RE: Satellite Bandwidth Questions

["Brooker, Ralph" <[e-mail]>]

     Chris,
     The "GHZ" numbers you mention are shorthand for the allocated band 
     pair (up/down) used by the satellite, and have no direct 
     relationship to the bandwidth of the channel.
     
     On "conventional" (geostationary, bent-pipe) satellites, one rents 
     the amount of bandwidth needed to transmit the desired signal(s), 
     typically from 100 kHz up to 36-72 MHz.
     
     The bandwidth in kHz of a signal is proportional to the data rate 
     in bps and depends on the type of modulation (BPSK/QPSK) and the 
     parameters of the forward error correction.  Signals using 
     band-limited QPSK modulation and Rate 3/4 convolutional encoding 
     plus Reed-Solomon outer block coding require approximately 1.1 Hz 
     per bps.  This is usually the best selection of parameters for low 
     BER links (as required for TCP), but in some circumstances, to 
     minimize satellite cost, reduce modem cost, and/or to enable the 
     use of smaller antennas, other parameters might be better, 
     resulting in anywhere from 0.5 to 2 Hz per bps.  For a symmetric 
     two-way point-to-point link, multiply by two; for other carrier 
     configurations, add up all the signals needed to form the network.
     
     Ralph Brooker
     Andrew Corp.


______________________________ Reply Separator
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Subject: Satellite Bandwidth Questions
Author:  "Chris Metz" [SMTP:[e-mail]] at AOP
Date:    12/29/98 10:49 AM


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