Research On Faster-than-Nyquist Signaling Based Low Probability Of Interception Communications

The increasing of wireless devices and diverse communication demands lead to an explosive growth in wireless traffic in next-generation wireless communications.The surge of wireless traffic has put forward higher requirements for the spectral efficiency(SE)of next-generation wireless communications.More importantly,the surge of wireless traffic means that more and more private data is transmitted by wireless channels,but due to the openness of wireless channels,how to ensure the information security of wireless communication and high SE at the same time poses a severe test for next-generation wireless communication.Faster-than-Nyquist(FTN)signaling improves the information transmission rate by packing the symbol interval of Nyquist orthogonal transmission,thereby achieving the purpose of improving SE.However,the inter-symbol interference(ISI)incurred by compressing the symbol interval in FTN signaling can provide indemnification for the information security of communication from the following aspects:(1)The ISI introduced by FTN may change the detection model of the illegal eavesdropper to deteriorate its detection performance and achieve signal stealth;(2)The changing acceleration factor introduced by FTN signaling can hide or disturb the characteristics of communication signals to achieve characteristics concealment;(3)The ISI introduced by FTN signaling can improve the decoding complexity of the illegal eavesdropper and further realizes information hiding.FTN signaling has potential to guarantee the security of wireless communication and achieve low probability of intercept communications,which further guarantee the information security of next-generation wireless communication on the condition of meeting the requirements of the communication system SE.However,there are few researches on FTN signaling based low probability of interception communications.Therefore,this dissertation is devoted to the research on FTN signaling based low probability of interception communications to solve problems of decoding complexity,mechanism analysis and technical scheme design.The main research contents of this dissertation include the following three parts:(1)low-complexity precoded FTN signaling scheme design;(2)performance analysis of covert communication under FTN signaling;(3)variable symbol rate communication based on FTN signaling.The first part focuses on the high decoding complexity problem in FTN signaling,and studies two precoding schemes,namely precoding FTN based on Cholesky and LDL decomposition,which aims to provide low-complexity decoding schemes for FTN signaling based low probability of interception communications.For the Cholesky decomposition aided precoding FTN,the precoding and decoding matrices are obtained by Cholesky decomposition of the ISI matrix,and the ISI elimination principle and complexity of the scheme are analyzed.For the LDL precoded FTN,the corresponding precoding and decoding matrices are obtained by LDL decomposition of the ISI matrix,the optimal symbol power allocation design is completed by the Lagrange multiplier method.Besides,the analysis of achievable rates,outage capacity,and complexity are given.The proposed LDL precoded FTN expands the applicable range of the acceleration factor and reduces the computational complexity and matrix storage consumption when the acceleration factor is small.The second part analyzes the performance of covert communication under FTN signaling for the first time from the perspective of signal stealth.Since FTN transmission will change the signal detection model of the illegal eavesdropper,it may deteriorate the detection performance of the illegal eavesdropper and bring gains to the covert rate of the legitimate users.Therefore,whether the covert communication under FTN signaling has advantages over Nyquist signaling or not deserves further exploration.In this dissertation,a covert communication system model under FTN signaling is established,the hypothesis test model of the illegal eavesdropper is given,maximum likelihood criterion-and Kullback-Leibler divergence-based detection performance constraints and covert rate are analyzed.Both theoretical analysis and numerical results prove that under the same detection performance constraints and detection time,the legitimate users using FTN signaling have higher transmit power and covert rate than Nyquist signaling.The third part studies the variable symbol rate communication based on FTN signaling from the perspective of information concealment and characteristics hiding.Specifically,this dissertation establishes a unified system model for variable symbol rate communication based on traditional FTN and precoding FTN,and uses parameters such as time-varying acceleration factor sequences generated by chaotic sequences as secret keys to achieve information concealment and characteristics hiding.In this dissertation,by constructing a sampling-level signal model,the security capacity of the legitimate users are analyzed under the condition that the illegal eavesdropper does not know the exact permutation of the acceleration factor sequence of the legitimate users.In addition,this dissertation analyzes the information entropy of the secret keys of the legitimate users and the decryption complexity of the illegal eavesdropper,which provides theoretical guidance for the design of the acceleration factor sequence.The analysis and numerical results show that in the variable symbol rate communication based on FTN signaling,the legitimate users can obtain a higher information rate than the illegal eavesdropper and realize information concealment and characteristics hiding.Besides,the variable symbol rate communication based on precoded FTN signaling is an effective and low-complexity technology solution for low probability of intercept communications.