Research On Key Technologies Of Artificial Noise Power Allocation Under Broadcasting Communication Channel

With the rapid development of wireless communication technologies,the data transmitted through the wireless channel have increased.Hence,how to ensure the data security is becoming a hot issue in the recent researches.Broadcasting is one of the major applications of wireless communication.It confronts a heavier security threat than that in the general point to point communication systems because the data transmitted to the users are the same and the opening broadcasting channel.This paper is trying to explore the role of physical layer security artificial noise technology in the security of broadcasting systems and to find a reasonable way to enhance the security of the broadcasting system by the power allocation between the secrecy messages and artificial noise signals.First of all,we build a general broadcasting model which can be used for the security analysis.Based on the theory of probability and communication,we derive the secrecy outrage probability and secrecy rate.With the assumption that the legal users and the eavesdropper is in the same wireless environment,we find that the system security will decrease when the number of the legal users increases.If the number of the users increases,the probability that the worst channel condition of the legal users will be worse than the wiretap channel condition is higher,which contributes to the rise of the secrecy outrage probability and a decline of the secrecy rate.The secrecy capacity is close to zero when none of the auxiliary physical layer security methods is used to ensure safety.Second,we propose a null space artificial noise-aided broadcasting system.In order to use the null space artificial noise technology,we analyze the basic generating condition.Only when the number of the transmitting antennas is more than the sum of the legal receivers,the null space of all legal users exists.Then we do some researches on the power allocation algorithms.When the precise channel state information is known,we propose two power allocation algorithms according to the maximum of minimum system secrecy rate and the maximum secrecy sum rate,respectively.The simulation results show that the reasonable use of artificial noise can enhance the safety of the system.Even if we cannot get the position and channel condition of the eavesdropper,the analysis of the ergodic secrecy capacity and secrecy outage probability also prove the artificial noise technology have contributed to the enhancement of the system safety.At last,to make the system model more practical,we propose a new security model including the connecting condition of the legal users with the impact of individual user distance attenuation in the system taken into consideration.We choose the Poisson Point Process model to simulate the distribution of the users,and we calculate the path loss of the distance.Then we define two connection scenes: one of the scene is the fullconnect scene that all the users should satisfy the connect threshold,and the other one is partial-connect scene that some users are allowed to fail to reach the connection threshold.Under the two scenes,the secrecy outage probability and secrecy rate are all relevant to the connect threshold,secrecy threshold and the artificial noise distribution factor.Through the comparison between the theoretical analysis and the simulation results,the ideal threshold setting scheme under the constrain of the safety indicator is obtained.