Research On Physical Layer Security In Heterogeneous Cellular Networks

As one of the important forms of future 5G network deployment,heterogeneous cellular networks(HCNs)can significantly improve spectrum utilization and network capacity through reasonably deploying different types of base stations(BSs),e.g.,pico and femto cell BSs.However,due to the open nature of wireless channel,HCNs are vulnerable to malicious attacks or eavesdropping.In recent years,physical layer security(PLS)techniques have attracted much attention since it can solve information security issues by utilizing the characteristics of wireless channel.PLS builds the security system in the wireless transmission process.Nevertheless,the large-scale of nodes and the randomization of the topology bring new challenges to the research and application of PLS technology.Specifically,there are still some problems need to be resolved: Firstly,there are severe intra-tier and inter-tier interferences in HCNs,the existing researches don't fully consider the use of existing interference in the network to improve network security.Secondly,the average distance between base station and eavesdropper becomes closer due to the coordinated multipoint transmission(Co MP)technology,security is limited to eavesdroppers closer to collaborating BSs.Thirdly,HCNs are facing serious energy consumption problems due to the fact that the nodes in HCNs are in large-scale.The existing physical layer security algorithm does not take into account the double demand for security performance and energy saving.Motivated by the above reasons,this paper aims at the design of physical layer security transmission scheme by using PLS technologies,such as Co MP,artificial noise and relay.Aiming at the problem that network security is limited to the complex interference in HCNs,we first propose a physical layer security interference coordination mechanism based on the dynamic business.Then,we propose an enhanced Co MP policy based on secrecy guard zone.Finally,the energy consumption problem is further considered on the basis of improving network security.We propose a theoretical framework for evaluating the tradeoff between secrecy spectrum efficiency(SSE)and Secrecy Energy Efficiency(SEE)in this paper.Main contributions are shown as:1.Aiming at the complex intra-layer and inter-layer interference in HCNs and the limited applicaton of existing interference to improve network security.A physical layer security interference coordination mechanism based on the dynamic business is proposed in this paper.Firstly,we develop a three-dimensional stochastic model by jointly taking into account the randomness of BSs in two spatial dimensions and user arrival and departure processes in one temporal dimension.Through this model,the dynamic business in the network is characterized.We dispatch the existing interference in the network to achieve the minimum interference to users and the greatest interference to the eavesdroppers,thus,the advantages of legal channels over eavesdropping channels are enhanced.Simulation results show that the user arrival and departure processes are key elements influencing the resource allocation factors.Further,the security performance can be enhanced by optimizing the user arrival rate.2.Aiming at the average distance between base station and eavesdropper becomes closer in Co MP,and the existing physical layer security algorithm can't reduce the private information of eavesdroppers which are close to the cooperative BSs.An enhanced Co MP policy based on secrecy guard zone is proposed.The cooperative policy is determined according to whether there is an eavesdropper in the secrecy guard zone.If there is an eavesdropper,the micro-base stations send the useful information and artificial noise based on the superposition coding theory,otherwise,the micro base stations only send the useful information.The security performance is further enhanced by mitigating the interference in the network and worsening the performance of eavesdroppers.Simulation results show that the proposed policy can improve the secrecy throughput of 76.1% at most when faced with small security threats(i.e.for smaller eavesdropper density).3.Aiming at the serious energy consumption problems due to the fact that nodes of HCNs are in large-scale,the existing physical layer security algorithm does not take into account the double demand for security performance and energy saving.A theoretical framework for evaluating the tradeoff between SSE and SEE is proposed in this paper.The security and energy consumption of network are characterized by SSE and SEE,respectively.Then,a heuristic iterative algorithm is proposed to optimize the transmission power and density of relay,which improves SSE and SEE tradeoff.Simulation results show that the optimal design of relay can improve the SSE and SEE tradeoff.