Research On Cooperative Relay Power Allocation In Cognitive Radio

Wireless communication has become one of the indispensable elements of people's daily life.With the increasing number of users and the high demand for quality of service(QoS),the scarcity of radio spectrum resources is becoming increasingly serious.In this case,cognitive radio(CR)technology emerges as the times require.Its birth brings hope to solve the problem of spectrum tension.CR obtains the primary user(PU)spectrum information through dynamic spectrum sensing technology,so as to ensure the primary user's QoS.In the case of using spectrum sharing technology,secondary user(SU)and primary user can share spectrum.Power control is the first mock exam of spectrum sharing technology.Power control technology adaptively distributive transmit power of SU under certain model in a certain model,and achieves spectrum sharing without affecting the quality of service of users in CR network.In order to ensure the primary user's QoS,the transmission power of the secondary user will be limited,and the cooperative relay technology can solve this problem perfectly.Now,the cooperative relay technology has been widely used in CR network.Based on the cooperative relay technology and trying to improve it,this paper constructs the cooperative relay transmission model of secondary user assisted primary user transmission,the cooperative relay transmission model of secondary user and the cooperative relay transmission model of virtual multiple input multiple output(MIMO),and studies the power allocation of these relay transmission models under different constraints and different algorithms.Considering the interference power threshold limit of PU in CR network and the target maximum transmit power of each user in SU.The idea of cooperative relay is introduced to form the system model of secondary user assisted authorized user transmission.The power allocation is based on decoding and forwarding and Lagrange dual optimization algorithm.It solves the problem of too much interference caused by secondary users' access to primary users' frequency band.The Simulation results show that the algorithm can greatly reduce the interference to the primary users.That is to say,this method can effectively increase the resistance of primary users to the external environment,and improve the system capacity of primary users.Conventional distributed power control algorithms in cognitive radio networks are based on the assumption of perfect channel estimation which may lead to performancedegradation in practical systems.Considering the uncertainty of the channel,this paper proposes a robust cooperative relay-based cognitive radio joint power allocation algorithm.This robustly optimized power allocation problem can be described by a semi-infinite programming.Suppose that under the worst constraints,this problem is transformed into a second-order cone programming problem.Considering the difference between the two transmission phases of the secondary users,a fairness interference weighting factor is introduced to constrain the interference of the SUs and the relay nodes to the primary users.The OFDM technology is used to eliminate interference between the first phase and the second phase in the SU transmission process.Simulation results show that the algorithm can guarantee the QoS of the primary user,Increased system capacity.Compared with the traditional robust algorithm,the proposed algorithm has better resistance to channel perturbation and greatly improves the spatial diversity gain of the SUs..In the case of relatively simple constraints,that is,only considering the interference power threshold constraints of PU and the target maximum transmit power constraints of Su,this paper proposes a cooperative relay cognitive radio power allocation algorithm based on Virtual MIMO,and constructs a virtual MIMO cognitive radio network by using adjacent cooperative relay to study the problem of maximizing the capacity of secondary user system.The performance of the algorithm is studied by increasing the number of cooperative relaying,and its superiority is verified by comparing with the common cooperative relaying and non cooperative relaying cognitive radio networks.The simulation results show that compared with the other two algorithms,the cognitive radio system based on Virtual MIMO has great advantages in reducing interference to primary users and improving system capacity.