基于水印位的信道估计对100 Gb/sPDM-DQPSK光通信系统中低密度奇偶校验码纠错性能的提升

针对高速光通信系统中高斯白噪声和偏振模色散(PMD)引起的干扰问题,研究了一种改进的前向纠错方法,通过向低密度奇偶校验(LDPC)码中插入具有固定信息的比特位("水印位")来估计信道,并将其与译码算法结合构成新的算法。研究发现,若以误比特率(BER)低于10-9为标准,则在纠错性能方面,高斯信道中含16、32位水印位的LDPC码与卡方信道中传统的LDPC码相比,所需的光信噪比(OSNR)值可分别减少约0.25dB、0.35dB;当考虑高速光通信中的PMD时,在差分群时延(DGD)为20ps和30ps时,含16、32位水印位的LDPC码与传统LDPC码字相比,所需OSNR值可分别减少约0.63dB、0.98dB和1.16dB、1.87dB。     

光通信系统中基于LDPC码的SFEC码型研究

基于光通信系统中低密度奇偶校验(LDPC)码型的构造原则和构造方法,构造了适用于光通信系统中冗余度为6.69%的新颖LDPC(3969,3720)和冗余度为4.56%的新颖LDPC(8281,7920)码。仿真分析表明:在10-12的误码率(BER)时,这两种新颖码型在迭代18次后的净编码增益(NCG)分别比ITU-TG.975中RS(255,236)码的NCG大1.63dB和1.49dB,并且LDPC码的译码可在硬件上并行实现;这两种新颖码型的译码速度相当快,与ITU-TG.975.1中级联码型相比,这两种LDPC码的实现复杂度要低得多,可在将来的硬件实现中节省存储空间和减少计算量。因而,所构造的这两种新颖LDPC码型都可作为超验前向纠错(SFEC)码的候选码型。     

非二进制LDPC码编码调制在光纤通信中的应用

为满足100Gb/s光纤通信的需求,提出了非二进制LDPC码编码调制(NB-LDPC-CM)方案.该方案通过使用频谱效率调制以及非二进制前向纠错LDPC码,提供了一种在高总比特率下实现可靠通信的前向纠错机制.与现有的BI-LDPC-CM方案相比,该方案在误比特率(BER)为10-7的情况下,采用16点、32点、和64点四维星座图时,额外提供的净编码增益分别为0.26dB、1.14dB和2.14dB.     

一种新的终止LDPC迭代译码算法

在传统的卫星广播系统中,信道纠错通常采用BCH码级联LDPC码的方案以达到良好的误码率性能,例如DVB-S2系统。作为内码的LDPC码通常采用迭代译码,且迭代次数较高才能实现比较好的系统性能。借助BCH级联LDPC的结构,文中提出了将BCH检错嵌套进LDPC每一次迭代译码过程中的新的迭代译码结构。仿真结果表明,新算法以较低的BCH码检错运算复杂度换取了LDPC码迭代次数的明显下降,从而极大降低了迭代译码总体复杂度和译码时延,且整体纠错性能与原始LDPC译码后BCH纠错的算法相比基本保持不变。     

光通信乘性噪声信道基于LDPC码的SNR估计方法

针对目前现有的信噪比(SNR)估计 方法不适用光通信中乘性噪声信道的问题,分析了乘性噪声信道下,SNR失配 对低密度奇偶校验(LDPC)码性能的影响,并通过仿真表明乘性噪声信道下 SNR精确估计的必要性。提出了一种基于量化的LDPC 码判决反馈的SNR估计方法,首先对接收到的光信号进行量化,利用 简化后的期望最大(EM)算法对量化后的SNR 进行一次粗估计,接着利用基于LDPC迭代译码的判决反馈结果对 SNR进行精估计。仿真结果表明,本方法能够在接收 信号的均值和噪声方差等参数未知情况下,能有效完成LDPC码迭代译码的辅助 工作;在误码率(BER)为10－5时,SNR估计后 ,LDPC码的译码性能距离理想情况下的译码性能,仅有约0.12dB以内损失。     

