Research On OFDM-oriented Physical Layer Key Generation In Wireless Networks

Currently,wireless network is widely used,so that more and more private data rely on it for transmission.Researchers designed a physical layer security scheme that does not require modification to existing access protocols to ensure wireless network security.Using the characteristics of the wireless channel for key generation is one of the current popular research directions for physical layer security.The widespread application of Orthogonal Frequency Division Multiplexing(OFDM)systems in wireless networks provides a large number of initial characteristic values for key generation.However,since the fading conditions of the transmitted pilot signal on the adjacent sub-carrier channels are very similar,the characteristic values obtained by the adjacent sub-carriers have a certain correlation.Therefore,the key extraction scheme based on the OFDM system has the problem of insufficient key randomness.Aiming at this problem,this paper adopts a pre-processing scheme based on two-dimensional principal component analysis to reduce this correlation and enhance the randomness of the key.At the same time,a disturbance scheme combining the phase of the sub-carrier and the strength of the received signal is designed to further improve the randomness of the key.The main paper is proposed as follows:(1)The entire system is divided by channel detection,quantification and key agreement progress.Then the preprocessing step is added in order to solve the problem of strong correlation between adjacent subcarriers in OFDM system,which can effectively reduce the correlation between the initial sampling feature values.This paper analyzes and compares several common pretreatment schemes,then an adaptive preprocessing scheme based on the OFDM system,OFDM subcarrier phase and two-dimensional principal component analysis method is proposed.The simulation results show that the scheme can effectively remove the coherence of adjacent sub-carriers and improve the randomness of the key.(2)Aiming at the insufficient randomness of keys generated by existing schemes,this paper designs a perturbation scheme that combines sub-carrier phase and received signal strength.Firstly,the bit string generated by the received signal strength value is collected as the perturbation sequence,then the quantized phase matrix is perturbed through the steps of complementing sequence number and XOR operation.Finally,this paper adopts an improved fuzzy extractor to negotiate the key of the disturbed bit string.As the simulation results showed that the key string generated by this scheme can pass the randomness test of the National Institute of Standards and Technology.