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����PRESENTATION ON �SATELLITE ELEVATION,VSAT

  • BRANCH-E & TC ENGG
  • SUBJECT- ADVANCE COMMUNICATION ENGINEERING
  • CHAPTER – 2 - SATELLITE COMMUNICATION
  • TOPIC- SATELLITE ELEVATION,VSAT
  • SEM-6TH
  • FACULTY – Er. UMASHANKAR PANDA(Sr. LECT. E & TC ENGG DEPARTMENT)
  • AY-2021-2022, SUMMER-2022

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Overview

  • Satellite 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.

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  • Satellite up links and down links can operate in different frequency bands:

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  • The up-link is a highly directional, point to point link
  • The down-link can have a footprint providing coverage for a substantial area "spot beam“.

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Band

Up-Link (Ghz)

Down-link (Ghz)

ISSUES

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C

4

6

Interference with ground links.

Ku

11

14

Attenuation due to rain

Ka

20

30

High Equipment cost

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Orbits:

  • LEO: Low Earth Orbit.
  • MEO: Medium Earth Orbit
  • GEO: Geostationary Earth Orbit

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  • At the Geostationary orbit the satellite covers 42.2% of the earth’s surface.
  • Theoretically 3 geostaionary satellites provides 100% earth coverage

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MAC(Media Access Control) � protocols for satellite links

  • ALOHA:
      • Every station can transmit any time
      • Very low efficiency 18- 36 %.
  • FDMA (Frequency Division Multiple Access)
      • It is the oldest and most common.
      • the available satellite channel bandwidth is broken into frequency bands for different earth stations.

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  • TDMA (Time Division Multiple Access)
      • channels are time multiplexed sequentially
      • Each earth station gets to transmit in a fixed time slot only.
      • More than one time slot can be assigned to stations with more bandwidth requirements.
      • Requires time synchronization between the Earth Stations.
  • CDMA : (Code Division Multiple Access)
      • Combination of time/frequency multiplexing

( a form of spread spectrum modulation).

      • It provides a decentralized way of providing separate channels without timing synchronization. It is a relatively new scheme but is expected to be more common in future satellites.

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VSAT Network

  • At the Very Small Aperture Terminal a lower performance microwave transceiver and lower gain dish antenna (smaller size) is used.

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  • VSAT networks are arranged in a star based topology.

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  • Ideal for centralized networks with a central host (Banking institutions with branches all over the country).

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  • Use the S-ALOHA and TDMA

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DirecPC services:

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  • One of the most useful applications of VSAT networks
  • Comes with an ISA computer card, a RF dish antenna (2 ft dia) equipped with an LNA, and supporting software.

Supporting two kinds of services

  1. Digital Package Delivery
  2. Turbo Internet

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  1. Digital Package Delivery�
  • downloading files at a speed 100 times faster than that supported by public telephone network.

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  • Large files can be received by multiple DirecPC end points.

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  • The download requests are made using the standard analog modem over telephone lines.

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  1. Turbo Internet�
  • The end user overcomes the telephone line barrier and is capable of receiving data at 400 kbps.
  • A connection is setup with the local ISP (internet server provider) using the analog telephone line modem.
  • All mouse and keyboard actions in the web browser are communicated to the web server on the other end using this link.

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THANK YOU