<p>A secondary relay station is used to assist the communication between the secondary source transmitter and the secondary destination receiver through careful resource scheduling, as long as the interference they cause does not exceed the maximum threshold tolerable to the primary user. Unlike traditional cooperative way, the relay station remained silent throughout the second phase. In order to maximize the full utilization of time and frequency resources, the secondary source transmitter is allowed to access the network to broadcast a new symbol when the relay station is idle. From the perspective of the entire transmission cycle, symbol transmission is never interrupted. This undoubtedly improves the spectral efficiency, so that the secondary user can transmit more information in a limited time. The sum rate of secondary users is the optimization objective of this paper, and a joint resource scheduling algorithm is formulated in a bid to satisfy the constraint of peak power and the requirement of interference threshold of primary users at the same time.</p>