Moble Communication

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Text of Moble Communication

  • 1. Mobile Communication Solutions for Test 2 Prof. Suthikshn Kumar

2. Part A Q 1

  • What is the distance of the GEO satellites from earths surface?
  • What is footprint of a satellite?
  • Define elevation angle of a satellite.
  • Why satellites cannot be placed in Van-Allen radiation belts?
  • What is the altitude of LEO satellites?
  • Calculate the latency of signal for GEO satellite.
  • Name one advantage of LEO satellite systems.
  • Name one disadvantage of MEO satellite Systems.
  • What is Iridium?
  • What is ISL?

3. Part A Q1 Answers:

  • GEO is 35,786KM
  • Each satellite can cover a certain area on earth with its beam called footprint.
  • Elevation angle is defined as the angle between the center of the satellite beam and the plane tangential to the earths surface.
  • Van Allen Radiation belts consists of ionized particles, at heights of about 2000-6000 km and about 15,000-30,000 Km make satellite communication very difficult in these orbits.
  • LEO satellites have altitudes in the range of 500-1500Km
  • 35,786 / 3,00,000 = 120ms RTT = 240ms
  • Advantages of LEO: Low transmit power, higher bandwidth, low delay, smaller footprint, better reuse of frequency, better global coverage.
  • Disadvantage of MEO: Increased delay ( 70-80ms), high transmit power, require special antennas for smaller footprints.
  • Iridium system is a constellation of 77 satellites ( Iridium atom has 77 electrons) for Global satellite communication.
  • ISL is Intersatellite Links with which satellites can communicate directly with each other.

4. Part A Q2

    • What is SUMR?
    • What is Gateway Handover?
    • Name one advantage of MEO Satellite System.
    • Name One Disadvantage of LEO satellite System.
    • Name one advantage of ISL.
    • Define Inclination angle of a satellite.
    • What is GPS?
    • Give an equation which can be used for calculating distance of the satellite from the earth using its frequency of rotation.
    • Name one advantage of GEO satellite system.
    • Name one disadvantage of GEO satellite system.

5. Part A Q2: Answers

    • SUMR: Satellite User Mapping Register stores current position of satellites and mapping of each user to the current satellite through which communication with a user is possible.
    • Gateway Handover: While the mobile user and satellite might still have good contact, the satellite might mover away from the current gateway. The satellite has to connect to another gateway.
    • Advantage of MEO Satellite System: Requires less number of satellites ( around 12) to give global coverage, Simpler system design due to slow moving satellites, MEO can cover larger populations, requires fewer handovers.
    • Disadvantage of LEO satellite System: Requires large number of satellites ( 50-200) for global coverage, Short time of visibility requires more handover, High complexity, Short lifetime of satellites, Requires routing of data packets from satellite to satellite.
    • Advantage of ISL: Reduces delay, reduces the number of gateways needed on earth.

6. Answer Part A Q2

    • 6. Define Inclination angle of a satellite: is defined as the angle between equatorial plane and the plane described by the satellite orbit.
    • 7. GPS stands for Global Positioning System used for precise localization worldwide.
    • 8. An equation which can be used for calculating distance of the satellite from the earth using its frequency of rotation.
    • 9.Advantage of GEO satellite system: Three GEO satellites are enough for global coverage, Senders and receivers can use fixed antenna positions, Life time expectation of GEOs are high, GEOs dont need any handover, GEOS dont exhibit any Doppler shift.
    • 10. Disadvantage of GEO satellite system: Northern or southern regions of the earth have more problems due to low elevation angle. Shading of signals in cities due to high buildings, Transmission power needed is high, High latency of .25 s. Large footprints mean frequencies cannot be reused.

7. Part B Q3

  • What is Asymmetrical communication system?
  • What is symmetrical Communication system?
  • What is broadcast disk?
  • What is flat disk and skewed disk?
  • What is Single Freqency Networks (SFN)?
  • What is DAB ensemble?
  • What is Program Associated data?
  • Which modulation technique is used in DAB?
  • What are the advantages of DAB?
  • What is the function of Fast Information Channel ( FIC) in DAB?

