Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering

We theoretically present the intrinsic limits to electron mobility in the modulation-doped AIGaN/GaN two-dimensional electron gas （2DEG） due to effects including acoustic deformation potential （DP） scattering, piezoelectric scattering （PE）, and polar-optic phonon scattering （POP）. We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.     

Modifications of the Cubic Phase Function

By introducing a symmetric pair of time instants, a modification of the Cubic phase （CP） function, named as the Quartic phase （QP） function, is proposed to estimate the quadratic FM signal. The performance in terms of estimate bias and variance is presented via the first-order permutation principle. Two extensions are presented for multiple components and the cubic FM signals. Both theoretical analysis and numerical examples confirm that the QP function and its extensions provide a number of advantages, such as： （1） lower asymptotic Mean-square error （MSE） for the estimate of the third-order phase pa- rameter at high SNR; （2） a better capability of discriminating multicomponent signals; （3） a lower SNR threshold for the estimates of the cubic FM signal.     

Wideband Direction of Arrival Estimation with Linear Array： Analysis and Closed-Form Formulae

To estimate the Direction-of-arrival （DOA） of a far-field wideband source using a linear array, the Time-difference-of-arrlval （TDOA） based and Steered- response power （SRP） algorithms are of the most useful. In this paper, for white Gaussian signal and noise, the esti- mation variances of both the methods and the Cramer-Rao lower bound （CRLB） are derived in closed-form for a lin- ear array. Meanwhile, a Gauss-Markov （GM） procedure is introduced to achieve optimal conversion of the estimated delay vectors for the TDOA based estimator. Moreover, a generalized SRP estimator is proposed for the generalized case with nonuniform SNR.     

Quick System-Level DDR3 Signal Integrity Simulation Research

Abstract---Double data rate synchronous dynamic random access memory （DDR3） has become one of the most mainstream applications in current server and computer systems. In order to quickly set up a system-level signal integrity （SI） simulation flow for the DDR3 interface, two system-level SI simulation methodologies, which are board-level S-parameter extraction in the frequency-domain and system-level simulation assumptions in the time domain, are introduced in this paper. By comparing the flow of Speed2000 and PowerSI/Hspice, PowerSI is chosen for the printed circuit board （PCB） board-level S-parameter extraction, while Tektronix oscilloscope （TDS7404） is used for the DDR3 waveform measurement. The lab measurement shows good agreement between simulation and measurement. The study shows that the combination of PowerSI and Hspice is recommended for quick system-level DDR3 SI simulation.     

Enhanced Frequency-Domain Frost Algorithm Using Conjugate Gradient Techniques for Speech Enhancement

In this paper, the frequency-domain Frost algorithm is enhanced by using conjugate gradient techniques for speech enhancement. Unlike the non-adaptive approach of computing the optimum minimum variance distortionless response （MVDR） solution with the correlation matrix inversion, the Frost algorithm implementing the stochastic constrained least mean square （LMS） algorithm can adaptively converge to the MVDR solution in mean-square sense, but with a very slow convergence rate. In this paper, we propose a frequency-domain constrained conjugate gradient （FDCCG） algorithm to speed up the convergence. The devised FDCCG algorithm avoids the matrix inversion and exhibits fast convergence. The speech enhancement experiments for the target speech signal corrupted by two and five interfering speech signals are demonstrated by using a four-channel acoustic-vector-sensor （AVS） micro-phone array and show the superior performance.     

Improved Parameter Estimation for Chirp Signals Based on Cyclostationarity

The problem of concern here is parameter estimation of chirp signals in the presence of multiplicative and additive noise. An improved cyclostationarity based algorithm is proposed to estimate the phase parameters. The novelty of the proposed algorithm lies in the iterative estimation of the second-order parameters. The main characteristics of the method include reduction in error propagation effect, increase in estimation accuracy, and operation over a wider range of phase parameter values. Simulation results demonstrate that the proposed algorithm has better performance than the conventional cyclostationary estimation method.     

DSP Based Optimal Switching Pattern SVPWM Technique Study and Realization

This paper presents a DSP based optimal switching pattern SVPWM （Space vector pulse width modulation） technique. Under this switching mode, the inverter PWM period begins and ends with zero voltage vector, which can effectively avoid the voltage vector sharp change problem in the PWM period and inverter voltage sector. The optimal switching pattern SVPWM technique reduced the inverter switching depletion and smoothed vector change in the PWM period. The inverter output distortion was been reduced. To prove the equivalence of optimal switching pattern SVPWM and carrier-based PWM, the carrier-based PWM form and zero-sequence signal of the optimal switching pattern SVPWM has been deduced. Finally, experiment has been taken to prove those ideal analysed in this paper.     

