Research On Improving Security Capacity Based On Time Reversal For Downlink Of MISO Wireless System

With the rapid development of communication technologies,the proper openness and broadcast performance of wireless channels have caused the problems of delay,attenuation and leakage of signals.These problems have become a huge challenge for many research institutions and scholars in wireless communication security research.The encryption algorithms what are based on secret key rely on computational complexity,they aren't able to meet the requirements of the fifth-generation communication systems.The physical layer security technologies utilize the inherent characteristics of the wireless channel to solve the security problem at the lowest layer,and it has the performance of universality,calculability and being easy to implement.In the physical layer security technologies,how to improve the security capacity of the wireless communication system is the core problem of the physical layer security research.The time reversal technology can automatically collect the signals' energy scattered on every multipath,and these energy coherently superimpose at the desired user to achieve simultaneous focusing of signals in the temporal and spatial.Therefore,time reversal technology has expansive application prospects in physical layer security research.The thesis studies the methods of improving security capacity based on the time reversal technology for downlink of multi input single output wireless systems.What main innovative work content in the thesis is:First,when wireless communication transmits signals in free space,the signals face the risk of being illegally eavesdropped.In order to improve the security capacity,the thesis proposes a secure transmission strategy.The strategy is optimized by beam forming technology,which is based on time reversal technology.It builds a multiple user multiple input single output wiretap channel model,takes the maximization of security capacity as a criterion of multiple user communication,and takes into account channel state and correlation between antennas.Firstly,the base station uses beam forming technology to transmit signals to the desired user,in which case the signal is enhanced in the direction of the legitimate channel transmission.Secondly,signals of the base station need to pass through the time reversal cavity before being sent,and it only processes single specific channel at a time.Theoretical research and simulation data show that the strategy has higher security capacity and lower bit error rate.Second,a secure transmission strategy that uses artificial noise consumes additional energy,and it will shorten the life cycle of the entire system.Therefore,in order to improve the security capacity of the system,the thesis proposes a secure transmission strategy.The strategy is optimized by simultaneous wireless information and energy transfer(SWIET)technology,which is based on time reversal technology.It models the system as a wireless channel model,and sends probe pulses to extract channel information.Firstly,in the multiple user multi input single output downlink system,the transmitter performs the time reversal processing on the signals.Secondly,using the zero-space artificial noise method consumes additional energy.Therefore,SWIET technology is introduced to effectively solve the problem,and enhance the security performance of the system.Theoretical analysis and simulation results show that the strategy has higher security capacity and less information leakage.