Research For Optical Spectrally Efficient Frequency-division Multiplexing (O-SEFDM) System Based On High-order Modulation

Driven by the Big Data Era,a large number of data centers are built.It led to a huge demand on transporting a large number of voice,video,entertainment and other data,so people are expected the speed and capacity of optical fiber communication system to experience fast growth in the near future.In the case of limited spectrum resources,improving spectral efficiency is undoubtedly one of the best ways to improve the speed and capacity of optical fiber communication system.Thus,designing spectrally efficient optical fiber communication system has become the long-term goal of optical communication development.Spectrally efficient frequency-division multiplexing(SEFDM)breaks the subcarrier orthogonality by squeezing the sub-carriers closer together below the orthogonality limit,so it can save bandwidth and achieve higher spectral efficiency than Orthogonal Frequency Division Multiplexing(OFDM).Thus,to design efficient optical SEFDM(O-SEFDM)communication system can further improve the speed and capacity of optical network.At present,researchers have implemented the O-SEFDM-4QAM system.However,it is desirable for people to have optical networks with higher rates and higher spectral efficiency.In this paper,we study the O-SEFDM system with high order modulation,including the detection algorithm of high-order SEFDM signal and the design of high-order O-SEFDM system.Thus,the main objectives of this paper are to study the SEFDM technique,to propose a detection algorithm which is suitable for SEFDM signals with high-order modulation,and to design the O-SEFDM system with high-order modulation.The main contents and research results in this paper are described as follows.Firstly,we introduce the principle of SEFDM.By analyzing the spectrum of the SEFDM signal,we get conclusion that the bandwidth of SEFDM comes at the expense of inter carrier interference(ICI).In order to study the method of compensating ICI,we analyze the advantages and disadvantages of several low-complexity algorithms for SEFDM systems.By simulation and performance comparison,we find that "Pre-estimator + Accurate Detector" is the most advantageous detector structure of SEFDM.Secondly,we propose BPSK iterative detection(BPSK ID)algorithm.Based on it,we propose a cascaded BPSK iterative detection(CBID)technique for SEFDM-MQAM signals.In addition,we use structure of "Pre-estimator + Accurate Detector" to make construct CBIDFSD hybrid detector,and analyze the complexity of ID-FSD and CBID-FSD algorithms.Simulation results show that the performance of CBID-FSD is better than that of ID-FSD,and replacing ID-FSD with CBID-FSD can improve the performance of SEFDM system.Finally,we design and implement a linear mapping direct detection optical SEFDM(LMDDO-SEFDM)system based on CBID-FSD algorithm,and describe the principle of this system such as system structure,the principle of SEFDM transmitter and receiver and so on.The maximum spectral efficiency of LM-DDO-SEFDM system is 1.25 times than that of OFDM-16 QAM.In addition,we test the performance of the system in detail.The results show that CBID-FSD algorithm can achieve lower bit error rate than ID-FSD algorithm in the same complexity,and the decoding complexity of FSD can be reduced to 1/4 with CBID-FSD replacing the ID-FSD algorithm to keep the same bit error rate.Since CBID-FSD algorithm can better balance the complexity and performance,CBID-FSD is a better algorithm for detecting SEFDM signals than ID-FSD.Thus,CBID-FSD is more suitable for using in the next generation of optical communication system than ID-FSD.