Implementation of ultrasound time-domain cross-correlation bloodvelocity estimators

The implementation of real-time blood velocity estimators using time-domain cross-correlation is investigated. The basic algorithm for stationary echo canceling, cross-correlation estimation and subsequent velocity estimation is presented. Sampled data acquired at rates of approximately 20 MHz are used in the algorithm, imposing a heavy burden on the signal processing hardware. The algorithm is analyzed with regard to the high sampling frequency, and a method for performing real-time high-speed-movement and cross-correlation is suggested. Implementation schemes based on using the sign of the data as well as the full precision are proposed. From an analysis of the process it is concluded that the sign data implementation can attain real-time processing. This can also be obtained for the full precision data, but at the expense of using a number of dedicated signal processing chips. Both implementations suggested can handle the estimation of velocities for A-lines acquired from multiple directions     

太赫兹时域光谱分析中回波滤除方法研究

回波处理是提高太赫兹时域光谱系统频谱分辨率的重要方法.为了研究样品存在非线性吸收情况下的回波滤除方法,在解卷积算法的基础上考虑介质对太赫兹脉冲的吸收情况和群延迟效应,将已有算法所需的四个参数缩减为与样品种类、厚度无关的两个参数,进一步提高了太赫兹光谱恢复的准确度.经实验验证,该方法可有效滤除太赫兹时域光谱系统中的GaAs天线基底以及ZnTe探测晶体产生的回波,将时间窗宽度增加一倍,使系统频谱分辨率提高到20 GHz.     

一种基于循环互相关的非相干源信号方向估计方法

给出了基于循环互相关运算的阵列信号模型,根据该信号模型,运用MUSIC算法得到了对空间非相干源信号方向进行估计的有效方法—CCC-MUSIC算法,定性的分析及仿真实验均说明了所给方法具有较好的抑制噪声和选择信号的能力。该算法将为利用天线阵列提取具有循环平稳特性的源信号方向这一问题提供较好的实现方法。     

Seismic velocity estimation

The estimate of propagation velocities in the reflection or refraction seismic method is essential to the effective imaging of the subsurface. Wave propagation in a fully elastic medium gives rise to several propagation modes, among them are the longitudinal and transverse compressional waves (P-waves and S-waves), which are commonly used in the reflection and refraction seismic methods. With appropriately sorted data, the arrival time of a wave returning from a particular reflecting interface in the subsurface will vary as a function of source-receiver offset. This variation in arrival time with offset is called "moveout" and is controlled by the propagation velocity. The velocity of propagation enters the processing of reflection seismic data first as an essential parameter of a time coordinate transformation required before data of varying source-receiver offsets can be stacked to enhance signal-to-noise ratio. Velocities estimated in this manner are called "moveout velocities." Velocities also enter the processing sequence as a parameter of an imaging operation called "migration." Early efforts at velocity estimation were only accurate enough to provide parameters to process data, but high-quality data collected using present-day technology allow us to make accurate enough estimates of propagation velocity to infer subsurface geology. Complications arise, however, due to the effects of reflector structure and lateral velocity gradients. Current developments in seismic velocity estimation include measurement of shear wave (S-wave) velocities, use of wide-angle arrivals for more accurate P-wave velocity estimates, and methods requiring areal coverage (three-dimensional seismic).     

基于散射中心模型的目标时域回波快速仿真

为快速获取超宽带电磁脉冲激励下雷达目标在时域上的电磁响应,提出一种基于属性散射中心正向建模的方法用于目标时域回波仿真。从目标几何模型出发,利用射线追踪、分集技术对空间中所有射线进行标记与归类,分离并定量表征目标的强散射源。基于属性散射中心模型,正向确定模型参数,构建出目标属性散射中心模型,在选定的辐射源激励下进行仿真计算,快速获取目标时域回波信号。以典型目标简化坦克为例,选取不同形式的超宽带电磁脉冲信号作为辐射源,基于正向建模方法构建简化坦克的散射中心模型,快速获取给定电磁脉冲激励下的雷达回波信号,并与利用高频仿真方法得到的一维距离像对比,结果具有较好的一致性,从而验证了利用散射中心模型快速进行不同辐射源激励下回波仿真的有效性。     

Comparison of autocorrelation and cross-correlation methods forsignal-selective TDOA estimation

Two algorithms for signal-selective time-difference-of-arrival estimation are compared in terms of their implementation and their mean-squared errors (MSEs). A tradeoff between ease of implementation and MSE performance is shown to exist. It is shown that MSE is independent of the distance between sensors for both algorithms     

Simple material parameter estimation via terahertz time-domain spectroscopy

A simple and precise method based on fixed-point iteration is used to estimate dielectric parameters using terahertz time-domain spectroscopy (THz-TDS). The method converges and gives correct parameters when the sample thickness is greater than 200 /spl mu/m at a frequency of 0.1 THz or 20 /spl mu/m at a frequency of 1.0 THz. The technique in validated using measured terahertz data, obtained by probing a sample of high-resistivity silicon.     

