In order to decrease the interference to the primary user (PU) caused by the secondary user (SU) in cognitive radio

a spectrum sensing method is proposed to cooperatively detect the PU through multi-slot energy sensing of the SU.Each transmission frame was divided into several time slots

and the SU sensed the PU at the beginning of each time slot.The SU could improve the performance of detecting PU through combining the multi-slot sensing results.In order to maximize the SU's spectrum efficiency

the PU state was built as a two-dimensional Markov random process

and according to this process

the single-slot sensing time was optimized.The simulation results show that compared to the listen-before-transmit spectrum sensing method proposed by Liang

the proposed method reduces the interference probability of 28% by only sacrificing the spectrum efficiency of 14%

and with the increase of the signal-to-noise ratio (SNR)

the maximal spectrum efficiency of the proposed method gradually approaches that of the listen-before-transmit spectrum sensing method.