Satellite Communications Part 4

December 24, 2017 | Author: Gilbert Hernandez | Category: Communications Satellite, Channel Access Method, Code Division Multiple Access, Cellular Network, Modulation
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Satellite Multiple Access Technique 1.

Frequency Division Multiple Access (FDMA) – a satellite transponder is divided into smaller frequencies hand segments where each segment is assigned to use for his uplink or downlink frequency.

Satellite Multiple Access Technique a.

Pre-assigned – a given number of available voice hand channels from each earth station are assigned dedicated destinations. This method is only economically feasible in situations where sources / destination locations have very low traffic density during the busy hour.

b.

Demand Assigned (DAMA) – voice band channels are assigned on “as-needed” basis. It provides more versatility and more efficient use of the frequency spectrum.

Satellite Multiple Access Technique Three Methods of Controlling DAMA Systems a.

Polling – a master station “polls” other stations sequentially. When a positive reply is received, a channel is assigned accordingly. As the polling interval becomes longer and the system tends to become unwieldy because of excessive post dial delay as a call attempt waits for the pulling interval to run its course

Satellite Multiple Access Technique b.

Random Access Central Control – a central computer located at the master station coordinates the status of the channels. Call requests are passed to the central computer and a channel is assigned if available. Once the call is completed and the subscriber goes on the hook, the speech path is taken down and the channel used is returned to the demand access pull of ideal channels.

Satellite Multiple Access Technique c.

Random Access Distributed Control – uses a processor controller at each earth station accessing the system. All earth stations in the network monitor the status information by means of the digital order wire circuit. When an idle channel is seized, all users are informed to the fact and the circuit is removed from the poll

Satellite Multiple Access Technique SPADE – Single Channel Per Carrier PCM Multiple Access Demand Assignment Equipment – an 800-PCM encoded voice band channels separately QPSK modulate an IF carrier frequency. Each 4 kHz voice band channel is sampled at an 8 kHz rate and converted into bit PCM CODE. This produces a 64 kbps PCM code for each band channel

Satellite Multiple Access Technique 2.

Time Division Multiple Access (TDMA) - works in the time domain and is applicable to digital systems because information storage is required. In this method, stations are restricted to precise time slot. It has no restrictions on frequency or bandwidth. Presently, it is the most dominant method used of providing the most efficient method of transmitting digitally modulated carries (PSK).

Satellite Multiple Access Technique - each earth station transmits a short burst of a digitally modulated carrier during a precise time slot which TDMA frame. Each burst is synchronized so that it arrives at the satellite transponder at a different time avoid collision with another station's carrier. It is a “store-and-forward” system whereby earth stations, can consult only during their specified time slot, although the incoming voice had signals is continuous.

Satellite Multiple Access Technique - in TDMA, only one user appears on the transponder at any given time. Each user is assigned a time slot to the satellite; transponder power and bandwidth are shared by several earth stations.

Satellite Multiple Access Technique Store and Forward – a technique in which a message received from earth termed is held in storage until the satellite is in view of a second earth terminal, at which time the message is transmitted.

Satellite Multiple Access Technique 3.

Code Division Multiple Access (CDMA) or Spread Spectrum Multiple Access (SSMA) - each station may transmit whenever it wishes and can use any or all of the bandwidth allocated. Transmissions are separated through envelope, encryption, and decryption techniques. It uses unique binary words called CHIP CODES to receive a particular earth station’s transmission.

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 CDMA where a digital code is used to continually change the frequency of the carrier. The total available bandwidth is partitioned to smaller frequency bands and total transmission time is subdivided into smaller time slots. Each station uses the entire RF spectrum but never occupies more than a small portion of that spectrum at any one time.

Satellite Organizations INMARSAT (International Maritime Satellite Organization) - recommended by the panel of experts commissioned by the Intergovernmental Maritime Consultative Organization (IMCO). They consider the introduction of satellite communications to the maritime sphere with the aim of improving communications with ships, particularly for safety and distress purposes.

Satellite Organizations - born in July 1979, very much along the INTELSAT lines, with COMSAT as the largest 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-ship communications via a dedicated geostationary satellite system, providing high-quality telephony, data and telex/telegraphy circuits

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

Questions 3.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 of geosynchronous satellites is about __________ years. a. 5 b. 10 c. 15 d. 20

Questions 5. A communication satellite is a repeater between a. A transmitting station and receiving station b. Many transmitting stations and many receiving stations c. A transmitting station and many receiving stations d. Many transmitting stations and a receiving station

Questions 6. One of the main applications of satellite communications is monitoring the ecological situation of the earth. This is known as a. Navigation b. Surveillance c. Remote control d. Remote sensing

