Impact of Primary User Activity on the Performance of Energy-Based Spectrum Sensing in Cognitive Radio Systems

Increasing numbers of wireless devices and mobile data requirements have led to a spectrum shortage. However spectrum utilization percentages are often low due to the current static spectrum allocation process where primary users (PUs) are given exclusive use to spectrum. Several mechanisms to increase spectrum utilization have been proposed including opportunistic spectrum access (OSA). Cognitive Radio (CR) is an emerging concept in wireless communication systems that aims to enable OSA in licensed frequencies by secondary users (SUs). CR systems are expected to sense the spectrum in order to determine if the PU is transmitting. Therefore OSA performance relies on the ability of the SU to accurately sense the spectrum and detect the PU activity. Numerous approaches have been studied for spectrum sensing; one of the most common is energy-based detection due to the SU needing no prior knowledge of the PU waveform. While energy detection has been widely studied, the assumption has been made that the PU status, either ON or OFF, does not change while the SU is actively sensing the spectrum. The work presented in this thesis examines specifically the impact to performance of energy detectors when the PU status changes during the spectrum sensing period. Two alternative analytic expressions for the probabilities of detection and false alarm are derived and corroborated with numerical results obtained from simulations. While the work presented in this thesis is discussed in terms of SU spectrum sensing performance, the analytic expressions apply to all applications in which energy detection is used.