Mechanisms for the Adaptation of the Physical Layer in a Cognitive Radio

During the last years a modification of the spectrum allocation policy has been discussed. The desired increase of spectral utilization can be realized using overlay systems. These systems allocate the temporarily unused frequency bands of established licensed systems. In order to minimize the interference to the primary system an adaptable and flexible mobile terminal is required. Due to the ongoing research of software defined radio technology, different wave forms can already be supported by the same hardware. In order to adapt the secondary user to the offered frequency bands a spectral monitoring is required. This enhancement to the classical software defined radio concept was introduced as a Cognitive Radio feature. In this paper we describe the additional demands to the physical layer of a Cognitive Radio. Furthermore, we present a mechanism for supporting QoS under different channel conditions and radio access technologies (RAT).