两种基于自适应相位补偿的FDOA估计算法

将约束的自适应相位差估计补偿算法引入到频偏估计当中,实现信号间相位对齐。然后,利用自适应相位补偿因子,根据估计方式的不同,给出了两种频偏估计算法:基于时间平均的算法与基于线性拟合的算法。基于时间平均的频偏估计算法是一种渐进无偏的估计算法,具有可控的误差和非常小的均方差,以及计算简单的特点。仿真结果表明当信号信噪比大于-3dB时,基于线性拟合的频偏估计算法性能与CRLB非常接近。     

相位分区和局部多项式曲面拟合的相位解缠绕

目的 准确的解缠绕相位是两点或三点Dixon技术等在磁共振临床应用的前提和关键,然而当相位图像中存在严重噪声、快速相位变换或不连通区域时,当前许多已经提出的相位解缠绕算法将会失败。为此本文提出一种基于相位分区和局部多项式曲面拟合的相位解缠绕新方法,该新方法在相位图像存在严重噪声、快速相位变换或不连通区域的情况下仍可以稳定可靠的工作。方法 首先将获得的相位图像分成连通块,块内相位都在给定的相位区间内,把像素个数小于给定阈值的块归类为残余像素。然后利用局域增长的局部多项式曲面拟合方法依次进行块与块之间相位解缠绕和残余像素相位解缠绕。最后使用仿真与真实磁共振Dixon数据来评价提出方法,并与PRELUDE （phase region expanding labeler for unwrapping discrete estimates）方法进行了比较。结果 在不同信噪比、快速相位变换或存在不连通区域的仿真实验中,即使当数据中存在信噪比为0.5、相邻相位变换大于π弧度或不连通区域时,提出方法的平均错误率不大于0.51%。对于100层真实的磁共振膝关节和踝关节水与脂肪分离图像,提出方法生成结果中发生明显解缠绕错误及水与脂肪互换的比率为6.00%,而PRELUDE却为42.00%。结论 本文提出了一种磁共振相位解缠绕算法,利用相位分区方法,可靠的实现相位图像分块;利用局部多项式曲面拟合方法,准确的实现相位解缠绕。提出方法能够更加鲁棒的实现相位解缠绕,这将有益于相位相关的磁共振临床的应用,如两点和三点Dixon水脂分离技术、磁敏感加权成像和人脑相位成像等。     

基于奇异值分解的方向估计改进方法

基于相位匹配原理的奇异值分解法(Singular value decomposition based on signal phase matching,SVDSPM)的波达方向估计的均方根误差在高信噪比下无法逼近克拉美罗界,针对该问题提出了基于相位匹配原理的修正奇异值分解法(Modified singular value decomposition based on signal phase matching,MSVDSPM)。该方法将阵列接收信号转换到频域,取相位匹配后各阵元中心频点频谱与其均值差值的距离平方和的倒数作为方向估计算子。仿真表明MSVDSPM方向估计的均方根误差可以在高信噪比下逼近克拉美罗界。MSVDSPM保持了SVDSPM在单源入射时的尖锐谱峰,它等价于常规波束形成方法,并且其主瓣宽度与分析频率无关。     

激光波数扫描干涉相位解卷绕算法研究

激光波数扫描干涉技术作为一种具有微米级检测分辨率和微应变级测量精度的新型干涉图像测量方法,能够透视测量复合材料内部的微观结构信息,实现材料的高精度无损透视成像检测。作为干涉图像数据处理至关重要的环节,相位解卷绕技术能将干涉图像信息从卷绕相位展开为解卷绕相位,还原干涉图像的真实信息。在传统相位解卷绕算法中,为了避免在噪声区域展开相位时相位展开错误进而导致误差的大面积传递,往往在存在噪声的区域停止相位展开,使得解卷绕后的数据存在缺陷及视场较小的问题,甚至可能无法正常解卷绕。针对以上传统算法的问题和研究了Goldstein枝切法在相位解卷绕中的应用。通过对噪声区域进行残差点判断设置枝切线,绕过枝切线进行相位展开,在所有正常点展开后结合枝切线周边的相位信息对枝切线上相位点完成最后的解卷绕,从而实现相位更有效地展开,减少相位展开后的数据缺陷,增大展开视场,精度更高。     

多项式相位信号参数估计新方法*

改进了多项式相位变换,并提出了多相位信号参数估计方法。仿真证明了在较低信噪比的情况下,参数估计的均方误差接近Cramer-Rao界。采用傅里叶系数插值的频率估计算法提高了该方法的运算速度。分析和仿真结果证明了该方法的有效性。     

