ND SatCom SKYWAN IDU 7000, Руководство пользователя

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74 Network Design and Engineering Guide 2010-10-26
Outdoor Unit and Satellite Link Design
Satellite Beam Footprints
Calculate Link Budget
The satellite transponder parameters together with the results of the TDMA calculation (TDMA
carrier modem rates, modulation and channel codings ) allow the calculation of the satellite link
budget. The result of this calculation determines the required ODU equipment: Antenna sizes
and amplifier power classes.
Perform Optimization
It is possible that the result of the link budget calculation requires very large antenna sizes or
high power classes for the amplifiers. In this case it might be necessary to go back to the carrier
design and to reduce power requirements by e.g. splitting the necessary bandwidth to more
carriers or changing the channel coding.
3.2 Satellite Beam Footprints
The first selection criteria for a satellite transponder is that its beam covers the area where the
earth stations are located. Typically two types of beams are available:
-
Wide beams (“global” or “hemispherical”) which cover a wide geographical area potentially
including multiple continents.
- Spot beams which cover a restricted geographical area with a diameter of typically ~ 2000-
3000 km.
Wide beams are typically available in the C-Band frequency band (uplink frequency ~ 5 GHz).
The advantage of this type of beam is that it supports networks with earth stations spread over
large geographical areas. The disadvantage is that the beam intensity is relatively low, as the
limited signal power available for a transponder on the satellite is dispersed over a large area.
Spot beams which are mainly available in the Ku-Band (uplink frequency ~ 14 GHz) offer a
higher beam intensity as their signal power is focused to a smaller area. The higher intensity
of the satellite signal allows a more compact design of the earth stations (smaller antenna sizes
and lower power level of the amplifiers) which reduces the earth station’s hardware cost.
Figure 3-2 SES World Skies NSS-7 Satellite Wide Beam Footprints