User Cooperation Under Multiplextransmission Scheme In Cognitive Radio Network

Radio spectrum has become a more and more precious resource especially with the wide-spread deployment of different wireless communication systems. In order to ease wireless spectrum shortage and interference between different wireless communication systems, meanwhile, base on the fact that cooperation communication and cognitive radio (CR) network are the most widely studied subjects in recent years, these two techniques are integrated to increase the capacity of wireless communication system and avoid interference.Due to the consideration of protecting primary system, there exists a No-Talk-Zone around primary receiver. In this scenario, if some CR users are located within in the No-Talk-Zone, the CR users cannot maintain CR communication with lower transmit power according to the traditional transmit power control strategy. However, higher transmit power of CR user will interference with primary system. Therefore, traditional transmit power control algorithm scheme becomes less effective here.The traditional Underlay transmission scheme has higher frequency usage, meanwhile, it is easy to interfere with primary system. The traditional Overlay has lower interference with primary system, meanwhile lower frequency usage. To address this issue, we propose a multiplex transmission scheme using both underlay transmission scheme and overlay transmission scheme. The Overlay transmission scheme is used in the protected area, while the Underlay transmission scheme is used outside. The main interference comes from the cognitive user in the protected area and less interference is from the outside of the protected area. Meanwhile, the cooperation between the CR users which are located inside and outside the No-Talk-Zone is also considered, hence the transmit power of CR user can be lowered through the cooperation. At last, the power allocation between CR users is optimized by linear programming simplex algorithm.The limitation of the traditional power control algorithm lies in that the cognitive system cannot maintain its communication while it is located near from the primary system geographically. The key feature of the multiplex transmission scheme is that CR user can communicate with CR receiver even if it is very close to the primary receiver, meanwhile get rid of the interference with the primary system.The achievable rate of the cognitive system under simplex algorithm is simulated and analyzed. At last, the achievable rate of the CR system under multiplex transmission scheme is simulated and analyzed, the simulation results demonstrate that the transmission rate of the proposed scheme is higher than that of underlay transmission scheme.