Secure And High Efficient Transmission Schemes And Their Performance Analysis In Amplify-and-forward Relaying Systems

As one of the key techniques of the fourth generation(4G)mobile communication systems,wireless relaying technique achieves significant advantages of extending wireless service coverage and improving the system reliability.But the openness of wireless communication brings serious challenges on the security of wireless relaying systems.Except for the security attacks from external eavesdroppers,the source's confidential message may be eavesdropped by an untrusted relay.The untrusted relay model has practical applications in defence,financial,and government intelligence networks,where the information the relay forwards has to be kept secret from it.Therefore,the study of secure transmission schemes and performance analysis for untrusted relay systems are of high importance.On the other hand,the fifth generation(5G)network will serve as a key enabler in meeting the continuously increasing demands for future wireless applications,including ultra-high data rate,ultra-large number of devices,and etc.In this context,the conventional orthogonal multiple access(OMA)based wireless relaying network cannot satisfy the above demands of 5G networks.Against this backdrop,the non-orthogonal multiple access(NOMA)scheme has been emerged as one of the key techniques to significantly improve the spectral efficiency of 5G mobile communication systems.As a natural extension,the NOMA-based wireless relaying systems has the advantages of highly improving the transmission effectiveness.Recently,hybrid wireless relaying thechnique and the NOMA scheme is a brand-new and interesting research direction and has gained significant attention in the research area.Aiming at satisfying the above demands of 4G/5G systems,this thesis takes the amplify-and-forward(AF)relaying system as the body for research,and mainly focus on the study of the following two hot topics: one is secure transmission in the untrusted AF relaying systems and the other is high efficient transmission in AF relaying systems with NOMA.This dissertation makes research on the drawbacks exsiting in the research and some novel results are presented.On the one hand,these results make contributions to the research on the physical layer security of wireless relaying systems.On the other hand,the analytical results provide theoretical guidance for the design of the application of NOMA in wireless relaying systems in practice.The main research works and innovations are outlined as follows:1.To understand the performance limit of untrusted relay networks,we investigate the secrecy outage performance of untrusted AF networks,in which cooperative jamming technique is employed at the destination to realize positive secrecy rate.Under Nakagami-m fading channels,tight closed-form and asymptotic expressions for the lower and upper bounds of the secrecy outage probability(SOP)are derived.The results explicitly show that a secrecy diversity order of 1 2n(m,m mi /2)is achieved,where 1m and 2m are the respective integer fading parameters of the source-relay and relay-destination links.Afterwards,an asymptotically optimal power allocation(OPA)scheme is proposed to minimize the SOP.Numerical and simulation results show that the proposed OPA offers significant improvement on the SOP performance.In particular,when 1 2m >m /2,the secrecy diversity order can be improved from 2m /2 up to 1 2 1 22 m m /(2 m+m).2.Motivated by the fact that the performance of multiuser untrusted AF networks have not been reported,a multiuser relay network(MRN)with an untrusted fixed-gain AF relay is considered.To harvest the multiuser diversity while satisfying the security constraint,a joint cooperative jamming and opportunistic scheduling(CJOS)scheme is proposed to combine the advantages of both strategies.Under Rayleigh fading,we derive approximated and asymptotic SOP expressions for the considered system with perfect and outdated channel state information(CSI).These results explicitly show that with perfect CSI,CJOS scheme can improve the secrecy diversity order from 1/2 in single-user networks up to full diversity of 1 in MRNs.However,the outdated CSI degrades the secrecy diversity order from 1 to 1/2.3.Secrecy performance analysis on multiple antenna satellite communication networks with untrusted relay(s)has not been reported so far,which motivates the work herein.We consider a multi-antenna satellite relay network,where an N-antenna terrestrial source communications with an M-antenna terrestrial destination via a single antenna untrsted satellite relay.To realize positive secrecy rate and harvest the multiple antenna diversity gain,a joint cooperative jamming and beamforming scheme is proposed.Moreover,both variable-gain relaying(VGR)and fixed-gain relaying(FGR)protocols are considered.Under Shadowed-Rician fading channels,we derive tight approximated and asymptotic expressions for the SOP in closed-form,which explicitly show that the achievable diversity order in terms of SOP is limited to min(N,M/ 2),rather than the full diversity order of min(N,M)in trusted networks.We then propose an asymptotic OPA scheme,which minimizes the SOP.We reveal that for the VGR system,OPA can help to improve the secrecy diversity order from M/ 2 up to 2NM /(2N + M)in case of N > M/2.However,OPA has no impact on the secrecy diversity order of the FGR system.4.In the literature on the NOMA-based multi-antenna relaying networks,only asymptotic expressions for users' ergodic rates were presented.Moreover,maximal ratio transmission at the multi-antenna source is another promising transmission scheme,while it has not been considered in the literature.Motivated by the above findings,this thesis provides a unified ergodic rate analysis of NOMA-based multi-antenna relay networks.Unified tight approximations for users' ergodic rates and system ergodic sum rate(ESR)are derived in closed-form,covering two attractive diversity configurations,i.e.,maximal ratio transmission with receive maximal-ratio-combining(MRC)and transmit antenna selection with MRC.Accuracy of the analytical results is verified by simulations.5.The previous work on NOMA-based relaying networks makes the assumption of ideal transceiver hardware.Motivated by this,we attempt to provide a framework on analyzing the effect of residual hardware impairments(RHI)on a NOMA-based relaying network.To this end,we derive new tight analytical and asymptotic expressions for each user's outage probability,ergodic rate,and system ESR.Analytical and simulation results reveal that if the critical condition that users' target rates and power coefficients are properly chosen,the presence of RHI does not affect the user's obtained diversity order.However,RHI decreases the array gain,thus increasing the OP.Moreover,the presence RHI results in a ceiling effect on the system ESR,which depends only on the hardware impairment levels.