Spectrum Efficient QoS Support for Secondary Users in Cognitive Radio Systems

The fundamental performance criterion for Dynamic Spectrum Access (DSA) approaches is the protection of the Primary U ser (PU). However, for DSA to become a reality, it is crucial to also ensure some Quality of Service (QoS) support for the Secondary U ser (SU) communication. In this paper, we propose sensing based opportunistic spectrum access approaches achieving both, protection of the PU, as well as QoS support for the secondary communication. Given the requirements of PU protection and secondary QoS support, we show that there is a tradeoff between the spectral overhead needed to achieve both requirements. PU protection is realized by a sensing process, for which the amount of spectral overhead drives the probability of false positives (the probability of declaring the PU to be present although it is not). This probability in turn influences the amount of spectral overhead required for secondary QoS support. We introduce performance metrics to quantify the spectral overhead and the spectral efficiency of DSA approaches. Furthermore, for a secondary QoS metric of uninterrupted data transmission, we show performance results for selected link maintenance approaches with respect to their spectral efficiency.