Study On Maximize Energy Efficiency Power Allocation For Underlay Relay-assisted Cognitive Radio Networks

With the rapid development of wireless communication technology,especially the rapid evolution of Internet of things and large data technology,as well as in the discussion of 5G technology,the problem of lack of spectrum resources which is non-renewable resource and low utilization of spectrum have become increasingly urgent.In order to alleviate this situation,people put forward the concept of cognitive radio(CR)in the last century.CR technology allows secondary user(SU)to access the authorized networks and share the same frequency with the primary user(PU)without affecting the normal communication of the primary user,which can greatly improve the efficiency of spectrum utilization and the transmission capacity of networks.CR technology provides unlimited possibilities for the future development of wireless communications.At present,many people have devoted to the study of various problems in this field.In the CR system,Orthogonal Frequency Division Multiplexing(OFDM)is widely used with its obvious advantages.In the multi-user CR networks,OFDM can dynamically allocate subcarriers to individual users,at the same time,the interference between adjacent subcarriers is very low.The combination of OFDM technology and CR system can realize the fully and reasonable utilization of spectrum resources.Because of the transmission distance constraints,edge effects,shielding effects and many other factors,information cannot be transmitted directly in the practical transmission environment.Relay-assisted technology gives an appropriate solution to this situation.Not only relay-assisted system can increase the diversity gain,but also can expand the topology range and transmission distance.In the previous studies of power allocation problems in CR networks,researchers often assume that the channel state information(CSI)is perfect.However,since the CSI is derived from the estimation of the channel state,the disturbance of CSI is unavoidable.The disturbance may cause a significant impact on communication performance of the system.In this case,it's necessary to study the robustness of the system.Robust optimization method will avoid the problems caused by the disturbance effectively and make the whole system improve the ability of resisting interference of the system.According to the above-mentioned problems and techniques,in this paper we propose a robust power allocation algorithm based on maximize energy efficiency for OFDM-based relay-assisted CR networks,while the uncertainties of various channels and the concept of green communication are also considered.The algorithm utilised the upper graph method,the Lagrangian multiplier method,the Karush-Kuhn-Tucker(KKT)condition and the robust worst-case method to derive the analytical solution of the transmit power.And then the iterative form of the algorithm is given in this article.The simulation results show the algorithm can adjust the transmit power to achieve the optimal energy efficiency of the system under the constraints of minimum throughput,maximum transmit power and interference temperature.Meanwhile,the algorithm has low computational complexity and fast convergence speed,and can effectively overcome the influence of the uncertainty of channel state information.