SDPSK调制参数的盲估计

SDPSK(Symmetrical DPSK)与DPSK相比,除同样有误码率特性好、适合非相干解调的特点外,在限带传输时还具有包络起伏小的优点,因此应用日益广泛。介绍了SDPSK的调制方法,通过分析SDPSK调制信号的特性,推导出调制参数(载波频率和码速率)的估计方法,并利用Matlab对算法进行了仿真,仿真结果验证了算法的正确性。所得到的参数估计方法,具有算法简单、估计精度高的特点,非常适合于硬件实现。所做的工作对SDPSK信号的侦察和盲解调具有重要意义。     

SDPSK调制信号参数估计

对称差分相移键控(Symmetrical Differential Phase Shift Keying,SDPSK)调制限带传输时包络起伏小,更适合在非线性信道中使用,因而日益受到重视。通过分析SDPSK调制信号特性,推导出码速率、载频等调制参数估计方法,并利用线性调频Z变换(Chirp-Z Transformation)算法对估计结果进行了修正,测量精度得到进一步提高。Matlab仿真试验表明,该算法参数估计精度高,运算量小,易于硬件实现。     

一种超宽带高速跳频信号实时非合作接收机

提出一种基于模数混合信道化宽带处理和实时流水处理技术的超宽带高速跳频信号实时非合作接收机结构,采用基于无盲区数字信道化、多通道数据融合的频率跳变时刻估计算法和针对差分相移键控(SDPSK)信号的实时解调方法,解决了超宽带高速跳频信号的实时解跳和解调难题。为进一步验证所提出结构和算法的有效性,设计并实现了一种针对2 GHz,20 000 Hop/s跳频信号的超宽带高速跳频实时非合作接收机。测试结果表明:该接收机能实现对超宽带高速跳频信号的实时解跳和解调。     

Frequency hopping modulation recognition based on time-frequency energy spectrum texture feature

For frequency hopping modulation identification,a novel method based on time-frequency energy spectrum texture feature was proposed.Firstly,the time-frequency diagram of the frequency hopping signal was obtained by smoothed pseudo Wigner-Ville distribution,and the background noise of the time-frequency diagram was removed by two-dimensional Wiener filtering to improve the resolution of the time-frequency diagram under low SNR conditions.Then,the connected-domain detection algorithm was used to extract the time-frequency energy spectrum of each hop signal and convert it into a time-frequency gray-scale image.The histogram statistical features and the gray-scale co-occurrence matrix feature were combined to form a 22-dimensional eigenvector.Finally,the feature set was trained,classified and identified by optimized support vector machine classifier.Simulation experiments show that the multi-dimensional feature vector extracted by the algorithm has strong representation ability and avoids the misjudgment caused by the similarity of single features.The average recognition accuracy of the six modulation methods of frequency hopping signals BPSK,QPSK,SDPSK,QASK,64QAM and GMSK is 91.4% under the condition of -4 dB SNR.     

Fast timing recovery for linearly and nonlinearly modulated systems

Digital phase lock loops (PLLs) are often used in timing acquisition systems. It is known that some non-data-aided timing error detectors occasionally cause hangup problems in digital PLLs. In this paper, we introduce a novel two step antihangup timing recovery scheme. Through intensive simulations, we show that this enhanced scheme greatly reduces the probability of hangup, and speeds up the timing recovery process for both linearly and nonlinearly modulated systems.     

Hangup in asynchronous timing recovery loops

The effects of hangup in digital asynchronous timing recovery loops are investigated. It is demonstrated that delay quantisation in the interpolation filter exacerbates the problem of hangup. It is also noted that the effects of hangup are worse for the non-data aided (NDA) loops than they are for the decision-directed (DD) loops. This may preclude the use of the former in TDMA applications.<>     

一种消除hangup现象的数字相位跟踪环

为实现对输入信号相位的快速捕捉,提出了一种有效消除高信噪比下hangup现象的数字相位跟踪环(DPTL)并应用有限状态Markov链理论求解其响应时间。计算和仿真结果均表明,环路克服了hangup效应,比常规采用死区(dead zone)量化器的过零采样数字锁相环(ZC-DPLL)具有更短的稳定时间。该DPTL可应用于测距等接收信号频率已知的场合。     

SDPSK的调制与解调

详细分析SDPSK（Symmetrical DPSK）的调制特性，提出一种基带编解码方法及定时同步方法。基带编解码器由开关、延时单元和逻辑运算单元构成，不涉及复杂运算；而定时同步方法，直接通过基带信号运算得到同步时钟，不需要锁相环，运算量小。因此，所提出的基带编解码方法和定时同步方法非常适合硬件实现。仿真结果验证了算法的正确性。另外，通过对解调器性能的测试，分析了算法的局限性及应用范围。     

