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:[email protected]] 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: [email protected]
phone: 212-714-4207
pager: 800-365-4578
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