Research On Power Control Method In Underlay Cognitive Radio Networks

The rapid development of communication technology has driven the explosive growth of emerging wireless services,and the demand for wireless spectrum resources is becoming stronger and stronger.As a non-renewable resource,the wireless spectrum is consumed,and the shortage of spectrum resources severely limits the development of wireless communication technologies.In order to solve the contradiction between the rapid development of communication technology and the shortage of spectrum resources,scholars have proposed Cognitive Radio Technology,which has quickly become a research hotspot and received wide attention.As one of the key technologies of cognitive radio,power control can ensure that the cognitive users can not affect the normal communication of authorized users,but also meet their own communication quality.Based on admission control theory,game theory and robust power control theory,this dissertation deeply studies the power control model and the related user selection,system capacity,system robustness,system energy consumption and other issues,and puts forward the corresponding solutions.Firstly,in order to solve the problem of increasing system interference and reducing system capacity caused by secondary users that unable to satisfy SINR in cognitive radio networks,a time-varying channel power control method based on user management is proposed.In the time-varying channel,when considering the small number of secondary users and uneven location distribution,we first let all users participate in the communication,and propose the max-min admission control algorithm,which can effectively prevent the excessive deletion of users and improve the system capacity.In the aspect of power control,an automatic power control game algorithm based on cost function is proposed to realize the fast power convergence and effectively reduce the system interference.In the fast time-varying channels,when considering the large number of secondary users and uneven distribution of secondary users,the strategy of screening the secondary users first and then implementing admission control for the screened secondary users is adopted.A complete iterative admission control algorithm is proposed to solve the problem of secondary users deletion that cannot meet the SINR requirements,thus increasing the number of secondary users that can be accommodated in the system.In addition,a robust power control method based on probability constraints is proposed to solve the problem that the channel parameters is time-variant and difficult to obtain.The system interference is effectively reduced and the performance of the network is greatly improved.Secondly,aiming at the problem of the power control algorithm in cognitive radio network is too conservative,a robust power control algorithm with bounded uncertainty and probability constrained double optimization is proposed.In this dissertation,the classification of channel parameters in cognitive radio system and its influence on system performance are analyzed.The channel parameters between primary and secondary users are cross system parameters,which are difficult to obtain in non cooperative mode.The channel parameters between secondary users are system parameters,which are easy to obtain.On the premise that the primary user is not interfered and the secondary user can allow a certain outage probability,on the one hand,the additive uncertainty method is used to describe the uncertainty of channel gain between primary and secondary users.On the other hand,the probability constrained algorithm is used to optimize the power between the primary and secondary users,and the bounded uncertainty and probability constraint are used to optimize the power A dual optimization power control method is proposed.This method can effectively reduce the outage probability of primary user in the probability constrained algorithm,and improve the conservative problem of the worst-case algorithm.Finally,aiming at the problem of power control energy consumption of mobile users in cognitive radio networks,a power control method based on the movement distance of the secondary user and the direction change of the motion vector is proposed.First,it analyzes and normalizes a variety of mobile scenes,such as static scene,single-user dynamic scene,multi-user dynamic scene,etc.,and constructs a more universal communication model to reduce signal loss caused by scene switching.Secondly,aiming at the irregularity of the moving direction and the variability of the moving speed of the secondary user,an interference model based on the moving distance and the motion vector direction of the secondary user is proposed,which realizes the real-time prediction of the interference intensity caused by the transmit power of the secondary user to the primary user,and this method simplifies the complexity of the interference estimation algorithm.Finally,an optimal power control algorithm for cognitive users in mobile scenarios is proposed to minimize the energy consumption and maximize the concurrent transmission area of cognitive users.The simulation results show that the algorithm effectively reduces the energy consumption of mobile users,and is superior to the fixed power strategy in improving the probability of network packet transmission.