Research On Physical Layer Security Key Technologies For Satellite Communication System

Satellite-to-earth communications security issues of satellite communication system are focused on,with the ultimate goal of improving the confidentiality of satellite communications.When legitimate users are close to eavesdropers,legitimate channels and wiretap channels are approximately equal so that the traditional physical layer security technology of wireless communication on the ground is not suitable for satellite security communications.As for this problem,a physical layer security communication model of the satellite communication network is proposed.Based on the model,technologies of relay selection and power allocation are studied in detail to achieve the purpose of enhancing the secrecy of satellite communications.Firstly,a cooperation-direct-connection hybrid satellite-ground physical layer security communication model is proposed.The transmission mode is determined according to the distance between the legitimate user and the eavesdropper.When the distance is relatively short,the co-frequency co-time collaborative interference relay is added to interfer the eavesdropper and reduce the eavesdropper's received signal quality and obtain the security capacity.Furthermore,the feasibility of the model to achieve satellite communications security is verified through theoretical derivation.Secondly,based on the model,the optimization of relay selection to enhance performance of the system on security outage probability is studied.Under the condition that the instantaneous channel state information(CSI)is known,the optimal relay selection criterion is deduced theoretically,which minimized the security outage probability.However,because the instantaneous CSI is constantly changing,the satellite communication system needs to constantly perform relay selection,which increasing signaling overhead.In addition,there may be situations that the system cannot obtain instantaneous CSI.Therefore,the relay selection under the known statistics CSI is studied.An approximately optimal relay selection criterion to minimize the probability of confidentiality outage is theoretically deduced.Simulation results demonstrate that the performance on secrecy outage probability of the relay selection with instantaneous CSI is better than one of the relay selection with statistics CSI.Considering environmental conditions of the system and the performance of two relay selection schemes,an adaptive relay selection scheme is summarized.Finally,based on the model,the optimization of power allocation to enhance the system's security outage probability performance is studied.When the total transmit power is constrained,the allocation of transmit power between the satellite and the relay is studied to enhance the performance on secrecy outage probability of systems.The optimal expression of the power distribution factor to minimize securi-ty outage probability of the system is deduced theoretically.However,due to the continuously change of the instantaneous CSI,the power allocation factor need to be updated continuously,which increases the system overhead.Meanwhile,the system may have a situation that instantaneous CSI cannot be obtained.To solve this problem,power allocation base on statistical CSI was studied.The non-closed expression of the system secrecy outage probability is dedrived theoretically.Further,the approximate closure expression of the system secrecy outage probability is deduced theoretically.The power allocation factor to minimize the secrecy outage probability is obtained by traversing.The simmulation results verified that the complexity of power allocation base on statistical CSI is available and the power allocation based on instantaneous CSI has better secrecy outage probability performance than the power allocation based on statistical CSI.Taking the environment conditions of the system and the performance of the two power distribution schemes into considerate,an adaptive power allocation scheme is summarized.