Digital Chaos-based Real-time High-speed Optical OFDM Secure Communication Technology

With the rapid development of Internet technology in the contemporary society,passive optical network(PON)technology has been more and more widely used in order to solve the bandwidth requirement of users.In PON,orthogonal frequency division multiplexing(OFDM)technology has gradually become the core modulation technology due to its high spectrum utilization,flexible subcarrier configuration and excellent anti-jamming characteristics.With the application of OFDM-PON technology in optical fiber communication systems,the related transmission technology of optical OFDM-PON has increasingly become a research hotspot.However,due to the broadcasting characteristics of downstream traffic in PON,data transmission is very easy to be eavesdropped.Therefore,it is urgent to solve the security problems in PON.Aiming at the security problem in optical OFDM-PON communication system,many technical solutions for encrypting optical OFDM signals in transmission using digital chaos have emerged internationally.It combines digital chaos with optical OFDM signal modulation technology,and uses chaotic parameters as security keys to ensure high security of optical signals in the transmission process.However,the digital chaos-based OFDM-PON secure communication system so far is basically implemented by the offline technology.Field programmable gate array(FPGA)not only has simple and flexible operation,but also has high parallelism and system clock.Therefore,it is expected to be used in real-time high-speed OFDM encryption communication technology.In this paper,the digital chaos-based real-time high-speed optical OFDM secure communication system is modularized using FPGA,and then the verification of the system is completed.The research work can be divided into four parts:(1)The FPGA-based optical OFDM data modem and Lorenz digital chaotic system have been studied: Firstly,since the FPGA can only deal with the discretized digital signal,the continuous state equation of the Lorenz chaotic system should be discretized.Then,the simulation verification is carried out by using MATLAB/Simulink and System Generator.Besides,FPGA is used to realize some basic modules in OFDM communication system,such as QAM modulation module,IFFT module and so on.(2)The FPGA-based encryption and decryption algorithms have been studied: The encryption and decryption algorithm is designed to realize the digital chaos-based OFDM communication system can be obtained.Furthermore,the feasibility of the encryption and decryption algorithm can be ensured by analyzing the security performance.(3)The high-speed optical OFDM secure communication system based on FPGA has been studied: In order to achieve high-speed data transmission,the number of parallel data channels is designed appropriately according to the sampling rate of DAC.Then,through the analysis of transmission performance and security performance,the practical feasibility of high-speed optical OFDM data secure transmission system based on FPGA can be ensured.(4)The method of evaluating the key space in FPGA has been studied: By analyzing the encryption algorithm in the OFDM system,the factors affecting the key space can be obtained.Then,it is possible to expand the key space by changing some parameters such as the order of QAM,the calculation accuracy of IFFT and so on.In summary,this paper designs the implementation of digital chaos technology in FPGA,and develops the key modules of optical OFDM-PON secure communication based on FPGA.In addition,the efficiency of the optical OFDM-PON communication system has been successfully analyzed,and then the security performance of the system has been evaluated.Further,the performance of high-speed data transmission and real-time data processing of this communication system has been verified.