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All wireless telecommunications make use of some portion of the electromagnetic spectrum. The electromagnetic spectrum consists of any signal whose frequency is between 3 kHz and 300 GHz. While the extreme low and high ends of this range are only used for highly specialized applications, the frequencies between 3 MHz and 40 GHz are used extensively for wireless communications. Even with such a vast range of frequencies available, there is fierce competition for access to this spectrum. Figure 2-19 contains a largely unreadable chart of all U.S. frequency allocations that illustrates just how much has been crammed into the RF spectrum. (A PDF version of this chart can be found at the NTIA Office of Spectrum Management website, http://www.ntia.doc.gov/osmhome/allochrt.pdf) Due to the large amount of demand, governmental regulatory agencies have been commissioned to regulate the usage of the electromagnetic spectrum. Probably the most well known of these agencies is the Federal Communications Commission (FCC).
The FCC determines how the electromagnetic spectrum is to be used in the United States and is also in charge of enforcing these regulations. While many people gripe about the FCC in terms of broadcasting regulations, the FCC is needed to prevent complete chaos in RF communications. Many regions in the world have their own regulatory agency that serves the same function as the FCC in the U.S. In fact, there is even an international committee called the International Telecommunications Union (ITU) that is made up of numerous member countries.
The manner in which each of these regulatory agencies has decided to divide up the RF spectrum sometimes varies. This means that a radio may be perfectly legal to operate in one region but violates government regulations in other countries. This presents a challenge for creating wireless telecommunication standards that are intended for international adoption. Compromises are often required in order to assure that the same wireless device can operate in all regions of the world. This can be seen in the 802.11 standards where only certain of the frequency channels defined by the standard can be used depending on the region in which a device is operating.
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