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Research On Physical Layer Security Technology In Non-orthogonal Multiple Access Network Based On Cooperative Communication

Posted on:2024-04-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:S XuFull Text:PDF
GTID:1528307136999169Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
As one of the potential key technologies of the sixth generation mobile communications(6G),non-orthogonal multiple access(NOMA)technology can effectively improve the spectral efficiency of the system,realize the requirements of high capacity,large connection and low delay,and is promising to be widely used in industry,agriculture,medicine and other fields.Since the transmission rate and communication distance are subject to the transmission power of the equipment,it is difficult to achieve the future communication requirements only depending on the source node.Cooperative communication technology employs relay,reconfigurable intelligent surface(RIS),simultaneously transmitting/refracting and reconfigurable rntelligent surface(STAR-RIS)and other equipments for signal aggregation and forwarding,which is capable of improving the coverage quality of wireless communication.Therefore,the integration of cooperative communication technology and NOMA is one of the key technologies of future communication.In addition,with the rapid development of the internet and the wide application of mobile payment,the security of wireless mobile communication is facing severe challenges.The physical layer security(PLS)technology has also become a research hotspot in the field of wireless communication.This is because it can employ the characteristics of wireless channels to realize the secure communication of information,complementing traditional security technologies such as key encryption that rely on the limited computing power of eavesdroppers,while meeting the reliability and security requirements of wireless communication.From the perspective of PLS communication,this thesis analyzes the shortcomings of traditional orthogonal multiple access(OMA)technology and relay technology in secure communication,studies how to meet the communication requirements of next generation networks,and comprehensively uses the advantages of relay technology,NOMA technology and RIS technology to improve the PLS performance of wireless networks.The main research contents of this thesis are listed as follows:Aiming at the secure communication problem in the multi-source and multi relay scenarios for the NOMA downlink network,a optimal two-stage secure signal source relay selection scheme is proposed,which maximizes the security capacity of one NOMA user while meeting the security transmission requirement of the other NOMA user.In addition,this paper analyzes the impact of amplifying and forwarding(AF)relay,decoding and forwarding(DF)relay and eavesdropping node using serial and non-serial modes on the communication security of NOMA network.Different from the existing researches,this paper deduces the corresponding closed expression of secrecy outage probability(SOP)by using gaussian chebyshev approximation.In addition,the optimal power allocation(PA)coefficient is obtained by minimizing the SOP of any source-relay pair.The simulation results show that NOMA network can achieve better security performance than OMA network and existing literature on maximum minimum selection scheme under the condition of limited transmission power.The source relay selection scheme based on NOMA proposed in this paper can guarantee the secure transmission system of multi-source and multi relay.In view of the security problem of the two-stage cooperative NOMA network of the AF relay,on the premise of saving the hardware overhead,each AF relay equipped with multiple antennas uses the selection combining(SC)method to process the received signal and the optimal antenna selection(OAS)method to transmit the signal,and proposes the optimal antenna-relay selection scheme,which maximizes the security capacity of nearby user while meeting the security transmission requirement of the remote user.With the help of chebyshev polynomial,the closed expression of SOP for the network under the single relay-antenna selection scheme is analyzed.On this basis,the asymptotic SOP and the security diversity order(SDO)of the network are derived using gamma functions.Different from the existing research,the optimal PA coefficient is obtained by minimizing the SOP of any relay-antenna pair.The simulation and experimental results show that the SOP of the NOMA network under the scheme of this paper is lower than that of networks with fixed PA coefficients and traditional OMA networks.The relay antenna selection scheme proposed in this paper can provide an excellent design scheme for the secure transmission of relay cooperative NOMA networks equipped with multiple antennas in actual communication scenarios.Aiming at the PLS communication problem in RIS cooperative NOMA network,the optimal RIS reflection unit phase shift and the selection of the number of reflection units are proposed,which meets the communication requirements of two NOMA users simultaneously by adjusting the RIS phase shift and the selection of the number of reflection units.The central limit theorem is used to approximate the cascaded channels of RIS.Then,we obtain the distribution characteristics of the channels,derive the SOP of RIS assisted NOMA network,and further analyze the asymptotic security and SDO of the network using inequality theory.Different from the existing research,in order to minimize the NOMA network SOP,two parameters that affect the network security performance,namely,the PA coefficient and the number of reflective units of RIS,are optimized to obtain the best PA coefficient and the optimal number of reflective units.The simulation results are consistent with the theoretical analysis,which proves that the RIS assisted NOMA network security communication scheme proposed in this paper can achieve better security performance than the traditional OMA network scheme,random phase shift adjustment scheme and design scheme without optimizing the number of reflection units.The research results can provide an effective transmission scheme for energy constrained NOMA network security communication.Aiming at the reliability and security problems of STAR-RIS assisted NOMA communication network,the K_G distribution function is used to approximate the distribution characteristics of cascaded channels,and the SOP of STAR-RIS aided NOMA network is derived,and further analyze the asymptotic security and SDO of the network using mathematical method of enlargement and reduction.Compared to traditional OMA networks,traditional relay networks,and RIS assisted NOMA networks,the best PA coefficient and energy splitting(ES)factor of STAR-RIS intelligent units are obtained by minimizing the average SOP of the network.The results show that,on the one hand,The K_G distribution function is used to approximate the distribution characteristics of the cascade channel,which is more practical than the non-central chi square distribution(NCCSD),thus the network security performance obtained is better than that of NCCSD.On the other hand,compared with the traditional OMA network security communication scheme and the traditional relay assisted communication scheme,the proposed STAR-RIS assisted NOMA network security communication scheme can obtain a lower average network SOP.The STAR-RIS cooperative NOMA network security communication scheme proposed in this paper can provide inspiration and guidance for cellular downlink security communication scenarios with limited wireless communication range.Aiming at the security problem of multi antenna STAR-RIS assisted NOMA network,a beamforming(BF)scheme is designed to maximize the cell center user channel gain.The cascaded channels of STAR-RIS are approximated to laguerre function,which is expanded by laguerre series and approximated to gamma function to characterize the distribution characteristics of the cascaded channels.The SOPs of two NOMA users in the network are analyzed and derived by inequality theory,and the asymptotic SOP and SDO of the network are further obtained using beta functions,and degenerate hypergeometric functions.Existing research often uses fixed PA coefficients and ES factors to analyze network SOP.However,based on the closed expression of network average SOP,an optimization problem is formulated with the goal of minimizing the network average SOP under the constraints of PA coefficient and ES factor of STAR-RIS units.The optimal PA coefficient and ES factor of STAR-RIS cells are obtained by using alternative optimization method.The simulation results are consistent with the theoretical analysis,which verifies that the STAR-RIS assisted NOMA network scheme proposed in this paper has higher security performance than the traditional OMA network scheme and the RIS assisted NOMA network scheme.The STAR-RIS cooperative NOMA network security communication scheme proposed in this paper can provide a theoretical basis for security communication of the next generation network.
Keywords/Search Tags:non-orthogonal multiple access, cooperative communication, reconfigurable intelligent surface, physical layer security, secrecy outage probability
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