Direct Receiver Detection Employing Semaphore In Cognitive Radio

Recently, cognitive radio has been a hot topic around the world. Cognitive radio is proposed to improve the spectrum untilization and solve the problem that the spectrum untilization of licensed system is low but the spectrum resource of unlicensed system is insufficient. Spectrum detection, spectrum assignment and spectrum management are the key technologies of cognitive radio, among which spectrum detection is the precondition of the implementation of cognitive radio. Accurate and reliable spectrum detection can avoid interference between primary users and secondary users when secondary users access to the spectrum holes, and then guarantee the implementation of cognitive radio.However, the collision of primary users and secondary users would happen if secondary users use unaccurate or wrong spectrum detection results. The collision would bring interference between primary users and secondary users, resulting in low spectrm untilization and even communication drop of primary users. Hidden terminal problem and exposed terminal problem are the classic examples for the collision. On the basis of hidden terminal problem/exposed terminal problem, the interference between primary users and secondary users are analyzed and the method of spectrum classification is come out with to solve the hidden terminal problem and exposed terminal problem.As the secondary users need to classify the spectrum holes into transmitting spectrum hole and receive spectrum hole, secondary users should implement transmitter detection and receiver detection. So reliable receiver detection is needed, and this paper proposed a Direct Primary Receiver Detection (DPRD) method based on the analysis of the current receiver detection shemes. In DPRD, primary receiver informs secondary users of its licensed receiving frequency according to semaphore architecture directly. The semaphore is used to determine the spectrum holes by secondary users. Frequency mapping method is come up with as a realization of DPRD. The procedure and the detailed techniques are illustrated to make DPRD scheme reasonable and feasible.Finally, simulation is used to evaluate the proformace of DPRD. The simulation results show that DPRD can effectively detect the frequencies of primary receivers, and solve the collision problem. Furthermore, the simulation results prove that DPRD can improve the accuracy of spectrum detection and improve the spectrum until ization.