相干光正交频分复用传输系统中的无导频相位纠偏方法

提出了一种适用于16-QAM的新型相位纠偏方法,克服了基于M次方算法的传统相位纠错方法不适用于高阶正交振幅调制的缺点.该方法结合正交频分复用调制方式,无需导频即可完成相位盲估计,且计算量较少.本文基于112 Gb/s 1040 km的相干光正交频分复用传输系统进行了算法验证,并与传统的4次方纠偏方法进行了比较,实验证明...     

大气激光通信非对称限幅光正交频分复用技术

将一种新的正交频分复用调制技术运用到大气激光通信系统中,分析了采用这种非对称限幅光正交频分复用调制技术的大气激光通信系统在大气湍流信道下的性能.在此基础上,把非对称限幅光正交频分复用调制方案与传统的开关键控及直流偏置光正交频分复用调制方案进行了比较,并在大气湍流信道中进行了仿真.仿真结果表明:非对称限幅光正交频分复用调制技术增强了系统对大气湍流的抗干扰能力,该方案可以满足大气激光通信系统的需要.     

一种光正交频分复用系统的联合相位均衡方法

正交频分复用（OFDM）技术加相干接收与数字信号处理法(DSP)的组合是超长距离光通信的理想模型。光OFDM系统对相位噪声十分敏感,必须对相位噪声进行补偿。提出一种基于正交小波基变换的光OFDM系统的联合相位均衡方案。该方案将块状导频周期性地插入OFDM信号,在接收端利用导频信息首先消除各个子载波的公共相位误差,然后采用自适应均衡方式消除每个子载波自身相位误差。仿真结果表明,对于二进制正交振幅键控(4QAM)调制信号,在采用常规的G.652光纤、100 Gb/s的相干光OFDM系统中,该联合相位补偿方法可使信号在满足传输系统的误码性能要求下,传输距离达到1000 km。     

大气激光通信非对称限幅光正交频分复用技术

将一种新的正交频分复用调制技术运用到大气激光通信系统中,分析了采用这种非对称限幅光正交频分复用调制技术的大气激光通信系统在大气湍流信道下的性能.在此基础上,把非对称限幅光正交频分复用调制方案与传统的开关键控及直流偏置光正交频分复用调制方案进行了比较,并在大气湍流信道中进行了仿真.仿真结果表明:非对称限幅光正交频分复用调...     

基于相位调制器产生六倍频光毫米波的OFDM信号光传输系统研究

提出了两个并行相位调制器产生六倍频光毫米波并传输正交频分复用信号的全双工光纤无线通信系统.将2.5 Gbt/s的正交频分复用信号调制到60 GHz光毫米波上.从理论上分析了毫米波产生的原理,并分别模拟了毫米波信号承载OOK信号和正交频分复用信号在光纤中的传输性能.从而验证系统的可行性.仿真模拟结果表明,在光纤无线通信系统中,正交频分复用比非归零码更具有优势.     

基于相位调制器产生六倍频光毫米波的OFDM信号光传输系统研究

提出了两个并行相位调制器产生六倍频光毫米波并传输正交频分复用信号的全双工光纤无线通信系统.将2.5Gbt/s的正交频分复用信号调制到60GHz光毫米波上.从理论上分析了毫米波产生的原理,并分别模拟了毫米波信号承载OOK信号和正交频分复用信号在光纤中的传输性能.从而验证系统的可行性.仿真模拟结果表明,在光纤无线通信系统中,正交频分复用比非归零码更具有优势.     

相干光正交频分复用系统中射频导频和扩展卡尔曼滤波联合的相位噪声补偿算法

针对大线宽和高阶圆形正交幅度调制(C-QAM)的相干光正交频分复用(CO-OFDM)系统,提出一种基于射频导频(RF-Pilot)和时域扩展卡尔曼滤波相结合的相位噪声补偿算法。该算法通过在接收端预设的RF-Pilot进行时域相位噪声粗补偿,并进行信道估计和均衡。再对信道均衡后的频域数据进行预判决,结合判决后的时域数据和信道均衡后的时域数据,进行扩展卡尔曼滤波,实现相位噪声的最终补偿。基于传输速率为50Gb·s~(-1)和传输距离为100km的CO-OFDM系统在C-16QAM和C-32QAM两种调制格式下进行了算法的仿真验证。仿真结果表明,该算法相较于原RF-Pilot算法,具有较好的相位噪声补偿效果,且频谱利用率并未显著降低,算法复杂度并未显著增加。激光器线宽为2.1MHz,且使用C-32QAM时,该相位噪声算法补偿的误码性能可达到前向纠错上限,从理论上证明使用该算法可提高CO-OFDM系统对激光器线宽的容忍度,线宽较宽的廉价分布式反馈激光器可作为CO-OFDM系统的发射端光源和接收端本地振荡。该算法能扩展大线宽CO-OFDM系统在长距离接入网和城域网中的应用。     

