Preview / Read the Current Issue of SSS
Updated 8/8/97Volume 4 - Number 3 -- Spring 1996
["SPREAD SPECTRUM COMMUNICATIONS"]Part 2
SPREAD SPECTRUM COMMUNICATIONS
A "New" Technology That is Fast Becoming One of the Hottest Things Around!A Background Article
by R. H. Roberts
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 wide variety of even consumer based applications. 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 (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 summarized the coming of commercial Spread Spectrum Technology in the article that appeared in the IEEE Spectrum, August, 1990, "Spread Spectrum goes commercial," by writing:
"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.HOW SPREAD SPECTRUM WORKS
"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. . . . "
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 to narrow band 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 narrow band 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:
1 -- The transmitted signal bandwidth is much greater than the information bandwidth.
2 -- Some function other than the information being transmitted is employed to determine the resultant transmitted bandwidth.
Most commercial FCC Part 15.247 (CFR47.15.247) SS systems transmit an RF signal bandwidth as wide as 10 to 254 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 creat jobs. Witness the success of the FCC's PCS / PCN "Airwaves" auctions and the FCC's announcement April 25 of 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 "Wireless" SS Pocket Homework Internet Terminals -- then you will know that SS technology is here to stay!
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