Satellite CommunicationSatellite Communication

Lecturers:Morteza TahzibiAli Reza KataniAdvisor:Dr. Golestani

1

OverviewOverviewSatellite is a microwave repeater

in the space.There are about 750 satellite in

the space, most of them are used for communication.

They are:◦ Wide area coverage of the earth’s surface.◦ Transmission delay is about 0.3 sec.◦ Transmission cost is independent of

distance.

2

Satellite MissionsSatellite Missions

3

Satellite History CalendarSatellite History Calendar 1957

◦ October 4, 1957: - First satellite - the Russian Sputnik 01◦ First living creature in space: Sputnik 02

1958◦ First American satellite: Explorer 01◦ First telecommunication satellite: This satellite broadcast a taped message: Score

1959◦ First meteorology satellite: Explorer 07

1960◦ First successful passive satellite: Echo 1◦ First successful active satellite: Courier 1B◦ First NASA satellite: Explorer 08

April 12, 1961: - First man in space- Boctok voyager 1962

◦ First telephone communication & TV broadcast via satellite: Echo 1◦ First telecommunication satellite, first real-time active, AT&T: Telstar 1◦ First Canadian satellite: Alouette 1◦ On 7th June 1962 at 7:53p the two-stage rocket; Rehbar-I was successfully launched from Sonmiani Rocket Range. It

carried a payload of 80 pounds of sodium and soared to about 130 km into the atmosphere. With the launching of Rehbar-I, Pakistan had the honour of becoming the third country in Asia and the tenth in the world to conduct such a launching after USA, USSR, UK, France, Sweden, Italy, Canada, Japan and Israel.

◦ Rehbar-II followed a successful launch on 9th June 1962 1963

◦ Real-time active: Telstar 2 1964

◦ Creation of Intelsat◦ First geostationary satellite, second satellite in stationary orbit: Syncom 3◦ First Italian satellite: San Marco 1

4

Satellite History CalendarSatellite History Calendar 1965

◦ Intelsat 1 becomes first commercial comsat: Early Bird◦ First real-time active for USSR: Molniya 1A

1967◦ First geostationary meteorology payload: ATS 3

1968◦ First European satellite: ESRO 2B

July 21, 1969: - First man on the moon

1970◦ First Japanese satellite: Ohsumi◦ First Chinese satellite: Dong Fang Hong 01

1971◦ First UK launched satellite: Prospero◦ ITU-WARC for Space Telecommunications ◦ INTELSAT IV Launched ◦ INTERSPUTNIK - Soviet Union equivalent of INTELSAT formed

1974◦ First direct broadcasting satellite: ATS 6

1976 ◦ MARISAT - First civil maritime communications satellite service started

1977 ◦ EUTELSAT - European regional satellite ◦ ITU-WARC for Space Telecommunications in the Satellite Service

1979◦ Creation of Inmarsat

5

Satellite History CalendarSatellite History Calendar 1980 

◦ INTELSAT V launched - 3 axis stabilized satellite built by Ford Aerospace 1983 

◦ ECS (EUTELSAT 1) launched - built by European consortium supervised by ESA 1984 

◦ UK's UNISAT TV DBS satellite project abandoned ◦ First satellite repaired in orbit by the shuttle: SMM

1985◦ First Brazilian satellite: Brazilsat A1◦ First Mexican satellite: Morelos 1

1988◦ First Luxemburg satellite: Astra 1A

1989 ◦ INTELSAT VI - one of the last big "spinners" built by Hughes◦ Creation of Panamasat - Begins Service

1990 ◦ IRIDIUM, TRITIUM, ODYSSEY and GLOBALSTAR S-PCN projects proposed - CDMA designs more popular ◦ EUTELSAT II

1992 ◦ OLYMPUS finally launched - large European development satellite with Ka-band, DBTV and Ku-band

SS/TDMA payloads - fails within 3 years 1993 

◦ INMARSAT II - 39 dBW EIRP global beam mobile satellite - built by Hughes/British Aerospace 1994 

◦ INTELSAT VIII launched - first INTELSAT satellite built to a contractor's design ◦ Hughes describe SPACEWAY design ◦ DirecTV begins Direct Broadcast to Home

1995◦ Panamsat - First private company to provide global satellite services.

