satellite communications part 4

Satellite Multiple Access

Technique1. Frequency Division Multiple Access (FDMA)

– a satellite transponder is divided into smallerfrequencies hand segments where eachsegment is assigned to use for his uplink ordownlink frequency.

a. Pre-assigned – a given number ofavailable voice hand channels from eachearth station are assigned dedicateddestinations. This method is onlyeconomically feasible in situations wheresources / destination locations have verylow traffic density during the busy hour.

b. Demand Assigned (DAMA) – voice bandchannels are assigned on “as-needed”basis. It provides more versatility andmore efficient use of the frequencyspectrum.

Satellite Multiple Access

Technique

Three Methods of Controlling DAMA Systems

a. Polling – a master station “polls” otherstations sequentially. When a positivereply is received, a channel is assignedaccordingly. As the polling intervalbecomes longer and the system tends tobecome unwieldy because of excessivepost dial delay as a call attempt waits forthe pulling interval to run its course

Satellite Multiple Access

Technique

b. Random Access Central Control – acentral computer located at the masterstation coordinates the status of thechannels. Call requests are passed to thecentral computer and a channel isassigned if available. Once the call iscompleted and the subscriber goes onthe hook, the speech path is taken downand the channel used is returned to thedemand access pull of ideal channels.

Satellite Multiple Access

Technique

c. Random Access Distributed Control –uses a processor controller at each earthstation accessing the system. All earthstations in the network monitor thestatus information by means of thedigital order wire circuit. When an idlechannel is seized, all users are informedto the fact and the circuit is removedfrom the poll

Satellite Multiple Access

Technique

SPADE – Single Channel Per Carrier PCMMultiple Access Demand AssignmentEquipment – an 800-PCM encoded voiceband channels separately QPSK modulatean IF carrier frequency. Each 4 kHz voiceband channel is sampled at an 8 kHz rateand converted into bit PCM CODE. Thisproduces a 64 kbps PCM code for eachband channel

Satellite Multiple Access

Technique

2. Time Division Multiple Access (TDMA)

- works in the time domain and is applicableto digital systems because informationstorage is required. In this method, stationsare restricted to precise time slot. It has norestrictions on frequency or bandwidth.Presently, it is the most dominant methodused of providing the most efficient methodof transmitting digitally modulated carries(PSK).

Satellite Multiple Access

Technique

- each earth station transmits a short burstof a digitally modulated carrier during aprecise time slot which TDMA frame. Eachburst is synchronized so that it arrives atthe satellite transponder at a differenttime avoid collision with another station'scarrier. It is a “store-and-forward” systemwhereby earth stations, can consult onlyduring their specified time slot, althoughthe incoming voice had signals iscontinuous.

Satellite Multiple Access

Technique

- in TDMA, only one user appears on thetransponder at any given time. Each useris assigned a time slot to the satellite;transponder power and bandwidth areshared by several earth stations.

Satellite Multiple Access

Technique

Store and Forward – a technique in which amessage received from earth termed isheld in storage until the satellite is in viewof a second earth terminal, at which timethe message is transmitted.

Satellite Multiple Access

Technique

3. Code Division Multiple Access (CDMA) or Spread Spectrum Multiple Access (SSMA)

- each station may transmit whenever itwishes and can use any or all of thebandwidth allocated. Transmissions areseparated through envelope, encryption,and decryption techniques. It usesunique binary words called CHIP CODESto receive a particular earth station’stransmission.

Satellite Multiple Access

Technique

- a correlator checks or compares orthogonal codes with original chip codes to allow access to users

- the transmitted signal is spread over part or all of the available transponder hand width in a time-frequency relationship by a code transformation. Typically, the modulated carrier is ten to hundreds of times greater than the information bandwidth.

Satellite Multiple Access

Technique

Frequency Hopping – is a form of CDMAwhere a digital code is used to continuallychange the frequency of the carrier. Thetotal available bandwidth is partitioned tosmaller frequency bands and totaltransmission time is subdivided intosmaller time slots. Each station uses theentire RF spectrum but never occupiesmore than a small portion of thatspectrum at any one time.

Satellite Multiple Access

Technique

Satellite OrganizationsINMARSAT (International Maritime Satellite

Organization)

- recommended by the panel of expertscommissioned by the IntergovernmentalMaritime Consultative Organization(IMCO). They consider the introduction ofsatellite communications to the maritimesphere with the aim of improvingcommunications with ships, particularlyfor safety and distress purposes.

