Abstract
Cognitive radio (CR) is an emerging communication technique which can enhance the spectrum-usage efficiency by allowing some secondary users (SUs) to operate over the licensed spectrum as long as a primary user (PU) is inactive. To sufficiently protect PU communications from interference imposed by SUs, a CR system requires reliable spectrum sensing to determine whether an SU is allowed to access the licensed spectrum or not. However, such an opportunistic spectrum access mechanism would lead to serious latency and buffer overflow problems. In this thesis, we propose a low-latency joint spectrum sensing and scheduling scheme based on an energy detector for opportunistic SU transmission. Unlike the conventional energy detector using a fixed threshold to detect the PU’s occurrence, the proposed scheme dynamically regulates the detection threshold according to the queue length at the SU transmitter, where the SU transmission power is adjusted properly to confine the PU’s outage probability at an acceptable level and two linear policy functions are adopted for the queue delay minimization. Numerical results indicate that the proposed approach has significant improvements over the conventional energy detection scheme with a fixed threshold in terms of the queue delay of SU transmission and the packet loss due to buffer overflow.