EEE 4283 Radar and Satellite Communication
❖Satellite Communication:
Overview of Satellite System Engineering. Spacecraft,
Introduction to Spacecraft Subsystem. (AOCS), Telemetry,
Tracking and command (TT&C). Spacecraft Antennas, Basic
Antenna Types and Relationships Spacecraft, Antennas in
Practice, Frequency Reuse Equipment Reliability and Space
Qualification, Reliability redundancy. Multiple Access. Earth
station Technology : Earth Station Design, Earth Station
Design for Low System Noise Temperature, Large Earth
Station Antennas. Satellite Television Broadcasting Networks,
VSAT technology.
Text Books
❑Satellite Communication- Denis Rody
❑Satellite Communication- D. C. Agarwal
❑Introduction to Satellite Communication- Bruce R.
Elbert
❑Satellite Communication Engineering- Michael O.
Kolawole
❑ Digital Satellite Communication- Tri. T. Ha
Earth Station Technology:
Earth station is a vital element in any satellite
communication network. The function of an earth station
is to receive information from or transmit information to,
the satellite network in the most cost-effective and reliable
manner while retaining the desired signal quality.
The design of earth station configuration depends upon many
factors and its location. But it is fundamentally governed by its
Location which are listed below,
• In land
• On a ship at sea
• Onboard aircraft
The factors are
• Type of services
• Frequency bands used
• Function of the transmitter
• Function of the receiver
• Antenna characteristics
Any earth station consists of four major subsystems
• Transmitter
• Receiver
• Antenna
• Tracking equipment
The earth segment of a satellite communications system
consists of the transmit and receive earth stations. The
simplest of these are the home TV receive-only
(TVRO) systems, and the most complex are the terminal
stations used for international communications
networks. Also included in the earth segment are those
stations which are on ships at sea, and commercial and
military land and aeronautical mobile stations.
Earth stations that are used for logistic support of
satellites, such as providing the telemetry, tracking, and
command (TT&C) functions.
Two other important subsystems are
• Terrestrial interface equipment
• Power supply
The earth station depends on the following parameters
• Transmitter power
• Choice of frequency
• Gain of antenna
• Antenna efficiency
• Antenna pointing accuracy
• Noise temperature
The functional elements of a basic digital earth station are shown in
the below figure: (Transmitter/ Receiver)
• Digital information in the form of binary digits from
terrestrial networks enters earth station and is then
processed (filtered, multiplexed, formatted etc.) by the
base band equipment.
• The encoder performs error correction coding to reduce
the error rate, by introducing extra digits into digital
stream generated by the base band equipment. The extra
digits carry information.
• In satellite communication, I.F carrier frequency is
chosen at 70 MHz for communication using a 36 MHz
transponder bandwidth and at 140 MHz for a transponder
bandwidth of 54 or 72 MHz.
• On the receive side, the earth station antenna receives the low-level
modulated R.F carrier in the downlink frequency spectrum.
• The low noise amplifier (LNA) is used to amplify the weak received
signals and improve the signal to Noise ratio (SNR). The error rate
requirements can be met more easily.
• R.F is to be reconverted to I.F at 70 or 140 MHz because it is easier
design a demodulation to work at these frequencies than 4 or 12 GHz.
• The demodulator estimate which of the possible symbols was
transmitted based on observation of the received if carrier.
• The decoder performs a function opposite that of the encoder. Because
the sequence of symbols recovered by the demodulator may contain
errors, the decoder must use the uniqueness of the redundant digits
introduced by the encoder to correct the errors and recover information-
bearing digits.
• The information stream is fed to the base-band equipment for processing
for delivery to the terrestrial network.
• The tracking equipments track the satellite and align the beam
towards it to facilitate communication.
INTELSAT:
INTELSAT stands for International
Telecommunications Satellite. The organization was
created in 1964 and currently has over 140 member
countries and more than 40 investing entities (see
http://www.intelsat.com/ for more details). In July 2001
INTELSAT became a private company and in May 2002
the company began providing end-to-end solutions
through a network of teleports, leased fiber, and points of
presence (PoPs) around the globe. Starting with the Early
Bird satellite in 1965, a succession of satellites has been
launched at intervals of a few years.
It may be noted that geostationary satellites orbit in the
earth’s equatorial plane and their position is specified by
their longitude. For international traffic, INTELSAT
covers three main regions—
the Atlantic Ocean Region (AOR),
the Indian Ocean Region (IOR),
the Pacific Ocean Region (POR) and what is termed
Intelsat America’s Region. For the ocean regions the
satellites are positioned in geostationary orbit above the
particular ocean, where they provide a transoceanic
telecommunications route.
