Interference from secondary users to primary users should be avoided in cognitive radio. However, it is difficult to solve the interference problem if the secondary users cannot get the information of the primary receivers. Insufficient information of primary users would result in inaccurate spectrum detecting result. To deliver the information of primary users, Receiver Detection Employing Semaphore (ReDES) is proposed in this paper. Primary receiver informs secondary users of its licensed receive frequency according to semaphore architecture directly in ReDES. The semaphore is used to determine the spectrum holes by secondary users. Frequency mapping method is come up with as a realization of ReDES. The procedure and the detailed techniques are illustrated to make ReDES scheme reasonable and feasible. Simulation results show that the proposed scheme can effectively detect the frequencies of primary receivers, and improve the accuracy of spectrum detection. Interference from secondary users to primary users should be avoided in cognitive radio. However, it is difficult to solve the interference problem if the secondary users can not get the information of the primary receivers. Insufficient information of primary users would result in inaccurate spectrum detecting result. To deliver the information of primary users, Receiver Detection Employing Semaphore (ReDES) is proposed in this paper. Primary receiver informs secondary users of its licensed reception frequency according to semaphore architecture directly in ReDES. The semaphore is used to determine the spectrum holes by secondary users. Frequency mapping method is come up with as a realization of ReDES. The procedure and the detailed techniques are illustrated to make ReDES schemes reasonable and feasible. Simulation results show that the proposed scheme can effectively detect the frequencies of primary receivers, and improve the accuracy of spectrum detection.