Research On The Robust Physical Layer Security Technology For Heterogeneous Networks

Due to the more open network architecture,more types and large number of network nodes,heterogeneous networks(HeNets)are vulnerable for wiretapping,which aggravates the risk of disclosing confidential information.In recent years,physical layer security(PLS),which exploits the physical characteristics of wireless channels to guarantee the communication security,provides a new method to secure HeNets.Meanwhile,it should be noted that the quality of channel state information(CSI)and anti-interference are very important to the robustness and security of PLS schemes.However,due to the influence of network topology,the channel errors appear in HeNets more easily.On the other hand,with the development of wireless communication technology,eavesdroppers(Eves)may have the malicious interference ability,and the open architecture of HeNets further aggravates this situation where the active Eves exist.Due to the complex inter-tier interference and dynamic network topology,the robust PLS progresses in passive wiretapping scenario with imperfect CSI and active wiretapping scenario in traditional networks cannot be applied to HeNets directly.Meanwhile,a few exsiting studies for HeNets only focused on the PLS model and analysis in passive wiretapping scenario with imperfect CSI,which did not explore how to design the transmitted signal to improve the system security and how to resist the active wiretapping.Specifically,there are three problems to be solved in the study of robust PLS for HeNets: 1)In the passive wiretapping scenario,CSI error will decrease the reliability and security of network,but the existing research lacks the relevant robust PLS schemes;2)In the passive wiretapping scenario,CSI error will decrease the security energy efficiency of system,but the existing research lacks the relevant robust PLS schemes;3)The existing research lacks the robust PLS schemes to resist active Eves,which can be applied to HeNets.For the above problems,this paper studies the robust PLS technology for HeNets to design robust PLS schemes in passive and active wiretapping scenarios,respectively.Firstly,in the passive wiretapping scenario,considering different channel error models,we propose an artificial noise(AN)-aided robust PLS scheme under the constraint of quality of service(QoS)and a robust PLS scheme based on cooperative beamforming to secure the delay tolerant system.Among them,the former and latter schemes can be respectively applied to the case of channel estimation and quantization error in practical networks.Then,we propose a robust PLS scheme with AN-assisted under the constraint of security outage probability to secure the delay sensitive system.Furthermore,considering the system security and energy efficiency comprehensively,we propose a robust security energy efficiency optimization scheme.Finally,to secure the HetNets in active wiretapping scenario,we propose a robust PLS scheme based on AN.Specifically,the main contributions of this paper are as follows:1.To secure the delay tolerant system under passive wiretapping,we propose an AN-aided robust PLS scheme under the constraint of QoS.Considering the gaussian random channel error,we jointly design the downlink information beamforming and AN vectors of the MBS and FBSs,which makes Eves jammed by the downlink signal of other users.The problem of maximizing the energy harvesting(EH)performance is modeled under the constraints on the total transmit power of base station,the outage probability of information transfer and confidential information eavesdropped.To obtain the optimal design,the originally non-convex problem is first transformed into an equivalent form;then,the Bernstein-type inequality and the Large-deviation inequality are utilized to transform the outage probability limits into convex linear matrix inequalities,respectively;finally,the rank-one beamforming constraints are processed with quadratic equality constraint procedure and successive convex approximation(SCA).Simulation results validate the security and the robustness of proposed scheme.2.To secure the delay tolerant system under passive wiretapping,we propose a robust PLS scheme based on cooperative beamforming.Considering the norm-limited channel error,we jointly optimize the downlink beamforming vectors of MBS and FBSs adjacent to Eves to make the mutual interference between network nodes imposed much on Eves.Based on above consideration,we first explore the scenario with un-colluded Eves,where the optimization problem is modeled to maximize the system security rate while satisfying the constraints of QoS on legitimate users and total transmit power of each base station.Firstly,the originally non-convex problem is transformed equivalently to acquire an equivalent form;then,the non-convex constraints are dealt with SCA algorithm and semi-definite relaxation(SDR)technology,respectively,and the infinite constraints caused by CSI error are furtherly dealt with Lagrange dual theory;finally,it is transformed into a series of convex estimation problems to acquire the optimal solution.Furthermore,the framework is extended to the case of colluded Eves.In this case,the modeled problem is transformed into a two-level optimization problem by equivalent transformation.Among them,the outer layer problem is a one-variable optimization problem,which can be solved directly by one-dimensional linear search method;the inner layer problem can be finally transformed into a convex semi definition programming(SDP)problem by semi definition relaxation(SDR)technology,Charnes Cooper transformation and Lagrange dual theory.The simulation results verify the security and robustness of the proposed scheme.3.To secure the delay sensitive system under passive wiretapping,we propose a robust PLS scheme with AN-assisted under the constraint of security outage probability.The inter-tier interference in networks can be applied much more on Eves while having lower effects on legitimate users by base station cooperation.Firstly,in the case of norm limited channel error,the downlink information beamforming and AN vectors of MBS and FBS are jointly designed to minimize the total transmission power of system,while satisfying the constraints of MU's downlink QoS,FU's EH and security outage probability.To obtain the approximate optimal design,the originally non-convex problem is transformed into a series of convex approximation problems by means of S-produre,SCA and SDR technologies.Furthermore,the framework is extended to the case of gaussian random channel error,where the optimization problem is a non-convex problem with the probabilistic constraints of MU's downlink QoS,FU's EH and security outage probability.Combining SDR and SCA technologies,we use Large-deviation inequality,Bernstein-type inequality and S-procedure to transform outage probability constraints into deterministic convex constraints.The simulation results verify the security and robustness of proposed scheme.4.To guarantee the secrecy energy efficiency in passive wiretapping scenario,we propose a robust security energy efficiency optimization scheme.The inter-tier interference in networks can be applied to decrease the reception of Eves to increase the utilization efficiency of transmit power by base station cooperation.Furthermore,AN is injected to improve the secrecy performance of system.In the case of norm limited channel error,AN is injected into the downlink information beams of MBS and FBSs,and then the downlink information beamforming and AN vectors are jointly optimized to maximize the secrecy energy efficiency of system.Firstly,the originally non-convex problem is transformed equivalently by SDR and SCA technologies;then,the infinite constraints caused by CSI errors are dealt with by Lagrange dual theory to obtain the optimal design.Furthermore,to reduce the cost of signaling interaction between base stations and relieve the computing pressure of central processing station,a distributed solution method based on alternative direction multiplier method(ADMM)is proposed.Simulation results validate the effectiveness and robustness of proposed scheme.5.To secure the system in active wiretapping scenario,we propose a robust PLS scheme based on AN.The secrecy performance of system is improved by injecting AN into the tramsmitted signal,and then optimizing the distribution of transmit power of useful an AN signal.Firstly,considering the situation that Eve sends the uplink pilot interference,the influence of the uplink pilot interference on the channel estimation of legitimate users is studied and the precoding matrices of downlink data and AN signals of MBS and FBS are designed,respectively.Based on the consideration,a solution method based on one-dimensional linear search is proposed to optimize the transmission power of the downlink data and AN signal of the base station for the aim of maximizing the secrecy rate of system.Furthermore,considering the situation that Eve interferes with the user's downlink communication after transmitting the uplink pilot interference,we propose a discrete zero sum game method to obtain the optimal transmission power design.The simulation results verify the security and robustness of proposed scheme.