Study On Physical Layer Security Of Multiple-level Relay Wiretap Channel

Broadcast transmission is a very important characteristic of the wireless communication. Each node could independently receiv the signal from the source in wireless communication system. Signal transmission becomes more convenient and efficient as the mutual help between the nodes. However, this feature also makes it vulnerable to eavesdropping signal, which has brought great challenges for security issues of wireless systems. Many studies in recent years prove that, use relay system can efficienttly improve the safety performance of the wireless communication system. This paper studies the physical layer security issues of the relay wiretap channel based on information theory.Firstly, this paper studies the one-level relay wiretap channel based on decoding and forwarding protocol, uses a relay cooperative system model which is widely used, adopt a jointly optimization algorithm to get the achievable secrecy rate under the constraints of the total transmit power.Secondly, this paper studies the two-level relay wiretap channel based on decoding and forwarding protocol, proposes a two-level relay cooperative system model. The source power and relay weights vectors are jointly optimized to maximize the achievable secrecy rate under the constraints of the total transmit power. This paper also compared the achievable secrecy rate of the one-level relay system and the two-level relay system. Simulation results demonstrate that the two-level relay scheme does achieved higher secrecy rate compared to the one-level relay system when the relay node is far away from the source.Lastly, this paper studies the two-level relay system without Eavesdropper’s channel state information, proposes a security scheme that the relay node use the the artificial noise. The relay nodes not only help the source to forward information but also transmit the the artificial noise to confuse the potential eavesdroppers. Simulation results also demonstrate that the two-level relay scheme does achieved higher secrecy rate compared to the one-level relay system when the relay node is far away from the source.To solve the optimization problem, the algorithm used in this paper are based on the theory of convex optimization. The initial optimization problem is also non-convex, which is difficult to directly solve. To solve the optimization problem and get the achievable secrecy rate, we change the non-convex optimization problem to a semi-definite programming(SDP) problem.