Research On Wireless Covert Communication Based On Spatiotemporal Uncertainty

In many scenarios with high security requirements such as modern battlefield,wireless covert communication can ensure that both sides of legitimate communication can transmit information without being detected by illegal parties,fundamentally solve the problem of data and privacy security,which has very important research value.The basic concealment principle of wireless concealment communication is to make use of the concealed random source which is inherent and artificially generated in the system to make the illegal party have uncertainty in connection with the received signal power,thus causing detection errors.At present,the research category of concealed communication based on the above uncertainty principle mainly includes two aspects of time and space uncertainty.Time uncertainty refers to the potential variability of the occurrence time of legitimate communication.If the French side is not certain about the communication time,all time Windows must be detected and the detection threshold must be improved so that detection errors may occur with a certain probability.At present,the research achievements of covert communication with time uncertainty mainly include covert technologies such as jump time and finite block length system.Spatial uncertainty refers to the use of natural or artificial random sources in the spatial dimension,so that the signal arrival Angle,waveform and energy at the illegal side are uncertain,which makes it impossible to accurately judge the signal source.At present,the research on spatial uncertainty covert communication mainly uses environmental noise,cooperative interference signal,open cover and reconfigurable intelligent surface to jointly realize covert communication.The above covert communication based on temporal and spatial uncertainty has achieved fruitful results,but there are still two problems: 1)Time domain hidden random source mining is not sufficient,unable to resist the time domain refinement detection of illegal parties;2)Existing hidden communication schemes based on fully passive RIS have limited performance improvement and limited freedom of signal reconstruction.In view of the above problems,this paper fully mines the potential advantages brought by the endogenous random sources of the system in time domain and space domain dimensions,and carries out research on wireless covert communication based on spatio-temporal uncertainty.In this paper,a hidden communication scheme based on random selection of symbolic period is proposed.Then,from the perspective of time and space uncertainty,a covert communication scheme based on hybrid relay RIS and channel using random selection is proposed.The specific research contents are as follows:(1)A covert communication scheme based on random selection of symbolic period is proposed.According to the minimum time window of illegal party signal detection,the granularity of signal sending time change is refined to the specific symbol period in the window.The sender transmits information by randomly selecting the communication window and the symbol period within the window,so that the illegal party has uncertainty about the time of communication and is forced to detect all the time Windows,resulting in uncertainty of the received signal power.Under the condition of satisfying the covert performance constraint,the optimal transmission power which can maximize the communication efficiency is determined.Simulation results show that compared with schemes with finite block length,the performance of this scheme can be improved by 25% and 20% respectively in the probability and rate of concealment.(2)A covert communication scheme based on hybrid relay RIS and channel using random selection is proposed.Firstly,active relay unit is introduced into all passive RIS,and hybrid relay RIS structure is designed.The relay unit can adjust the amplitude and phase of the incident signal and improve the degree of freedom of signal reconstruction.The sender then randomly selects the communication block and the channel used within the block.Then,RIS restructures the incident signal.According to the current channel status information,the legitimate signal is reasonably amplified and forwarded at the specified Angle,so as to enhance the legitimate signal intensity at the legitimate receiver,reduce the energy leakage at the illegal side,and widen the difference between the legitimate channel and the illegal detection channel.Finally,an iterative search algorithm based on particle swarm optimization is designed to determine the optimal transmission power,RIS relay and reflection coefficient matrix that can maximize the communication efficiency under the condition of satisfying the covert performance constraint.The simulation results show that compared with the schemes assisted by all passive RIS with finite block length,the performance of this scheme can be improved by 20% on average in terms of covert probability and covert rate.