A New Positioning Method for Location-Based Services in Wireless LANs

Positioning techniques are crucial to achieve location-based services. Location estimation systems using received signal strength in wireless LANs （Local area network） have attracted great attention for the advantages of low cost, ubiquitous coverage and ease of deployment. Existing methods neglect the difference between contributions of access points to location estimation results. Signals from far access points travel long distance and thus more uncertainty is added to the receive signal strength. This paper proposed a positioning method based on the Dempster-Shafer evidence theory. Different belief was assigned to signal strength from different access points according to its importance to location estimation. We carry out a series of experiments to evaluate the method and compare with other related work. Experimental results show that the approach gives a higher degree of positioning accuracy.     

Defending Against Sybil Attacks Based on Received Signal Strength in Wireless Sensor Networks

Sybil attacks is a particularly harmful attack against Wireless sensor networks （WSN）, in which a malicious node illegitimately claims multiple identities, and forges an unbounded number of identities to defeat redundancy mechanisms. This paper proposes using received signal strength of the nodes to defend against Sybil attacks when the Jakes channel was established. Aiming at improving the detection accuracy and reducing power consumption, we put forward the mutual supervision between head nodes and member nodes to detect Sybil attacks together, and compared the related detection scheme for Sybil attacks. The simulation results show that our scheme consumes lower power, and the detection accuracy is over 90%.     

探测受声波调制的激光漫反射回波信号

基于光电接收目标的漫反射光原理,采用红外激光探测室内声波,在对目标特性研究和漫反射回波信号光功率估算的基础上,设计和研制了实验系统。用红外激光探测从玻璃目标返回带有受声波调制的激光漫反射回波信号,在6-63 m距离及直接反射光线与探测器光轴之间的夹角β≤±4°时,可以听见所探测到回波信号中的声音;当β=4°-15°时,可以探测到激光漫反射回波信号,但听不到声音。实验证明,利用漫反射激光探测室内声音的方法是可行的。     

First principle studies of structural, elastic, electronic and optical properties of Zn-chalcogenides under pressureMuhammad Bilala, M. Shafiqa, Iftikhar Ahmada, Imad Khana,*

Structural, elastic, electronic and optical properties ofzinc-chalcogenides （viz. ZnX, X = S, Se and Te） are studied in zinc-blende structure under hydrostatic pressure using the full-potential linearized augmented plane wave method. Generalized gradient approximation is used for exchange correlation potentials. Pressure-dependent lattice constants and bulk moduli are obtained using the optimization method. Young＇s modulus, Poisson＇s ratio, internal strain parameter and anisotropy are also calculated. The higher values of Young＇s modulus in comparison to the bulk modulus show that these materials are hard to break. Poisson＇s ratio is computed for the first time for these materials to the best of our knowledge and its values show higher ionic contribution in these materials. Modified Becke and Johnson （mBJ） method is used to study band gaps, density of states, dielectric function and refractive index. Electronic study shows direct band gaps convert to indirect band gaps with increasing pressure in the case of ZnS and ZnTe. We compared our results with other theoretical and experimental results. Our results are far better than other theoretical results because mBJ is the best technique to treat Ⅱ-Ⅵ semiconductors.     

基于粒子受激散时的烟雾粒子的检测与识别

本文提出了一种基于粒子激光散射来检测和识别非火灾烟雾的吸气式多传感器阵列烟雾探测系统,详细阐述了该系统的结构和信号处理方法;同时提出了利用计算机求解不同物质粒子Mie散射系数的实际计算公式并推导出典型物质粒子的散射光强分布。     

Influence on Multimode Rectangular Optical Waveguide Propagation Loss by Surface Roughness

Optical scattering loss coefficient of muhimode rectangular waveguide is analyzed in this work. First, the effective refrac tive index and the mode field distribution of waveguide modes are obtained using the Marcatili method. The influence on scattering loss coefficient by waveguide surface roughness is then analyzed. Finally, the mode coupling efficiency for the SMFOpticalWaveguide （SOW） structure and MMFOptical Waveguide （MOW） structure are presented. The total scatter ing loss coefficient depends on modes scattering loss coeffi cients and the mode coupling efficiency between fiber and waveguide. The simulation results show that the total scatter ing loss coefficient for the MOW structure is affected more strongly by surface roughness than that for the SOW struc ture. The total scattering loss coefficient of waveguide decreas es from 3.97 x 10^-2 dB/cm to 2.96 x 10^-4 dB/cm for the SOW structure and from 5.24 - 10^-2 dB/cm to 4.7 x 10^-4 dB/ cm for the MOW structure when surface roughness is from 300nm to 20nm and waveguide length is 100cm.     

