基于Simulink的窄带OFDM系统设计与仿真

为有效提高短波通信系统的数据传输速率,可采用正交频分复用（OFDM）技术。OFDM是一种特殊的多载波数字调制方案,各子载波之间的正交性使得频谱可重叠从而提高了频带的利用率,同时能有效对抗频率选择性衰落或窄带干扰。采用Simulink建模对窄带OFDM系统进行设计并仿真,仿真结果表明,在3kHz的带宽内,短波通信系统的数据传输速率能够达到12800b／s,而且具有良好的误码性能。     

基于SOA的平行双抽运结构偏振复用OFDM信号的全光波长变换

理论研究并模拟仿真了在半导体光放大器(SOA)中的基于平行双抽运结构的偏振复用十六进制正交幅度调制-正交频分复用(16QAM-OFDM)信号的全光波长变换(AOWC)。理论推导及仿真结果表明偏振复用16QAMOFDM信号可以经过全光波长变换实现偏振不敏感信号无串扰直接接收,并对影响系统转换效率的因素,如频率间隔、SOA注入电流、信号光功率及信号光入射角等进行了分析,同时分析结果验证了理论推导的正确性。     

一种正交码时分多子信道扩谱方案及其在卫星通信中的应用

文中从提高卫星通信的抗干扰能力出发，基于M-ary扩频、直接序列扩频、跳频及正交频分复用等技术思想，提出了一种正交码时分多子信道扩谱调制（OC-TDMSCSSM）新技术，建立了数学模型，推导了信号格式，给出了实验系统的输出信号频谱，分析了其在加性白高斯噪声信道下误码率性能。理论分析与仿真表明，该方案与DS／FH系统相比，具有良好的误码性能及较强的抗干扰能力。     

基于子载波补给索引调制的OFDM传输方案

针对基于索引调制的正交频分复用（OFDM-IM）技术存在子载波激活模式（SAP）不能匹配二进制数、影响系统性能的缺点,提出了基于子载波补给索引调制的正交频分复用（OFDM-SSIM）传输方案。所提方案通过在OFDM-IM的索引信息中加入补给索引,提高了系统的索引利用率,提升了系统的频谱效率（SE）。同时,由于所提方案的子载波激活模式与二进制数字相匹配,使系统易于采用低复杂度对数似然比（LLR）检测,并且保持良好的误码率（BER）性能。理论分析与仿真结果表明,在加性白高斯噪声（AWGN）信道和瑞利衰落信道下,相比传统OFDM-IM方案,所提方案有效地提升了SE和BER性能。     

采用TAS/RAS的CE-OFDM系统性能分析

研究平坦信道上采用收发天线选择的恒包络正交频分复用系统的误码性能。采用矩生成函数方法,推导矩形M进制正交幅度调制的恒包络正交频分复用系统的平均误符号率下界的解析表达式。仿真表明在大信道衰落参数、小相位调制系数和高信噪比时下界与平均误比特率非常吻合。数值计算和仿真结果均阐明收发天线数目、信道衰落参数与相位调制系数对分集接收恒包络正交频分复用系统误码性能影响。     

基于MATLAB的OFDM系统仿真分析

正交频分复用（OFDM）是一种多载波宽带数字调制技术，它具有频带利用率高和抗多径干扰能力强等优点，因而适合于高速率的无线通信系统。分析了OFDM技术的实现原理，用MATLAB软件对OFDM的传输性能进行了仿真模拟并对结论进行了分析。     

排列模式索引调制正交频分复用系统

多模索引调制正交频分复用系统(MM-OFDM-IM)在索引调制正交频分复用系统的基础上采用不同星座集对系统中的全部子载波进行索引调制,能有效地提高系统的子载波利用率和频谱效率。但全部子载波的利用影响了系统的子载波间抗干扰能力,导致误码率性能下降。针对这一问题,该文提出排列模式索引调制正交频分复用系统(PM-OFDM-IM)。该系统在MM-OFDM-IM的基础上重新引入静默子载波,既能保证系统较高的频谱效率,又能提高系统的误码率性能。同时该文提出一种基于幅值相移键控的分类映射模式,即按半径大小排列的星座集分类模式(PCC-R),该模式能够良好结合系统传输的额外信息。最后仿真结果验证,该系统能够更优地均衡系统的频谱效率和误码率性能,且所提分类映射方案可以达到更优的系统性能。     

排列模式索引调制正交频分复用系统

多模索引调制正交频分复用系统(MM-OFDM-IM)在索引调制正交频分复用系统的基础上采用不同星座集对系统中的全部子载波进行索引调制,能有效地提高系统的子载波利用率和频谱效率.但全部子载波的利用影响了系统的子载波间抗干扰能力,导致误码率性能下降.针对这一问题,该文提出排列模式索引调制正交频分复用系统(PM-OFDM-IM).该系统在MM-OFDM-IM的基础上重新引入静默子载波,既能保证系统较高的频谱效率,又能提高系统的误码率性能.同时该文提出一种基于幅值相移键控的分类映射模式,即按半径大小排列的星座集分类模式(PCC-R),该模式能够良好结合系统传输的额外信息.最后仿真结果验证,该系统能够更优地均衡系统的频谱效率和误码率性能,且所提分类映射方案可以达到更优的系统性能.     

一种新的卫星通信抗干扰技术研究

卫星通信抗干扰技术是国内外研究的热点课题。本文从提高卫星通信的抗干扰能力出发，基于M-ary扩频、直接序列扩频、跳频及正交频分复用等技术思想，提出了一种正交码时分多子信道扩谱调制（OC-TDMSCSSM）新技术，建立了数学模型，推导了信号格式，给出了实验系统的输出信号频谱，分析了其在加性白高斯噪声信道下误码率性能以及抗干扰能力。理论分析与仿真表明，该方案与DS／FH系统相比，具有良好的误码性能及较强的抗干扰能力。     

子载波OFDM毫米波接入信号的光学产生与应用研究

研究了一种下行链路采用64 阶正交幅度调制-正交频分复用(QAM-OFDM)信号和上行链路采用8阶相移键控(PSK)-OFDM 信号的全双工光载无线通信(RoF)系统。其中,下行链路承载的是60GHz不同子载波数量(64,256)的 光生64QAM-OFDM毫米波接入信号。数值模拟仿真证明:光生 64QAM-OFDM毫米波接入信号 的峰均比(PAPR)随着子载波数量的增加而增大;当下行链 路接收功率为－18dBm时,相比较其它3种子载波数量而言, 子载波数为256QAM-OFDM毫米波接入信号 的接收灵敏度最好,误码率(B ER)近似为10－3.7;当上行链路的接收功率高于 －28.5dBm时,接收信号的BER在 10－3以下。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

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.     

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.