第一行The security 改为 the security 逗号后面字母小写
第三行researching 也可改为investigating
第三行末,so 也可改为Therefore,
第四行 it has a very significant research value
第四行 This paper introduces the basic concepts and theorems of the wiretap channel, on the base of which several different kinds of wiretap channels and their basic coding methods are discussed. Moreover, according to the knowledge that we have learned about BSC wiretap channel, a three-time alternate communication wiretap channel model is established and its basic encoding method is studied as well. Compare with the one alternate communication wiretap channel, it can ensure the communication security even in the case that the noise in eavesdropper's channel is tiny little.