线性变换和预留子载波降低光OFDM系统的PAPR

正交频分复用(OFDM)技术存在着高峰值平均功率比(PAPR)的缺点,在光OFDM系统中,由于其调制器、D/A转换器件、功率放大器及光纤本身的非线性,较大PAPR的信号将会产生严重的畸变,从而大大降低系统的有效性.为抑制光OFDM系统中的PAPR,提出了一种基于线性变换和预留子载波技术的光OFDM系统PAPR降低算法.仿真结果表明,该方案不仅有效地降低了峰均功率比,而且对系统误码率的影响较小,能够获得可靠的系统误码率性能.     

通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。     

非线性功放条件下的恒包络OFDM系统性能

正交频分复用技术具有较高的频谱效率和好的抗频率选择性衰落性能,被广泛应用于无线通信系统中。但是OFDM信号具有较高的峰均比,当系统采用非线性功放时,OFDM系统需要较大的输入功率回退以避免信号失真。为了研究非线性功放条件下的系统性能,分析了恒包络OFDM系统的实现方式,并以误码率为指标,在加性高斯白噪声信道和多径衰落信道场景下对比了恒包络OFDM系统与采用传统迭代限幅滤波PAPR抑制技术的OFDM系统的性能。     

OFDM技术及其峰均功率比降低的一种有效方法的研究

正交频分复用（OFDM）是一种多载波调制技术，其特有的调制特性决定了它有较高的峰均功率比值。高峰均功率比信号会对实际放大器提出很高的线性要求，因此它是限制OFDM技术实用化的主要障碍。目前虽然有很多降低OFDM信号的峰均功率比（PAPR）的方案，但大多是以增加系统的复杂程度为代价的。本文提出了一种降低OFDM信号PAPR的方法，可以在不过分增加系统复杂性的基础上解决其PAPR在一定程度上降低的问题。     

降低OFDM信号峰均比融合方法的研究

针对正交频分复用(OFDM)信号峰均比(PAPR)高的问题,提出了一种降低PAPR的融合算法,通过在发射端对OFDM信号进行两次降低PAPR处理来降低系统的峰均比.仿真结果表明,该算法可以大幅度的降低OFDM信号的PAPR.     

OFDM无线通信中高峰均比及其抑制算法研究

凭借很强的抗符号间干扰(ISI)和抗衰落能力,采用正交频分信道的OFDM技术的无线通信越来越受到人们的重视。但是作为一种多载波调制方式,OFDM技术同样存在着高峰均比(PAPR)的问题,高的PAPR会导致信号畸变,造成子信道间的相互干扰,从而影响OFDM的性能。针对此,重点介绍了OFDM系统中的PAPR比问题的概念,并对降低PAPR的主要算法进行了论述。     

用多幅值CPM减小OFDM信号的PAPR

正交频分复用(OFDM)是一种多载波调制(MCM)技术,其具有良好的抗多径衰落的能力和非常高的信道利用率.但是OFDM有一个固有缺点就是存在较高的峰平功率比(PAPR),本文提出将多幅值的连续相位调制信号与部分响应序列相结合的方法来减少OFDM信号的PAPR.     

OFDM信号限幅滤波的性能分析

OFDM是一种多载波调制技术,其特有的调制特性决定了它有较高的峰均功率比值PAPR（Peak-to-Average Power Ratio）。高峰均功率比信号会对实际放大器提出很高的线性要求,因此它是限制OFDM技术实用化的主要障碍。目前虽有很多降低OFDM信号的PAPR的方案,但大多是以增加系统的复杂程度为代价的。限幅滤波法是一种计算复杂度较小的算法。文中针对600Mb/s高速数传数据经4路子载波（每路150Mb/s）调制后的OFDM信号的PAPR进行了分析,并对限幅滤波法进行了仿真。     

OFDM系统降低PAPR技术的比较

OFDM信号存在高峰平比(PAPR)的问题,该问题直接增加了系统实现的难度.本文对近年来OFDM系统中30种具有代表性的降低PAPR方法进行了研究和分析,指出了这些算法的优缺点,提出了下一步的研究方向,对OFDM系统降低PAPR技术的研究具有指导意义.     

调制与解调技术、调制解调器、时分复接

0617444无线信道中OFDM技术和QAM技术传输的性能差异〔刊,中〕/陆峰//信息技术与信息化.—2006,(1).—46-48(D)0617445基于LSTBC-OFDM系统的信道估计简化算法〔刊,中〕/胡静//系统工程与电子技术.—2006,28(3).—454-457(E)0617446OFDM信号峰平功率比的一种简单的分布边界〔刊,中〕/颜彪//系统工程与电子技术.—2006,28(3).—366-368(E)假设基带OFDM信号为一带限复高斯过程,研究了带限OFDM信号峰平功率比(PAPR)的分布。基于越幅率理论提出了带限OFDM信号PAPR分布的一种简单闭合形式的上边界。针对一个16QAM-OFDM系统,对…     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

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.     

Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers

A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers(M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Home-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.     

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.     

Diode-end-pumped Nd:YVO4/LBO lasers with 4.2W continuous-wave output at 457 nm

A continuous-wave (CW) 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd: YVO4 and using LBO as the intra-cavity SHG crystal With the optimization of laser cavity and crystal parameters, the laser operates at a very high efficiency. When the pumping power is about 31 W, the output at 457nm reaches 4.2 W, and the optical to optical conversion efficiency is about 13.5% accordingly. The stability of the out putpower is better than 1.2% for 8 h continuously working.