Research On Chaotic Encryption Technology In OFDM-PON System

With the increasing of bandwidth services,orthogonal frequency division multiplexing passive optical network(OFDM-PON)system is one of the best candidates for meeting the requirements of next-generation networks.However,due to its system structure characteristics,data transmission is easily intercepted by illegal users.Large-scale data security transmission of OFDM-PON system has become an important problem to be solved.At the same time,high peak-to-average power ratio(PAPR)of OFDM signal will also affect transmission performance.Based on these problems,this paper integrates the chaotic encryption technology into the OFDM-PON system and encryption methods are performed on the physical layer of the system.The data are encrypted to improve their security by using the characteristics of self-similarity,intrinsic randomness,sensitivity to initial values,ergodicity,and statistical characteristics of chaotic system.Therefore,in order to improve the security of information transmission in optical fiber transmission system,theoretical analysis and experimental verification of several schemes have been proposed to improve the performance of optical fiber transmission system.The proposed schemes in this paper have theoretical reference and practical application significance for the future large-scale secure transmission of optical fiber data.The main work and achievements of this paper are as follows:Firstly,aiming at the security and high PAPR characteristics of OFDM-PON systems,a time-frequency hybrid domain encryption scheme based on multi-chaos is proposed,and SLM technology is used to reduce PAPR of the OFDM signal.The difference and advantage of multi-chaos compared to single chaos are described.The features and functions of the time-frequency hybrid domain encryption system are analysed.A simple and easy to implement SLM technology is applied to reduce the PAPR of the OFDM signal.An OFDM-PON intensity modulation direct detection(IM/DD)system with a fiber transmission length of 100 km was experimentally demonstrated.Experimental results show that this scheme can improve the security performance of OFDM-PON system.Second,a two-level encryption scheme based on multi-scrolls chaotic systems is further proposed.The four-order grid multi-scrolls system is used as the chaotic key source.The data are encrypted by using the two-stage encryption scheme of IQ encryption and row-column transformation,and the encrypted data are processed using Discrete Fourier Transform(DFT)precoding to reduce the PAPR of signal.At the same time,in order to verify the influence of the number of scrolls in the multi-scrolls chaotic system on the encryption effect of the system,the parameters of the chaotic system are changed,and the optimal parameter is selected as the experimental parameter value.An OFDM-PON direct detection system with an optical fiber transmission length of 50 km has been set up in the experiment.Experiments have verified that this solution can effectively improve system security,and the encryption scheme has more key space,and improve the transmission performance of the system.