The satellites that make up the system
are located on a number of orbital planes, which are
equally distributed along a common axis that passes
through the centre of the earth.
Inclination:
It is the angle formed by the
intersection of an orbital plane with the equator. It can
vary from zero (equator) to ninety degrees (polar orbit).
Period:
Time it takes a satellite to travel an
entire orbit.
Average satellite visibility time:
Time in which it is possible to see a
satellite from a fixed point on earth.
Minimum elevation angle of the terminal:
Angle formed by the earth's surface and
by the imaginary conductor that unites the mobile terminal
to the satellite.
Single delay:
Propogation time needed for the radio
signal to reach the satellite from the mobile terminal or
vice versa.To obtain the complete delay (round trip), you
must double this value.
Number of Gateways on Earth:
Number of land radio stations which,
through the satellite links, are responsible of
interfacing mobile terminals with the terrestrial
telephone network.
Voice:
Speed used for conversation transmission.
Data:
Speed used for data and fax transmission.
Number of Voice Circuits per satellite:
Number of conversations that a
satellite can maintain simultaneously. (To be evaluated
together with the diametre of the beam).
Dual-Mode Terminals:
Network predisposed to the use of
dual-mode terminals, capable of using a terrestrial
cellular network and a satellite network alternatively
based upon the radio coverage and the roaming agreements.
Beams per satellite:
Number of radio signals transmitted
simultaneously to each satellite of the constellation.
Beams per satellite:
Number of radio signals transmitted
through directional antennas used by every satellite in
the constellation.
Diametre of one beam:
Diametre of the radio signal
transmitted from every directional antenna.
Diametre of the footprint:
Diametre of the area on the earth's
surface covered by each satellite.
Types of cells:
Mobiles: Radio cells move
together with the constellation, with respect to the
earth's surface. Fixed: Radio cells are fixed on the earth's surface
even if the constellation is rotating.
On Board Processing:
On board the satellite there are
computers that communicate with the other satellites. This
makes it possible to carry on a conversation between two
subscribers who find themselves connected to different
satellites, without passing through the terrestrial
gateways.
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