Re: Satellite Bandwidth Questions

[Andreas Voigt <[e-mail]>]

> Hi-
> I am studying TCP over Satellite considerations and have reviewed
> draft-ietf-tcpsat-stand-mech-06.txt. I live in a "bits per second" world in
> terms of bandwidth I would like to understand how bps relates to the terms
> used to describe satellite bandwidth. So is there a reference somewhere or
> good book on satellite basics that can fill in the following terms:
>
> Band     Uplink (GHZ)    Downlink (GHz)    Uplink (bps)    Downlink (bps)
>
> C            6              4                 ??               ??
>
> Ku           14             12                ??               ??
>
> Ka           30             20                ??               ??
>
> I suppose I am asking how does one convert MHz and GHz into conventional
> bandwidth (bps) terminology. This for clearing this up for me and my
> apologies for the "simpleton" question.
>
> Chris Metz
> Consulting Systems Engineer
> Cisco Systems
> email: [e-mail]
> phone: [phone]
> pager: 800-365-4578

Hi Chris,

how are you doing? I hope everything is going well.

Concerning the Satellite application, unfortunately, you can't specify a
velocity in the range of several kbps to several hundreds of Mbps directly
while regarding the frequency band.

It depends, more or less, on the Bandwidth you have available on the satellite
transponder, which does not make any difference to throughput by using C-, Ku-
or Ka-Band. Concerning cost and availability, it does, but that is not the
question here. If the satellite is not a regenerative one like some Txps of
ACTS or the Txps of the Skyplex System of EUTELSAT, Up- and Downlink are the
same Signal (hopefully :-) ), so Up- and Downlink are considered to have the
same velocity.

For example:

You have 20 MHz available and you are using plain QPSK Modulation with Viterbi
1/2 Encoding. Then you will be able, depending on the correct Linkbudget, to
transmit and receive a 20 Mbps Carrier, on which you can play with the TCP
enhancements to increase throughput. It does not make a difference if this
carrier is distributed in C-, Ku- or Ka-Band.

So, i.e., the more bandwidth you have, the more maximum theoretical throughput
you get. The transponders with the highest bandwidth of GEO satellites on the
world are the Ka-Band ones of ACTS, but how ever, tests can be carried out on
smaller ones in Ku- or C-Band as well. Regard also the fact of the Ka-Band
availability problem in the linkbudget due to rain in comparison with Ku- and
ecspecially C-Band!

I hope I have been able to help you with this question.

Kind regards,

Andreas Voigt
GMD - German National Research Center for Information Technology
Dep. Networking - Satellite Communications



Kind regrad