Research On MB-OFDM Ultra-wideband Over Fiber Systems Based On Joint Channel Estimation Method

In order to meet the need of broadband services which grow explosively,large-capacity,high-speed,flexible and effective optical transmission systems are desired for the future optical networks.In recent years,the multiband orthogonal frequency division multiplexing ultra-wideband(MB-OFDM UWB)over fiber technology combined with UWB signal and optical fiber communication has been concerned extensively.The main advantages are high transmission rate,high spectrum efficiency,high capacity,and low power consumption.In this paper,the channel estimation method for intensity-modulation and direct-detection MB-OFDM UWB over fiber system and the transmission performance of MB-OFDM UWB over fiber wavelength division multiplexing passive optical network(WDM-PON)system based on optical frequency comb technology are studied.The innovations of the work are as follows:1.A joint channel estimation scheme based on training sequences and pilot symbols is proposed and experimentally demonstrated in 64-QAM MB-OFDM UWB over fiber system.The MB-OFDM UWB signal is generated by offline method at the transmitter,the training sequences and pilot symbols are inserted to realize the channel estimation at the receiver.The joint channel estimation scheme takes into account the variation from time and frequency.By selecting the appropriate weight factor L,the channel frequency response can be estimated to compensate the loss of channel transmission accurately.After 50km standard single mode fiber transmission,compared with the channel estimation schemes based on only pilot symbols and training sequences,joint channel estimation method can effectively improve the accuracy of channel estimation and the receiver sensitivities of the 64-QAM MB-OFDM UWB over fiber system.2.A high-speed,high-capacity and flexible WDM-PON system based on MB-OFDM UWB signal is proposed and experimentally demonstrated.The five lines optical frequency combs are generated by using one MZM.The 5 channels carrying 15 sub-bands can be transmitted over 50km standard single mode fiber successfully.Adaptive modulation scheme is employed to generate the 128/64/32-QAM encoded MB-OFDM UWB signal.Different sub-bands of MB-OFDM UWB signal are adaptively modulated with different modulation formats to provide services with multiple data rates flexibly.Meantime,the joint channel estimation scheme based on training sequences and pilot symbols is used to realize the data recovery of the receiver,and the BER performance of system can be improved.After removing the 7%hard-decision forward error correction(HD-FEC)overhead,the highest net bit rate per sub?band is 2.078Gb/s and the lowest net bit rate per sub-band is 1.484Gb/s.If one user needs broader bandwidth,two or more sub-bands resources can be served.The highest transmission rate can be up to 5.343Gb/s.The integration of MB OFDM UWB service and the optical frequency comb can increase the flexibility and capacity of the whole system.It has great potential for the applications in future 5G communications.