Research On Secure Communication And Efficient Energy Transmission For SWIPT Systems

Simultaneous wireless information and power transfer(SWIPT)is a new and hot research area in recent years,which enables the so-called green radio communications by integrating radio frequency(RF)energy harvesting technologies into traditional wireless communication networks.Yet,the technology of SWIPT brings a paradigm shift in resource allocation scheme design due to the imposed new challenges.Moreover,in practice,secrecy communication is also an essential issue in the SWIPT systems in view of the broadcast nature of the wireless information transfer.Therefore,the research on resource allocation schemes considering both secrecy communication and efficient wireless energy transfer for SWIPT systems has important practical significance.In this thesis,based on the traditional information-theoretic physical(PHY)layer security and transmit beamforming technologies,the robust secrecy beamforming for wireless information and power transfer fairness in multiuser MISO communication system,the efficient energy transmission solutions for MIMO wiretap channels with SWIPT,energy transfer fairness precoder design for multi-user MIMO wiretap channels,the precoder design for energy harvesting maximization in secure MIMO systems and the robust secure beamforming for wireless powered full-duplex(FD)systems with self-energy recycling are studied.The main results and contributions are summarized as follows: 1.For the multiuser MISO communication system with SWIPT,a robust secrecy beamforming design is proposed to overcome the energy harvesting imbalance among the energy receivers(ERs).By taking into account of the imperfect channel state information(CSI),power splitting(PS)information receiver(IR)and the potential eavesdropping from the ERs,this design is modeled as an optimization problem that maximizes the minimum harvested energy among the multi-antenna ERs.Besides,both the secure communication requirement and the lowest electrical energy storage threshold at IR are also guaranteed in the formulated optimization problem.The considered max-min problem is non-convex and hard to tackle.By introducing the technique of semidefinite relaxation(SDR),the optimal solution of this problem is obtained and the tightness of this relaxation is revealed.Besides,a suboptimal beamforming design scheme is proposed with low computational complexity.Simulation results show that the proposed robust schemes are more efficient than other schemes in terms of energy harvesting and transmit power saving.2.For the MIMO wiretap channels with SWIPT,an efficient transmission solution which both guarantees the secure communicaton and promotes the wireless energy transfer is proposed.In particular,the transmit covariance matrix is optimized for the energy harvesting maximization(EHM)problem under the constraint of secrecy rate and transmit power.Note that the formulated problem is nonconvex and hard to tackle.To circumvent it,the Taylor series expansion is firstly employed to convert the problem into a convex optimization problem.Then,based on the analysis of its dual problem,an iterative algorithm,which includes a semiclosed-form solution,is proposed to handle this EHM problem.The scenario of imperfect CSI of the energy receiver that could be the potential eavesdropper is also considered.In this scenario,a Bernstein-type inequality-based iterative algorithm is proposed to deal with the challenging outage-constrained EHM problem.Simulation results demonstrate the efficiency of the proposed designs.3.For the multiuser secure MIMO communication system with SWIPT,the max–min fairness for wireless energy transfer is studied.In particular,the minimum harvested energy among the multiple multi-antenna energy receivers that could be potential eavesdroppers is maximized while guaranteeing secure communication for multi-antenna information receiver.The dual use of artificial noise to facilitate both wireless energy transfer and secure communication is exploited in the formulated problem.Both scenarios of perfect and imperfect channel state information(CSI)known at the transmitter are considered.For the perfect CSI case,the formulated max–min energy harvesting(MM-EH)problem is non-convex and intractable.To circumvent it,an iterative optimization algorithm based on Taylor series expansion is proposed.Then,for the imperfect CSI case,a max–min robust energy harvesting(MMR-EH)problem is considered.Though the MMR-EH problem is more complicated than the MM-EH problem,it is revealed that the iterative optimization method can be extended to deal with the former,wherein the convex problem with linear matrix inequalities(LMIs)is solved iteratively.Simulation results show the efficiency of the proposed solutions in terms of energy harvesting.4.The weighted-sum energy harvesting maximization(WS-EHM)problem in mutiuser secure MIMO system with SWIPT is further investigated.Two scenarios that the interference from the energy signal can and can not be eliminated at the receivers are taken into account.For each type optimization problem in each scenario,the joint design of the information and energy transmission covariances is studied and the secure transmission solution is proposed.Both two types of the WS-EHM problems are nonconvex,and hard to tackle.For the first type optimization problem,it is solved optimally under the general and special cases.A sequential convex optimization method is proposed for the general case problem,while a layered iterative algorithm with closed form solution is proposed for the special case problem.For the second type optimization problem,a judicious transformation is firstly performed on it.Then,a block Gauss-Seidel(GS)algorithm based on logarithmic barrier method and gradient projection(GP)is derived to obtain the optimal solution of the reformulation by solving convex problems alternately.Furthermore,the resulting block GS method is proven to converge to a Karush-Kuhn-Tucker(KKT)point of the original WS-EHM problem.Simulation results show the outstanding energy harvesting performance and computational efficiency of the proposed algorithms.5.For wireless powered full-duplex(FD)communication system,where an energy-constrained FD information transmitter(IT),powered by wireless energy transfer from a dedicated energy transmitter(ET),intends to send confidential information to the information receiver(IR)in the presence of multiple idle users(IUs)that could be the potential eavesdroppers,the robust secure beamforming design is studied.Considering the scenario of imperfect channel state information(CSI)and assumming that the IUs are able to harvest energy from radio frequency signals,the worst case secrecy rate at the IR is maximized by jointly optimizing the transmit covariance matrix at the ET,information beamforming and artificial noise(AN)covariance at the IT and power splitting ratios at the IUs,while ensuring their individual transmit power constraints and the minimum required power transferred to the IUs.Semidefinite relaxation(SDR)and extended S-Procedure approaches are employed to transform the original non-convex optimization problem into convex problem,which can be efficiently solved by solving a sequence of semidifinite programs.Furthermore,the tightness of the SDR is revealed by showing the existence of the rank-one optimal solutions.For performance comparison,two heuristic schemes for ease of implementation are also developed.Numerical results are presented to show the efficiency of the proposed schemes.