Hangup in Phase-Lock Loops

A phase-lock loop occasionally will take a long time to settle to equilibrium. Phase dwells at a large error for a prolonged interval. This phenomenon has been dubbed "hangup." The periodic nature of phase detectors is responsible for hangup, which occurs near the reverse-slope, unstable null. Restoring force is small in the vicinity of the reverse null, and noise causes the loop to equivocate about the null. Hangup is very troublesome when fast acquistion is needed with high reliability. One example is synchronization of digital communications. Hangups can be avoided if a large restoring force is applied for large phase errors and if equivocation is prevented. An implementation of an antihangup circuit is proposed.     

MEMS薄膜平均应力梯度及弹性模量在线提取方法

提出了一种利用静电作用下悬臂梁的吸合电压提取MEMS薄膜沿厚度方向的平均应力梯度及弹性模量的方法,该方法的关键在于实现悬臂梁吸合电压的快速、精确计算.考虑了悬臂梁由应力梯度引起的沿宽度方向的弯曲,提高了吸合电压的计算精度.实际模拟表明该测量方法计算速度快、精度高,能够应用于实际工艺过程中材料参数的在线测量.     

The Limit-Switched Loop: A Phase-Locked Loop for Burst Mode Operation

In a time-division or burst mode communications systems, synchronization must be achieved within a short preamble time at the beginning of each burst. When used in such a system, a conventional phase-locked loop (PLL) occasionally exhibits a prolonged phase acquisition transient. This effect, known as hangup, occurs at a large value of phase error and may cause loss of a data burst. The present paper investigates a modification of a PLL known as a limit-switched loop (LSL). The LSL offers faster phase acquisition and better hangup immunity than a PLL. The LSL estimates its position in the phase plane at the beginning of acquisition and, if hangup is about to occur, makes a phase correction so as to forestall its occurrence. The structure and properties of the LSL are investigated in this paper.     

串联电容对扭转静电微执行器Pull-in稳定的影响

在MEMS执行器的设计中,求出准确的Pull-in电压值是至关重要的.针对扭转式静电微执行器,采用串联电容方法来拓宽MEMS执行器的Pull-in行程,提出了相应的Pull-in模型,并给出了算例的数值结果.这些结果对扭转式静电微执行器的设计具有一定的参考价值.     

Nonlinear electrostatic behavior for two elastic parallel fixed–fixed and cantilever microbeams

In this paper, the electrostatic pull-in behavior of two elastic parallel fixed–fixed and cantilever microbeams in microelectromechanical systems (MEMS) are investigated. The nonlinear electrostatic equations are considered due to some important effects including: residual stresses, fringing field and axial stresses. Various residual stresses in two elastic parallel fixed–fixed models are considered. Step by step linearization method is used to solve the equations. The numerical results reveal that the step by step linearization method is highly efficient, and it is the easiest one to calculate the pull-in voltage. In the proposed models, the pull-in voltages are considerably decreased when compared to the pull-in voltages of simple fixed–fixed and cantilever models.     

基于FFT的微弱GPS信号频率精细估计

为了解决传统GPS接收机对弱信号频率牵引速度比较慢、成功率较低的问题,该文提出基于FFT的频率估计方法。为了克服导航数据比特反转带来的影响,用平方法和差分法分别构造的新变量作为FFT运算的输入。实验结果显示,没有比特边沿先验信息的情况下,差分构造变量的方法在21 dBHz弱信号时正确估计频率概率在95%以上,有比特边沿先验信息的情况下,平方构造变量的方法在19 dBHz弱信号下正确检测频率概率仍能达到95%。     

Design optimization of RF-MEMS switch considering thermally induced residual stress and process uncertainties

This paper presents the Design of Experiments (DOE) based parametric design optimization of the Symmetric Toggle RF-MEMS Switch (STS) for minimizing the actuation voltage considering the fabrication process uncertainties and thermally induced residual stress. Initially, three-dimensional (3D) non-linear Finite Element Method (FEM) models are developed and the formation of residual stress during the plasma etching step of the microfabrication process is explained using the Bauschinger effect. The pull-in voltage values and the switch profiles obtained after the thermal loading–unloading cycle in the FEM models are compared with the experimental values and optical profile measurements which showed a close agreement. A DOE based Dual Response Surface Methodology (DRSM) is implemented to identify the significant design parameters affecting the STS switch pull-in voltage in the presence of thermally induced residual stress. Two separate response surface empirical models are developed; one for the mean pull-in voltage and other for variation in the pull-in voltage due to microfabrication process tolerances. The developed response surface models are optimized simultaneously using the desirability function approach. The optimal levels of the design parameters that result in minimum pull-in voltage with increased insensitivity to process uncertainties are obtained using the direct search algorithm.     

