相干光正交频分复用系统定时同步的改进算法

分析了当前相干光正交频分复用(CO-OFDM)系统中Schmidl&Cox经典算法在光纤信道的定时同步,针对其产生平波现象和对光纤色散(CD)的缺点,提出了改进算法,并通过MATLAB在光纤信道中对两种算法进行了仿真,结果表明,在光纤信道下,改进方法的性能有远优于经典算法,因此改进方法更适合于光纤信道。     

一种降低相干光正交频分复用系统序列相关性的方法

分析了相干光正交频分复用(CO-OFDM)系统中四波 混频(FWM,four-wave mixing)效应对系统性能的影响,提出了一种新的降 低CO-OFDM系统中各个子载波序列相关性的方法——偏载波填充法(PCF,partial carrier filling)与部分序 列传输(PTS,partial sequence of transmission)相结合。理论分析和仿真表明,这 种方法能有效降低 CO-OFDM系统的序列相关性,从而抑制信道内FWM效应对CO-OFDM系统带来的损伤。研究结 果表明, 本文提出的方法在传输距离达10^3km的情况下,误码率(BER)仍然低于10－3,与PTS方法相比,降低了将近1个数量级。     

CO-OFDM系统中一种改进的同步算法方案

对相干光正交频分复用(CO-OFDM)系统时序和频率 同步算法进行了改进,消除了Park的方法中由于时间标尺旁瓣引起 的定时模糊性,利用单个训练符号实现了和Schmidl方法一样宽的频偏估计范围,且保持 同等的估计精 度。在20Gb/s的CO-OFDM系统上对改进算法进行仿真测试的结果表 明,通过色散补偿的辅助,改进的同步 算法方案实现了精确的定时估计,和节省训练符号且宽范围的频差估计。此外,色散补偿的 辅助提升了子载波恢复的性能,使得误比特率(BER)为10－3时系统的光信噪比(OSNR)要求降低了3dB。     

CO-OFDM系统不同调制方式的性能分析(本期优秀论文)

在没有色散补偿的情况下,对不同调制方式的相干光正交频分复用(CO-OFDM)系统的性能进行研究.结果表明:2PSK抗误码性能较好,频带利用率较低;4QAM频带利用率是2PSK的两倍,当系统误码率在10<'-3>以内时,所需OSNR约为9dB;8QAM频带利用率比前两者高,但抗误码性能较前两者差.因此,设计通信系统时,要...     

一种基于限幅的降低相干光OFDM系统非线性效应的方法

相干光正交频分复用系统(Coherent Optical-orthogonal frequency division multiplexing,简称CO-OFDM)可有效降低光纤色散效应,是近年来光传输领域研究热点之一.由于 OFDM 信号具有较高的峰均值功率比(Peak-to-average Power Ration,PAPR)和较窄的载波间隔,系统对非线性效应十分敏感,严重影响传输性能.文章介绍了一种基于信号限幅的CO-OFDM系统,通过载波选择和信号限幅,有效提高系统非线性容限,同时消除限幅噪声带来的影响.理论分析和仿真结果表明,在不需任何在线色散补偿条件下,基于限幅的CO-OFDM系统在单模光纤中传输960km,系统Q值较传统CO-OFDM系统有2dB提高,可完全消除限幅噪声影响.     

基于相干光OFDM的WDM系统传输性能分析

首先对相干光OFDMWDM系统理论模型和基本原理进行了研究,然后基于Opt i syst em仿真软件,对相干光OFDMWDM传输系统进行了仿真分析,并研究了该系统的传输性能,发现基于相干检测的光OFDM技术和WDM技术结合,可以有效抑制光纤色散和非线性影响,提高系统的性能。将此系统与传统的NRZ WDM光传输系统进行比较,发现系统性能较NRZ系统有很大的提高。     

Data-aided linear fitting blind phase estimation method for coherent optical OFDM system

In this paper, a novel data-aided linear fitting-based (DALF-based) blind phase estimation method for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) is proposed. Similar to our previous work done in the pilot-based blind phase estimation method, the pilot subcarriers are used to transmit unknown amplitude modulation signals in order to improve spectral efficiency. But the so-called pilot subcarriers can be reduced to only two in the DALF-based method, while the conventional pilot-aided-based (PA-based) method requires almost four real pilot subcarriers. A performance comparison of the conventional PA-based and DALF-based phase estimation methods has been demonstrated through a 16-QAM CO-OFDM simulation. The results show that the performance of the proposed DALF-based method is better than the conventional one with higher SE and has the potential in the large capacity CO-OFDM systems.     

