The FCC is an independent U.S. government agency under the U.S. Congress.
The U.S. FCC was established by the Communications Act of 1934 and is
responsible for regulating interstate and international communications by
radio, television, wire, satellite, and cable. The FCC logo is shown in Figure
.
Each
node on a radio-based wireless network is required to have a radio transmitter
and a receiver. There is tremendous potential for the various transmitters and
receivers to interfere with each other. Therefore, nearly every nation in the
world has some regulatory agency that oversees the use of radio spectrum in
that country. In the United States, the FCC is the controlling agency. In many
other countries it is a ministry of posts and telecommunications (PTT), or an
agency with a similar name.
Government control does prevent chaos on the
airwaves, but it does create an extra burden for anyone planning to operate a
transmitter. They must comply with the bureaucratic restrictions and possible
expenses of obtaining a license.
Fortunately, there are exclusions to
the licensing requirement. The FCC Part 15 regulations permit unlicensed
operation of spread-spectrum devices in the 902 to 928-MHz, 2.4 to 2.5-GHz, and
5.8 to 5.9-GHz frequency bands. These three frequency bands have been allocated
for various industrial, scientific, and medical applications. Therefore, they
are often referred to as the ISM bands.
Much of the pre-802.11
spread-spectrum gear used the 900-MHz ISM band. The 802.11 standard for FHSS
and DSSS, 802.11b for DSSS, and 802.11g for OFDM all specify that the 2.4-GHz
ISM band should be used. The 802.11a standard specifies the 5-GHz band. One of
the reasons for the choice of these bands is that they are available worldwide
for unlicensed operation, although the precise band limits vary from country to
country. In the United States, the FCC has set the band limits at 2.4 GHz and
2.4835 GHz.
In addition to the spectrum allocations, the U.S. FCC also
regulates other details of the standards. For example, this band has been
divided into 1-MHz channels for frequency-hopping radios. The FCC requires that
the transmitter must visit at least 79 of the channels at least once every 30
seconds. The hop sequence is a pseudorandom pattern, so that the
frequency-hopping transmission appears to be nothing more than low-level
background noise to conventional radios.