Digital Signal Processing for Optical Access Networks

In this paper, we investigate advanced digital signal process ing （DSP） at the transmitter and receiver side for signal pre equalization and postequalization in order to improve spec trum efficiency （SE） and transmission distance in an optical access network. A novel DSP scheme for this optical super Nyquist filtering 9 Quadrature Amplitude Modulation （9 QAM） like signals based on muhimodulus equalization with out post filtering is proposed. This scheme recovers the Ny quist filtered Quadrature PhaseShift Keying （QPSK） signal to a 9QAMlike one. With this technique, SE can be increased to 4 b/s/Hz for QPSK signals. A novel digital superNyquist signal generation scheme is also proposed to further suppress the Nyquist signal bandwidth and reduce channel crosstalk without the need for optical prefiltering. Only optical cou plers are needed for superNyquist wavelengthdivisionmulti plexing （WDM） channel multiplexing. We extend the DSP for shorthaul optical transmission networks by using highorder QAMs. We propose a highspeed Can＇ierless Amplitude/Phase 64 QAM （CAP64 QAM） system using directly modulated la ser （DML） based on direct detection and digital equalization. Decisiondirected least mean square is used to equalize the CAP64QAM. Using this scheme, we generate and transmit up to 60 Gbit/s CAP64QAM over 20 km standard single mode fiber based on the DML and direct detection. Finally, several key problems are solved for real time orthogonalfre quencydivisionmultiplexing （OFDM） signal transmission aml processing. With coherent detection, up to 100 Glfit/s 16 QAMOFDM realtime transmission is possible.     

激光信号大气散射探测分析

有些应用场合需要利用大气气溶胶对激光的散射来探测激光。在都市郊区大气模型条件下,利用米氏散射理论,对1.06μm激光在低空大气中传输时散射辐照度的分布进行了理论分析和数值计算。得到激光大气散射辐照度随离轴距离的增大近似按反比规律缓慢下降、能见度仅影响散射强度的大小而不影响散射强度的分布等特征。这些特征在激光散射实验中得到了初步的验证,可为激光信号的散射探测提供理论依据和参考。     

星载SAR海面场景回波仿真

利用分形海面模型、Kirchhoff近似电磁散射模型和基于时序的动态场景回波仿真模型得到星载SAR海面场景回波.给出理想单色波海浪和分形海面回波仿真实例,回波成像结果符合倾斜调制、速度聚束调制和实际海面SAR图像的统计特性,表明该方法有效.仿真得到的回波数据可为星载SAR海面顺轨干涉(ATl-SAR)测洋流、海洋全极化探测、反演海谱等仿真研究提供源数据.     

激光雷达视场角的研究

在激光雷达的研究中,接收机视场角是一个非常重要的参数.作者利用一种改进的半解析Monte Carlo方法对激光雷达接收信号进行了模拟.在作者的模拟中,采用Henyey-Grenstein函数的修正公式、加入权值以及放宽判决门限等方法来增进光子的利用效率.由计算结果可以看出,不同的接收机视场角使得接收信号波形有很大的差异.通过分析,我们认为接收机视场角FOV=20～30mrad时能够获得较佳的接收信号.     

子波长粒度光信号传输的频域均衡设计和性能分析

针对弹性光网络(EON)的应用,提出了一种基于电域子载波复用的子波长粒度光信号传 输技术,具有高灵活性、细 粒度、高效率等特点。同时,电域数字信号处理技术的使用,支持对不同的子波长粒度信号 进行独立的调 制方式、传输速率等灵活配置。为了适应子波长粒度光信号在EON中的传输要求 ,还提出了一 种基于线性频率啁啾导频信号的信道估计和频域均衡(FDE)的方法,重点研究和分析了基于 导频的FDE和基 于训练序列的时域均衡(TDE)的性能对比,以及不同的FDE算法的性能对比。仿真结 果表明,基于线性频率 啁啾导频信号的迫零FDE算法,不仅能有效进行色散补偿,改善系统传输性能,而 且具有低算法复杂 度的优势。同时,为了满足了子波长粒度EON对频隙和路由配置的灵活性需求, 通过仿真详 细研究子波长粒度光信号的数目、传输距离和调制阶数等对传输性能的影响。仿真结果表 明,基于线性 频率啁啾导频信号的信道估计和FDE的方法,在不同的光网络配置下均具有良好的 适应性,是实现灵 活可调的光收发机和子波长信号动态重构的关键技术之一。     

Capacity Scaling Limits and New Advancements in Optical Transmission Systems

Optical transmission technologies have gone through several generations of development.Spectral efficiency has significant ly improved,and industry has begun to search for an answer to a basic question：What are the fundamental linear and nonlin ear signal channel limitations of the Shannon theory when there is no compensation in an optical fiber transmission system？Next-generation technologies should exceed the 100G transmis sion capability of coherent systems in order to approach the Shannon limit.Spectral efficiency first needs to be improved be fore overall transmission capability can be improved.The means to improve spectral efficiency include more complex modulation formats and channel encoding/decoding algorithms,prefiltering with multisymbol detection,optical OFDM and Ny quist WDM multicarrier technologies,and nonlinearity compen sation.With further optimization,these technologies will most likely be incorporated into beyond-100G optical transport sys tems to meet bandwidth demand.     

射频收发机电路的电磁干扰问题

现代无线通信收发机中，广泛应用了高集成度的芯片，元器件的布局也高度密集。在得到了低功耗、小尺寸的同时，有可能导致通信系统不能正常工作。