An all-digital clock-smoothing technique - counting-prognostication

This article presents a novel universal all-digital clock-smoothing technique - counting-prognostication. Operation principles, performance analysis, and comparisons are given. Analysis and measurement results show that this technique can efficiently smooth jitter and wander for a wide pull-in range and pull-out range, and jitter accumulation is small. A cycle-varying counting-prognostication method, which decreases pull-in time, is also suggested.     

Frequency-locked loop circuit providing large pull-in range

Presents a frequency-locking circuit that provides a larger pull-in bandwidth than that of a conventional automatic frequency control (AFC) circuit. In addition, the proposed circuit has a stable mode of operation over the full frequency response of the frequency discriminator, and locks the oscillator at exactly the centre frequency of this discriminator. The frequency offset and the unstable mode of operation presented by the conventional circuit outside its pull-in range can thus be eliminated.<>     

基于局部相关函数插值的二进制偏移载波调制信号码相位估计与鉴相方法

为了进一步提高卫星导航接收机对BOC(1,1)及其衍生类型调制信号的码鉴相的质量和跟踪能力,尤其是在高动态下的跟踪性能。该文提出一种基于局部相关函数插值的方法确定BOC(1,1)调制信号的码相位。该方法基于相关器阵列的结构,根据相关器阵列的输出值判断相关峰值的大致范围。利用广义延拓逼近的方法估计码相位的位置,同时在缺少延拓空间的情况下构造一个虚拟的相关器以完成对码相位的估计。该文具体分析了单侧相关器个数对牵入范围的影响,在此基础上对所提方法进行了计算机仿真实验。理论和仿真证明:所提方法能够在不增加过多硬件资源的条件下扩大码鉴相函数的线性牵入范围,进而能够提高接收机对于BOC调制信号的跟踪精度。     

An isochronous and asynchronous traffic scheduling algorithm fordual-star WDM networks

In this paper, based on the concept of wavelength reusing, a new architecture for interconnecting two wavelength division multiplexing (WDM) star networks is proposed. According to this architecture, the problem of scheduling isochronous as well as asynchronous traffic is investigated. The lower bounds for the problem of minimizing the switching duration and the number of switching modes are derived. A transmission scheduling algorithm for the proposed architecture to efficiently reuse the wavelength is also proposed. For only asynchronous traffic, the analytical result shows that the proposed scheduling algorithm produces solutions equal to the lower bounds. For both isochronous and asynchronous traffic, simulation results show that the average switching duration and the average number of switching modes obtained by the proposed algorithm are quite close to the lower bounds. Simulation results also show that given the same number of users and available wavelengths, the solutions (in terms of the average switching duration and the average number of switching modes) obtained by the proposed scheduling algorithm on the dual-star WDM networks are better than the solutions obtained by the two-phase algorithm on the similar dual-star WDM networks     

Effect of thermal stresses on stability and frequency response of a capacitive microphone

This article deals with effects of thermal stresses on stability and frequency response of a fully clamped circular microplate, which acts as the diaphragm of a capacitive MEMS microphone. Static and dynamic pull-in phenomena limit the stable regions of a capacitive MEMS microphone. The results show that the non-dimensional static pull-in voltage of the studied case is about 5.23 (38.6 V). On the other hand, according to the results, the non-dimensional dynamic pull-in of the diaphragm is about 4.74 (34.98 V), which is as low as 90.63% of the static pull-in threshold. Because of the thermal expansion coefficient, diaphragm temperature increment leads to compressive thermal stresses and conversely, decrement of the diaphragm temperature creates tensile thermal stresses. The effect of temperature on the pull-in parameters is given by a design-correcting factor.As results demonstrate, the deflection of the diaphragm subjected to a given electrostatic force can be controlled by means of the temperature changes. In the absence of electrostatic force, as the results show, although temperature changes do not create any deflection, but for a critical temperature increment the diaphragm stiffness vanishes and the buckling phenomenon takes place. Effects of the electrostatic force and the temperature variation on the frequency response of the microphone subjected to a sound pressure wave are investigated. As the results illustrate, increment of the electrostatic force or increment of the diaphragm temperature increases the output level and sensitivity of the microphone and decreases the fundamental frequency of the microphone, limiting the upper band of its bandwidth. It is obvious that decrement of the diaphragm temperature acts conversely. In addition, the results show that in the presence of the electrostatic force sensitivity of the output level of the diaphragm to the temperature change increases.