6

Satellite History CalendarSatellite History Calendar 1996 

◦ INMARSAT III launched - first of the multi-beam mobile satellites (built by GE/Marconi) ◦ Echostar begins Direct Broadcast Service

1997 ◦ IRIDIUM launches first test satellites ◦ ITU-WRC'97

1999 ◦ AceS launch first of the L-band MSS Super-GSOs - built by Lockheed Martin ◦ Iridium Bankruptcy - the first major failure?

2000 ◦ Globalstar begins service ◦ Thuraya launch L-band MSS Super-GSO

2001◦ XM Satellite Radio begins service◦ Pakistan’s 2nd Satellite, BADR-B was launched on 10 Dec 2001 at 9:15a from Baikonour Cosmodrome,

Kazakistan 2002

◦ Sirius Satellite Radio begins service◦ Paksat-1, was deployed at 38 degrees E orbital slot in December 2002, Paksat-1, was deployed at 38

degrees E orbital slot in December 2002 2004 

◦ Teledesic network planned to start operation 2005 

◦ Intelsat and Panamsat Merge ◦ VUSat OSCAR-52 (HAMSAT) Launched

2006◦ CubeSat-OSCAR 56 (Cute-1.7) Launched◦ K7RR-Sat launched by California Polytechnic University

2007◦ Prism was launched by University of Tokyo

2008◦ COMPASS-1; a project of Aachen University was launched from Satish Dawan Space Center, India. It

failed to achieve orbit.

7

Satellite-Related TermsSatellite-Related TermsEarth Stations : antenna systems on or

near earth.Uplink : transmission from an earth station

to a satellite.Downlink : transmission from a satellite to

an earth station.Transponder : electronics in the satellite

that convert uplink signals to downlink signals.

8

Geometry TermsGeometry TermsElevation angle : the angle from the

horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite

Minimum elevation angle

Coverage angle : the measure of the portion of the earth's surface visible to the satellite

9

10

Minimum Elevation AngleMinimum Elevation AngleReasons affecting minimum

elevation angle of earth station’s antenna (>0o)◦ Buildings, trees, and other terrestrial

objects block the line of sight◦ Atmospheric attenuation is greater at low

elevation angles◦ Electrical noise generated by the earth's

heat near its surface adversely affects reception

11

Satellite Link Performance FactorsSatellite Link Performance Factors

Distance between earth station antenna and satellite antenna

For downlink, terrestrial distance between earth station antenna and “aim point” of satellite◦ Displayed as a satellite footprint (Next

Figure) Atmospheric attenuation

◦ Affected by oxygen, water, angle of elevation, and higher frequencies

12

Satellite FootprintSatellite Footprint

13

Atmospheric LossesAtmospheric Losses

Different types of atmospheric losses can disturb radio wave transmission in satellite systems:◦ Atmospheric absorption◦ Atmospheric attenuation◦ Traveling ionospheric disturbances

14

15

Atmospheric AbsorptionAtmospheric Absorption Energy absorption by atmospheric

gases, which varies with the frequency of the radio waves.

Two absorption peaks are observed (for 90º elevation angle):◦ 22.3 GHz from resonance absorption in

water vapor (H2O)◦ 60 GHz from resonance absorption in

oxygen (O2)

16

Atmospheric AttenuationAtmospheric Attenuation Rain is the main cause of atmospheric attenuation

(hail, ice and snow have little effect on attenuation because of their low water content).