- born in July 1979, very much along theINTELSAT lines, with COMSAT as thelargest shareholder.

Satellite Organizations

INTELSAT (International Telecommunications Satellite

Consortium)

- Founded in 1964 at Washington D.C. by COMSAT (Communication Satellite Corporation) of the United States, Overseas Telecommunications Commission of the Australia and nine other world communications agencies

Satellite Organizations

Satellite Organizations

MARISAT

- a ship-to-shore and shore-to-shipcommunications via a dedicatedgeostationary satellite system, providinghigh-quality telephony, data andtelex/telegraphy circuits

Satellite Organizations

Questions

1. The first passive satellite

a. Telstar

b. Early Bird

c. Sputnik I

d. Moon

Questions

2. The first active satellite

a. Sputnik I

b. Telstar

c. INTELSAT I

d. Explorer I

Questions3.The first geostationary satellite launched in 1965 is

a. Syncom I

b. Sputnik I

c. Explorer I

d. Early Bird

Questions

4. The average lifetime ofgeosynchronous satellites isabout __________ years.

a. 5

b. 10

c. 15

d. 20

Questions5. A communication satellite is a repeater

between

a. A transmitting station and receivingstation

b. Many transmitting stations and manyreceiving stations

c. A transmitting station and manyreceiving stations

d. Many transmitting stations and areceiving station

Questions6. One of the main applications ofsatellite communications ismonitoring the ecological situation ofthe earth. This is known as

a. Navigation

b. Surveillance

c. Remote control

d. Remote sensing

Questions7. What vacuum tube used toamplify RF signal for transmissionthrough the downlink to stationreceiver?

a. Magnetron

b. Klystron

c. Twystron

d. TWT

Questions

8. A high power tube used intransmission of RF signaluplink

a. Magnetron

b. Klystron

c. BWO

d. TWT

Questions9. A stage in transponder anddownlink system which amplifiesthe signal and ensuring thatnoise is suppressed as possible

a. Mixer

b. Demodulator

c. LNA

d. IF amplifier

Questions10. A transponder is a satelliteequipment which

a. Receives a signal from earthstation and amplifies it

b. Changes the frequency of thereceived signal

c. Retransmit the received signal

d. All of the above

Questions

11. Multiple repeaters incommunications satellites areknown as

a. Transponders

b. Detectors

c. Modulators

d. Transceivers

Questions

12. Satellite-to-satellite link is also called

a. Uplink

b. Downlink

c. Crosslink

d. Weakest link

Questions13. The expression for satellite link

frequencies such as 14/12 GHz denotesthat

a. 12 GHz is the uplink frequency and 14GHz is the downlink frequency

b. the system is operating at a meanfrequency of 13 GHz

c. 14 GHz is the uplink frequency and 12GHz is the downlink frequency

d. the 14 GHz frequency is backup for 12GHz frequency or vice versa

Questions

14. The most widely usedmicrowave bands forcommercial applications are

a. C band and X band

b. X band and S band

c. C band and Ku band

d. S band and Ku band

Questions

15. At present, the RF band mainly used by most satellites is

a. EHF

b. UHF

c. SHF

d. VHF

Questions16. The required antenna size__________ as the operatingfrequency of a system increases,assuming that antenna gain remainsunchanged.

a. Remains the same

b. Increases

c. Decreases

d. All of the above

Questions17. A 20-m antenna gives a certainup-link gain at frequencies of 4/6GHz. For getting the same gain in20/30 GHz band, antenna sizerequires __________ meters.

a. 100

b. 4

c. 1

d. 10

Questions

18. Orbital disturbances of ageosynchronous satellite arecaused by

a. Moon

b. Sun

c. Earth

d. All of the above

Questions

19. Geosynchronous satellites

a. Has the same period asthat of the earth

b. Has a circular obit

c. Rotates in the equatorialplane

d. All of the above

Questions20. To cover all inhabited regions ofthe earth, the number ofgeosynchronous satellites required is

a. 5

b. 10

c. 2

d. 3

Questions21. A geostationary satellite is onewhich

a. Hangs motionless in space about36,000 km above the earth

b. Travels around the earth about 24hrs.

