Research On Physical Layer Secure Transmission Technology In Multicell Multicast Systems

By utilizing broadcast nature of wireless channel,multicast technology can serve a group of user simultaneously and have higher efficiency in communication.However,due to the openness of transmission medium,security has always been a key issue in wireless multicast systems.Physical Layer Security technology,which encrypts by exploiting characters of wireless channels and signal processing technologies,is identified as a promising encryption method.In this dissertation,physical layer secure transmission problems in multi-cell multicast systems are studied.Specific contents are as follow.Based on multi-cell cooperation,a secure transmission strategy for multi-cell multicast networks is proposed.By utilizing semi-definite relaxation technology and linear search method,the transmission power minimization problem under constraints that reliability and security are satisfied is studied.And the beamforming vector and power allocation for each base station are joint optimized by proposed algorithm.Simulation results reveal that the proposed algorithm can decrease the power consumption of local cell and network efficiently.In the second part of this dissertation,the secrecy problem in multi-cell multicast networks with multiple eavesdroppers is studied.In this scenario,users in neighbor cell are all considered as potential eavesdroppers.In the case of perfect channel state information,this paper studies the secrecy rate maximization problem under power constraint and proposes a cooperative beamforming algorithm.Furthermore,a robust beamforming vector is design by utilizing worst case optimization approach on the premise of knowing the region of uncertainties of channel state information.Simulation results reveal that,comparing to independent beamforming method,the proposed cooperative beamforming algorithm can improve the secrecy rate efficiently.And the robust beamforming strategy can have good secrecy performance as well.