中国低轨移动卫星通信系统星座设计

本文研究低轨移动卫星通信系统设计中的一个基本问题－－星座设计问题，并给邮了我国低圆轨道移动卫星通信系统的星座设计方案，该星座是以三个轨道平面组成的２４颗星系统，它的高度为１３２６ｋｍ，轨道参数由本文提出的优化算法进行设计，本文用统计的方法对我国低轨系统方案和Ｇｌｏｂａｌｓｔａｒ系统（２４颗星方案）的覆盖性能进行分析比较，结果表明本文提出的系统对我国的覆盖特性优于Ｇｌｏｂａｌｓｔａｒ系统，本文还对圆     

面向应急通信的低轨短数据通信星座优化设计

针对军民各行业的应急通信需求,开展了基于低轨卫星的短数据通信系统设计和优化分析。借鉴全球星优化设计方法,得到了由分布在7个轨道面的49颗低轨卫星组成的短数据通信卫星星座。系统内各卫星通过激光链路为用户信息传递提供实时传输通道,任意时刻卫星与周边不少于10颗卫星存在通信链路。效能仿真结果表明,系统能够实现对我国陆地领土无缝覆盖,对周边区域和低纬度区域实现不小于90%的覆盖率,满足信息的应急传递需求。     

世纪之交的移动通信（下）

3卫星移动通信3．1个人卫星移动通信发展现状个人卫星移动通信近年来已逐渐成为移动通信产业发展的热点。当前正在开发的卫星移动通信系统以中低轨道的系统为主。主要有“铱”系统（66颗主用,6颗备用,轨道高度780km）,“全球星”系统（48颗主用,8颗备用,轨道高度1414km）以及国际海事卫星组织的“ICO”系统（IO颗主用,2颗备用,轨道高度10354km）。我国正在参与开发的地区高轨（轨道高度35786km）卫星移动通信系统有亚太卫星移动通信（APMT）系统和合诺卫星移动通信（SINDSAT）系统。此外,尚有极低轨道的Teledesic系统（288颗…     

星载GNSS反射信号时-空性能仿真分析

针对星载全球导航卫星系统(GNSS)反射信号时-空性能问题,该文从1阶统计量角度定义了平均空间覆盖次数、全球覆盖面积百分比和平均回访时间3个衡量星载GNSS反射信号时-空性能的指标,并通过建立GNSS和低轨卫星轨道仿真研究了低轨卫星轨道高度、倾角、升交点赤经以及天线波束对星载GNSS反射信号时-空性能的影响。结果表明:单颗卫星无法满足全球探测的任务需求,当轨道高度为1300 km,倾角为98.7°,天线波束为40°时,平均覆盖次数、平均覆盖面积百分比和平均回访时间分别为1.6, 36.5%和8 h;通过单一轨道的卫星组网可有效提高星载GNSS反射信号的时-空性能,当卫星数目为4,高度为635 km,倾角为98.7°,波束宽度为40°时,星载GNSS反射信号的时-空性能指标高于单颗ASCAT卫星24 h覆盖地球65%的指标;当卫星数目增加至8颗时,星载GNSS反射信号可在平均4.5 h内观测地球88.9%的区域。     

ICO公司推出卫星移动通信服务,使全球个人移动通信成为可能

ＩＣＯ全球通信公司将从２０００年８月开始推出通过一个由１２颗中轨通信卫星组成的卫星通信网及地面设施,为用户提供个人全球卫星移动通信服务。ＩＣＯ的卫星移动通信系统由ＩＮＭＡＲＳＡＴ－Ｐ演变而来,分为“天”、“地”两大部分,构成ＩＣＯＮＥＴ。太空部分由１２颗中轨卫星组成,其中１０颗是运营卫星,２颗是备份卫星。卫星轨道面相互正交,并与赤道面成４５°角,使整个卫星网能够完全覆盖地球表面。卫星采用数字化星上处理和时分多址方式,与现在的ＧＳＭ移动通信系统相同,每颗卫星能够同时处理４５００个电话。地面系统由１…     

我国广播卫星备份星的定点位置的建议

我国自行研制的鑫诺-2广播卫星失败后,由2008年6月9日成功发射的中星-9广播卫星执行卫星广播业务。这颗卫星由法国泰雷兹·阿莱尼亚公司研制,定点在国际电联分配给我国的轨道位置92．2°E。据悉,近期我国要发射重新研制的鑫诺-2接替星,仍将定点在92．2°E,作为广播卫星的备份星。本文认为这颗备份卫星不宜定点在92．2°E,建议在国际电联分配给我国的其他轨道位置中选择一个。     

IGSO在卫星移动通信中的应用研究

研究利用IGSO星座提供卫星移动通信业务所涉及到的星座覆盖性能、多普勒频移及业务支持能力等问题。研究表明,采用2颗或3颗IGSO卫星构成的星座能够对我国区域提供较好的覆盖性能(单星和多星覆盖率及平均通信仰角),而引入的多普勒频移并不大。链路计算结果表明,采用IGSO卫星能够有效解决GEO卫星在高纬度区域的低仰角问题,并能用比较小的IGSO卫星来达到非常大的GEO卫星才能实现的性能。因此,采用IGSO的区域卫星移动通信系统具有较好的技术可行性。     

计算机仿真在混合星座通信性能研究中的应用

目前卫星通信系统中的混合星座设计是一个热点研究问题.本文分析了GEO和IGSO组成的混合星座的星座覆盖性能、对地通信时长等问题.研究表明,采用2颗或3颗IGSO卫星构成的星座能够提供较好的覆盖性能(多星覆盖率及高通信仰角),采用混合星座能够有效解决GEO卫星在高纬度区域的低仰角问题,满足某些特殊区域的应用需求.因此,采用GEO和IGSO的混合星座通信系统具有较好的技术可行性.     

适合中国的卫星通信组网的星座方案

针对我国地域分布的实际情况及通信业务量各时段的差异，提出适合中国的卫星无线光通信系统星座方案，利用3颗中轨卫星和16颗低轨卫星组成的通信系统能够覆盖我国区域，满足通信要求。     

一种单星对同步轨道卫星的仅测角定位跟踪算法

针对中低轨卫星对同步轨道卫星定位时存在的可观测时间短等限制,结合同步轨道卫星轨道的特点,利用测角信息计算出距离信息。将距离信息与测角信息一起建立新的测量方程,进而提出一种新的基于J2000.0惯性系的单颗中低轨卫星对同步轨道卫星的扩展卡尔曼仅测角被动跟踪定轨方法,并对测量方程的变量和坐标转换给出了明确定义。仿真结果表明,该算法实现了单颗中低轨卫星对同步轨道卫星的仅测角被动跟踪定轨,若已获得被测星的先验知识,该算法收敛时间优于未引入距离信息的常规算法。     

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-