c. Remains stationary above the earth

d. Appears stationary above the earth

Questions22. Geosynchronous Communicationsatellites travel around the earth incircular orbits with forward speed ofabout __________km/hr.

a. 100,000

b. 36,000

c. 11,200

d. 22,800

Questions23. The period of the satellite is

a. The amount of time it takes for asatellite to complete one orbit

b. The point on an orbit where satellite tocomplete one orbit

c. The time it takes the satellite to travelfrom perigee to apogee

d. An orbital arc that extends from 60degrees west longitude to 145 degreeswest longitude

Questions24. What is the satellite's period orbiting in a circular pattern with elevation of 1000 km?

a. 1 hr 45 mins

b. 2 hrs 45 mins

c. 2 hrs 30 mins

d. 3 hrs

Questions

25. A satellite, orbiting in a circular orbit,

a. Has constant velocity

b. Has varying velocity

c. Is not moving at all

d. Both a and b

Questions

26. What is a descending passfor a satellite?

a. A pass from west to east

b. A pass from east to west

c. A pass from south to north

d. A pass from north to south

Questions

27. Satellite rotating in anorbit takes it over the northand south poles is in

a. Inclined orbit

b. Polar orbit

c. Equatorial orbit

d. Declined orbit

Questions

28. The farthest point asatellite can reach is

a. Apogee

b. Perigee

c. Altitude

d. Attitude

Questions

29. Include all earth stationswithin line-of-sight path of asatellite

a. Satellite shadow

b. Earth shadow

c. Zonal

d. Global

Questions30. The different multiple accesseswhich permit many satellite users tooperate in parallel through

a. A Single Transponder WithoutInterfering With Each other are

b. FDMA

c. TDMA

d. CDMA

e. All of the above

Questions31. A digital technology that uses a low

power signal spread across a widebandwidth. With this technology, a phonecall is assigned a code instead of a certainfrequency. Using identifying code and alow power signal, a large number ofchannels can used the entire bandwidth

a. TDMA

b. PCDMA

c. PMA

d. CDMA

Questions

32. The use of the samefrequency on the samegeographical area

a. Frequency reuse

b. Roaming

c. Homing

d. Cellular

Questions

33. In selecting a satellitesystem, the first determiningfactor is

a. Coverage area

b. EIRP

c. Antenna size

d. Antenna gain

Questions

34. The earth's area or regionthat the satellite can receivefrom or transmit to

a. Footprint

b. Skip zone

c. Primary area

d. Finger print

Questions

35. Satellite radiation patternthat covers 1/3 of the earth'ssurface

a. Earth

b. Zonal

c. Spot

d. Global

Questions36. A satellite position ismeasured by its _________angle with respect to thehorizon.

a. Elevation

b. Depression

c. Azimuth

d. Incidence

Questions37. The _________ anglemeasures the satellite positionclockwise from the direction oftrue North

a. Elevation

b. Depression

c. Azimuth

d. Incidence

Questions

38. GPS has a total numbersatellites equal to

a. 12

b. 24

c. 36

d. 48

Questions

39. How many elliptical orbitsdoes Navstar GPS have?

a. 5

b. 6

c. 7

d. 8

Questions40. What is the free spaceattenuation of a satellite systemoperating at 36,000 km abovethe earth operating at 5 GHz?

a. 180 dB

b. 190 dB

c. 198 dB

d. 189 dB

Questions41. The FDMA technique whereinvoice band channels areassigned on “as needed" basis.

a. PAMA

b. DAMA

c. SSMA

d. CDMA

Questions42. A satellite equipped withelectronic devices to receive,amplify, convert, and retransmitsignals.

a. Passive

b. Active

c. Uplink

d. Downlink

Questions43. An earth station transmits signal toa satellite 38,500 km, directlyoverhead it. What is the propagationdelay when the signal is received backat the same earth station, inmilliseconds?

a. 257

b. 200

c. 285

d. 185

Questions44. A satellite communication link between

Pinugay Earth Station, Philippines and Mt.Fucino Earth Station, Italy is to beestablished. If the assigned uplinkfrequency at Pinugay Earth Station is6175 MHz, what is the downlink frequencyat Mt. Fucino Earth Station, in MHz?

