Optimization of out-band sensing time in cognitive radios

When the present channel used by the secondary user (SU) is detected to be busy due to the re-appearance of the primary user (PU) in cognitive radios, the SU has to search an out-band so that its transmission can be continued. In order to meet the QoS requirement, out-band sensing speed should be as fast as possible. How to reduce out-band sensing time employing cooperative spectrum sensing is proposed in this paper. We formulate the nonlinear constrained optimization problem for the described network model to make a tradeoff between cooperation and local processing. Simulation results indicate that the joint selection of the number of cooperative users and local observation time can minimize the out-band sensing time. In addition, applying different fusion rules may obtain different performance and it is showed that the majority-rule performs the best.