Femtosecond time-domain measurements of group velocity dispersion in AlGaAs diode lasers

Femtosecond optical pulses are used to determine the round-trip propagation delay in AlGaAs diode lasers. By using pulses at different wavelengths, the authors have determined the dispersion in group index to be dn/sub g//d lambda =-2.9 mu m/sup -1/ in these devices.<>     

Enhancing echo cancellation via estimation of delay

The advent of packetized audio transmission, such as voice over IP (VoIP), has resulted in challenging requirements for echo cancellation technology. One key aspect of this technology is the need to characterize, quickly and accurately, the echo paths in the transmission media. Echo paths consist of a constant time delay with no echo signal and active regions in which the echo signal is present. When an adaptive filter echo cancellation algorithm is used, its performance can be greatly increased, and its complexity can be reduced if it is only applied to the active regions. This requires an algorithm to estimate the constant delay and locate the active regions. Traditionally, delay estimation has been based on direct application of cross-correlation. This method has poor performance because the input signals are highly correlated and has a high implementation cost because many cross-correlation lags have to be computed for longer time delays. The delay estimation addressed in this paper has two major advantages over the traditional methods. The first is that it has improved performance because the input signals are processed to have less correlation. The second is that the implementation cost is significantly reduced because fewer cross-correlation lags are computed, and an efficient method to estimate lags is created.     

电离层闪烁对GNSS信号影响的相位屏仿真方法

获得闪烁相关电离层不均匀体参数是建立闪烁预测模型的基础. 针对长期历史数据为单站观测的情况,提出利用闪烁谱拟合方法,通过最大似然估计（maximum likelihood estimation, MLE）获得多个闪烁相关参数的最优估计,并利用Monte Carlo方法对谱参数MLE结果进行分析. 结果表明：利用单指数谱模型可以获得谱参数的无偏最优估计,估计参数的90%置信度范围可以覆盖真实值;利用双指数谱模型可以获得谱参数的近似无偏最优估计,绝大部分估计参数的90%置信度范围可以覆盖真实值;两种模型估计的统计结果均符合预定分布. 利用实测数据对本文方法进行进一步验证,估计参数的统计分析结果符合预期分布,验证了该方法的有效性;仿真数据和实测数据分析结果同时还表明,该方法可适用于中等及强闪烁情况. 本文方法为利用长期历史数据建立闪烁预测模型提供了重要实现途径.

     

MIMO SC-FDE系统的时域信道估计新算法

研究了循环正交训练序列的设计,并提出了适用于多入多出单载波频域均衡系统的时域信道估计新算法。首先选取Chu序列作为基准序列,并引入循环前缀与循环后缀构成循环正交序列,从而在接收端通过相关运算得到多天线信道的时域冲激响应估计。进一步,将长训练序列替换为多组连续重复且总长度相等的循环正交短训练序列,并利用时域相关和时间分集达到与原有长序列法相同的性能。仿真结果表明,所提时域信道估计算法不仅能够抑制天线间的干扰,而且有效地降低了噪声的方差,即使在低信噪比下也能获得较好的误比特率性能。     

Time delay estimation between two phase shifted signals via generalized cross-correlation methods

This paper examines the generalized cross correlation (GCC) method for estimating time delay between two phase shifted replicas of a common signal which are embedded in additive noise. The analysis applies for widesense jointly stationary narrow-band signal and noise and is independent of signal, noise, and phase distributions. The paper derives expressions for the estimation error, specifically bias and mean square error (MSE), by starting with the cross correlation method and then extending the results to the GCC method. Assuming symmetric spectra signals, we derive two optimal weigth functions (OWF) that minimize the above MSE. With the first OWF the maximum of the absolute value of the GCC function has to be found; this is identical to the Wax maximum likelihood (ML) method where Gaussian signals possessing uniformly distributed phase were assumed. With the second OWF the zero of the absolute value of the GCC function has to be found. For signals possessing non-symmetric spectra (e.g. single side band modulated signals) the OWF can be obtained numerically, by minimizing the MSE, e.g. by using variational techniques. Using the cross correlation method we derive a simplified expression for the MSE, which is to be used instead of a previously published result.     