a. 4545

b. 3950

c. 3789

d. 4200

Questions45. "The orbit of any planet is anellipse with the sun at onefocus". This is

a. Kepler's First Law

b. Kepler's Second Law

c. Kepler's Third Law

d. Law of universal Gravitation

Questions46. When a satellite orbits in theopposite direction as the earth'srotation with an angular velocityless than that of the earth

a. Orbital

b. Prograde

c. Retrograde

d. Geostationary

Questions47. The actual user informationconveyed through the satellitesystem

a. Bus transmission

b. Payload

c. Prograde

d. Retrograde

Questions

48. The spatial separationbetween geosynchronoussatellites

a. 1-3 degrees

b. 3-6 degrees

c. 6-8 degrees

d. 8-10 degrees

Questions

49. The footprint which coversa very small geographicalarea.

a. Spot coverage

b. Zonal coverage

c. Earth coverage

d. Regional coverage

Questions50. The satellite frequency reuse method

which sends different informationsignals using vertical or horizontalelectromagnetic polarization

a. Multiple coverage areas

b. Dual polarization

c. Spatial separation

d. Spread spectrum

Questions51. __________ detects thesatellite signal relayed from thefeed and converts it to an electriccurrent, amplifies and lower itsfrequency.

a. Feedhorn

b. Satellite dish

c. Satellite receiver

d. LNA

Questions52. Satellites used for intercontinental communications are known as

a. Comsat

b. Domsat

c. Marisat

d. Intelsat

Questions53. What is the basic function of acommunications satellite?

a. To act as a receiving antenna forbroadcast FM

b. To compensate for the antennalimitations

c. To eliminate aerodynamic drag

d. To act as a receiving antenna forbroadcast AM

Questions54. What do you call of a satelliteused to provide satellite serviceswithin a single country?

a. Orbital satellite

b. Geostationary satellite

c. Non-synchronous satellite

d. Domestic satellite

Questions

55. A satellite beam thatcovers almost 42.5% of theearth's surface.

a. Zone beam

b. Hemispheric beam

c. Spot beam

d. Global beam

Questions

56. The first Philippine satellitehas how many channels?

a. 30

b. 24

c. 48

d. 50

Questions

57. Aguila I has how manytransponders?

a. 36

b. 48

c. 24

d. 12

Questions58. How many satellite orbitalslots were requested by thePhilippine Government fromITU?

a. 2

b. 4

c. 6

d. 8

Questions

59. The most commondevice used as an LNA is

a. Zener diode

b. Tunnel diode

c. IMPATT diode

d. Shockley diode

Questions60. The radiation patterns ofearth coverage antennas have abeamwidth of approximately

a. 21degrees

b. 5 degrees

c. 17 degrees

d. 35 degrees

Questions

61. The main power sourcesfor satellites are

a. Batteries

b. Solar cells

c. Fuel cells

d. Thermoelectric generators

Questions62. What is the common up-converter and down-converterIF?

a. 36 MHz

b. 40 MHz

c. 70 MHz

d. 500 MHz

Questions63. When the satellites are spaced 4degrees of the 360 degreescomplete circle, how many parkingspaces or orbit slots are available?

a. 90

b. 85

c. 95

d. 80

Questions64. The first satellite launched fora geosynchronous orbit butunfortunately lost during orbitinjection.

a. Syncom I

b. Telstar I

c. Sputnik I

d. Early Bird

Questions

65. Geostationary satellitesare located _______ withrespect to the equator.

a. 0 deg longitude

b. 0 deg latitude

c. 90 deg latitude

d. 45 deg latitude

Questions

66. Incidentally proposed thegeostationary scheme ororbit of satellites in 1940's.

a. Clarke

b. Gauss

c. Morse

d. Gray

Questions67. The control routine necessaryto keep the satellite in position isreferred to as

a. Station keeping

b. Station tracking

c. Station monitoring

d. Station maintenance

Questions

68. A satellite which simplyreflects the signal withoutfurther amplification.

a. Passive

b. Active

c. Geostationary

d. Posigrade

Questions69. What is the line joining theascending and descending nodesthrough the center of the earth?

a. Line of apsides

b. Line of nodes

c. Line of shoot

d. Line of sight

Questions

70. The line joining theperigee and apogee throughthe center of the earth.

a. Line of sight

b. Line of nodes

c. Equatorial belt

d. Line of apsides