Total attenuation from rain can be determined by:◦ A = L [dB]◦ where [dB/km] is called the specific attenuation, and can

be calculated from specific attenuation coefficients in tabular form that can be found in a number of publications

◦ where L [km] is the effective path length of the signal through the rain; note that this differs from the geometric path length due to fluctuations in the rain density.

17

Traveling Ionospheric DisturbancesTraveling Ionospheric Disturbances

Traveling ionospheric disturbances are clouds of electrons in the ionosphere that provoke radio signal fluctuations which can only be determined on a statistical basis.

Scintillation◦ variations in the amplitude, phase, polarization, or

angle of arrival of radio waves, caused by irregularities in the ionosphere which change over time.( time-varying model)

◦ The main effect of scintillations is fading of the signal.

18

What is PolarizationWhat is Polarization??Polarization is the property of electromagnetic

waves that describes the direction of the transverse electric field.

Since electromagnetic waves consist of an electric and a magnetic field vibrating at right angles to each other.

it is necessary to adopt a convention to determine the polarization of the signal.

Conventionally, the magnetic field is ignored and the plane of the electric field is used.

19

Types of PolarizationTypes of Polarization Linear Polarization

(horizontal or vertical):◦ the two orthogonal

components of the electric field are in phase;

◦ The direction of the line in the plane depends on the relative amplitudes of the two components.

Circular Polarization:◦ The two components are

exactly 90º out of phase and have exactly the same amplitude.

Elliptical Polarization:◦ All other cases.

Linear Polarisation Circular Polarisation Elliptical Polarisation

20

Satellite CommunicationsSatellite Communications Alternating vertical and

horizontal polarization is widely used on satellite communications

This reduces interference between programs on the same frequency band transmitted from adjacent satellites (One uses vertical, the next horizontal, and so on)

Allows for reduced angular separation between the satellites.

21

Classification of Satellite Classification of Satellite OrbitsOrbits

Circular or elliptical orbit Circular with center at earth’s center Elliptical with one foci at earth’s center

Orbit around earth in different planes Equatorial orbit above earth’s equator Polar orbit passes over both poles Other orbits referred to as inclined orbits

Altitude of satellites Geostationary orbit (GEO) Medium earth orbit (MEO) Low earth orbit (LEO)

22

OrbitsOrbits LEO: Low Earth Orbit. Low power, Low latency, More Satellites, Small

Footprint MEO: Medium Earth Orbit High bandwidth, High power, High latency GEO: Geostationary Earth Orbit 36000 Km = 22300 Miles, equatorial, High latency

23

LEO Satellite CharacteristicsLEO Satellite Characteristics

Circular/slightly elliptical orbit under 2000 km

Orbit period ranges from 1.5 to 2 hoursDiameter of coverage is about 8000 kmRound-trip signal propagation delay less than

20 msMaximum satellite visible time up to 20 minSystem must cope with large Doppler shifts

24

LEO CategoriesLEO CategoriesLittle LEOs

◦ Frequencies below 1 GHz ◦ 5MHz of bandwidth ◦ Data rates up to 10 kbps◦ Aimed at paging, tracking, and low-rate

messagingBig LEOs

◦ Frequencies above 1 GHz ◦ Support data rates up to a few megabits

per sec◦ Offer same services as little LEOs in

addition to voice and positioning services

25

MEO Satellite CharacteristicsMEO Satellite Characteristics

Circular orbit at an altitude in the range of 5000 to 12,000 km

Orbit period of 6 hoursDiameter of coverage is 10,000 to

15,000 kmRound trip signal propagation delay

less than 50 msMaximum satellite visible time is a few

hours

26

GEO OrbitGEO OrbitAdvantages of the GEO orbit

◦No problem with frequency changes◦Tracking of the satellite is simplified◦High coverage area

Disadvantages of the GEO orbit◦Weak signal after traveling over

35,000 km◦Polar regions are poorly served◦Signal sending delay is substantial

27

At the Geostationary orbit the satellite covers 42.2% of the earth’s surface.

