Abstract
Cognitive radio (CR) which is one of the candidate communication techniques for solving the spectrum scarcity problem. In order to enhance the spectrum-usage efficiency, secondary users (SUs) are allowed to operate over the licensed bands while the bands are not being used by primary users (PUs) at a particular time or specific geographic area. CR systems require reliable spectrum sensing to protect communications of PUs from interference of SUs. In this thesis, an energy detector is equipped for spectrum sensing because of the low computational complexity. In consideration of protecting PUs, the CR users must perform spectrum sensing before transmitting data. However, the spectrum sensing periods arranged in the frame makes the packet delay of CR transmissions increasing; a large packet delay is harmful to real-time applications. In the periodic sensing frame structure, the longer the sensing time, the later the SUs begin to transmit data. Hence, the packet delay may increase with the increasing of the sensing time. However, the shorter the sensing time, the higher the false alarm happened; the packet delay may increase with the decreasing of the sensing time. In this thesis, we address a new sensing issue in which a tradeoff exists between sensing capability and the packet delay of SUs. Furthermore, we construct a novel scheme and formulate the issue as a convex optimization problem. Then, by using the Newton’s method, we can find an optimal sensing time with a minimal packet delay; the constraints include the requirement of the protection with PUs and the QoS of SUs. Computer simulation results indicate the theoretical result matches with the simulated result very well. In addition, the optimal sensing time in the proposed scheme satisfy the requirements of the CR systems in the IEEE 802.22.