Although the main use of spectrum is for communication purposes, there are also other uses such as cooking food in microwave ovens, medical applications, garage door openers and so on. Some frequency bands are allocated for these purposes in what is known as the Industrial, Scientific and Medical (ISM) bands. This spectrum usage is normally for short distance applications.
A breakthrough occurred in 1985 when the Federal Commission of Communications (FCC), the agency that oversees the spectrum in the U.S., allowed use of this spectrum for communications applications, provided that the transmission power was kept to a very low level to minimize interference. People could freely use these “unlicensed” bands without applying for a license, provided that the equipment used had been certified by an authorized laboratory that ensured compliance with interference mitigation measures. It is a mistake to imagine that unlicensed spectrum is a complete free-for-all, that it is unregulated. It is precisely the detailed technical regulation of unlicensed devices that makes it possible for them to co-exist together. Probably most significant factor in this respect is the fact that unlicensed devices are regulated to have comparatively low power outputs to limit their ability to interfere with each other.
As the ISM or unlicensed bands were opened to data communication, several manufactures began taking advantage of this opportunity to offer equipment that could communicate among computers without the need for cables. Wireless data networks covering significant geographic areas were built.
Note that open spectrum used in unlicensed bands cannot prevent interference issues, especially in very crowded areas. Nevertheless, open spectrum has proven a success for short distance applications in cities and for long distance applications as well in rural areas.
It is therefore advisable to investigate new forms of spectrum allocation, taking into consideration the needs of many stakeholders and strike a balance among them. Recent advances in technology make a dynamic spectrum allocation mechanism a feasible alternative.
As an analogy, the current method of spectrum allocation is similar to a railway system, the railroads can be idle a considerable amount of time. The dynamic spectrum allocation is akin to the highway system that can be used at all times by different users.