Theoretically 3 geostationary satellites provides 100% earth coverage

28

29

Satellite OrbitsSatellite Orbits

30

Ways to CategorizeWays to CategorizeCommunications SatellitesCommunications Satellites

Coverage area◦Global, regional, national

Service type◦Fixed service satellite (FSS)◦Broadcast service satellite (BSS)◦Mobile service satellite (MSS)

General usage◦Commercial, military, amateur,

experimental

31

Frequency Bands Available for Frequency Bands Available for Satellite CommunicationsSatellite Communications

32

NetworkingNetworking

33

What is the problemWhat is the problem??

HOW can we divide a common source between some users?◦ TDMA / FDMA

wasting channel resource large delay at low loads

◦ Statistical Multiplexing Low delay at low load wasting channel resource at collisions.

34

What is the best choice for satelliteWhat is the best choice for satellite

Large BDP (bandwidth delay product).◦ there will be much resource waste when

collision resolution.◦ TDM or SM◦ A reservation system!

a combined version of TDM and statistical Multiplexing.

35

RESERVATION SYSTEMSRESERVATION SYSTEMSThe most widely used method for satellite communication

36

Reservation systemReservation system

A reservation system with 4 users

37

Reservation systemReservation system Throughput is

1. Reservation contain no data:

2. Reservation carry some portion of data:

38

1 2 3 1 2 3 1

Transmission interval for user 1

Arrival interval for user 1 in an exhaustive system

Arrival interval for user 1 in a partially gated system

Arrival interval for user 1 in a gated system

Packets arriving in the arrival interval shown are transmitted in the transmission interval shown

Reservation systemReservation system

39

}{}{}{}{ )(iliiii VENEREWE

Single user reservation systemSingle user reservation system

40

Multiuser reservation systemMultiuser reservation system

}{}{}{}{ iiiii YENEREWE

41

Delay formulas for reservation Delay formulas for reservation systemsystem

A multiuser reservation system

•A single user reservation system

42

How to use reservation system in How to use reservation system in satellite networkssatellite networks??

43

Is the above relation true?

NO

44

Disadvantages of the proposed Disadvantages of the proposed algorithmalgorithm

If any error happen in feedback signal received from channel by user synchronization will lost.

Violating of fairness.

What to do now??

• Fix the frame time slot to a specified value larger than channel propagation delay.

• Using a separate frequency channel for sending reservation.(to obtain a closed form expression for delay)

45

Analyzing Delay formulaAnalyzing Delay formula

46

Additional pointsAdditional pointsWe can not increase number of usersIncreasing users mean wasting

bandwidth!(γ=mν/2β)

What is the solution?

Use the below system!

47

IINTERLEAVED NTERLEAVED FFRAME RAME FFLUSH LUSH OOUTUT

Is suitable and can be general for satellite use

48

IFFO-System considerationIFFO-System considerationGEO satelliteTime is normalized to 22.5 millisecond

(one slot duration)M users with infinite buffer capacityArrival process is Bernoulli with

parameter λEach frame duration is at least 12 slot

49

Interleaved Frame Flush OutInterleaved Frame Flush Out

50

How this protocol workHow this protocol work??

51

Different kinds of IFFODifferent kinds of IFFO!!PR-IFFO: Pure Reservation IFFOF-IFFO: Fixed Contention IFFOC-IFFO: Controlled Contention IFFO

52

F-IFFOF-IFFO

53

C-IFFOC-IFFO

54

Performance evaluationPerformance evaluationPR-IFFO

• Infinite Markov chain

55

• F-IFFO

PDF of not transmitted packets

Performance evaluationPerformance evaluation

56

Performance evaluation

• F-IFFO

57

Performance evaluation• F-IFFO

58

Performance evaluation

• C-IFFO

The main issue in C-IFFO is obtaining the optimum set for sending probabilities

59

SOME NEWER SOME NEWER PROTOCOLSPROTOCOLS

They all have the same basics for transmitting data

60

What is the problemWhat is the problem??the kind of traffic that we should pass

through satellite is bur sty.◦Web based traffic.◦Position reporting or other signaling

information in mobile networks.DAMA (demand assignment multiple

access protocols) is not a suitable choice for this kind of traffic.