利用FFT相位差校正信号频率和初相估计的误差分析

对利用分段FFT的相位差估计正弦信号的频率和初相的误差进行了分析。首先分析了在FFT幅度最大处FFT相位噪声的统计特性，从而得到了在高斯白噪声背景下频率和初相估计均方根误差的计算公式，指出了频率和初相估计均方根误差与信噪比及FFT长度有关，讨论了信号实际频率与FFT离散谱线对应的频率的偏离程度对频率和初相估计均方根误差的影响，给出了计算机Monte Carlo模拟结果，模拟结果与本文得到的公式计算结果相吻合。     

时间相位解包裹算法仿真与实验研究

为提高基于编码光栅的物体三维轮廓重构的精度,消除多频时间相位解包裹算法的相位跳跃性误差。采用一种改进的三频相位解包裹算法,通过相位与光栅节距的关系,实现了精准的相位解包裹。相比于传统方法和已提出的方法,提出的方法解相精度更高。通过仿真分析可得,改进方法展开相位无跳跃性误差,无需相位矫正,且在外加较大干扰的情况下也不会产生2π周期性误差,减小了相位解包裹的非线性误差。通过实验分析可得该方法实现了较高精度的物体三维轮廓重构。     

OFDM系统中基于全相位算法的最大似然信道估计器

在OFDM系统中设计了一种基于全相位快速傅里叶变换算法的最大似然信道估计器。全相位傅里叶变换相对于快速傅里叶变换呈现平方的幅度增益性质,在高信噪比情况下可以抑制最大似然估计器中的自带噪声,由此能够更准确地估计出信道冲击响应,并用来均衡信号。同时,OFDM采用全相位傅里叶变换作为解调算法克服了系统晶振不匹配以及信道传输过程中产生的频偏。在3GPP的空间信道模型下,设计了基于全相位最大似然估计器的OFDM系统,并与传统的最大似然估计器系统比较,使用蒙特卡洛方法仿真证明:信道冲击响应估计的均方误差和系统误码率均有所下降。     

基于DSP双相位检测微弱信号的仿真分析

针对数字信号处理器（DSP）系统集成度高、速度快、适合大量数据实时处理的特点,分析微弱信号的双相位相干检测原理,从应用的角度研究基于DSP实现的双相位检波模式的优点。利用DSP产生精确的相干波,从而使谐波的抑制能力可以达到一120dB。随机噪声中的信号幅值误差可以达到0．45％,相位误差0．228％。构建了一个以DSP为核心高精度的微弱信号检测系统。     

SIMO信道下MPSK信号的载波相位盲估计

提出了一种SIMO信道下多个MPSK信号的载波相位联合盲估计算法,以提高低信噪比条件下载波相位的估计性能.该算法综合利用多路接收信号以去除调制信息对相位估计的影响,构建与各信号相位相关的多个方程,并最终通过加权最小二乘解算方法完成对信号相位的联合估计.仿真结果表明,与传统的V&V算法相比,本算法在低信噪比条件下具有更加...     

The structured phase margin for robust stability analysis of linear systems with phase and time delay uncertainties

In this paper, we introduce the notion of the structured phase margin for characterising stability margins for a dynamical system with block-structured phase uncertainty. Since the structured phase margin may in general be difficult to compute, we derive an easily computable lower bound in terms of a generalised eigenvalue problem. This bound is constructed by choosing stability multipliers that are tailored to the structure of the phase uncertainty. The results in this paper complement and generalise phase information results presented in the literature involving principal phases, multivariable phase margin, phase spread, phase envelope, phase matching, and phase-sensitive structured singular value. Finally, using the structured phase margin, we present new and improved delay-dependent stability criteria for stability analysis of time-delay systems.     

MEMS variable‐capacitor phase shifters part II: Reflection‐type phase shifters

A novel design procedure for reflection‐type phase shifters using capacitive devices is developed. Using this approach, a phase shifter for operation at 26.5 GHz is developed using MEMS variable capacitors reported in Part I of this article. A design optimization procedure is discussed. Design of a CPW hybrid at 26.5 GHz (as needed for this phase shifter) is also discussed. Experimental results validate the design procedure and yield a phase shift of 179.30° at 26.5 GHz. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 415–425, 2003.     

Variational phase recovering without phase unwrapping in phase-shifting interferometry

We present a variational method for recovering the phase term from the information obtained from phase-shifting methods. First we introduce the new method based on a variational approach and then describe the numerical solution of the proposed cost function, which results in a simple algorithm. Numerical experiments with both synthetic and real fringe patterns show the accuracy and simplicity of the resulting algorithm.     

