Subject: [NEXTEL-1] Avoiding Interference Surprises in Unlicensed Spread Spectrum Deployment

From: [email-masked]
Date: Wed, 28 Apr 2004 19:36:38 -0400

Avoiding Interference Surprises in Unlicensed Spread Spectrum Deployment

By F.H. “Rick” Smith
ChevronTexaco

April 2004

Unlicensed spread spectrum systems are easy to engineer.
You select equipment with the right features, look at a
simple table to see what kind of antennas you need to cover
a specified distance, and you are done. Can it be that simple?

Yes and no. Many people have successfully engineered
unlicensed systems just this way. Most of those systems
are working just fine, yet an increasing number of systems
are becoming partially, or fully, debilitated as the result of
interference from other new systems.

There are two parts to engineering any radio system. The first
part is to make sure you have enough signal to make the system
talk. This is often handled very simply in the case of unlicensed
spread spectrum systems by using a look up chart and a general
disclaimer that line of sight is assumed.

The second part is an interference analysis. This is often skipped
in the case of unlicensed spread spectrum systems, resulting in
interference surprises that could have been avoided.

The Illusion of Simplicity

Why is the interference analysis aspect of unlicensed spread
spectrum system engineering often overlooked? There are at
least two reasons.

First, vendors do not want to undermine the image of simplicity that
accompanies unlicensed products, and often point to the partial truth
that the spread spectrum technology solves interference problems.

The second reason is that the equipment designs invariably provide
some form of data packetization and retransmission process that will,
most of the time, redo particular transmissions when necessary so that
the user’s data goes through.

This leaves you, the user, in a life of luxury, not unlike the rock star

who’s manager keeps the champagne and caviar flowing, meanwhile
the bank account may be nearing a zero balance.

As we start looking at the interference side of unlicensed spread
spectrum engineering, we realize that the issue isn’t whether or not you are
hearing your neighbors, but rather can you talk over the top of them, or even
sneak a transmission by when they are not talking.

Your position of security rapidly erodes as you slip from a position of
RF dominance over all the subject frequencies all the time, to dominance
over all the frequencies some of the time, to some of the frequencies some of
the time, to essentially none of the frequencies most the time.

http://www.ita-relay.com/magazine/PW2004/April2004/RickSmith.pdf

------------------------ Yahoo! Groups Sponsor ---------------------~-->
Buy Ink Cartridges or Refill Kits for your HP, Epson, Canon or Lexmark
Printer at MyInks.com.  Free s/h on orders $50 or more to the US & Canada.
http://www.c1tracking.com/l.asp?cid=5511
http://us.click.yahoo.com/mOAaAA/3exGAA/qnsNAA/61FxlB/TM
---------------------------------------------------------------------~->

-- 
    "NEXTEL-1 IT'S NOT JUST NEXTEL"
  Note The New address 
Subscribe to Nextel-1: http://www.groups.yahoo.com/subscribe/NEXTEL-1

  "NEXTEL2 FOR iDEN SOFTWARE DEVELOPERS"
Subscribe to Nextel2: http://www.groups.yahoo.com/subscribe/NEXTEL2

  "WIRELESS FORUM HOMELAND SECURITY GROUP"
     The Complete Resource for Wireless Homeland Security.
Subscribe to WFHSG:  http://www.groups.yahoo.com/subscribe/WFHSG

Yahoo! Groups Links

<*> To visit your group on the web, go to:
     http://groups.yahoo.com/group/NEXTEL-1/

<*> To unsubscribe from this group, send an email to:
     [email-masked]

<*> Your use of Yahoo! Groups is subject to:
     http://docs.yahoo.com/info/terms/