Fusion-based sensing for uncertain primary user signal in cognitive ratio networks

In cognitive radio networks, secondary users can use the licensed frequency bands if the primary user is idle. In order to protect the privilege of the primary user, detecting the presence of the primary user in cognitive radio networks is important. Collaborative sensing is a possible method to improve the detection performance for the presence of the primary user. The IEEE 802.22 standard provides an appropriate topology to perform collaborative sensing. This paper addresses the problem of collaborative sensing in cognitive radio networks. The proposed sensing mechanism is not based on any known signal or noise distributions. The approximations of the distributions for the signal energy measurements are first derived. The SUM fusion rule is adopted to make the final consensus about the presence of the primary user. Based on the derived measurement distributions, detection performance in terms of detection probability subject to a fixed false alarm probability is evaluated analytically. The analytic results of the measurement distributions and the detection performance are very close to the simulation results. In particular, it is found that adding more users to participate in the fusion does not improve the detection performance. In fact, it may hurt the detection performance. A better strategy is to include only a few users with the highest SNR in the fusion. In this way, the detection performance is higher while communication costs can be reduced.