Research On The Physical Layer Security In Cooperative Communication And Non-orthogonal Multiple Access Networks

With the increasing demands of wireless communication and the improvement of wireless communication technology,there are more and more complicated communication environment and secrecy problems for 5G mobile communication.Despite the introduction of a new encryption algorithm based on key encryption technology,the security of wireless mobile communication is facing a severe challenge with the rapid development of mobile internet and the rapid promotion of mobile payment.The physical layer security technology utilizes the wireless channel characteristic to realize the secure communication,and effectively overcomes the traditional security technology based on the eavesdropper limited ability flaw,and then satisfies the wireless communication reliability and the security demand.Physical layer security as a complementary and alternative cryptographic method to defend against eavesdroppers from information-theoretic perspective has drawn numerous research interests.From the point of view of physical layer security,this paper analyzes the shortcomings of traditional relay transmission and orthogonal multiple access,and studies how to use hybrid relay,full-duplex,and non-orthogonal multiple access in order to improve the physical layer security in the new network environment.The main contributions of this paper can be listed as follows:Aiming at the network security issue,the influence of the traditional DF,IDF,and SDF schemes on the network communication is analyzed,and the IHDAF scheme combined with the characteristics of AF is introduced.For the first time,in order to reduce the network feedback overhead and hardware cost,the IHDAF scheme based on TAS method(i.e.,the TAS-IHDAF scheme)is proposed.The secrecy outage probability of the TAS-IHDAF scheme is derived by analyzing secrecy performance.Theoretical analysis and simulation results demonstrate that the proposed TAS-IHDAF scheme outperforms the IDF and SDT schemes in terms of secrecy outage probability.This is due to the fact that the proposed TAS-IHDAF scheme takes into the advantages of both the AF and DF modes.Furthermore,in order to fully examine the benefits of the proposed TAS-based IHDAF scheme,the CB(i.e.,codebook-based beamforming)scheme is introduced.Theoretical analysis and simulation results demonstrate that the proposed TAS-based IHDAF scheme can outperform the CB scheme with less feedback overhead due to the use of TAS method.The analysis results show that the proposed TAS-IHDAF scheme provide an effective transmission strategy for secure communication in multi-antenna communication networks.FD(full-duplex)technique has now been proved to be feasible in practice to offer high spectrum efficiencies due to the development of the SIC(self-interference cancelation)techniques,it can also improve the secrecy performance of communication networks.Based on the analysis of the selection and FD techniques,a JURS(joint user and relay selection)scheme to enhance physical layer security in a multi-user multi-relay network is proposed,where the best pair of the user and relay that maximizes the user-to-destination SINR(signal-tointerference-to-noise ratio)is jointly selected.To avoid the high complexity of the joint selection scheme,a SURS(separate user and relay selection)scheme is also proposed,where one relay is firstly selected to maximize the relay-to-destination SINR and a useris then selected to maximize the SINR from the user to the selected relay.Asexpected,the JURS scheme can outperform the SURS scheme.However,simulation results also indicate that the low-complexSURS scheme can achieve similar secrecy performance as the high-complex JURS scheme under some specific conditions,e.g.,when the number of users is much larger than that of the relays or when the average signal-to-noise ratio of user-to-relay channel is much higher than that of the relay-to-destination channel.Hence,our work provides a flexible choice for system design.Specifically,if the system has a powerful computational capability,the JURS scheme is preferred to achieve the best secrecy performance.Otherwise,the SURS scheme can be used to reduce the implementation complexity.A new TSSRS(two-stage secure relay selection)method for NOMA(non-orthogonalmultiple access)transmission systems(i.e.,the TSSRA-NOMA scheme)is proposed.The operate mode of the proposed scheme is to maximize the capacity of one source-destination pair,while guaranteeing the successful communication of the other source-destination pair.As a benchmark,the secrecy performance of the TSSRS strategy with orthogonal multiple access(OMA)scheme(i.e.,the TSSRSOMA scheme)is also analyzed.Both theoretical analysis and simulation results demonstrate that the proposed