Real-time Optical OFDM Transmitter Design Based On FPGA

Optical orthogonal frequency division multiplexing is a new type of optical transmission technology,not only can resist the chromatic dispersion in optical fiber transmission link,polarization mode dispersion and nonlinear effects of factors can also increase the spectral efficiency of the system,thereby greatly enhancing its transmission capacity.However traditional O-OFDM digital signal processing in optical fiber transmission systems are mostly offline,as the O-OFDM processing speed increases and business applications,the offline approach can not meet the requirements of commercial and real-time processing.Meanwhile,field programmable gate arrays has a strong real-time,scalability and parallel processing capabilities,and it can reduce signal processing latency.Therefore,the real-time processing system of high-speed O-OFDM is particularly important.Recently,existing real-time systems are in the development of the higher-order modulation and high speed.But those real-time O-OFDM systems do not use electric absorption laser modulation and LDPC-coded module at home and abroad.Therefore,further exploratory work is based on the O-OFDM transmission systems FPGA-based,the research can be divided into the following sections:1.In this paper,real-time O-OFDM baseband signal processing transmitter based on the FPGA,which adopts the direct detection of OFDM systems(DDO-OFDM)structure,and adopted the high order modulation(256-QAM)baseband modulation scheme.Meanwhile,combined with electrical absorption modulation laser modulation,we build the experimental platform,and we have realized the OFDM signal transmission with high rate.At the same time,through the experimental analysis,we can learn the BER performance and EVM performance under different transmission distance.Experimental data show that bit error rate performance decrease with the light receiving power reduction and the increase of fiber distance.But in the short distance,optical fiber transmission system performance and optical transmission system performance of back-to-back are the same.Higher-order modulation real-time O-OFDM system is suit for high-speed short distance transmission.2.The overall performance of real-time baseband OFDM system is tested and experimented.And we use high throughput LDPC module to improve the BER performance of high-order modulation real-time O-OFDM system.This article usesthe double diagonal quasi-cyclic LDPC check matrix IEEE 802.11 n standard,improved the traditional bidirectional recursive coding algorithm,so as to adapt to the high real-time O-OFDM system throughput.Meanwhile,the performance comparison between LDPC-coded signals and un-coded signals is investigated.The experimental results show that,in the case of different optical fiber transmission distance,after joining the encoding module system BER performance improved significantly.The greater the check digit of bit rate,the system to improve the effect is more obvious.At the same time,the longer the distance,to improve the performance of LDPC codes on the system is more obvious.