The Performance Of Cooperative Spectrum Sensing In Cognitive Radio

With the rapid development of wireless communication, the scarcity of spectrum resources becomes the bottleneck to providing new communication services. A major shift in wireless communications is now emerging with the development of cognitive radios, which attempt to share spectrum in a fundamentally new way. Cognitive radios address the problem of poor spectrum utilization exhibited in many frequency bands. Spectrum sensing technique through primary user detection can obtain as many available transmission opportunities as possible, which thus is identified as a key enabling functionality of cognitive radios.The goals of this dissertation are study the cooperative spectrum sensing and propose methods for obtaining the good performance of cooperative spectrum sensing.1. The sensing performance of a cognitive user U1 by allowing another cognitive user U2 to act as its relay is studied. We take the average power rather than the instantaneous power as the decision statistic. Then we pay much attention to studying how to find a proper relay U2 for U1 so that the detection capability of U1 can be improved. Results show that, the normalized received power of U2 should be larger than a certain value which is called gain point if U1 can benefit from the cooperation. We find that, by varying the scaling factors of the unconstrained scheme, the gain point of the constrained scheme equals that of the unconstrained scheme when the transmission powers of U1 and U2 are equal. Next, by varying the scaling factors of the unconstrained scheme, the gain point of the constrained scheme equals that of the unconstrained scheme when the transmission powers of U1 and U2 are unequal.2. In cooperative spectrum sensing, softened hard combination scheme with two-bit overhead for each cognitive radio (CR) user can achieves a good tradeoff between detection performance and complexity. In this paper, we study the performance of two-bit hard combination scheme under imperfect reporting channel. Also the comparison of performances between two-bit hard combination scheme and one-bit hard combination scheme in imperfect reporting channel is exhibited. Numerical results will show that the performance is affected by the SNR of reporting channel and much better than convention hard combination scheme.