Research On Physical Layer Security Of Non-Orthogonal Multiple Access System With Wireless Energy Harvesting

With the rapid development of the Internet of Things(Io T),the massive popularity of wireless devices and the proliferation of wireless data communication have brought significant challenges to the 5th generation mobile communication system.Non-orthogonal multiple access(NOMA)technology and wireless energy harvesting technology are two promising technologies for improving spectral efficiency and energy efficiency,respectively,and have received widespread attention in the field of wireless communications.At the same time,although the development of Io T has made convenient and fast services available to all industries,Io T system must provide appropriate security mechanisms due to the importance of ownership and privacy protection.Physical layer security provides secure data transmission by exploiting the inherent characteristics of the wireless channel without the need for keys or complicated coding and decoding algorithms,and thus has become a hot research topic for solving security problems.In this context,this dissertation focuses on improving the physical layer security of cooperative NOMA system with wireless energy harvesting.Considering the shortcomings of the conventional cooperative NOMA system,the impact of artificial noise(AN)on the transmission security performance of cooperative NOMA system is mainly studied.The main contributions and novelties of the dissertation are summarized as follows:1.A secrecy-enhancing transmission scheme for cooperative NOMA system with wireless-powered full-duplex relaying is proposed.For the studied system model,this dissertation adopts a joint time and power allocation scheme and proposes a strategy for ANassisted secure transmission to ensure the security of the system.Specifically,the full-duplex relay node in the proposed scheme can harvest energy from the transmit signal of the source node and self-interference signal,of which the energy harvested in the first time phase can be used to emit interference signal to reduce the decoding performance of the eavesdropper.For the proposed AN-assisted secrecy-enhancing scheme,the closed-form expression for the lower bound of the ergodic secrecy sum rate(ESSR)is analyzed,and the scheme achieves a positive lower bound of the ESSR,thus showing that the security of the system can be achieved.Finally,the simulation results verify the accuracy of the theoretical analysis of the proposed scheme,and the proposed scheme can obtain higher ESSR performance compared to the conventional cooperative NOMA transmission scheme.2.An energy harvesting friendly AN-assisted secure transmission scheme in cooperative NOMA system is proposed.Due to the power limitations of the nodes in the actual network,many nodes are reluctant to expend their energy transmitting AN to assist other users in transmission.For this reason,we introduce energy harvesting friendly jammer in the cooperative NOMA system,and use friendly jammer to emit AN to confuse eavesdropper in order to improve the security transmission performance of the system.In this system,there is no direct transmission link between the source node and the far user,which requires the relay node to assist in transmission,and there exists an eavesdropper who can eavesdrop the signal sent by the relay node.Specifically,in the proposed scheme the friendly jammer harvests energy from the source node in the first time phase,and use it to generate AN signal to interrupt eavesdropper in the second time phase.For the proposed scheme,we derived a closed-form expression for the secrecy throughput to evaluate the secure performance of the system.Finally,the accuracy of the theoretical analysis of the proposed friendly AN-assisted transmission scheme is verified by simulation results,and the scheme achieves better secure transmission performance compared with the conventional cooperative NOMA scheme.