INTRODUCTION
Spread Spectrum Communications (SS for short) is a mostly digital
communications technology that was originally developed during World
War II. First used for "Secret" military communications and later
for Radar countermeasures, SS has been improved, honed, refined and
applied to a wide variety of consumer-based applications as well. SS
systems like GPS (Global Positioning System) and Wireless Local Area
Networks (WLANS) are being used by literally millions of people
today. Why is Spread Spectrum so hot -- why does the FCC want to
encourage the use and proliferation of this new technology -- just
what is SS anyway? These are some of the questions that this article
will address. Along the way, I hope I can shed some light on this
fascinating subject and encourage readers to learn more about SS and
modern telecommunications.
Over the last several years a new commercial SS marketplace
has been emerging. SS Technology covers the art of secure digital
communications that is now being exploited for commercial and
industrial purposes. In the next four or five years hardly anyone
will escape being involved, in some way, with SS Communications
Technology. Applications for commercial spread spectrum range from
"Wireless" LAN's (WLANs are wireless computer-to-computer local area
networks), to integrated bar code scanner / palmtop computer / radio modem
devices for warehousing, to digital dispatch, to digital cellular
telephone communications, to "information society" city/area/state or
country wide networks for passing faxes, computer data, email, or
multimedia data.
Donald L. Schilling, Raymond L. Pickholtz and Laurence B.
Milstein predicted in August, 1990 the coming of commercial spread spectrum
technology in an article that appeared in the IEEE Spectrum, "Spread
Spectrum Goes Commercial," as follows:
"Spread-spectrum radio communications, long a favorite
technology of the military because it resists jamming
and is hard for an enemy to intercept, is now on the
verge of potentially explosive commercial development.
The reason: spread-spectrum signals, which are
distributed over a wide range of frequencies and then
collected onto their original frequency at the receiver,
are so inconspicuous as to be 'transparent.' Just as
they are unlikely to be intercepted by a military
opponent, so are they unlikely to interfere with other
signals intended for business and consumer users --
even ones transmitted on the same frequencies. Such an
advantage opens up crowded frequency spectra to vastly
expanded use.
"A case in point is a two-year demonstration project
the Federal Communications Commission (FCC) authorized
in May (1990) for Houston, Texas and Orlando, Fla. In
both places, a new spread spectrum personal
communications network (PCN) will share the 1.85-1.9
Gigahertz band with local electric and gas utilities.
The FCC licensee, Millicom Inc., a New York City-based
cellular telephone company, expects to enlist 45000
subscribers.
"The demonstration is intended to show that spread-
spectrum users can share a frequency band with
conventional microwave radio users--without one group
interfering with the other -- thereby increasing
the efficiency with which that band is used. . . . "
This prediction has now become fact. Qualcomm and
Omnipoint are both operating Spread Spectrum Code Division Multiple Access
(CDMA) Personal Communication Services (PCS) in the 1.9 GHz frequency
range. These new SS CDMA technologies now have even their own technical
standards and are actively being expanded and improved.
PCS and PCN systems are not the only SS applications that have
recently become reality. WLANs are now available in PC-Card size and
almost as popular as their wired brethren. Other SS applications like
wireless barcode readers, built by Symbol Technologies, are now in use in
nearly every Post Office in the US. Metricom, Inc. in the San Francisco
Bay Area is even offering a Wireless SS Internet connection service called
"Ricochet."
HOW SPREAD SPECTRUM WORKS
Spread Spectrum Technology uses wide band, noise-like signals.
Because Spread Spectrum signals are noise-like, they are rather hard
to detect or intercept. Spread signals are intentionally made to be
much wider band than the information they are carrying to make them
more noise-like.
Spread Spectrum signals use fast codes that run many times the
information bandwidth or data rate. These special "Spreading" codes are
called "Pseudo Random" or "Pseudo Noise" codes. They are
called "Pseudo" because they are not real gaussian noise.
Spread Spectrum transmitters use similar transmit power levels
as narrowband transmitters. Spread Spectrum signals are so wide, they
transmit at a much lower spectral power density, measured in Watts per
Hertz, than narrowband transmitters. This lower transmitted power
density characteristic gives spread signals a big plus. Spread and
narrowband signals can occupy the same band, with little or no
interference. This capability is the main reason for all the interest
in Spread Spectrum by the government, the FCC and industry today.
To qualify as a spread spectrum signal, two technical criteria
should be met:
- The transmitted signal bandwidth is much greater than the
information bandwidth.
- Some function other than the information being transmitted is
employed to determine the resultant transmitted bandwidth.
signal bandwidth as wide as 10 to 1000 times the bandwidth of the
information being sent. Common spread spectrum systems are of the "direct
sequence" or "frequency hopping" type, or else some combination of these
two types (called a "hybrid").
SPREAD SPECTRUM TECHNOLOGY DRIVEN OPPORTUNITIES
As the technologies of Spread Spectrum Communications, Computers,
"Semiconductor Chips" and networking mature, many opportunities are being
created for the entrepreneur. Right now there is a need for knowledgeable
consultants and contract workers in software, technical and user manual
copy preparation, hardware design and test, field service and installation
and system planning and marketing. Other opportunities are presenting
themselves in the service sectors of the SS and Networking
technologies. Other service sector possibilities exist, such as on call
service and installation, repair and maintenance, software development,
test, or integration and verification and finally, small manufacturing or
product development start-ups.
These exciting opportunities will provide an outlet for a lot of
smart, ambitious people who will also help create job opportunities for
other well prepared, knowledgeable individuals. While very few entrepreneurs
will get rich in their own small businesses, many people can make
comfortable livings in their own SS-based small businesses.
To make certain that this new technology really takes off, the
government is actively encouraging small, medium-sized and large businesses
to invest money and create jobs. Witness the success of the FCC's PCS / PCN
"Airwaves" auctions and the FCC's announcement on April 25, 1998
about the "NII/SUPERNet"
initiative, as signs of this government encouragement.
CONCLUSION
It seems that we are living in a "gadget" crazy world! Is SS
technology just another set of "gadgets," like PDAs (aka Apple's NEWTON) or
is this technology going to be a lasting, profit sustaining, necessary part
of the twenty first century civilization? I believe that this technology
is here to stay! I also believe that today's rapidly changing world really
needs some of these new advanced products and services. Just wait until
your kids start asking for "Wireless" SS Walkie-Talkies or battery powered
"Wireless" SS Pocket Homework Internet Terminals -- then you will know that
SS technology is here to stay!
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