The Research On Spectrum Handoff Technology In Cognitive Radio

Spectrum handoff is one of the key technologies in cognitive radio. Spectrum is theimportant carrier in wireless communications and is non-renewable. Current spectrumallocation system not only leads to the low spectral utilization, but also results in spectralresources shortage and highly restricts the further development of wireless communications.Original spectrum allocation system is expected to be broken with the research and thedevelopment of cognitive radio technology. In cognitive system, cognitive users canintelligently sense the surrounding environment and change their parameters through learning.If cognitive users can change to available idle spectrum without affecting the business ofauthorized users, the aim of improving the spectrum efficiency can be achieved. Hence, thekey to the issue is how to reduce blocking, how to decrease the forced interruption and howto reduce the handoff frequency.This thesis mainly studies the spectrum handoff technology in cognition radio. In orderto reduce the blocking probability, lower the forced interruption probability and reduce thehandoff frequency of cognitive users, and to improve the spectrum efficiency of the wholesystem, this study has conducted following works:Firstly, the second chapter primarily studies the relations between spectrum handoff andspectrum sharing, and further analyzes factors which affect spectrum handoff of cognitiveusers and the relevant access standards in spectrum sharing. It lays theoretical foundation forthe following studies about occupation of spectrum resources by both authorized users andcognitive users.Secondly, aiming at the issue that blocking and forced interruption are either strong orweak which is caused by the spectrum pool and the channel reservation, this research studiesthe hybrid algorithm that combines the spectrum pool and the channel reservation. Then itanalyzes every status of the spectrum pool and the channel reservation in this algorithm withthe help of3-D Markov model and derives the probability of blocking, forced interruptionand channel utilization. It displays the emulation results through MATLAB platform andconducts comparison analysis of the emulation results.Lastly, in the premise of the hybrid model of spectrum pool and channel reservation, inorder to prevent cognitive users from frequent handoff which will increase the systemworkload, it studies the handoff probability under following three rules:1, the handoffprobability of cognitive users’ random access of the hole to the spectrum pool;2, theprobability changing with the idle time of the hole;3, the probability of the intelligentmatching of cognitive users with the hole. It also conducts a detailed inference of handoffprobability from the first to the fourth handoff. Through the comparison analysis of theemulation results, the latter two can obviously decrease the frequent handoff probability of cognitive users. Afterwards, it studies the handoff throughput under the above three rules.Emulation result displays that the handoff throughput under the case of intelligent matchingof cognitive users with the hole is the least. That is, the handoff cost is the least and theimprovement in system performance is better. Through the theoretical analysis, the formulaededuction and the emulation analysis, it proves that hybrid model can effectively improve thehandoff performance of cognitive system.