Adaptive Threshold Judge Algorithm for Spectrum Sharing in Cognitive Radio Based on Energy Sensing Method

The secondary users can share the same frequency band with the primary user without interference to each other, if it locates out of the boundary of the primary users and transmits low power that the primary receiver´s SINR(Signal to Interference and Noise Ratio) is large enough to decoding properly. We analyze the coexistent system model for sharing spectrum in cognitive radio and propose a method to determine the sensing threshold for the secondary users in the cognitive radio system, in which the secondary user controls its sensing threshold and its transmission power in order to guarantee the minimum decodable SINR for the primary receiver. Furthermore, we also analyze the interference to each other for both the primary user and the secondary users. The analysis and numerical simulation indicate that the coexistence for the primary user and the secondary users is available under the cases that the secondary users locate the outside of the minimum distance decided by the primary and the secondary transmission power.