MEMS variable‐capacitor phase shifters part I: Loaded‐line phase shifter

This article describes the design and characterization of a continuously variable loaded‐line phase shifter using micro‐electro‐mechanical system (MEMS) variable capacitors as phase shifting components. The design and characterization of micro‐electro‐mechanical system (MEMS) variable capacitors for operation at 26.5 GHz is described. A lumped‐element model is obtained from measurements and physical consideration. Experimental results show a capacitance‐tuning ratio of 3.7:1. The capacitor's characterization results are used for designing the phase shifter. A phase shift of 40.5° at 26.5 GHz for a loaded‐line type has been measured. There is good agreement between simulated and measured results. A companion article (Part II) describes the application of these variable capacitors to the design of reflection‐type phase shifters. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 321–337, 2003.     

Analyzing and addressing false interactions during compiler optimization phase ordering

Compiler optimization phase ordering is a fundamental, pervasive, and long‐standing problem for optimizing compilers. This problem is caused by interacting optimization phases producing different codes when applied in different orders. Producing the best phase ordering code is very important in performance‐oriented and cost‐constrained domains, such as embedded systems. In this work, we analyze the causes of the phase ordering problem in our compiler, Very Portable Optimizer (VPO), and report our observations. We devise new techniques to eliminate, what we call, false phase interactions in our compiler. We find that reducing such false phase interactions significantly prunes the phase order search space. We also develop and study algorithms to find the best average performance that can be delivered by a single phase sequence over our benchmark set and discuss the challenges in resolving this important problem. Our results show that there is no single sequence in VPO that can achieve the optimal phase ordering performance across all functions. Copyright © 2013 John Wiley & Sons, Ltd.     

Differential phase shifters based on Schiffman type‐C and type‐F networks with wide phase shift range

This study proposes a class of differential phase shifters based on the Schiffman type‐C and type‐F networks with wide phase shift range. After the phase and bandwidth properties of these two distinct networks are numerically analyzed, two unique advantages of wide phase shift range and wide phase shift bandwidth are revealed. Next, the optimal design parameters for different phase shift values up to 405° are presented to allow for a quick design process. To verify the proposed approach, a 180° differential phase shifter is designed, fabricated and measured. Good performance is achieved with an impedance ratio of 1.959 and 3.7° phase deviation over a phase shift bandwidth of 61%.     

相位一致性的理解及两种新的相位一致性模型*

首先研究了1D方波信号边缘处的相位分布特点,发现不同频率分量在边缘处的相位不一定收敛于同一个角度值,而是会随着占空比的变化而变化。因此,基于局部能量的相位一致性模型实际上是不同频率分量利用幅度加权后的平均结果。由于在多数自然图像中,图像频率分量的幅度会随着频率的增加而呈反比下降,基于局部能量的相位一致性模型主要由低频分量决定,这样在一定程度上降低了对边缘空间定位的精度。为了提高边缘检测的空间分辨力,提出了两种新的相位一致性模型。利用二维Log Gabor 滤波器提取图像的局部相位信息,分析了利用这三种相位一致性模型进行边缘检测的结果。实验表明,利用两种新的相位一致性模型可以检测到更加细致的图像边缘信息,具有更高的边缘空间定位能力。     

Compact wideband phase shifter

A compact phase shifter is presented for wideband applications consisting of circular patches located at close proximity to each other which are coupled with interconnected ground‐plane circular slots located beneath the circular patches. In the proposed technique the slot‐line length and radius of patch determines the magnitude of phase shift. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Molecular dynamics simulation for phase behavior of amphiphilic solution

The phase behavior of amphiphilic solution is investigated by molecular dynamics simulation of amphiphilic rigid dimers with explicit solvent molecules. Our simulations show that three kinds of phases (isotropic micellar, hexagonal and lamellar phases) are formed at a lower temperature by quenching from a random configuration of amphiphilic molecules in solution at a higher temperature. It is ascertained that an isotropic micellar phase changes into a hexagonal phase, and then into a lamellar phase as the amphiphilic concentration increases. It is also found that the global orientational order parameter can be used to distinguish these three kinds of phases. From the detailed analyses of the phase behavior, it is concluded that the hydrophilic repulsion plays an important role in the formation of the hexagonal phase while the hydrophobic attraction plays a crucial role in the formation of the lamellar phase.     

Examining the effects of social influence in pre-adoption phase and initial post-adoption phase in the healthcare context

Despite the widespread adoption of healthcare information technology (HIT) in hospitals, fostering physicians’ acceptance of this system is a challenging task. This study focuses on and compares two critical phases for user acceptance of HIT, namely, pre-adoption phase and initial post-adoption phase. Based on the psychological attachment theory, we propose that social influence factors exert differentiated effects on physician acceptance of HIT in these two phases. Survey results show that reward, sanction, and informational influence affect physicians’ HIT acceptance in the pre-adoption phase, whereas reward and image are significantly associated with HIT acceptance in the initial post-adoption phase.