I read with interest the assertion that satellite links may be
"engineered" to give a BER of 10-9... Sure they can, the ways of
doing this are either lowering the bit rate (through FEC) or/and by
increasing the received energy per bit (i.e. utilising more
satellite transmit power). Both of these approaches are valid for
high bit rate systems > 4 Mbps, say, but for lower bit rate systems,
it may be the wrong solution, and providing error control techniques
in some way from the protocol is a very sound approach, providing it
is transparent enougth to TCP (Hmmmm.... this is tricky)
Consider for example, the power budget required to overcome
interference from a noise source close to a satellite terminal, or
the potential for the satellite terminal to be obscured partially
(a friendly bird perched on the antenna feed?). If one chooses
to only optimise the bearer network by providing an error-free physical
transmission path, then that's one way of building of network,
it is certainly NOT the only way.
Is the group interested in 2 Mbps and lower data rates too?
Gorry Fairhurst
Communication Group,
Dept Engineering
University of Aberdeen.
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