ND SatCom SKYWAN IDU 1070, Manual

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82 Network Design and Engineering Guide 2010-10-26
Outdoor Unit and Satellite Link Design
Considerations for SkyWAN
®
Link Budget Calculations
Figure 3-8 Power Conditions with Uplink Power Control
Note that a further reduction to the minimum power requirement for clear sky conditions X
T
is
possible but unnecessary.
This functionality is generally called “Uplink Power Control (UPC)” and is implemented in Sky-
WAN
®
networks as the built-in automatic Transmission Power Control (TPC). Generally the
power requirement for the satellite transponder including rain margin is given by:
With UPC: EIRP
S
= EIRP
S,clear Sky
+ Downlink rain fade
Without UPC: EIRP
S
= EIRP
S,clear Sky
+ Downlink rain fade + Uplink rain fade
Note that the power requirement for the transmitting earth station is not affected by UPC, but
is always given by:
EIRP
T
= EIRP
T,clear Sky
+ Downlink rain fade + Uplink rain fade
3.4 Considerations for SkyWAN
®
Link Budget Calcu-
lations
3.4.1 Network Topology
So far we have considered satellite links which include a transmitting and a receiving earth sta-
tion using a specific satellite transponder. Most widely used link budget tools actually are de-
signed for such point-to-point links, where each station uses a dedicated carrier to reach
another station. In
Sky WAN
®
networks however, we have to take into account the following
specific points:
- A Sky WAN
®
station in a meshed network communicates not only with one remote station
but with up to 509 remote stations.
- A Sky WAN
®
carrier is typically not only used by a single station but by a whole group of
stations.
- A Sky WAN
®
station may use not only one carrier but different carriers which may be locat-
ed on different transponders on a satellite.
To calculate the power requirement for a Sky WAN
®
earth station, the individual power require-