无边带信息的多输入多输出正交频分复用水声通信图样选择峰均比抑制算法

针对多输入多输出正交频分复用 图样选择 峰均比(peak-to-average-power-ratio PAPR)抑制算法需要传递边带信息的缺点, 提出了一种无边带信息传输的图样选择峰均比抑制算法. 该算法利用不同分布图样的梳状导频携带加扰相位序列选择信息, 结合浅海水声信道的稀疏特性在接收端对加扰图样进行自主区分, 实现了无边带信息的图样选择峰均比抑制.仿真和水池实验结果证实: 无边带信息传输的图样选择峰均比抑制算法可以在不损失PAPR抑制性能的前提下, 准确解算出传输相位序列选择信息、对抗突发噪声、实现无边带信息传输的可靠水声通信. 关键词： 水声通信 正交频分复用 峰均功率比 边带信息     

用于FTN系统的二阶导频辅助载波相位恢复算法

针对超奈奎斯特系统引入的码间干扰使载波相位估计难度增大的问题，提出了一种二阶电域导频辅助载波相位估计方案，将导频辅助相位噪声补偿模块与基于Viterbi的最大似然相位估计模块级联，牺牲约1.7%的带宽开销，可以有效克服超奈奎斯特系统引入的码间干扰，对激光器线宽导致的相位噪声进行准确估计。在调制格式为16进制正交幅度调制的超奈奎斯特系统中，经仿真验证可知：该算法在加速因子不超过Mazo极限时可以有效跟踪相位噪声；在加速因子低至0.833、误码率为2×10^-2、光信噪比代价为1 dB的条件下，该算法能容忍的最大线宽乘积为5×10^-4；相较于一阶导频辅助载波相位恢复算法，该算法具有更大的线宽容忍度，所需的光信噪比也更小。     

基于数字相干叠加的相干光正交频分复用系统中光纤非线性容忍性研究

光正交频分复用系统中的光纤非线性效应制约着系统进一步的扩容. 针对此问题, 提出一种数字相干叠加的方法, 用于提高相干光正交频分复用系统对光纤非线性的容忍性. 仿真中, 5通道的波分复用下偏振复用相干光正交频分复用系统的每个通道传输四进制正交振幅调制映射的71.53 Gbit/s信号在光纤中传输400 km. 首先, 通道间隔为25 GHz, 与传统相干光正交频分复用系统相比, 色散补偿前后, 使用数字相干叠加的相干光正交频分复用系统的信噪比分别提升了6.02 dB和9.05 dB, 最佳入纤光功率均增大了2 dB; 其次, 通道间隔为50 GHz, 色散补偿前后, 信噪比分别提升了4.9 dB和8.75 dB. 通过理论推导及仿真, 验证了所提方法能有效消除相干光正交频分复用系统的一阶非线性失真, 进而提高系统对光纤非线性的容忍性.     

A novel timing synchronization for CO-OFDM systems using chirp signals

A fast and efficient timing offset correction is an essential function in the coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The timing synchronization schemes for OFDM systems in wireless communications can be used for CO-OFDM systems. However, the performance of these schemes is reduced due to the chromatic dispersion. To fulfill the requirement of the CO-OFDM systems, a novel symbol timing synchronization scheme based on chirp signals has been proposed. The simulation results show that the proposed method is robust in CO-OFDM systems which is suffering from noise.     

Coherent optical OFDM scheme with inter-carrier interference self-cancellation and common phase error compensation

Schemes integrating inter-carrier interference （ICI） self-cancellation and common phase error （CPE） com- pensation for coherent optical orthogonal frequency division multiplexing （CO-OFDM） systems are investi- gated. The purpose of our research is to counteract the impacts of laser phase noise and fiber nonlinearity. We propose two ICI self-cancellation-based CO-OFDM schemes, and adopt a pilot-aided decision feedback （DFB） loop for CPE compensation. The proposed schemes are compared with conventional CO-OFDM schemes at the same spectral efficiency. Simulations show that our schemes can not only enhance laser linewidth tolerance of the CO-OFDM system, but also present strong robustness against fiber nonlinearity.     

