Research On Key Technologies Of OFDM Optical Access Based On Sparse Code Division Multiple Acces

With the rapid development of various emerging technologies such as the Internet of Things,big data,virtual reality,Artificial Intelligence(AI)and fifth-generation mobile communications(5G),the volume of network services is growing exponentially and spectrum resources and access capacity are becoming increasingly tight.At the same time,information security is gaining more and more attention due to the lack of a global network regulatory system and the vulnerability of information technology.Non-Orthogonal Multiple Access(NOMA),represented by Sparse Code Multiple Access(SCMA),has many advantages over traditional orthogonal solutions,such as high spectrum utilisation,high access capacity and low latency.The combination of this technology and Orthogonal Frequency Division Multiplexing(OFDM)to form a SCMA-OFDM system can well meet the needs of next-generation optical networks for different scenarios.This paper focuses on enhancing the security of optical access networks,especially the mainstream Passive Optical Network(PON),and uses common chaotic digital signal processing(DSP)techniques to design SCMA codebooks and reduce the non-linear impairment of optical access systems.In this paper,we investigate the SCMA-OFDM transmission system in terms of designing SCMA codebooks and reducing the non-linear impairment of optical access systems.The main research elements and innovations of this paper are as follows:(1)From the aspect of designing SCMA codebook,a high security SCMA-OFDM multi-core fiber transmission system based on regular hexagon chaotic codebook is proposed.In the process of designing regular hexagon chaotic codebook,the optimization of constellation points on orthogonal resource blocks is taken as the starting point of research.Firstly,the chaotic factor generated by the four-dimensional Rossler chaotic model is deployed to interfere with the parent constellation.Then,by rotating parent constellation and multiplying the sparse matrix,the chaotic codebook corresponding to each user is formed.The designed codebook logically avoids the degradation of transmission performance caused by rough scrambling of codebook constellation.Meanwhile the chaotic codebook has a greater improvement in Bit Error Rate(BER)than Huawei codebook.Through the 42 Gb/s encrypted SCMA-OFDM data transmission experiment on a 2km multi-core fiber,the security and reliability of the transmission system are well verified.(2)In order to reduce the nonlinear damage of optical access system,a Peak-to-Average Power Ratio(PAPR)suppression algorithm based on chaotic IDHT-PTS is proposed.The main idea is to first use the four-wing hyperchaotic system to scramble the time-frequency matrix,then perform chaotic segmentation to form each sub-block of the Partial Transmit Sequence(PTS)algorithm.After that replace the Inverse Fast Fourier Transform(IFFT)of each sub-block with the Inverse Fast Hartley Transform(IFHT),and finally output a set of signals with the lowest PAPR.IFHT,as a fast algorithm of Discrete Hartley Transform(DHT),can greatly improve the computational efficiency and transmission rate.Through the analysis of simulation results,the chaotic IDHT-PTS algorithm can reduce the PAPR of the SCMA-OFDM signal by 2.7 d B,which has a good PAPR suppression effect.In addition,SCMA-OFDM-PON optical access system based on chaotic IDHT-PTS algorithm shows high security and reliability after 84 Gb/s encrypted data transmission over 2km multi-core fiber.