The classic approach to radio communications is to confine an information-carrying signal to a narrow frequency band and pump as much power as possible (or legally allowed) into the signal. Noise is simply the naturally present distortion in the frequency band. Transmitting a signal in the face of noise relies on brute force—you simply ensure that the power of the transmitted signal is much greater than the noise.
In the classic transmission model, avoiding interference is a matter of law, not physics. With high power output in narrow bands, a legal authority must impose rules on how the RF spectrum is used. In the United States, the Federal Communications Commission (FCC) is responsible for regulating the use of the RF spectrum. Many FCC rules are adopted by other countries throughout the Americas. European allocation is performed by
CEPT's European Radiocommunications Office (ERO) and the European Telecommunications Standards Institute (ETSI). Other allocation work is performed by the International Telecommunications Union (ITU).
For the most part, an institution must have a license to transmit at a given frequency. Licenses can restrict the frequencies and transmission power used, as well as the area over which radio signals can be transmitted. For example, radio broadcast stations must have a license from the FCC. Likewise, mobile telephone networks must obtain licenses to use the radio spectrum in a given market. Licensing guarantees the exclusive use of a particular set of frequencies. When licensed signals are interfered with, the license holder can demand that a regulatory authority step in and resolve the problem, usually by shutting down the source of interference.
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