figure of merit used to represent the quality of a satellite or an represent the quality of a satellite or an earth station receiver.earth station receiver.

G/TG/Tee = A = Arr + A + ALNALNA

TTee



Carrier-to-Noise Density RatioCarrier-to-Noise Density Ratio – defines – defines as the ratio between the carrier power to noise as the ratio between the carrier power to noise densitydensity

(C/No )(C/No )dBdB = C = CdBWdBW - No - No(dBW)(dBW)



System Carrier-to-Noise Density System Carrier-to-Noise Density RatioRatio

11 == 11 ++ 11

CC CC CC

NoNo SS NoNo ULUL NoNo DLDL


Satellite Communications

Documents

satellite communications

satellite tv

satellite communicationsengr

transmission of traffic

transmitting earth station

transmission uplink

radio communications

downlink frequency