ND SatCom SKYWAN IDU 7000, Manual

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2010-10-26 Network Design and Engineering Guide 103
Outdoor Unit and Satellite Link Design
Link Budget Examples
Link Budget Calculation Result Analysis
- Modulation and coding of both carriers is limited by the earth station in Casablanca which
is located in a weaker part of the satellite footprint. Any increase of modulation and coding
on carrier 1 and carrier 2 would increase the power requirement in Casablanca beyond
30 W.
- The network is not using the full power of the satellite transponder. On both carriers the
PEB is less than 1/3 of the carrier bandwidth.
Conclusion
To further optimize the network, the earth station EIRP
max
, especially on the Casablanca sta-
tion, must be increased by
- either using higher power classes for the amplifiers or
- larger antennas.
This increases the hardware cost of the station but saves transponder bandwidth by allowing
higher modulation and FEC coding factors. An economic analysis has to take into account that
hardware cost is a one-time item, whereas transponder bandwidth is a recurring cost which has
to be paid for the whole operation time of the network.
Another option to decrease the earth station power requirement would be to split the network
capacity into more than 2 carriers. For small networks this may however cause inefficiencies if
too few stations are sharing a carrier leading to a smaller statistical multiplexing gain.
The applications may also prevent further splitting of the bandwidth: If an application requires
a high bandwidth data stream (e.g. high quality video streaming) this may not be transported
over multiple carriers.
Before looking into the effects of ODU optimization in the next scenario 2 a slightly different
network is considered.
3.6.2 Scenario 2: Ku-Band 5 Stations Star Network with 2 Hubs
If the network traffic is mainly between hub and remote stations with only negligible traffic be-
tween remotes a fully meshed network may not be necessary.
We consider now that the 5 station network is a star network with hub stations in Madrid and
Berlin and remote stations in Rome, Casablanca and Tunis. If the topology parameter for car-
rier 2 on the summary sheet is changed from ’Mesh in ULA1’ to ’Star in ULA1’ only satellite links
from Rome, Casablanca and Tunis to the hub stations are calculated.
Note that the hub stations themselves are still operating fully meshed, i.e. links to all stations
are calculated for them. In this star network the “weak” remote stations do not transmit anymore
on carrier 2.