Research On Transmission Technology Based On Wireless Energy Harvesting In Cooperative Non-Orthogonal Multiple Access System

The internet of things(Io T)as the key scenario of the fifth generation mobile communications,the massive communication devices and the limited battery capacity put higher requirements on the communication system.Therefore,non-orthogonal multiple access(NOMA)and wireless energy harvesting have been extensively studied in both academia and industry.Specifically,NOMA serves multiple users with the same block of time and frequency resources,thus providing higher spectral efficiency compared to traditional multiple access technologies.Wireless energy harvesting technology utilizes radio frequency signals in the wireless environment for energy harvesting,thus enhancing the communication performance of energy-constrained devices.In addition,cooperative NOMA,which design near users to help far users with the goal of improving transmission reliability,has also received a lot of attention.Due to the broadcast character of the wireless channel,the security of communication in cooperative NOMA also urgent to be solved.Physical layer security(PLS)technology does not require complex coding and decoding algorithms,but directly exploits the natural characteristics of the wireless channel to improve the performance of energy-constrained cooperative NOMA systems.Based on the above inspiration,this dissertation firstly proposes a multi-user impartial cooperative NOMA transmission scheme based on wireless energy harvesting with the goal of improving system reliability,and then proposes a security cooperative NOMA transmission scheme based on wireless energy harvesting with statistical channel state information(CSI)with the goal of improving system security.The specifics of this paper can be summarized as follows:1.In this dissertation,we propose a multi-user impartial cooperative NOMA transmission scheme based on wireless energy harvesting,which includes a source node and multiple user nodes.Unlike the traditional cooperative NOMA,this paper designs that when the far user can satisfy the decoding demand,wireless energy harvesting will also be performed and the signal will be forwarded in the cooperative transmission phase to improve the transmission performance of the near user.In addition,based on the considered multi-user scenario,this paper also proposes three user pairing strategies to investigate the impact of user location on the proposed scheme.Finally,closed-form expressions for the outage probability of near and far users are obtained using mathematical tools such as Gaussian Chebyshev approximation,and closed-form expressions for diversity order,diversity-multiplexing trade-off and system throughput are obtained.By comparing with the existing scheme,the proposed scheme can obtain lower outage probability,higher diversity order,better diversity-multiplexing trade-off performance.2.In this dissertation,we propose a security cooperative NOMA transmission scheme based on wireless energy harvesting under statistical CSI,which includes a source node,two user nodes,and an eavesdropper.The near user acts as an energy harvesting relay to assist the far user in communication.In this paper,we consider a more practical scenario where eavesdropper is wiretapping in both direct and cooperative transmission phases,and design idle nodes to send artificial noise to disrupt the eavesdropper.Closed-form expressions for the secrecy throughput of the near and far users are obtained by using mathematical tools such as Gaussian Chebyshev approximation and Gaussian Laguerre approximation.Subsequently,closed-form for the system sum secrecy throughput is also obtained.Based on the obtained closed-form expressions,an alternating optimization algorithm based on statistical CSI is proposed in this dissertation with the objective of maximizing system sum secrecy throughput,and the codebook rates and power allocation factors are jointly optimized.Finally,the simulation results verify the correctness of the theoretical derivation of this paper.By comparing with existing scheme,it is verified that the proposed scheme can obtain better security performance.