Research On Beamforming Technology In Cognitive Satellite-terrestrial Networks

With the rapid development of wireless communication industry,a variety of new intelligent devices and wireless services continue to emerge,resulting in a sharp increase in wireless data flow,which also puts forward higher requirements for the utilization efficiency of spectrum resources.However,under the current policy of fixed spectrum allocation,most of the allocated spectrum resources are not fully utilized,which contributes to the contradiction between the growing spectrum demand and its low utilization more and more prominent.Cognitive radio technology is considered to be an effective means to solve this problem,which has been widely concerned by scholars all over the world.In addition,the combination of beamforming technology and cognitive radio can not only improve the spectrum utilization,but also bring the advantages of effectively resisting the multi-path channel fading,suppressing the interference between users,and improving the system capacity,which has important research value.In this paper,beamforming technology in cognitive satellite-terrestrial networks is studied.The main work is summarized as:1.Considering the cognitive satellite-terrestrial networks,the beamforming algorithm based on signal to noise ratio(SNR)maximization is studied.Taking the SNR received by the secondary user as the index,and meeting the constraints of transmitting power limitation of the secondary network and interference power less than the threshold value to the primary user,aiming at different interference power constraints,the closed expression of the weight vector of beamforming at the starting end is derived by orthogonal beamforming and KKT conditions respectively.Simulation results show that the algorithm can reduce the complexity of the system and meet the actual communication requirements.2.Considering the cognitive satellite-terrestrial relay networks,a beamforming algorithm based on the two criteria of maximizing signal to interference plus noise ratio(SINR)and minimizing interference power is proposed.Considering that the cognitive relay network using the Amplify-andForward(AF)protocol as the secondary network and the satellite communication network as the main network to achieve spectrum sharing,first of all,the goal of maximizing the SINR received by the secondary users is met,and at the same time meet the secondary network transmit power limit For the constraint condition that the interference of the primary user is less than the threshold,the relay beamforming weight vector is designed by Rayleigh quotient;then the interference received by the primary user is used as an indicator,and at the same time,the received SINR of the secondary user of the secondary network is greater than the threshold.The constraint condition is to design the beamforming weight vector at the relay end by the Lagrange multiplier method.Simulation results show that the two proposed beamforming algorithms can ensure the normal operation of the primary network and the secondary network in the case of spectrum sharing,thereby improving the spectrum efficiency.3.Considering the cognitive satellite-terrestrial networks with multiple eavesdroppers,the beamforming algorithm of the network under physical layer security is studied.Considering the existence of multiple eavesdroppers in the secondary network,a beamforming weight vector is designed based on the security rate of the secondary network.First,the zero limit position of the beam is controlled by the zero forcing criterion,and then the problem is simplified to take the SINR of the secondary user as the index.The simulation results show that the algorithm can effectively suppress eavesdropping and ensure the communication quality of the primary network,while maximizing the security rate of the secondary network.