Resarch On Proactive Spectrum Handoff Algorithm In Cognitive Radio Network

The static spectrum allocation strategy leads to the low utilization of the licensed spectrum.The cognitive radio technology can improve the utilization rate of the spectrum and alleviate the shortage of resources by searching and using the resources that are not fully utilized in the time domain,frequency domain and space domain.This thesis studies and analysis the spectrum handoff technology in cognitive radio networks and proposes improved algorithms to solve the existing algorithms.The existing spectrum handoff algorithms are usually based on the ideal detection,however,it is inevitable that there are some non-ideal spectrum detection situations of false alarm and missed detection in the realistic cognitive radio network,which lead to the wrong handoff decision and thus affect the system performance.Therefore,this thesis proposes an proactive spectrum handoff algorithm based on non-ideal detection.Firstly,the traffic flow of the licensed user is set up as an ON/OFF exponential alternating model,and the false alarm probability is used to correct the perceived information,which improves the prediction accuracy of the spectrum state probability in future.Then,a dynamic correction value is added to achieve a more accuration estimate of the channel's idle time by using the historical information of the local channel when calculating the remaining idle time of the channel,and the remaining idle time of the current channel is used as the decision condition of the handoff.Finally,the corresponding handoff strategy is given.The simulation results show that the proposed algorithm eliminates the influence of non-ideal detection on system performance,and improves the spectrum utilization rate and reduces the number of frequency handoff.For the existing distributed proactive spectrum handoff strategy,the target channel is usually selected by users only according to the availability and stability of the licensed spectrum,with the QoS of the cognitive user not being taken into account,and thus the cognitive user usually selects the same channel in the case of multi-user,which will lead to the interference between users.Therefore,this paper proposes a target channel selection algorithm based on jointly consideration of the multi-attribute decision and ant colony division of labor.Firstly,the spectrum handoff process of the cognitive network is mapped to the ant colony division model,where the stimulus intensity is determined by the maximum transmission power allowed by the licensed channel to calculate the selection probability of each users for the candidate channels and sort it.Then considering the influence of the bandwidth,delay,bit error rate,signal-to-noise ratio and channel idle time on the channel selection,the TOPSIS algorithm is used to calculate the integrated quality of the previous K candidate channel.The weights are collective determined by the fixed weights assigned by the nine scale method and the dynamic weights of the mutative variance between the channels.When a handoff is needed,the cognitive user selects the best-quality channel in the first K candidate channels.The simulation results show that the proposed algorithm reduces the conflict among cognitive users,and has a great advantage on the performance link retention probability and blocking probability.