用π旋转型低密度奇偶校验码提升100Gb/s偏振复用差分正交相移键控光通信系统性能

将π旋转型低密度奇偶校验(LDPC)码应用于100Gb/s偏振复用差分正交相移键控(PDM-DQPSK)光通信系统中,进行了相应的数值仿真和性能分析比较,其中采用打孔技术得到了高码率的改进码型,并在纠错性能方面与原始码型进行了对比。在译码方面,推导了PDM-DQPSK系统的卡方统计模型,并与高斯统计模型进行了对比。结果表明,码率为0.5的π旋转型LDPC码在采用卡方统计信道概率模型时性能最佳,可使系统光信噪比(OSNR)在14.2dB时保证误码率(BER)在10-9以下;在2dB的OSNR代价情况下,系统可容忍102ps/nm的色度色散(CD)、18ps的一阶偏振模色散(PMD),以及4.88×10-2 rad的非线性引起的最大相位偏移,由此可知π旋转型LDPC码可以极大地提高高速光通信系统的传输可靠性。     

高速光通信的前向纠错技术研究

根据高速光通信系统对于OSNR(光信噪比)的要求,提出了一种基于非规则LDPC(低密度单奇偶校验)长码的Super-FEC(超级前向纠错)方案。Super-FEC方案采用以不同进制的BCH(博斯-查德胡里-霍昆格姆)码为外码,LDPC码为内码的级联方式。针对系统不同的码率需求,分别设计了不同的级联构造形式。仿真结果表明,这些Super-FEC方案的净编码增益为6.18～7.63dB,高于传统方案。     

一种多进制LDPC码加权符号翻转译码算法

提出了一种低复杂度基于翻转规则的多进制低密度奇偶校验(Low-Density Parity-Check ,LDPC)码符号翻转译码算法。为寻求有效码字,该算法在符号向量空间迭代地更新硬判决的接收符号向量。每一次迭代只改变一个符号,其符号翻转函数综合考虑了不满足校验式的个数和接收比特和计算出符号的可靠性度量。在高阶伽罗华域中采用一种无限环路规避和翻转符号选取方法,同时提出了翻转规则设计方法,该设计决定了计算复杂度和差错性能。仿真结果表明,该符号翻转算法在帧长为150符号的16进制LDPC码中取得了纠错性能和计算复杂度的有效权衡。     

一种光通信系统中基于16-QAM的LDPC编码调制方案

设计了一种适用于16-QAM( quadrature amplitude modulation)系统的LDPC(low density parity check)级联编码调制方案。方案采 用了 本文所设计的一种低复杂度的软解调与二进制LDPC结合的算法,降低译码复杂度并增加方 案的实用性;同时方案 兼容当前OUT-4帧的级联码结构,这样可以利用级联码巧妙有效地解决LDPC码的错误平层问 题。仿真结果表明,本文 提出的LDPC级联编码调制方案,在误码率(BER)为10－8时,较G.709标准中的RS(255,9)的NCG(net code gain) 提高了2.8dB;同时,较ITU-T G.975.1标准 中两种码率相近的RS(255,9)+CSOC(n/k=7/6,J=8) 级联码和正交级联BCH码,在BER为10 －8时, 本文方案的NCG分别提高了1.3dB和0.2dB,且冗余度较两种方 案都低。此外,本文方案实现了3.28bits/symbol的SE (spectra l efficiency)。在BER为10－8时 ,本文方案较频谱效率低 于它的4-QAM、8-QAM以及8-QAM-RS(255,9)分别有着3.5、6.4和2dB的增益 。比较标准中建议的FEC(forward error correction)方案,本文提出的方案在NCG和SE两方面性能上都有所提升。     

光通信系统中一种改进的LLR-BP译码算法

光通信系统中低密度奇偶校验(Low-density Parity-check,LDPC)码采用对数似然比置信传播(Log-likelihood Ratio Belief Propagation,LLR-BP)算法进行译码时,在高信噪比区域迭代译码过程中会出现变量节点外部信息振荡不收敛而导致译码纠错性能的降低.为满足光通信系统的要求,提出了一种削弱外部消息振荡的改进LLR-BP译码算法.该算法通过引入加权系数平衡前后两次迭代之间变量节点传递的外部信息,明显减缓了外部信息的振荡现象.仿真结果表明:与传统LLR-BP译码算法相比,该改进LLR-BP算法具有更佳的误码性能,同时降低变量节点外部信息振荡现象并加快了译码的收敛速度.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

中国建立EB级存储实验室,致力云计算应用(英文)

正With the support of 863 programs,Sugon Information Industry Co.,Ltd.,set up a dawning EB-class storage laboratory to address massive data storage requirements and largescale cloud computing demonstration applications.The Dawning EB-class cloud storage system adopts advanced fault-tolerant architecture,efficient data fault-tolerant algorithms with user authentication and data encryption policies to deal with the"lost""wrong"and"stolen"problems of data for ensuring the reliability and safety of the EB-class storage system in the public network application environments.The Dawning EB-class Storage Laboratory taking advan-