Research On The Key Technologies For Low Probability Of Intercept Wireless Communication

With the highly developed wireless technique,wireless communication is becoming a necessary part of our daily life.Since more and more information is sent through wireless channels,(including some private and sensitive information,e.g.financial information,private identification information and medical information),the security is the main concern of wireless communication systems.On one hand,wireless transmission is vulnerable to illegal intercepts and attacks,owing to its broadcast nature.On the other hand,the current encryption techniques are incapable to handle the wireless physical layer attacks,e.g.signal capture,characteristics extraction and jamming.Hence,deigning more secure communication schemes becomes a key issue for future wireless communication systems.Low probability of intercept(LPI)communication is a promising wireless security technique.Based on the features of wireless communication,it employs the physical layer techniques,e.g.coding,modulation and waveform design,to protect the communication signal,the signal characteristics and the information.More specifically,it contains issues in three layers: 1)preventing the signal from being detected,i.e.,signal stealth,2)preventing the characteristics of signal from being extracted,i.e.,characteristics hiding,3)preventing the information from being eavesdropped,i.e.,information concealing.This dissertation investigates signal stealth and information concealing for LPI communications,i.e.covert communication and physical layer security,to ensure the security of wireless communication system and simultaneously improving the capacity.The main contributions are summarized as follows.The first part of this dissertation investigates the asymptotic capacity of covert communication in the additive white Gaussian noise channel.By employing the random coding and Berry-Essen's theorem,the total variation based first and second order asymptotic capacities are obtained,and the results are proved by the achievability and converse parts.The theoretical analyses and numerical results show that the total variation based asymptotic capacity is higher than the traditional relative entropy based one.The second part of this dissertation investigates the constant rate covert communication.According to the square root law,the information rate of the traditional covert communication decreases with the code blocklength increasing.Hence,it is necessary to implement the blocklength free constant rate covert communication.By employing the uncertainties of relay networks,the detection performances and the achievable rate of covert communication system are analyzed.It is also proved that the constant rate covert communication can be achieved by employing specific transmission power.The numerical results show the trade-off between the achievable rate and the detection performance constraint.The third part of this dissertation investigates the optimal strategy for covert communication when some system parameters are unknown.By employing game theory,the optimal strategies for covert communications are proposed in both single-hop and two-hop networks.In the single-hop network,according to the different parameter knowledge,the optimal strategies are proposed based on the power threshold game and Bayesian game.In the two-hop network,the optimal strategy is proposed based on the jamming added power threshold game.The numerical results show the impacts of the key parameters to the strategies and the system performances.The fourth part of this dissertation investigates the faster-than-Nyquist system based physical layer security method.Unlike the traditional artificial noise based physical layer security method,the proposed method changes the parameters of the pulse shaping filter in the transmitter to introduce serious inter-symbol-interference(ISI)at the eavesdropper.Through this way,the physical layer security is achieved.We also analyze the secrecy capacity of the proposed method by employing the whiten filter and Z-transformation.The numerical results show that the proposed method can obtain higher secrecy capacity comparing with the current ISI based physical layer security method.