Research On Channel Estimation And Adaptive Modulation Scheme In MB-OFDM Ultra-wideband Over Fiber System

Multiband orthogonal frequency division multiplexing ultra-wideband(MB-OFDM UWB)over fiber technology,combined the high spectral efficiency(SE),robust against multi-path effects and flexible spectrum resource allocation of UWB signal with the long transmission distance,high data capacity and low loss of optical access technology,has been attracting great interest in broadband wireless communications and wireless local area networks.However,MB-OFDM UWB signal can be subject a lot of impairments in optical fiber transmission system.These impairments including intensity noise converted by laser phase nosie after fiber dispersion,nonlinear effects from MZM,power attenuation of double sideband signal caused by fiber dispersion and non-ideal frequency response of optical or electrical components.In order to compensate the non-linear effect and dispersion impairments and improve the transimisson performance,in intensity-modulation and direct-detection(IM/DD)MB-OFDM UWB over fiber system,the low cost and high performance of the digital signal processing(DSP)technology is proposed and experimentally investigated in this paper.The main works are as follows:1.An intra-symbol frequency-domain averaging(ISFA)-combined pilot-aided channel estimation scheme at the receiver is proposed and investigated in intensity-modulation direct-detection(IM/DD)MB-OFDM UWB over fiber system.The pilot-aided channel estimation based on LS algorithm,due to its low complexity,is widely used in OFDM-based system.However,the impact of noise is never considered in the LS algorithm.Considering that the ISFA-based channel estimation scheme is found to be highly robust against transmission impairments such as PD noise,CD,and fiber nonlinearity.Therefore,to improve the accuracy of channel estimation,an ISFA-combined pilot-aided channel estimation scheme is proposed,and the feasibility of this scheme is demonstrated in the MB-OFDM UWBoF system.After transmitted over 50km standard single mode fiber(SSMF),the experimental results show that,at the bit error rate(BER)of 1×10-3,the receiver sensitivity of 64-QAM have improved about 1.2dB by using the proposed ISFA-combined pilot-aided channel estimation scheme,compared to the traditional pilot-aided channel estimation method.2.A MB-OFDM UWBoF system based on the 64/16/4-QAM adaptive modulation scheme is proposed at the transmiter.To overcome the unbalanced error bit distribution among subcarriers caused by inter-subcarriers mixing interference(ISMI)and frequency selective fading(FSF)in the IM/DD MB-OFDM UWB over fiber system,and reduce the complexity of adaptive modulation algorithm in optical fiber communication system,an static adaptive modulation scheme based on 64/16/4-QAM modulation is proposed and experimentally investigated.After 50 km SSMF transmission,at the BER of 1×10-3,compared to that with the 64-QAM and 16-QAM modulation scheme,the experimental results show that the power penalty of the IM/DD MB-OFDM UWBoF system with 64/16/4-Q AM adaptive modulation scheme is about 3.3 dB and 1.4dB,respectively.The experiment results show that the transmission performance can be improved by using the proposed adaptive modulation scheme in MB-OFDM UWB over fiber system.Moreover,the receiver sensitivity is improved about 0.52 dB when the intra-symbol frequency-domain averaging(ISFA)algorithm at the receiver is employed in the receiver of the 64/16/4-Q AM-encoded adaptively modulated IM/DD MBOFDM UWBoF system.