61

What is the problemWhat is the problem??

RA are robust to this kind of traffic.RA is not suitable for satellite links.RA use in initial network logging and the

transmission of capacity requests in contention mini slot.

Solution is the combination of RA and DAMA.

62

SOME NEW PROTOCOLSSOME NEW PROTOCOLSthese protocols will work well

under bursty traffic generated by large population of users

CRDSACRDSA++E-SSA

63

CRDSACRDSADiversity Slotted ALOHA has used

in TDMA systems with low efficiency and reliability typically for logging into the network.◦It has very low throughput.

Contention Resolution DSA.◦Diversity such as DSA but with

additional signaling to indicate the twin packet location.

64

CRDSACRDSAContention Resolution DSA.

◦ In successful packet reception allows to locate the twin packet within the frame and to accurately cancel it in addition to the one successfully decoded.

◦ By iterating the process a number of times some of the initially lost packets can be recovered and the DSA performance enhanced.

65

Enhancement of DSA with additional signaling information indicating the location of twin packet in CRDSA

Throughput versus load

66

Throughput is not so highThroughput is not so high!!CRDSA++

◦Increased number of packet repetitions(3-5)

◦exploitation of the received packets power unbalance to further boost the RA performance.

67

The increased diversity allow to better clean

up the collisions through iterative

processingThroughput versus load

68

CRDSACRDSACRDSA++ performance are

further enhanced by power unbalance.◦Successive interference cancellation

is inherently enhanced by the received packet power unbalance allowing to resolve collisions that were destructive otherwise.

69

Questions without Questions without answersanswers!!

How to combine CRDSA with DAMA?

Adjusting the coding rate and transmit energy in a fading environment for CRDSA.

Power control issues for SSA protocols

Interference cancelation for E-SSA

70

LEO PROTOCOLSLEO PROTOCOLSSome simple sample protocols

71

LEO ProtocolsLEO Protocols◦ SALOHA

Is relatively simple to realize. It can not adapt well to dynamic traffic pattern.

◦ VCR-SALOHA(varying call rate SALOHA) Can adapt to load changes. Its maximum efficiency is 38%. Its reservation period length is fixed.

◦ AP-SALOHA(adaptive polling and SALOHA)(is for terrestrial stations). Variation of reservation interval adaptively with

respect to load. 19% improvement over VCR-SALOHA.

72

SALOHASALOHA1993 in PACSAT time = channel reservation period(SALOHA) +message

delivery period.An invitation frame is broadcast by the satellite to start a

reservation period of N request slot longA station waits a random number (between 0 and N -1) of time

slots before it sends its request.Main problem is: N is constant but M (the number of users)

and traffic are time varying

73

Success probability is heavily dependent on M and N

Success probability versus M the number of users

74

Reservation period

Gnd1-TX

Gnd1-RX

Sat-TX

Sat-RX

Gnd2-TX

Gnd2-RX

invitation

invitation

invitation

(1)U/D Req

(1)U/D Req

Request slot-1 Request slot-N

(2)U/D Req

Back off N-1 slot(2)U/D Req

75

VCR-SALOHAVCR-SALOHAImprovement with respect to SALOHA:

◦ Sending invitation packet is adjusted by change of station request traffic.

◦ Adjust the calling rate to maintain the maximum 38% throughput.

Disadvantages:◦ Additional control packet to adjust success

probability.◦ N is fixed. More overhead in bandwidth.◦ Maximum throughput is 38%

76

Question: Why we should change N Question: Why we should change N adaptively with respect to Madaptively with respect to M??

with decreasing N we can use channel in favor of sending more data than reservation packets but success probability will decrease and vice versa.

for every fix M there is an optimum value for N in which success probability is maximized.

