Research On Spectrum Sensing Optimization In Cognitive Radio Networks

With the rapid development of wireless communication and networks, a largenumber of wireless communications services and applications spring up and thedemand for spectrum resources is constantly increasing, so the phenomenon ofspectrum resources scarcity is more and more evident. But, the traditional and fixedwireless spectrum allocation strategy leads to extremely unbalanced distribution ofthe spectrum resources. Then the phenomenon that the utilization of most licensedspectrum is very low appears. Thus, it’s in urgent need of a new technology to supportthe wireless communication systems for further advance. As a sort of intelligentwireless communication technology, cognitive radio enables the ability to sharewireless channel with the primary user in a opportunistic approach. Spectrum sensingis the key and prerequisite of the cognitive radio technology. In the cognitivenetworks, the optimization of spectrum sensing plays a very important part inthroughput of cognitive systems and the collision and interference to the primary userand has become a hot topic to study. Based on the periodic channel sensing mode inthis paper, spectrum sensing optimization has been studied in depth. The maincontents are as follows:Considering the effect of the data transmission outage on the performance ofcognitive radio networks, the throughput optimization model based on thetransmission outage probability is constructed in the Rayleigh fading channel.Simulation results show that when the frame length is constant, there exits a optimalsensing time that can achieve the maximum throughput and the normalizedtransmission delay nearly reaches the minimum value at different transmission ratesand signal to noise ratios of the cognitive user.Considering the energy-constrained cognitive radio system, the joint optimizationproblem of sensing duration and transmission power is constructed under theconstrains of energy and interference to the primary user. Simulation results show thatthe CR system should adaptively change the sensing duration and transmission power according to the energy level to obtain the the maximum throughput and make bestuse of the limit energy effectively.Based on the ON-OFF primary channel model, the two cases that the cognitiveuser may cause collision and interference to the primary user are analyzed and theexpressions of the accumulated mutual interference time is derived. Then theinterference probability model is established. Based on the interference probabilitymodel, the joint optimization problem of sensing time and transmission time tomaximize the maximum throughput of cognitive networks is constructed under theconstraint of the interference probability to the primary user. Satisfying certainconditions, this optimization problem can be transformed into a convex optimizationproblem by the theoretical derivation and proof. The rationality and validity of theproposed optimization model is verified from the numerical results. Meanwhile, thesimulation results show that it is necessary to optimize and design the sensing andtransmission durations according to the activity distribution of the primary user andthis conforms to the need of the practical ever-changing scenario.