Study On Performance Optimization Of OFDM-PON System

With the rapid development of high speed,large bandwidth and wide coverage of access network in the future,Orthogonal Frequency Division Multiplexing(OFDM)is considered to be the core technology of the future communication network development because of its high spectrum efficiency,strong narrowband interference ability,overcome the frequency selective fading,and it has been widely used in the fields of Digital Communication,Wireless Local Area Network(WLAN,IEEE802.11)and the 4th Mobile Communication System(4G).In order to reach the requirement of the rapid growth of users' information and diversified business,it is imperative to find a new technology for the next generation optical access network.The application of OFDM technology in PON(Passive Optical Network)system has become one of the research focuses of optical access network NG-PON2.Compared to other PON systems,the application of OFDM technology in PON system not only integrates the advantages of high spectral efficiency of OFDM technology,but also makes the system bandwidth scheduling and allocation of more flexible,more resistant to dispersion.So it is considered as optimal solution of "Last Mile" broadband bottleneck of future optical access network.This paper introduces the development history and research status of OFDM technology and OFDM-PON system,as well as its basic principles and related technologies,and mainly focuses on the optimization of OFDM-PON system performance.Firstly,low density parity check(LDPC)codes are introduced into the OFDM-PON system,and the system performance can be optimized by the high coding gain of LDPC codes.Through the simulation compares the performance of ofdm-pon system downlink transmission by uncoded,back-to-back uncoded and LDPC-OFDM coded modulation,the results show that the performance of OFDM-PON system is improved obviously by LDPC code in 20 km single mode optical fiber.It also analyzes the influence of different construction methods and decoding algorithms of LDPC codes on OFDM-PON system performance.Secondly,by analyzing the OFDM signal generated high PAPR(Power Ratio Peak-to-Average),this paper analyzes the influence on optical transmission system by the high PAPR of optical OFDM signal generated in the transmission process.And by analyzing the existed PAPR suppression technology,the paper proposes a combined method by the LDPC coded of the modified Selected Mapping(SLM)method and the clipping method to suppress the high OFDM signal PAPR,for the purpose of suppressing the PAPR of the optical OFDM signal,to achieve the OFDM-PON system signal transmitter PAPR suppression,and then through the improvement of the quality of optical OFDM signal to improve the performance of the OFDM-PON system.The downlink transmission performance of the OFDM-PON is verified by the simulation analysis,the simulation results show that in the OFDM-PON system,the improved combination method can suppress the high optical OFDM signal PAPR and reduce the nonlinear effect caused by the optical devices,and the improved combination method not only suppresses the high PAPR of OFDM,but also reduce the effect of the ordinary SLM technique is introduced in the band edge information,so as to enhance the performance of the system.