Resource Allocation For Physical Layer Security In Relay-based Cooperative Systems

In recent years,with the popularity of the Internet,smart home,and mobile devices,wireless network has become an indispensable part of our daily life,and is widely used in civil and military fields.However,due to the open and broadcast characteristics of wireless communication,the wireless network especially mobile communication network is vulnerable to attack by eavesdroppers.The eavesdroppers can obtain and modify information through the attack,or block the transmission of information.Therefore,security issue has become a key problem in wireless network applications,and the ability to safely transmit information is particularly important.Physical layer security can ensure the security of information transmission by using the physical characteristics of wireless channel,and can be combined with multi-antenna,beamforming and relay cooperation technologies to enhance the security performance.In particular,the use of relay technology can not only expand the scope of communication and improve network throughput,but also significantly improve the physical layer security.In this thesis,the physical layer security in relay cooperative systems is studied.The contributions are:(1)A wireless transmission network with a source node,multiple intermediate cooperative nodes and a destination node,in the presence of an eavesdropper,is considered.Assuming that each intermediate cooperative node can act as relay or jammer,this thesis proposes a cooperative node mode selection strategy based on Q-learning method.The proposed node mode selection strategy trains the selection behavior of all intermediate cooperative nodes,and optimizes the mode selection of each intermediate cooperative node to maximize the total secrecy rate of the system.Simulation results show that the proposed cooperative node mode selection strategy can improve the total secrecy rate of the system.(2)An orthogonal frequency division multiplexing(OFDM)system with multiple intermediate cooperative nodes is considered.The system includes a source node,multiple intermediate cooperation nodes,a destination node and a potential eavesdropper.It is assumed that each intermediate cooperative node can act as relay or jammer,and the source node and the intermediate cooperative nodes can use different subcarriers for information transmission.In order to maximize the total secrecy rate of the system,a resource allocation algorithm based on three-dimensional matching is proposed.Firstly,the subcarrier allocation problem is modeled as a three-dimensional matching problem,and stable matching results are obtained.Then,all the intermediate cooperative nodes change their working modes to improve the total secrecy rate of the system,and the mode selection of the intermediate cooperative nodes is optimized.Finally,based on the iterative power allocation strategy,the transmission power of the source node and the intermediate cooperative node is optimized.Extensive simulation results show that the proposed resource allocation algorithm can significantly improve the physical layer security.