Research On Chaotic Encryption And Improvement Of Transmission Performance For OFDM-PON

With the advent of new information technologies such as 5G,big data,the Internet of Things,and artificial intelligence,more and more information is transmitted and stored through the network.Due to the frequent occurrence of information leakage incidents caused by illegal monitoring,brute force cracking,etc.,information security issues have focused more and more attention from government,companies,and other institutions.Passive optical network(PON)is an important part of the physical layer data transmission in communications,where downstream signal transmission is a broadcast mode,and the transmitted data is easily copied to eavesdropping and attacks by illegal users.In order to improve the security of PON data transmission,the security technique of data transmission based on PON in the physical layer has been studied by more and more scholars.The security technique of physical layer communication can be divided into the following types:quantum encryption,laser chaotic communication,microwave photonic chaotic communication,digital chaotic security technique based on digital signal processing(DSP),etc.Quantum communication,microwave photonic chaotic communication,and chaotic laser communication have additional requirements for the equipment.It is difficult to conduct in industrial application.Because of this,the digital chaotic technique has no requirements for hardware,convenient operation and processing,which have become a hot topic in recent years.At the same time,the orthogonal frequency division multiplexing-passive optical network(OFDM-PON)is one of the excellent candidates in wired and wireless communication due to its anti-fiber dispersion,multipath interference etc.The combination of the digital chaos technique and OFDM-PON not only enhances the security of data transmission but also improves the performance of data transmission,which will be one of the key techniques of the security of optical communication in the future.In this thesis,under the funding of the National Natural Science Foundation of China(NSFC)(NO.62071088,61571092),the physical layer security enhancement technology based on OFDM-PON is studied.The main innovations and contributions of this dissertation are as follows:(1)A novel security enhancement method for a physical layer secure orthogonal frequency division multiplexed passive optical network(OFDM-PON)based on3-dimensional Brownian motion and chaos in cell(3DBCC)is proposed.This method confuses an OFDM signal via transforming it into a 3D symbol matrix and a 3D cell matrix with different size lengths.Different dividing-confusion rules then generate different complementary cumulative distribution functions(CCDFs)of peak-to-average power ratio(PAPR).And we can pre-estimate bit error rate(BER)performance by calculating the CCDF values.We also find that the processing time decreases with the matrix's side length decreasing simultaneously.A new weighted comprehensive value(Q_w)is further used to evaluate the overall performance between the processing time and the BER performance.The proposed encryption technique is promising for building physical layer security enhanced OFDM-PON system with a low processing time delay and low BER for future access network systems.(2)An approach for peak to average power ratio(PAPR)reduction and security improvement in OFDM-PON is proposed by using optimum block dividing with2-dimensional logistic adjusted sine map(2D-LASM)and dynamic key assignment technique.One frame of OFDM signal can be regarded as a symbol matrix.All the divisors of length and width of a matrix can be calculated out,and each divisor of length and width can be arbitrarily combined to divide the matrix into blocks.A 4D hyper-chaotic system is applied to generate a cipher book for 2D-LASM.And we assign different dynamic key groups from the cipher book for 2D-LASM to encrypt different block dividing situations.Different encrypted divisor blocks can obtain different values of PAPR.The optimum dividing situation is obtained by calculating out the minimum value of PAPR(V_PAPR).The processing time can be decreased with the number of quadrature amplitude modulation(QAM)symbols increasing in each block.PAPR reduction can improve the BER performance of data transmission.In addition,the hyper-threading technique with two algorithms is applied to improve the performance of the encryption method.They promote the processing time by 38.6%and 50%respectively.(3)A deoxyribonucleic acid(DNA)extension code with 3-bit binary streams is proposed to encrypt the downlink data for OFDM-PON.It has 8 bases to make up 4pairs of complementary codes.And it can obtain 384 matching rules,which greatly improves the randomness of matching.Here,two DNA addition operation rules are also proposed to encrypt the data.DNA extension rules can reduce half coding operations.Three 1-dimensional(1-D)chaotic systems are used to encrypt the code and control the rules.The encryption method based on the uplink streams from optical network units(ONUs)makes the security of downlink signals not just depending on the security of chaotic systems.The proposed method not only improves the security but also reduces the computational complexity.The experimental results show that the proposed method has the ability to resist optical channel response and fiber nonlinearity,which is a promising candidate for solving the security enhancement in optical access networks.(4)The chaotic compressive sensing(CS)encryption algorithms for OFDM-PON are proposed to compress the transmitted data and enhance the security of the data transmission.Bitstream transmission using CS directly is restricted due to its inability to satisfy the sparsity in neither time nor frequency domain.While the sparsity of the transmitted data can be constructed when transmitting the multimedia.A sensor can be then used to identify whether the data is multimedia.If it is,the CS technique is used,and the sensor's result is set as the side information inserted into the pilot and transmitted to the terminal simultaneously.For encryption processing,a 2-dimensional logistic-sine-coupling map(2D-LSCM)is used to generate pseudo-random numbers to construct the first row of a measurement matrix to encrypt the system.Four transform formats are then applied to generate the sparsity of the transmitted data.Due to the restriction of data transmission in the physical layer,the discrete cosine transform(DCT)is chosen to conduct the CS technique.Four approximation algorithms are also proposed to optimize the performance of compressing the length of bits.Finally,the‘Round+Set negative to 0'is chosen as the optimal algorithm.The combination of this chaotic CS encryption technique with the OFDM-PON systems saves the bandwidth and improves security.