The Federal Communications Commission (FCC) regulates the devices operating in all frequency bands and provides unlicensed spectrums. The FCC is specific to the United States; other countries have different guidelines and regulatory organizations.
For devices that fall in the licensed spectrum, the consumer must register the devices, perform tests, and so on. The industrial, scientific, and medical band (ISM band), which includes 2.4 GHz (802.11b and 802.11g) and 5 GHz (802.11a), falls in the unlicensed spectrum category. In most countries, the ISM band is in the range of 902 MHz to 5.850 GHz. Cordless phones (900 MHz, 2.4 GHz, and 5 GHz), microwave ovens (2.4 GHz), garage door openers, and so on fall into this unlicensed spectrum category; this is why you do not have to register your cordless phones and ovens with the FCC and get a license to operate them. The disadvantage of using the unlicensed spectrum is the interference?many devices (in homes, for example) use the same frequency and cause interference. The 902-MHz and 2.4-GHz ranges are used by most of the devices, and the 5-GHz range is relatively sparse in terms of usage by appliances and devices.
The FCC rules are under title 47 of the Code of Federal Regulations, and Part 15 (47CFR15) covers the unlicensed ISM band employing the spread spectrum modulation. Quoting the CFR 15.47, it "sets out the regulations under which an intentional, unintentional, or incidental radiator may be operated without an individual license."
The FCC website is http://www.fcc.gov/, and you can find Part 15 at http://www.fcc.gov/oet/info/rules/PART15_8-26-03.pdf.
Since its initial publishing in 1985, the 47CFR15 has changed with the times; the August 2003 version describes such twentieth century necessities as digital TV, picture-in-picture (PIP), and more.
It is interesting to follow the radio technologies and trace the capabilities as the 802.11 standard evolved from 1997 to present day. The capabilities are as follows:
The original 802.11 PHY standard supported 1 and 2 Mbps using the 2.4-GHz spectrum. The original specification included Direct Sequence Spread Spectrum (DSSS), infrared, and Frequency Hopping Spread Spectrum (FHSS).
The 802.11b specification added the 5- and 11-Mbps speeds to the 2.4-GHz spectrum. It was considered high speed at the time of its introduction. The 802.11b specification includes only DSSS.
The 802.11g specification is attempting to add 22 and 54 Mbps to the 2.4-GHz spectrum.
The 802.11b and 802.11g specifications use the DSSS modulation.
The preceding PHY specifications used the 2.4-GHz spectrum, but the 802.11a PHY specification introduced the 54-Mbps speed in the 5-GHz spectrum using Orthogonal Frequency Division Multiplexing (OFDM). (Technically speaking, the 802.11a specification operates in the UNII-1 and UNII-2 bands?Unlicensed National Information Infrastructure bands were set aside by the FCC in 1997 in the unlicensed spectrum in the 5.15-GHz to 5.825-GHz band.)
As throughput increases, range decreases. (Moreover, higher frequencies are more susceptible to degradation and thus possibly result in reduced range.) Hence, the 802.11a has less range than the 802.11b specification.
Range and other characteristics can be improved by methods such as increasing power, but the manufacturers are limited by the FCC rules. For example, the CFR15.47 limits the power to 1 watt for the 802.11, 802.11b, and 802.11g specifications. The UNII-1 and UNII-2 bands limit the power at 40 to 800mW. As a result, the manufacturers resort to optimizing the range based on the allowed power characteristics.
IEEE standards are worldwide and might conflict with the FCC rules.