Research On Physical Layer Security Techniques Based Oon Superposition Modulation

Due to the open characteristics of the wireless channel,wireless transmission is vulnerable to eavesdropping or jamming attacks.With the rapid growth of mobile communication data,it is becoming more and more important to ensure the security of wireless communication.Physical layer security(PLS)technologies do not need key management and algorithm,and has good security performance.Specially,the methods based on superposition modulation are easy to be implemented in practice and with very low complexity,and thus is one of the most important research directions.Superposition Modulation(SM)distributes the information bits for parallel transmiting symbols which can naturally superpose into the final information symbols at the target receiver.However,due to the difference between wireless channels,the received symbols may be distorted constellations.This is very important for wireless security,which however has been ignored by current resarches in the area of PLS.In this thesis,the PLS methods based on SM is studied as follows:(1)In order to solve the problem of passive eavesdropping,a PLS modulation technique based on phase superposition is proposed.The principle is to adjust the phases of two transmitted signals according to the propagation characteristics of the target receiver’s channel.In this case,the constellation phase of the signal received by the eavesdropper will be seriously distorted.The expressions of the demodulation results under coherent demodulation are derived respectively for the target node and the eavesdropper,and the influence of the phase estimation error is also analyzed.The simulation results show that compared with the scheme without superposition modulation,the proposed scheme can ensure that the bit error rate(BER)of the target node is not affected,while the BER of the eavesdropper is doubled.(2)In order to improve the anti-eavesdropping performance,the advantage of amplitude superposition is further introduced on the basis of the above phase superposition,and the influence of power allocation on the security performance of the double superposition scheme is studied.Based on the maximum likelihood demodulation,the demodulation expressions of the target node and the eavesdropper are derived,and the influence of channel estimation error is analyzed.The simulation results show that compared with the phase superposition scheme,the physical layer security technology with double information SM has better security,and the symbol error rate(SER)of eavesdropper is increased by 25%.Even if there is channel estimation error,the proposed scheme can still achieve better security performance and ensure that the SER of eavesdropper is doubled.(3)In order to solve the problem of spoofing attack,a scheme of SM is proposed to reduce the influence of attack signal generated by attacker on the real signal by using the advantage of SM of decentralized transmission information.This thesis analyzes the mode and flow of active attacker interference in communication system using SM technology,and deduces the expression of demodulation error rate after the target node receives malicious interference signal.The simulation results show that the proposed scheme has better anti-spoofing attack performance than the scheme without SM,and the BER of the target node is twice as low.