Joint Design Of Spectrum Sensing And Management Strategy In Cognitive Radio Networks

With the rapid development of wireless communication technology, there is an increasing demand for wireless spectrum. However, most of the wireless spectrum has been already allocated. On the other hand, according to the recent research of Federal Communications Commission (FCC), most of the allocated spectrum is severely under-utilized. Cognitive radio which provides an efficient spectrum sharing framework has been proposed for solving the above problem. Cognitive radio networks consist of licensed users (primary users, PUs) and unlicensed users (secondary users, SUs). SUs are allowed to detect, identify and opportunistically access the licensed band at the absence of PUs. Thus the spectrum efficiency can be promoted effectively in cognitive radio networks.A common simulation platform is very necessary in the study process of cognitive radio networks. It is the basis of protocol analysis, performance validation and algorithm optimization. Based on NS2, CR Simulation Platform is developed for cognitive radio networks simulation. This platform can simulate the working mechanism of all the protocols of cognitive radio networks accurately. Moveover it provides a GUI for user's convenience. This platform provides a solid basis for the following research and simulation on cognitive radio networks.In cognitive radio networks, the SU is required to carry out periodic in-band spectrum sensing to detect the PU's activity once it occupies the licensed channel. A priority queuing model is formulated to abstract the working procedure of Periodic In-band Sensing Mechanism (PISM). The SU performance metrics of in-band working mechanism can also be derived including mean queue waiting time, mean queue length, idle probability of SU, etc.Based on the analysis of this model, it can be found that the idle in-band time of SU has not been utilized yet. Thus an Idle Time based Active In-band Sensing Mechanism (ITAISM) is proposed. In addition to performing periodic in-band sensing, ITAISM uses the idle in-band time gaps of the secondary user to detect the primary user's return actively. The simulation results show that the analytical results have a good match with the simulation results and the model can describe the in-band working mechanism of PISM accurately. The simulation results also show that ITAISM can shorten the detection delay significantly and reduce the interference on the primary user efficiently without degrading the data transmission performance of SU, especially in low data load cases.Furthermore, based on the Single-channel Sharing Scheme (SSS) which is wildly used in broadband cognitive radio networks, a Preemptive Resume Priority queuing model is formulated to evaluate the performance characteristics of the spectrum management mechanism in SSS. The SU transmission performance of SSS can also be derived including mean queue waiting time, mean interrupted times, average throughputs, etc.Since the traffic load condition hasn't been taken into account in SSS, the idle spectrum will not be fully utilized in some load imbalance cases of SUs. To solve this problem, a Multi-channel Sharing Scheme (MSS) for broadband cognitive radio networks is proposed. This scheme allows secondary users to dynamically share all the sub-channels of the broadband channel in the form of a mixed queue. Thus the idle channel can be fully utilized according to the demands of different SUs.Theoretical analysis shows that the proposed scheme can reduce the queue waiting time and the interrupted times for data packets of secondary users significantly. The overall throughput of secondary users in the broadband channel can be improved as well. The analytic results have been verified by numerical simulations.