WLANs are only one usage of the radio frequency (RF) spectrum. Figure
illustrates the
distance versus data rate relationships that exist in different wireless
technologies. Figure
lists
the different radio frequency bands, along with the name of the transmitted
waves in each band and typical usages. A multitude of different and complex
technologies crowd the frequency spectrum and cannot be fully covered in this
course.
The U.S. General Services Administration definition of radio is
as follows:
- Telecommunication by modulation and radiation of electromagnetic waves
- A transmitter, receiver, or transceiver used for communication via
electromagnetic waves
- A general term applied to the use of radio waves
Wireless technologies are comprised of many variable parameters, as
listed in Figure
. Some
technologies provide one-way communications while others provide two-way
simultaneous communications. Some operate at low power levels, whereas others
operate at high power levels. Some are digital and some are analog. Some
operate at short distances of 30.5 m (100 ft.) or less, and others operate over
larger spans, even across continents. The cost of various wireless technologies
can vary from several U.S. dollars to billions of U.S. dollars.
Wireless
technologies, some of which are shown in Figure
, have been
around for many years. Television, AM/FM radio, satellite TV, cellular phones,
remote control devices, radar, alarm systems, weather radios, CBs, and cordless
phones are integrated into everyday life. Beneficial technologies that depend
on wireless include weather radar systems, x-rays, Magnetic Resonant Imaging
(MRIs), microwave ovens, and Global Positioning Satellites (GPSs). Wireless
technology surrounds humanity on a daily basis, in business and in personal
life.