Cognitive radio as enabling technology for dynamic spectrum access

Frequency spectrum scarcity is currently one of the mostly discussed topics in wireless communications. When there is no free spectrum available, no new broadband communication techniques can be put into operation, which leads to disadvantages in competition and an impact on capabilities. The double use of already assigned frequencies on the other hand leads to interferences, which may result in a less robust communication. A possible solution to this problem is Dynamic Spectrum Access (DSA), realized by the use of Cognitive Radio (CR) technology. Cognitive Radios have the ability to detect unused spectrum segments and to adapt to it dynamically. This adaptation does not only concern a change of frequency, but may also include changes in waveform, bandwidth, or whatever leads to an optimal communication link. This paper gives an overview of the state-of-the-art Cognitive Radio approaches and points out opportunities offered by this technology to overcome the threat of spectrum scarcity.