一种改进的QC_LDPC码在MIMO-OFDM系统中的性能研究

由于规则的QC码的校验矩阵是奇异的,那么虽然QC码在硬件上较之于一般的LDPC码更容易实现,但是其性能往往比一般的LDPC码对系统的性能要差,为此本文基于此种考虑,设计了一种新的快速编码的不规则QC码,FQC-LDPC码,并就其构造方法和在MIMO-OFDM系统的性能进行了研究.     

性能优异的FEC技术:LDPC码的性能差异与分析

对前人得到的性能良好的规则LDPC码和不规则LDPC码进行仿真分析,分别得到性能曲线。结合规则码和不规则码的特点,并从译码BP算法、校验矩阵结构、环(circle)、误码平台(errorfloor)及可实现性等角度进行比较,分析了导致性能差异的原因,进而对构造在光通信系统中具有实用价值的LDPC码提出了看法。     

MIMO-OFDM系统中LDPC编码和自适应比特功率分配算法研究

该文提出了将LDPC码与自适应比特功率分配相结合应用于MIMO-OFDM系统中的算法。文中分别对两种不同码率的LDPC码与自适应OFDM,自适应MIMO-OFDM相结合的算法进行了仿真,同时还对未编码的自适应OFDM以及MIMO-OFDM进行了仿真。仿真结果显示,在相同的传输带宽以及相同的传输信息量（即数据净码率）情况下,采用低码率LDPC编码的自适应OFDM系统的性能要比未编码的自适应OFDM以及自适应 MIMO-OFDM系统的性能好;采用高码率LDPC编码的自适应OFDM系统的性能比未编码的自适应OFDM系统性能好,但比未编码的自适应MIMO-OFDM系统性能差。     

基于QC-LDPC码的MIMO-OFDM系统的性能仿真

QC-LDPC码是一个十分重要的LDPC码研究分支。QC-LDPC码(准循环低密度奇偶校验码)是一类结构化的LDPC码,其校验矩阵H采用准循环方式构造,具有实现复杂度低的特点,易于硬件实现。大量研究人员认为,MIMO-OFDM技术将会成为4G的核心技术。将QC-LDPC码与MIMO-OFDM系统相结合,分析了在时变频率选择性衰落信道下的系统性能。仿真结果表明,在时变频率选择性衰弱信道下,QC-LDPC码与随机构造的LDPC码具有接近的系统性能。     

在BIAWGN信道下规则LDPC码的设计与仿真分析

LDPC码是一种逼近香农限 ,实现容易 ,系统复杂度低的优秀的线性纠错码。奇偶校验矩阵 H是决定一个 LDPC码性能的关键。本文针对规则 LDPC码 ,提出了两种随机构造 H的方式 :行列都均匀的 evenboth和仅列均匀的 evencol。通过仿真分析发现 ,由 evenboth方式生成的规则 LDPC码性能更好。本文还对规则 LDPC码与卷积码的性能进行了对比 ,证明了规则 LDPC码在中短帧传输下的优异性能。这对 LDPC码投入实际应用具有重要的意义     

投影几何LDPC码的构造及其在MIMO-OFDM系统中的性能分析

简要介绍低密度奇偶校验码（LDPC码）的发展历史及其码结构，重点研究基于投影几何的LDPC码的系统化构造方法，并将其作为信道编码加入基于IEEE802．16d标准的MIMO-OFDM系统中进行仿真，与级联RS-CC码进行性能对比与分析。最后得出结论，投影几何LDPC码将有可能作为下一代无线通信系统的一项关键技术被广泛采用。     

不规则LDPC码构造方法研究及其改进

通过对码的度数分布进行设计,非规则LDCP码能获得比规则LDPC码更好的性能,但非规则LDPC码在高SNR区会出现错误平层.在本文中,利用ACE算法,对非规则LDPC码的构造方法PEG算法进行改进,以降低非规则LDPC码的错误平层.最后Matlab模拟证明此算法有效提高了非规则LDPC码在加性高斯白噪声通道中的纠错性能.     

光传输系统中LDPC码的新颖随机构造方法

分析光传输系统的传输特性与规则LDPC码的随机构造方法之后,提出LDPC码的一种新颖随机构造方法。基于该构造方法构造了一种新颖的码率为93.7%、冗余度为6.69%的规则SCG-LDPC(3969,3720)码,该规则LDPC码在将来的硬件实现中可相对地节省硬件存储空间和减少计算量。仿真分析表明:该新颖的SCG-LDPC(3969,3720)码在BER为10-8时,与同码率同冗余度的ITU-T G.975建议中RS(255,239)码和ITU-T G.975.1建议中LDPC(32640,30592)码相比,其净编码增益(NCG)和距离Shannon限都分别改善了约1.92dB和0.97dB。因而该规则LDPC码的纠错性能更为优越,更适用于光传输系统。     

规则LDPC码在瑞利平坦衰落信道下的设计和仿真

针对规则LDPC码,采用了行列都均匀的(evenboth)随机构造H的方式,在瑞利平坦衰落信道下和卷积码的性能进行了对比,证明了规则LDPC码在中短帧传输下在瑞利平坦衰落信道的优异性能。这对LDPC码应用于实际无线通信系统具有重要参考价值。     

基于LDPC码的MPEG-2 TS流UEP电路设计

不规则LDPC码具有天然的不等错误保护(UEP)能力,利用不规则LDPC码的不等错误保护特性,设计了针对MPEG-2TS流的不等错误保护电路,对MPEG-2 TS流的包头和适配域等重要信息进行重点保护.将输入的MPEG-2 TS码流的包头和适配域映射到不规则LDPC码度较高的变量节点上.显著提高这些重要信息的抗误码能力,使重要信息的BER下降1到2个数量级(在相同信噪比下),明显提高了通信系统性能.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

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.     

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.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

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.