Date Added: Mar 2012
The lack of communication resources - especially because of overloaded frequencies - is seen during the last years when wireless communications has been increasingly taken into use by consumers. Wireless operators are now continuously looking for solutions to avoid overloading their frequencies. Much can be done by using existing resources more effectively by taking cognitive radio systems into use. A Cognitive Radio System (CRS) is aware of its environment and makes decisions considering the performance of the whole radio system and is able to learn of its environment and performance. The spectral efficiency in bit/s/Hz of modern systems in a given frequency band is rather high.