Questions 7. What vacuum tube used to amplify RF signal for transmission through the downlink to station receiver? a. Magnetron b. Klystron c. Twystron d. TWT

Questions 8. A high power tube used in transmission of RF signal uplink a. Magnetron b. Klystron c. BWO d. TWT

Questions 9. A stage in transponder and downlink system which amplifies the signal and ensuring that noise is suppressed as possible a. Mixer b. Demodulator c. LNA d. IF amplifier

Questions 10. A transponder is a satellite equipment which a. Receives a signal from earth station and amplifies it b. Changes the frequency of the received signal c. Retransmit the received signal d. All of the above

Questions 11. Multiple repeaters in communications satellites are known 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

Questions 13. The expression for satellite link frequencies such as 14/12 GHz denotes that a. 12 GHz is the uplink frequency and 14 GHz is the downlink frequency b. the system is operating at a mean frequency of 13 GHz c. 14 GHz is the uplink frequency and 12 GHz is the downlink frequency d. the 14 GHz frequency is backup for 12 GHz frequency or vice versa

Questions 14. The most widely used microwave bands for commercial 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

Questions 16. The required antenna size __________ as the operating frequency of a system increases, assuming that antenna gain remains unchanged. a. Remains the same b. Increases c. Decreases d. All of the above

Questions 17. A 20-m antenna gives a certain up-link gain at frequencies of 4/6 GHz. For getting the same gain in 20/30 GHz band, antenna size requires __________ meters. a. 100 b. 4 c. 1 d. 10

Questions 18. Orbital disturbances of a geosynchronous satellite are caused by a. Moon b. Sun c. Earth d. All of the above

Questions 19. Geosynchronous satellites a. Has the same period as that of the earth b. Has a circular obit c. Rotates in the equatorial plane d. All of the above

Questions 20. To cover all inhabited regions of the earth, the number of geosynchronous satellites required is a. 5 b. 10 c. 2 d. 3

Questions 21. A geostationary satellite is one which a. Hangs motionless in space about 36,000 km above the earth b. Travels around the earth about 24 hrs. c. Remains stationary above the earth d. Appears stationary above the earth

Questions 22. Geosynchronous Communication satellites travel around the earth in circular orbits with forward speed of about __________km/hr. a. 100,000 b. 36,000 c. 11,200 d. 22,800

Questions 23. The period of the satellite is a. The amount of time it takes for a satellite to complete one orbit b. The point on an orbit where satellite to complete one orbit c. The time it takes the satellite to travel from perigee to apogee d. An orbital arc that extends from 60 degrees west longitude to 145 degrees west longitude

Questions 24. 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 pass for 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 an orbit takes it over the north and south poles is in a. Inclined orbit b. Polar orbit c. Equatorial orbit d. Declined orbit

Questions 28. The farthest point a satellite can reach is a. Apogee b. Perigee c. Altitude d. Attitude

Questions 29. Include all earth stations within line-of-sight path of a satellite a. Satellite shadow b. Earth shadow c. Zonal d. Global

Questions 30. The different multiple accesses which permit many satellite users to operate in parallel through a. A Single Transponder Without Interfering With Each other are b. FDMA c. TDMA d. CDMA e. All of the above

Questions 31. A digital technology that uses a low power signal spread across a wide bandwidth. With this technology, a phone call is assigned a code instead of a certain frequency. Using identifying code and a low power signal, a large number of channels can used the entire bandwidth a. TDMA b. PCDMA c. PMA d. CDMA

Questions 32. The use of the same frequency on the same geographical area a. Frequency reuse b. Roaming c. Homing d. Cellular

Questions 33. In selecting a satellite system, the first determining factor is a. Coverage area b. EIRP c. Antenna size d. Antenna gain

Questions 34. The earth's area or region that the satellite can receive from or transmit to a. Footprint b. Skip zone c. Primary area d. Finger print

Questions 35. Satellite radiation pattern that covers 1/3 of the earth's surface a. Earth b. Zonal c. Spot d. Global

Questions 36. A satellite position is measured by its _________ angle with respect to the horizon. a. Elevation b. Depression c. Azimuth d. Incidence

Questions 37. The _________ angle measures the satellite position clockwise from the direction of true North a. Elevation b. Depression c. Azimuth d. Incidence

Questions 38. GPS has a total number satellites equal to a. 12 b. 24 c. 36 d. 48

Questions 39. How many elliptical orbits does Navstar GPS have? a. 5 b. 6 c. 7 d. 8

Questions 40. What is the free space attenuation of a satellite system operating at 36,000 km above the earth operating at 5 GHz? a. 180 dB b. 190 dB c. 198 dB d. 189 dB

