The research of the cognitive radio networks is facing rigorous challenges with the insufficience of the radio spectrum resources and multi-user contention environment.The fundamental principles of the spectrum handoff was elaborated
including the concepts and characteristics of the spectrum handoff
the classification of the proactive and reactive decisions of the spectrum handoff
spectrum handoff process abstract modeling methods
etc.Then five spectrum handoff algorithms based on the probability theory
Markov process
queuing theory
fuzzy logic
fuzzy neural network
were summarized
which were mainly on the ground of mathematic modeling tools.Some significant research findings of each spectrum handoff algorithm in the academic circle were reviewed.Finally
on account of the analysis of the existing algorithms and research achievements
some important problems of imperfect spectrum detection
target channel selection
idle channel dynamic character that were existed in the current research were summarized and the future research direction of the spectrum handoff were predicted.