Recognition of spectral amplitude codes by frequency swept coherent detection for flexible optical label switching

We propose a new method of recognizing spectral amplitude codes by using optical coherent detection with a frequency swept local light source oscillator. Our proposed method offer a substantial simplification in terms of required components to built optical label processing units with enhanced flexibility to accommodate for wavelength tuneability and a large number of labels. We present a performance analysis, comparison with conventional spectral codes recognition methods, based on computer simulation results. We consider a payload bit rate of 40 Gb/s.     

相干光OFDM系统中的相位估计分析

相干光正交频分复用(Coherent Optical Orthogonal Frequency Division Multiplexing,简称CO-OFDM)可有效降低光纤色散和偏振模色散影响,由于系统采用相干检测,对相位噪声的分析及信道估计尤为重要.文章对CO-OFDM系统数学模型进行了具体分析;OFDM作为一种特...     

基于DFT的信道估计算法在CO-OFDM系统中研究

信道估计作为相干光OFDM(CO-OFDM)系统的一种 关键技术对系统的性能有着十分重要的影响, 光纤通信系统通过信道估计,可以将信号经过光纤传输后的影响,如损耗、色散、非线性等 ,通过在发送 端发送已知数据,在接收端利用均衡等恢复出原始信号。本文首先介绍了相干光OFDM系统, 并使用 optisystem和matlab软件搭建了相干光OFDM系统仿真平台,提出了适用于相干光OFDM系统 的基于DFT 算法及其进一步的改进算法,并在此平台上进行了仿真试验。结果表明,基于DFT算法及其 改进算法能够 很好地提高相干光OFDM系统的传输性能,改进的DFT算法与DFT算法在BER的值 为10－4的条件下,有1dB的光信噪比增益;与LS算法比较, 有3dB的光信噪比增益。     

自由空间光通信中相干OFDM系统性能分析

结合正交频分复用（OFDM）技术和相干探测的优势,研究了相干OFDM自由空间光通信（FSO）系统的误码性能,考虑了OFDM映射方式以及映射阶数对系统误码性能的影响。在Gamma-Gamma大气湍流信道下,分别从平均信噪比和所需平均接受光功率的角度考虑了系统在弱、中和强湍流三种情况下的误码性能。在此基础上,推导了系统误符号率的闭合表达式。仿真结果表明,相干探测下OFDM FSO系统可以较好地克服大气湍流效应,在弱、中湍流情况下,QAM映射方式下系统的误码性能明显优于PSK方式,在强湍流下这种优势不明显,此外随着映射阶数的增加,系统误符号率增加,因此在实际应用中可以通过降低映射阶数来提高系统误码性能。     

基于相干光正交频分复用的WDM传输系统及其性能分析

相干光正交频分复用由于其良好的传输性能成为近年来光传输领域的研究热点,波分复用技术可以在光纤中通过增加并行波长的数量来提高系统的容量,将CO-OFDM和WDM技术结合,可以构造出高速率、大容量、低成本的光传输网络。文章首先对基于CO-OFDM的WDM传输系统的理论模型和基本原理进行了研究,然后对基于CO-OFDM的100Gb/s×32-信道WDM传输系统进行了仿真分析。并研究了该系统的传输性能。结果表明：在没有任何光纤的色散及非线性补偿的情况下,当信号速率为3.2 Tb/s时,系统的Q因子高于16.0 dB,在标准单模光纤中的传输距离可达1500km。     

Performance evaluation of (D)APSK modulated coherent optical OFDM system

Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40 Gbit/s single-channel and 5 ^* 40 Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q² factor of 16(D)APSK modulated OFDM signal are respectively 2 dB and 0.5 dB higher than 16QAM modulated optical OFDM signal after 640 km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000 km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.     

