The Research Of Spectrum Handoff Algorithm In Cognitive Radio Networks

Cognitive radio (CR) is a promising solution to improve the spectrum utilization. The unauthorized users(the secondary users) can access the authorized spectrum when the channel is free. Based on the demand of protecting the primary user’s(PU) entitlement, if the primary user (PU) hasto take up the channel which is using by the secondary user (SU), SU need to leave immediately. At this time, SU must be switched to another channel timely and effectively in order to ensure its QoS(quality of service).Spectrum handoff is an indispensable component in cognitive radio networks. In this thesis, we mainly study the spectrum handoff technology and how to guarantee the QoS of the secondly users when they have to switch channel. The main works are as follows.(1) The existing spectrum handoff technology is researched. There are two kinds of handoff scheme:active handoff and reactive handoff. The advantage of the reactive handoff is that it has better switching accuracy, but it has to sense the available spectrum before the switch which will cause a larger handoff latency. In reactive handoff, the Predefined Target Spectrum List (PTSL) model can effectively improve the accuracy of handoff and reduce handoff latency. This model is learned in this thesis particularly.(2) In this thesis, the sorting algorithm of PTSL model is studied and an improved algorithm is put forward. The traditional sorting algorithm just considered two elements, the channel bandwidth and quality. We take the predicted channel available time into consideration. When spectrum handoff occurs, the secondary user can choose the channel that not only the bandwidth and quality can satisfy the request, but also the available time can suit the business. Simulation results show that the improved algorithm can avoid the secondary handoff effectively and improve the performance of the whole system.(3) In order to guarantee the QoS of the SUs who have to switch channel, we studied the existing scheduling algorithms. Based on the researches, we give full consideration to the problem that the SUs who have to change channels should have a higher priority when scheduling. We propose an improved scheduling algorithm based on the M-LWDF algorithm. When the switching SUs join in the scheduling team, they will add in the front of the line so they can be distributed the spectrum resources timely to accomplish the communication business. The simulation results show that the improved algorithm can effectively reduce the drop call rate of the SUs and ensure the quality of service.