Research On Physical Layer Secure Transmission In Cloud Radio Access Network

With the rapid de velopment and continuous update of wireless communication technology,Cloud Radio Access Network(C-RAN),as a clean and efficient Network architecture,has gradually come into people's view,and plays an important role in the popularization of 5G.Therefore,the research on C-RAN has become a hot research field of wireless communication.However,the current research mainly focuses on the optimization of resource allocation in C-RAN,and there are not many relevant studies on the secure communication.However,people are becoming more and more aware of privacy.Therefore,how to ensure that users can communicate safely in C-RAN without being eavesdropped is a problem that researchers need to pay attention to and has a very important research significance.However,the traditional cryptography upper layer encryption technology,in the face of the current situation of the rapid growth of computer's hash rate,has to constantly improve the complexity of the design algorithm,appears to be limited.Therefore,it is an inevitable trend to focus on physical layer security technology.Physical layer security technology,using the transmission characteristics of wireless channel,is a more effective security scheme.In the C-RAN architecture,the SINK of the users can be improved by the coordinated transmission of Remote Radio Head(RRH)similar to COMP,and the interference in RRH can be used as green interference to improve the physical layer security.Therefore,the architectural characteristics of C-RAN enable it to be organically combined with physical layer security technology to ensure the safe transmission of user information.In this paper,a series of secure-related optimization problems of the physical layer of cloud radio access network are constructed from simple to complex,and corresponding algorithms are proposed to solve them.Specifically,the main research contents and work results of this paper are as follows:(1)In the third chapter of this paper,the simple eavesdropping channel model is used as the foundation:a simple eavesdropping channel with limited security capacity is constructed to imitate the situation that the fronthaul capacity of cloud radio access network is limited.A convex optimization algorithm based on successive convex approximation is proposed,and the precoding and artificial noise of the system are designed together to achieve the ultimate goal of improving the secure communication rate of the system.The research of this chapter lays a foundation for the research of physical layer security under unicast and multicast scenarios in the following chapters.(2)The fourth chapter of this paper advances the problem to the cloud radio access network under the unicast scenario:the system model and the problem model of inter-user interference under the unicast scenario are constructed.In addition to the joint design of precoding and artificial noise,the physical layer security method used also adds the link selection design between RRH-users.RRH-user association embodies the idea of user-centric clustering.The problem of the difficulty lies in the optimization problem in introducing the binary integer variables to express the link connection relationship,this chapter proposes three successive convex approximation algorithms to solve the problem:MI-SOCP algorithm,Continuous relaxation algorithm,and Sparsity algorithm.Finally,the three algorithms are compared and analyzed by simulation.(3)The fifth chapter of this paper studies the security transmission of cloud radio access network under multicast scenario.The problem is more complex in the multicast scenario,and harder to solve,because the user with the lowest secure transfer rate in each user group determines the security performance of the entire user group.Once an eavesdropper eavesdrops on that individual user,he or she can gather information about the entire group of users,which is defined by the Content-Centric Grouping feature.Therefore,each group of users with the minimum secure transmission rate is used as one of the constraints in the optimization problem in this chapter,which not only ensures the secure transmission of the whole system,but also saves the capacity of the fronthaul.However,this constraint will become difficult to deal with.In this chapter,an approximate scheme is proposed to deal with this constraint,and three iterative algorithms based on successive convex approximation are also used to jointly design precoding,artificial noise and link selection of RRH-user groups.