Path: utzoo!attcan!uunet!know!zaphod.mps.ohio-state.edu!rpi!bu.edu!buit13!kwe
From: kwe@buit13.bu.edu (Kent England)
Newsgroups: comp.dcom.lans
Subject: Re: Motorola wireless lan?
Summary: This is spread spectrum technology
Message-ID: <67070@bu.edu.bu.edu>
Date: 25 Oct 90 14:23:23 GMT
References: <418@bartal.CRLABS.COM>
Sender: news@bu.edu.bu.edu
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston U. Information Technology
Lines: 45

In article <418@bartal.CRLABS.COM> phillip@bartal.crlabs.com
 (Phillip M. Vogel) writes:
>
>---begin unauthorized quote from WSJ---
> "....a new method for sending data within buildings using
>digital radio transmission......based on several components,
>including an omnidirectional antenna, a miniaturized digital
>transmitter and receiver

	You are describing one of several varieties of wireless LAN
technology that will be coming to market in the near future.  Unlike
older technologies that sent radio signals on power lines or used
infrared, these new technologies are based on a type of radio
modulation invented many years ago for the military: spread spectrum
technology.

	Spread spectrum involves spreading a "narrow" bandwidth signal
across a much larger spectrum using pseudo-random number sequences
known to both transmitter and receiver.  The spectrum spreading
improves signal to noise dramatically (if done right) in the presence
of multi-path, which is a severe problem at these frequencies in the
steel-lattice buildings most of us work in.

	But beware of corner cutting vendors whose spectrum spreading
is just within FCC definitions.  Not all implementations are created
equal.  Look for at least 10:1 spreading.  More is better, but costly.

	You still have to install wire and repeater units, so you
don't get rid of upfront costs altogether.  What you will eliminate is
the necessity of "installing" new nodes.  The headache you get, of
course, is you will have to look to find out who is using your radio
LAN and you won't know til you look how crowded it is getting.

	And like cellular phones, the spectrum will get crowded and
will be regulated eventually, so your systems are somewhat vulnerable
to future interference.  Remember the early cordless phones?

	I think we will have to build a lot of these systems before we
can find out how many of these wireless LANs can share the same
bandwidth space before the noise floor gets too high.  Does anyone
have an test data for how many wireless LANs can co-exist
independently in the ether?

	--Kent England
	  Boston University