Novel iteration-free blind phase noise estimation for coherent optical OFDM

We propose a novel iteration-free blind phase noise estimation scheme for coherent optical orthogonal frequency division multiplexing （CO-OFDM） systems. In the new algorithm, the cost function is selected as the similar expression with real and imaginary parts as that in the modified constant modulus algorithm, and the new cost function is derived under some assumptions, where it is infinitely approximated by the sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common phase error can be obtained with only some samples, where the algorithm avoids computational complexity of conventional blind phase noise compensation scheme. In CO-OFDM systems with high-order modulation format （32 quadrature amplitude modulation） and narrow linewidth lasers, it is proved by the simulation results that the nhase noise can be effectively compensated with the proposed blind estimation method.     

一种基于星座恢复的相干光OFDM系统非线性抑制方法

 鉴于相干光正交频分复用系统（CO-OFDM）易受非线性效应影响,严重制约系统传输性能, 提出一种基于星座恢复的降低系统峰均值功率比（PAPR）的方法。对系统模型及作用机理进行分析,仿真结果显示,以10 Gbit/s的速率通过单模光纤传输720 km,基于星座恢复的CO-OFDM系统Q值较无非线性抑制的CO-OFDM系统有3 dB提高;另外,系统最佳限幅比例系数受色度色散影响,随着色散因子的增大,星座恢复效果也逐渐减弱,在传输240 km条件下,色散因子为12 ps/nm·km较6 ps/nm·km,限幅比例系数从0.9降低至0.8。     

A novel adaptive synchronization algorithm for intermediate frequency architecture CO-OFDM system

An adaptive algorithm of fine synchronization for intermediate frequency architecture coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission system is proposed. The whole synchronization procedure is separated into two steps. In the first step, we use an auto-correlation-style algorithm to achieve the coarse symbol synchronization. In the second step, the proposed algorithm is used to achieve the adaptive fine synchronization. The merit of the proposed algorithm is that it can realize fine synchronization under different environments without adjusting the detect-threshold of timing metric in a dynamically reconfiguration network. And also the algorithm can implement in field-programmable gate array (FPGA) or other digital signal processing (DSP) chips easily. In this paper, the CO-OFDM model is analyzed in theory firstly. Secondly, an analysis on the performance of coarse synchronization algorithm used in this paper is made. Finally, the proposed fine synchronization algorithm is introduced in detail. The simulation experiment result demonstrates that the proposed algorithm achieves fine synchronization under different signal noise ratio (SNR) conditions after 6 fiber-spans transmission.     

基于小波变换的长距离光正交频分复用系统中四波混频引起的相位噪声分析

四波混频（FWM）效应是相干光正交频分复用（CO-OFDM）系统中最主要的非线性作用。分析基于小波变换的相干光正交频分（WT-OOFDM）系统原理,研究小波变换对FWM效应和光放大器自发辐射（ASE）引起的相位噪声的改善效果。数值结果表明,在采用常规G. 652光纤,100 Gbit/s的WT-OOFDM传输1500 km时,非线性相位噪声降低20%,总相位噪声降低15%。     

An improved least square channel estimation algorithm for coherent optical OFDM system

This paper presents an improved processing added to conventional least square (LS) channel estimation to modify its performance for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. By testing selected limitation factors of the existing algorithms, the influence of our improved algorithm to the performance of CO-OFDM system were studied and compared with other published algorithms. The simulation results of the study demonstrated that the proposed approaches achieved better channel estimation performance and are considered as a more appropriate alternative for CO-OFDM system with the tradeoff between complexity and performance.     

Improved dichotomous search frequency offset estimator for burst-mode continuous phase modulation

A data-aided technique for carrier frequency offset estimation with continuous phase modulation(CPM) in burstmode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio(SNR) required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods: it eliminates the need for fast Fourier transform(FFT) and modulation removal, and exhibits faster convergence rate without accuracy degradation.     

前后向子分段相位差频率估计法

为提高直接频率估计法的精度并推导出估计误差方差的闭合表达式,本文提出基于前后向子分段相位差的直接频率估计法. 该方法对样本的前向和后向两个子段做快速傅里叶变换,再提取这两个子段变换后的峰值谱相位差而获得频率估计. 本文证明了该估计器具有无偏性,并推导出其频率估计方差的闭合理论表达式. 仿真实验验证了该闭合表达式的正确性,故本文方法具有更高的测频精度和广泛的应用前景. 关键词： 频率估计 前后向子段 相位差 克拉美罗限     

Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system

The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing(PDM) coherent optical systems by mid-span optical phase conjugation(OPC) based on four wave mixing(FWM) effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing(CO-OFDM)system and the single carrier(SC) PDM quadrature phase shift keying(QPSK) system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system.