[621] in Commercialization & Privatization of the Internet
Perhaps dismissal of packet radio in the classroom is unwarranted
daemon@ATHENA.MIT.EDU (Brian Lloyd)
Wed Apr 24 14:00:32 1991
Date: Wed, 24 Apr 91 10:55:02 PDT
From: Brian Lloyd <brian@napa.telebit.COM>
To: jhaverty@us.oracle.com
Cc: tmn!cook@uunet.UU.NET, com-priv@psi.com
In-Reply-To: Jack Haverty's message of Wed, 24 Apr 91 09:10:18 PDT <9104241610.AA08565@rivendell.us.oracle.com>
Reply-To: brian@napa.telebit.COM
One interesting question is how many of these radio links can be
simultaneously in use within the same 1/4 mile radius.
Each pair of communicating radio use a different spreading sequence.
If you have the wrong sequence when you try to decode the other signal
you only see an increase in background noise (because the energy
from the transmitter is "spread" over a wide chunk of spectrum). If
you have the correct sequence the transmitted signal is correlated and
out pops the signal you are looking for. Pretty neat stuff actually.
As for how many links, that is a function of the necessary
carrier-to-noise ratio. Each transmitter spews out a signal that
appears as additional noise in a noncorrelated receiver's passband.
The more transmitters you have, the more noise appears. The answer is
a function of proximity more than anything else. If you are trying to
do point-to-point in the same room you can squeeze a lot of these into
the same general area. If you are trying to do central-site to
classroom you may have more difficulty because the transmitter in the
next class may raise your noise floor so much that you can't hear the
central site.
Bottom line is this: get a wire, it is much simpler and cheaper. (I
can't believe that a radio-head like me just said that :-).
Brian Lloyd, WB6RQN Telebit Corporation
Network Systems Architect 1315 Chesapeake Terrace
brian@napa.telebit.com Sunnyvale, CA 94089-1100
voice (408) 745-3103 FAX (408) 734-3333