A coherent photonic wavelength-division switching system forbroad-band networks

A coherent photonic wavelength-division (WD) switching system, utilizing a coherent wavelength switch (λ switch), is proposed. In the proposed coherent λ switch, the tunable wavelength filter function is accomplished using coherent optical detection with a wavelength tunable local oscillator. The coherent photonic WD switching system has the following features; (1) low crosstalk switching for dense WDM signal, and (2) large line capacity capability. Design considerations show that 32 wavelength division channels can be available with a coherent λ switch. It is also shown that a broadband metropolitan-area-network with over 1000 line capacity is possible, using a multistage connection in the coherent λ switches. The switching function of the coherent λ switch is demonstrated in a two-channel wavelength-synchronized switching experiment, using 8-GHz-spaced, 280-Mb/s optical FSK signals     

相干光OFDM系统中IQ不平衡的时域补偿算法

通过研究相干光正交频分复用(CO-OFDM)系统中正交/同相(IQ)不平衡对系统性能的影响,提出一种新型IQ不平衡时域补偿TS(基于训练序列)算法,并与传统的时域格拉姆-施密特正交化(GSOP)算法进行了对比。     

A coherent optical FDM CATV distribution system

A coherent optical frequency-division-multiplexing (FDM) experimental system for an optical CATV distribution service has been developed. This system employs a channel frequency spacing locked optical FDM transmitter and a random access optical heterodyne receiver. In the transmitter, ten 1.54-μm wavelength tunable distributed-Bragg-reflector laser-diode (DBR LD) modules were FSK modulated with a 400-Mb/s PN pattern. A reference pulse method is used for channel space control. Individual channel spacings for ten LDs are stabilized to 8 GHz. The random access optical heterodyne receiver is realized with a wavelength tunable local DBR LD, polarization diversity reception technique, and random access automatic frequency controller. A current address method realizes the random access function. The results of a ten-channel FDM transmission experiment carried out to evaluate these techniques are presented. It is estimated that over 80 channel high-definition TV signals can be distributed to 2000 subscribers with 500-GHz frequency tunable DBR LD. The feasibility of expanding the subscriber number to over 10000 was confirmed by an experiment with a traveling-wave optical amplifier     

相干光OFDM通信系统中的IQ补偿和相位估计

文章首先研究了相干光OFDM(正交频分复用)通信系统中的线性损耗,包括IQ(同相/正交相)不平衡以及线性相位噪声;提出了一种DA(基于决策)的不需要周期性地插入训练数据的方法。计算机仿真结果表明,所提出的方法可以有效估计并补偿这两类线性损耗;在此基础上,提出了一种在考虑信道色散噪声的情况下,联合补偿IQ不平衡和线性相位噪声的新算法。     

Characterisation of nonlinearity performance for coherent optical OFDM signals under influence of PMD

The first experiment of polarisation-mode dispersion (PMD) impact on fibre nonlinearity in coherent optical OFDM (CO-OFDM) systems is reported. The optimal Q value at 10.7 Gbit/s has been improved by 1 dB after introduction of differential group delay (DGD) of 900 ps.     

相干光OFDM系统中MMSE信道估计研究

信道估计作为相干光正交频分复用(CO-OFDM)的 一种关键技术对系统的性能有着十分重要的影响。本文重点对系统信道估计的实现进行了数 学 分析,搭建起了CO-OFDM系统仿真平台,并在此平台上将提出的最小均方误差(MMSE)及其改进算法应用到CO- OFDM系统中进行信道估计。结果表明,MMSE及其改进算法能够很 好地提高CO-OFDM 系统的传输性能,在误码率(BER)为10－3时,与最小 二乘(LS)算法相比有约2dB的光信噪比(OSNR)增益,且改进型MMSE算 法的复杂度要比MMSE算法低2个数量级。