77

AP-SALOHAAP-SALOHAWhen satellite is invisible there will be more packet

arrival in terminal. We will use this property in AP-SALOHA

Visible station are divided to ◦ High probability set.◦ Low probability set.

◦Station after viewing the satellite is in high probability set and after serving all waiting packets it go to low probability set.

◦If its probability of having data packets is higher than a threshold it goes to high probability set.

78

AP-SALOHAReservation interval is divided into polling

part and SALOHA part.

◦ Polling part is for stations in high probability set.◦ S-ALOHA part is for stations in low probability set

79

Advantages of Satellite Advantages of Satellite CommunicationCommunication

Can reach over large geographical areaFlexible (if transparent transponders) Easy to install new circuits Circuit costs independent of distance Broadcast possibilities Temporary applications (restoration) Niche applications Mobile applications (especially "fill-in") Terrestrial network "by-pass" Provision of service to remote or

underdeveloped areas

80

Disadvantages of Satellite Disadvantages of Satellite CommunicationCommunication

Large up front capital costs (space segment and launch)

Terrestrial break even distance expanding (now approx. size of Europe)

Interference and propagation delay Congestion of frequencies and orbits

81

When to use SatellitesWhen to use Satellites When the unique features of satellite

communications make it attractive When the costs are lower than terrestrial routing When it is the only solution Examples:

◦ Communications to ships and aircraft (especially safety communications)

◦ TV services - contribution links, direct to cable head, direct to home

◦ Data services - private networks ◦ Overload traffic ◦ 1 for N diversity

82

When to use TerrestrialWhen to use Terrestrial PSTN - satellite is becoming increasingly

uneconomic for most trunk telephony routes

but, there are still good reasons to use satellites for telephony such as: thin routes, diversity, very long distance traffic and remote locations.

Land mobile/personal communications - in urban areas of developed countries new terrestrial infrastructure is likely to dominate (e.g. GSM, etc.)

but, satellite can provide fill-in as terrestrial networks are implemented, also provide similar services in rural areas and underdeveloped countries

83

ReferencesReferences1. Satellite communications systems engineering, by Louis J.

Ippolito, 2008 JohnWiley & Sons Ltd.2. The Satellite Communication Applications Handbook, by Bruce

R. Elbert.3. Satellite Communications, by Dennis Roddy.4. Satellite Communications Tutorial, by John P. Silver,” RF,RFIC

and microwave theory, Design.5. Modeling the Effects of Ionospheric Scintillations on LEO

Satellite Communications, by Sheng-Yi Li and C. H. Liu, Fellow, IEEE, IEEE COMMUNICATIONS LETTERS, VOL. 8, NO. 3, MARCH 2004.

6. R. Gallager “Data network” Prentice Hall 1987.7. Simon Lam ,“Satellite Packet Communication-Multiple Access Protocols and

Performance” IEEE Trans On communication Oct 1979. 8. Baozhong Cheng Jeff Ward, Marting Sweeting“An Optimized Multiple Access Control

Protocol for a ‘little LEO’Satellite Store-and-Forward Global Data Network” IEEE 2003.9. Riccardo De Gaudenzi and Oscar del Rio Herrero, “Advances in Random Access Protocols

for Satellite Networks” IEEE 2009. 10. J. E. Wieselthier, A. Ephremides, “A New Class of Protocols for Multiple Access in

Satellite Networks” TRANSACTIONS ON Automatic control, VOL. AC-25, NO. 5, October 1980.

11. A. F. Canhoto, A. Anzaloni“Performance Evaluation of SSTP- a Transport Protocol for Satellite Channels” 2009 International Conference on Advanced Information Networking and Applications Workshops.

12. Http://en.wikipedia.org

84