Abstract: Based on characteristic of periodic sequence,a novel spectrum sensing method that takes the correlation calculation was proposed in OFDM systems.Firstly,divided the received sequence into two part,and took average calculation respective to reduce the noise variance in an OFDM symbol,then used the two sub-sequences to take the correlation calculation,the influence brought by time-vary channel could be reduced.And the expectation and variance of correlation value were analyzed,verifying the new method was of validity.The experiments showed that the new method outperforms the traditional method in time-vary channel,reduces the number of symbols involved in the calculation,and has the low calculation complexity.

Key words: Cognitive radio, OFDM, Spectrum sensing, Timcvarying channel, Time domain correlation