Blind channel estimation and echo cancellation using chaotic codedsignals

A novel dynamic-based deconvolution (DBD) algorithm is presented that can be exploited in blind channel estimation as well as in telephony echo cancellation. Chaotic coded signals generated by the logistic map are employed while the channel is represented by an autoregressive model. The applicability is demonstrated in a speech transmission scenario using chaotic coded speech showing a modeling misadjustment improvement of 24 dB/100 iterations which is sixfold that obtained by the LMS for a 128 tap digital adaptive filter driven by ideal white Gaussian noise excitation     

气液两相流中改进图像互相关测速的完整实现

针对气液两相流中密集气(液)相速度场准确测量的需要,提出了改进图像互相关测速的完整实现方法。基于傅里叶变换的图像互相关测速原理,采用回归迭代互相关算法以提高测量精度,基于相邻速度属性对误矢量进行修正,并采用亚像素拟合方法准确定位,通过对不同拟合算法进行比较,验证了3点高斯拟合算法的优越性。实验结果表明,本文提出的测量方案可以有效提高图像互相关测速的精度。     

传递函数快速相关法的激光测速技术研究

激光技术测量是实现传送带、热轧钢板等运动物体测速的主要手段，为了改善测量精度和响应速度，提出系统传递相关分析测速技术。采用计算发射端和接收端之间两路信号的系统传递函数进行相关性分析的方法，进行了理论验证和实验分析，得到了相对误差小于0.1%的实验结果。结果表明，利用系统传递函数相关分析构建激光测速系统，代替解调电路，简化信号调理电路，可降低电路部分引起的不确定度；互功率谱函数法实现快速相关分析和频域求得系统传递函数，可提高系统响应速度；合理设置发射端间距，取样积分提高测量信噪比，降低环境引起的不确定度，测量不确定度小于0.2%。该研究对传送带速率的实时测量有一定指导意义。     

Deconvolution estimation of nerve conduction velocity distribution

A conduction velocity distribution (CVD) estimator that incorporates volume conductor modeling of the nerve-evoked response is introduced in this paper. The CVD estimates are obtained from two compound nerve action potentials (CNAP) recorded at the skin surface. A third channel is introduced in order to assess the estimator performance in the experimental case. The relevance of using an accurate signal model is shown by comparing the performance of the proposed estimator with a previous approach based on a different CNAP model. The performance of the proposed estimator is evaluated for simulated and experimental data. The study assesses signal-to-noise ratio immunity and sensitivity to errors in the model parameters.     

Noise canceling LNA with gain enhancement by using double feedback

In this paper we present a balun low noise amplifier (LNA) in which the gain is boosted by using a double feedback structure. The circuit is based on a conventional balun LNA with noise and distortion cancelation. The LNA is based on the combination of a common-gate (CG) stage and common-source (CS) stage. We propose to replace the load resistors by active loads, which can be used to implement local feedback loops (in the CG and CS stages). This will boost the gain and reduce the noise figure (NF). Simulation results, with a 130 nm CMOS technology, show that the gain is 24 dB and the NF is less than 2.7 dB. The total power dissipation is only 5.4 mW (since no extra blocks are required), leading to a figure-of-merit (FOM) of 3.8 mW⁻¹ using a nominal 1.2 V supply. Measurement results are presented for the proposed DFB LNA included in a receiver front-end for biomedical applications (ISM and WMTS).     

An adaptive filtering algorithm of velocity estimation

In this paper, a novel adaptive filtering algorithm using real-time deviation of velocity estimation is presented for maneuvering target tracking. This new algorithm will be called adaptive filtering algorithm of velocity estimation. A number of simulation results indicate that the algorithm not only has good performance on tracking maneuvering target, but also greatly improves the capacity for tracking non-maneuvering target. So it is worthy to be applied widely in practice.     

Control of loudspeakers using disturbance-observer-type velocity estimation

A new approach to obtain sensorless velocity feedback for loudspeakers is developed. The back electromotive force (back-EMF) of the moving coil is estimated by using a disturbance-observer-type estimator based on the coil current measurement. The cone velocity of a loudspeaker can be obtained based on its proportionality to the back-EMF. Instead of relying on the coupled mechanical dynamics as reported in previous work, the proposed velocity estimation is based on the precise knowledge of electrical impedance, which makes it more robust to changes in acoustic loading. The proposed approach enables the development of a robust velocity controller for a subwoofer without an expensive velocity measuring device. Experimental results demonstrated that closed-loop velocity control using the proposed scheme of velocity estimation achieved a performance comparable to that obtained by using measured velocity feedback. The proposed approach can be easily adapted to other moving-coil-type linear actuators.     

基于RCCF‒PCT的机动目标运动参数估计

针对高速机动目标的运动参数估计问题,基于鲁棒互相关和多项式调频小波变换(RCCF-PCT),提出了一种高速机动目标运动参数估计方法。该方法首先采用幂率变换增强信号,利用距离像互相关和鲁棒多项式回归完成距离徙动校正;再采用多项式调频小波变换对多普勒徙动初步补偿后的信号进行参数化时频分析,利用提取的时频脊特征完成目标运动参数的精确估计。通过数值实验验证了算法的有效性。