Questions 41. The FDMA technique wherein voice band channels are assigned on “as needed" basis. a. PAMA b. DAMA c. SSMA d. CDMA

Questions 42. A satellite equipped with electronic devices to receive, amplify, convert, and retransmit signals. a. Passive b. Active c. Uplink d. Downlink

Questions 43. An earth station transmits signal to a satellite 38,500 km, directly overhead it. What is the propagation delay when the signal is received back at the same earth station, in milliseconds? a. 257 b. 200 c. 285 d. 185

Questions 44. A satellite communication link between Pinugay Earth Station, Philippines and Mt. Fucino Earth Station, Italy is to be established. If the assigned uplink frequency at Pinugay Earth Station is 6175 MHz, what is the downlink frequency at Mt. Fucino Earth Station, in MHz? a. 4545 b. 3950 c. 3789 d. 4200

Questions 45. "The orbit of any planet is an ellipse with the sun at one focus". This is a. Kepler's First Law b. Kepler's Second Law c. Kepler's Third Law d. Law of universal Gravitation

Questions 46. When a satellite orbits in the opposite direction as the earth's rotation with an angular velocity less than that of the earth a. Orbital b. Prograde c. Retrograde d. Geostationary

Questions 47. The actual user information conveyed through the satellite system a. Bus transmission b. Payload c. Prograde d. Retrograde

Questions 48. The spatial separation between geosynchronous satellites a. 1-3 degrees b. 3-6 degrees c. 6-8 degrees d. 8-10 degrees

Questions 49. The footprint which covers a very small geographical area. a. Spot coverage b. Zonal coverage c. Earth coverage d. Regional coverage

Questions 50. The satellite frequency reuse method which sends different information signals using vertical or horizontal electromagnetic polarization a. Multiple coverage areas b. Dual polarization c. Spatial separation d. Spread spectrum

Questions 51. __________ detects the satellite signal relayed from the feed and converts it to an electric current, amplifies and lower its frequency. a. Feedhorn b. Satellite dish c. Satellite receiver d. LNA

Questions 52. Satellites used for intercontinental communications are known as a. Comsat b. Domsat c. Marisat d. Intelsat

Questions 53. What is the basic function of a communications satellite? a. To act as a receiving antenna for broadcast FM b. To compensate for the antenna limitations c. To eliminate aerodynamic drag d. To act as a receiving antenna for broadcast AM

Questions 54. What do you call of a satellite used to provide satellite services within a single country? a. Orbital satellite b. Geostationary satellite c. Non-synchronous satellite d. Domestic satellite

Questions 55. A satellite beam that covers almost 42.5% of the earth's surface. a. Zone beam b. Hemispheric beam c. Spot beam d. Global beam

Questions 56. The first Philippine satellite has how many channels? a. 30 b. 24 c. 48 d. 50

Questions 57. Aguila I has how many transponders? a. 36 b. 48 c. 24 d. 12

Questions 58. How many satellite orbital slots were requested by the Philippine Government from ITU? a. 2 b. 4 c. 6 d. 8

Questions 59. The most common device used as an LNA is a. Zener diode b. Tunnel diode c. IMPATT diode d. Shockley diode

Questions 60. The radiation patterns of earth coverage antennas have a beamwidth of approximately a. 21degrees b. 5 degrees c. 17 degrees d. 35 degrees

Questions 61. The main power sources for satellites are a. Batteries b. Solar cells c. Fuel cells d. Thermoelectric generators

Questions 62. What is the common upconverter and down-converter IF? a. 36 MHz b. 40 MHz c. 70 MHz d. 500 MHz

Questions 63. When the satellites are spaced 4 degrees of the 360 degrees complete circle, how many parking spaces or orbit slots are available? a. 90 b. 85 c. 95 d. 80

Questions 64. The first satellite launched for a geosynchronous orbit but unfortunately lost during orbit injection. a. Syncom I b. Telstar I c. Sputnik I d. Early Bird

Questions 65. Geostationary satellites are located _______ with respect to the equator. a. 0 deg longitude b. 0 deg latitude c. 90 deg latitude d. 45 deg latitude

Questions 66. Incidentally proposed the geostationary scheme or orbit of satellites in 1940's. a. Clarke b. Gauss c. Morse d. Gray

Questions 67. The control routine necessary to keep the satellite in position is referred to as a. Station keeping b. Station tracking c. Station monitoring d. Station maintenance

Questions 68. A satellite which simply reflects the signal without further amplification. a. Passive b. Active c. Geostationary d. Posigrade

Questions 69. What is the line joining the ascending and descending nodes through 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 the perigee and apogee through the center of the earth. a. Line of sight b. Line of nodes c. Equatorial belt d. Line of apsides

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