Physical Layer Secure Transmission Against Pilot Contamination Attack

The physical layer security technology utilizes the fundamental properties of the wireless channel and provides new solutions to the wireless security communication.The existing physical layer security transmissions are mainly designed for passive eavesdropping attack.However,malicious attackers may launch active attacks instead of passively intercepting information.Especially in the time division multiplex communication system,the pilot contamination attack will interfere with the channel estimation process and result in new challenges to wireless communication.There are several problems in the research of physical layer security technology for pilot contamination attacks.The detection schemes work by changing the structure of pilot sequence,which makes it inconvenient to be applied to the practical communication system.When the active attacker is detected,the research is limited to theoretical analysis and lacks of specific communication solutions.Therefore,this paper studies the physical layer security transmission against pilot contamination attack.(1)We analyze the impact of pilot contamination attack on system security.In the channel estimation process,the existing structure of the pilot sequence is kept unchanged.Active pilot attackers are detected by the difference between uplink and downlink channel estimation results.Besides,the detection performance of the joint estimation detection scheme is explored at different pilot attack power level.Based on pilot attack detection,a secure transmission scheme is proposed.In the scheme,the sender corrects the primary channel estimation result according to the feedback information from the legitimate user.At the same time,the transmitter performs random scrambling preprocessing on the signal to further enhance the security.The random scrambling matrix is confined to the corrected primary channel information,disturbing the eavesdropper's received signal while not affecting the legitimate receiver's signal detection performance.Simulation results show that the secure transmission scheme based on active detection can effectively detect active attackers and ensure the information security between legitimate users.(2)For the pilot attack scenario where the sender does not know the prior knowledge of legal users,a physical layer cooperative transmission scheme based on random scrambling is proposed.In the secure transmission based on uplink and downlink joint channel estimation,the sender has already obtained priori knowledge of the legal receiver and performs signal pre-processing design based on the corrected main channel information.When the pilot contamination attack occurs at the initial stage of legal communication establishment,the lack of prior knowledge of the legitimate user at the sender results in a difficulty in executing the active attack detection scheme.In the cooperative scheme,a new eavesdropping communication model is formed by introducing an assistant node for system analysis.When designing a signal random scrambling preprocessing matrix,the transmitter does not forcibly distinguish the main channel from eavesdropping channel.The design of the random scrambling matrix is directly based on the channel estimation result with the pilot attack interference and the channel information between the auxiliary node and the transmitter.Simulation results and security analysis show that the information of the legitimate receiver and the assistant node is one-way combined to perform joint signal detection,which can eliminate the influence of pilot interference.For the eavesdropper,the received signal is randomly changed due to the random scrambling matrix,resulting in a high bit error rate.The random scrambling-based physical layer cooperation scheme enhances the security performance of the system against active pilot contamination attack.