8. Answers: Part B Q3

  • Asymmetrical communication system: Unidirectional distribution systems or broadcast systems where tycpically a high bandwidth data stream exists from one sender to many receivers.
  • Symmetrical Communication system offer the same transmission capabilities in both communication directions.
  • Broadcast disk refers to cyclical repetition of data blocks sent via broadcast.
  • Flat disk : is a broadcast disk with all blocks are repeated one after another, every block is transmitted for an equal amount of time, average waiting time is same for all the blocks.Skewed disk favor one or more data blocks by repeating them once orseveral times.
  • Single Freqency Networks (SFN): DAB uses SFN where all senders transmitting the same radio program operate at the same freqeuncy.
  • .

9. Answers: Part B Q3

  • 6. DAB ensemble: With every frequency block of 1.5MHz, DAB can transmit up to six stereo audio programmes with a data rate of 192 kbits/s each. The DAB ensemble may consist of six radio programs and two data channels.
  • 7. Program Associated data: PAD is the information accompanying an audio stream. It may contain program information, still pictures for display on a small LCD, title display etc.
  • 8. Modulation techniqueused in DAB: DQPSK
  • 9. Advantages of DAB: CD-like audio quality, immune to interference and multipath propagation effects.
  • 10. Function of Fast Information Channel ( FIC) in DAB: FIC carries all control information required for interpreting the configuration and content of the MSC

10. Part B Q4

  • What is the problem addressed by Multimedia Object Transfer Protocol?
  • Name some of the formats supported by MOT.
  • What is Multiprotocol Encapsulation?
  • Draw the block diagram of DAB sender?
  • What is OFDM?
  • What is the advantage of OFDM?
  • How DVB can be used for High speed internet access?
  • What are interaction channels?
  • What is a data carousel?
  • What are the bandwidths and data rates of DAB and DVB?

11. Answers: Part B Q4

  • The problem addressed by Multimedia Object Transfer Protocol is the broad range of DAB receiver capabilities such as simple audio-only devices with single line text displays or more advanced radios with extra color graphics displays or multimedia PCs. All DAB receivers should atleast be able to recognize all program associated dataand process some of it.
  • Some of the formats supported by MOT: MHEG, JPEG, ASCII, MPEG, HTML, HTTP, BMP, GIF
  • Multiprotocol Encapsulation: Transport of arbitrary data network protocols on top of the MPEG-2 transport stream;optimized for IP, support for 48 bit MAC addresses, unicast, multi-cast and broadcast.
  • Block diagram of DAB sender ( see next Slide)
  • OFDM: Orthogonal Frequency Division Multiplexing :Parallel data transmission on several orthogonal subcarriers with lower rate

12. Answers Part BQ4

  • 6.The advantage of OFDM: no equalizer necessary,no expensive filters with sharp edges necessary, better spectral efficiency (compared to CDM)
  • 7. DVB can be used for High speed internet access: See next slide
  • 8. Interaction channels:Through GSM, UMTS, user interaction is added to DAB, DVB.
  • 9. Data carousel: Also Broadcast disk, periodic transmission of data.
  • 10. The bandwidths and data rates of DAB are 1.5MHz and 1.5Mbps. The DVB has bandwidth of 8MHz and data rate of 5-30Mbps

13. DAB sender Trans- mitter Trans- mission Multi- plexer MSC Multi- plexer ODFM Packet Mux Channel Coder Audio Encoder Channel Coder DAB Signal ServiceInformation FIC Multiplex Information Data Services Audio Services Radio Frequency FIC: Fast Information Channel MSC: Main Service Channel OFDM: Orthogonal Frequency Division Multiplexing 1.5 MHz f carriers 14. DVB forhigh-speed Internet access

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