The main body of this article is pided into four parts: the first part is the background, purpose and significance of the research and the brief introduction of structure; the second part reviews the research status and trends of this subject; Base on the basis of previous research, the third part puts forward the methods and experimental program; the fourth part is the analysis of previous results。 The last part summarizes the whole research findings, and points out the deficiency of the paper and the next work plan。