TSSRS-NOMA scheme significantly outperforms the TSSRS-OMA scheme when the transmit power at the source and relay are in the low and medium regimes.In addition,the analysis results also show that the advantage of the TSSRS-NOMA scheme over the TSSRS-OMA scheme becomes obvious when the two source-destination pairs have profoundly different secrecy requirements.The two schemes based on OMA and NOMA method can provide the optimal design basis for multi-user pairs in relay selection networks with different transmit power.Considering the communication scenarios with multi-user and large-scale antenna at base station,a novel beamforming to enhance physical layer security in a NOMA system with the aid of AN is proposed.The proposed scheme uses two scalars to balance the useful signal strength and interference between bat the strong and weak users,which is a generalized version of the existing beamforming designs in the context of physical layer security for NOMA.The optimal power allocation among useful signals and AN together with the two optimal beamforming scalars are determined in order to maximize the secrecy sum rate.The asymptotic analysis in the high signal-to-noise ratio regime provides an efficient and near-optimal solution to optimize the beamforming scalars and power allocation coefficients.The asymptotically optimal power allocation shows that,as the transmit power increases,more power should be allocated to the weak user or AN signals,while the power allocated to the strong user keeps constant.Furthermore,simulation result also shows that the proposed novel beamforming design can significantly outperform two benchmark schemes.The proposed NOMA transmission mode can provide an effective transmission reference standard for downlink multiuser communication in 5G cellular cells.For the first time,the dependence between the eavesdropper'sability to conduct SIC(successive interference cancellation)and her channel quality is considered.In addition,in a NOMA system,the transmitted signals to a weak user should be decoded by the strong user in order to enable SIC at the strong user.This leads to the fact that the achieved security of the weak user is conditioned on the assumption that the strong user will not release any information transmitted to the weak user.Based on the above analysis,and considering NOMA transmissionin with a passive eavesdropping scenario,an optimal problem is formulated to the maximize the secrecy rate for the strong user subject to a maximum allowable secrecy outage probability,while guaranteeing a constraint on the transmission rate to the weak user.And then the exact and asymptotically optimal power allocation and redundancy rate were determined.Both theoretical analysis and simulation results demonstrate that the asymptotic results accurately approach to the corresponding exact results in the high main-toeavesdropper ratio(MER)regime.Besides,the analysis reveals that the cost of the considered security decreases and the optimal power allocation becomes less sensitive to the maximum allowable secrecy outage probability as the transmission rate requirement to theweak user increases.Furthermore,the equal power allocation is optimal under the high transmit power with a small quality of service(QoS)requirement for the weak user.The proposed NOMA transmission scheme provides an effective design discipline to satisfy different users' QoS requirement in 5G network systems.Based on the previous analysis of single relay and relay selection,a new beamforming strategy with relay cooperation is proposed to achieve secure SWIPT communication.The traditional CB(cooperative beamforming)and CJ(cooperative jamming)in relay network is analyzed.Based on this analysis,employing the CB-ES(cooperative beamforming and energy signal)method for providing both secure communication and efficient wireless energy transfer(i.e.,simultaneous wireless information and power transfer: SWIPT)for the first time.By considering colluding eavesdroppers with imperfect channel state information,an optimization problem for maximizing the secrecyrate between the source and the legitimate information receiver under both the power constraints at the relays and the wireless power transfer constraint at the energy-harvesting receiver is formulated.Since such a problem is nonconvex and hard to tackle,and then a two-level optimization approach that involves aone-dimensional search and the semidefinite relaxation(SDR)technique is proposed to solve this problem.Simulation results show that the proposed robust scheme achieves better worst-case secrecy rate performance than other nonrobust schemes and the CB-AN(cooperative beamforming and artificial noise)scheme.Furthermore,the proposed CB-ES scheme can provide new experience and reference in the practical application of SWIPT.