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Dynamic spectrum access

Although all available spectrum is currently allocated in developed countries, many independent studies have found that the total amount of spectrum in use at any one time in any one place is a tiny fraction of the total. This is due to the way spectrum was originally allocated and to the fact that spectrum is often used intermittently; for instance some TV broadcasting stations do not transmit 24 hours a day.
As a consequence, a radically new way to use spectrum has been suggested. Instead of leasing spectrum to a given organization on an exclusive basis, a new dynamic spectrum management paradigm proposes to use whatever spectrum is available in a certain place at a certain time and switch to another frequency whenever interference is detected in a given band.

Of course to implement dynamic spectrum access requires new technologies and new legislation and many vested interests are fighting this, alleging possible interference. The key issue is how to determine when a particular spectrum band is really being used in a particular geographic region and how to move quickly to a new frequency band when an existing user with higher priority is detected. Thus in the VHF and UHF bands, television broadcasters transmitting at high power in specific frequencies and regions would have first priority. They are the primary license-holders in the spectrum. TVWS broadband devices would have a secondary priority and would be obliged to ensure that they do not interfere with the primary license holder.

The technology to accomplish this feat has been demonstrated and implemented in the new IEEE802.22 standard recently approved, as well as in other standards currently being considered.

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