Coherent Optical Ofdm System Based On Pilot Channel Estimation Research

Optical orthogonal frequency division multiplexing have integration the dualadvantages of optical fiber communication and OFDM technology, it become one of thehot research field of high-speed optical transmission. According to the detected atreceiving, it can be divided into the direct detection optical OFDM system and the coherentdetection optical OFDM system. Furthermore, the coherent optical OFDM system couldmore effectively suppress chromatic dispersion, polarization mode dispersion, and adopthigher order modulation scheme, it can aslo use more balanced and become a majorresearch focus in the field of optical communications. When the single-channel ratereached40Gbit/s or100Gbit/s or even higher, the channel impact become a majorrestriction factors of high-speed coherent optical OFDM transmission system, the system isvery sensitive to dispersion, noise, and other factors, which need to use the effectivechannel estimation method, real-time to accurately track the changes of the channel. Thepurpose is to estimate the channel estimation in the time domain or frequency domain toobtain the channel response, to ensure the received data correction and recovery. Accuratechannel estimation is the key factor to improve the reception quality of the receiver, and isalso primarily a means to improve data transmission performance of the coherent opticalOFDM communication system.The channel estimation technology be a pplied to coherent optical OFDMcommunication syst em, which can effectively solve the high-speed, long-distance opticaltransmission system channel signal, thereby improving the reliability of the opticalcommunication system. Coherent optical orthogonal frequency sub-cha nnel multiplexing system can adopt generally be divided based Pilot Symbol Aided channel estimation,judgment-based channel estimation and blind or semi-blind letter Road estimated, in thispaper, we mainly adopted based on pilot of the frequency of channel estimation techniquescommon least squares (LS), minimum mean square error (MMSE), linear minimum meansquare error (LMMSE) channel estimation algorithm for in-depth study, because of LSalgorithm noise immunity, its noise reduction algorithms are based on the average of theaverage time domain and frequency domain there are some flaws, and MMSE algorithmcomplexity is too high, and on this basis, these algorithms has been improved.In this paper, we mainly around based on the pilot coherent optical OFDM systemsand channel estimation were studied, mainly including coherent optical OFDM systemstheory model and its key technology, fiber channel characteristics, channel estimatedalgorithm based on the pilot and its improved, the structures of system simulation platformand simulation. Specific work are as follows:(1) On the basis of the basic principles of OFDM technology and its key technology,we start the basic theory derived from the formula, in-depth study of the optical OFDMsystem, especially the principle of coherent optical OFDM system components, combinedwith the current research status of domestic and outside, a detailed analysis of the strengths,and analysis the weaknesses and potential applications of coherent optical OFDM system.(2) Depth study of the characteristics of fibre channel based on the pilot channelestimated algorithm, and traditional LS channel estimated algorithm has been improved,proposed the applicable in the coherent optical OFDM system based on improved LSalgorithm of DFT channel estimation algorithmthe algorithm can effectively remove thetraditional LS algorithms which do not consider the influence of noise, greatly improve theaccuracy of channel estimation, and its complexity does not become very complex.However, although the algorithm can remove the noise other than the cyclic prefix and cyclic prefix noise persists, therefore, in order to further improve the system performance,on this basis we further improved and optimized.(3) We firstly use wireless communication MMSE channel estimation techniques tocoherent optical OFDM communication system, because of its high complexity, weproposed an improved low-complexity algorithm based on the MMSE algorithm, itscomplexity is two orders of magnitude lower than the traditional MMSE algorithm, but theperformance of improved the MMSE algorithm almost equivalent to the MMSE algorithm.(4) We firstly use the simulation software Optisystem and Matlab that constructedcoherent optical OFDM system simulation platform with channel estimation module, andfirstly verify the correctness of the coherent optical OFDM system, and then based on thisplatformtime simulation, analysis and verification the LS algorithm, the MMSE algorithm,the noise reduction algorithm based on the frequency and time domain,and we proposedthe improved channel estimation algorithm.