LMS ADAPTIVE TIME DELAY ESTIMATION WITH TWO WINDOWS

An LMS adaptive time delay estimation method with two windows is presented. This method can reduce the superfluous calculation greatly when the time of correlation is long. It is suitable for the time delay estimation of white band-limited random signals. The feasibility and the performances of this method are also studied.

Adaptive sliding mode control of modular self-reconfigurable spacecraft with time-delay estimation

The reconstruction control of modular self-reconfigurable spacecraft (MSRS) is addressed using an adaptive sliding mode control (ASMC) scheme based on time-delay estimation (TDE) technology. In contrast to the ground, the base of the MSRS is floating when assembled in orbit, resulting in a strong dynamic coupling effect. A TED-based ASMC technique with exponential reaching law is designed to achieve high-precision coordinated control between the spacecraft base and the robotic arm. TDE technology is used by the controller to compensate for coupling terms and uncertainties, while ASMC can augment and improve TDE’s robustness. To suppress TDE errors and eliminate chattering, a new adaptive law is created to modify gain parameters online, ensuring quick dynamic response and high tracking accuracy. The Lyapunov approach shows that the tracking errors are uniformly ultimately bounded (UUB). Finally, the on-orbit assembly process of MSRS is simulated to validate the efficacy of the proposed control scheme. The simulation results show that the proposed control method can accurately complete the target module’s on-orbit assembly, with minimal perturbations to the spacecraft’s attitude. Meanwhile, it has a high level of robustness and can effectively eliminate chattering.

Application of adaptive filter in time delay estimation——generalized quadratic interpolation method

The time delay estimation (TDE) of two different received signals from the same source has attracted many interests of researchers in the field of signal processing. A method described for precisely estimating time delay in this paper is based on the assumption that little priori knowledge on statistical characteristics is available for the received signals. The variance of the estimate is derived . The basic architecture of this method is to use the adaptive noise canceller, in the steady state , and to interpolate the weight coefficients by using a generalized quadratic interpolation matrix. The formula of the time delay estimation is presented . The method proposed by F.A. Reed is a special case of this method . The hardware implementation is much easier than that of the conventional time delay estimation method . The results of the system simulation and the experimental results at sea show a good agreement with the theoretical analysis.

Time delay recursive neural network-based direct adaptive control for a piezo-actuated stage

Piezo-actuated stage is a core component in micro-nano manufacturing field.However,the inherent nonlinearity,such as rate-dependent hysteresis,in the piezo-actuated stage severely impacts its tracking accuracy.This study proposes a direct adaptive control(DAC)method to realize high precision tracking.The proposed controller is designed by a time delay recursive neural network.Compared with those existing DAC methods designed under the general Lipschitz condition,the proposed control method can be easily generalized to the actual systems,which have hysteresis behavior.Then,a hopfield neural network(HNN)estimator is proposed to adjust the parameters of the proposed controller online.Meanwhile,a modular model consisting of linear submodel,hysteresis submodel,and lumped uncertainties is established based on the HNN estimator to describe the piezoactuated stage in this study.Thus,the performance of the HNN estimator can be exhibited visually through the modeling results.The proposed control method eradicates the adverse effects on the control performance arising from the inaccuracy in establishing the offline model and improves the capability to suppress the influence of hysteresis on the tracking accuracy of piezo-actuated stage in comparison with the conventional DAC methods.The stability of the control system is studied.Finally,a series of comparison experiments with a dual neural networks-based data driven adaptive controller are carried out to demonstrate the superiority of the proposed controller.

Research on Estimation of Time Delay Difference in Passive Locating for Impulse Signal

Analyzed the relation between time delay difference and time delay estimation errors, based on the principles of three-point locating, a reformed threshold method for time delay difference estimation of impulse signals, called as amendment estimation for short, is developed by introducing channel equalization technique to its conventional version, named as direct estimation in this paper, to improve the estimation stability. After inherent relationship between time delay and phase shift of signals is analyzed, an integer period error compensation method utilized the diversities of both contribution share and contribution mode of concerned estimates is proposed under the condition of high precision phase lag estimation. Finally, a cooperative multi-threshold estimation method composed of amendment and direct estimations to process impulse signals with three thresholds is established. In sea trials data tests of passive locating, this method improves the estimation precision of time delay difference efficiently. The experiments verify the theoretical predictions.

Multipath tracking with LTE signals for accurate TOA estimation in the application of indoor positioning

Indoor positioning with high accuracy plays an important role in different application scenar-ios.As a widely used mobile communication signal,the Long-Term Evolution(LTE)network can be well received in indoor and outdoor environments.This article studies a method of using different reference signals in the LTE downlink for carrier phase time of arrival(TOA)estimation.Specifically,a solution is proposed and a multipath tracking Software Defined Receiver(SDR)is developed for indoor positioning.With our SDR indoor positioning system,the pilot signals of the LTE signals are firstly obtained by the coarse synchronization and demodulation.Then,with the assistance of the pilot signals,the time delay acquisition,the multipath estimating delay lock loop(MEDLL)algorithm,and the multipath anomaly detection are sequentially carried out to obtain navigation observations of received signals.Furthermore,to compare the perfor-mance of different pilot signals,the Secondary Synchronous Signals(SSS)and Cell Reference Signals(CRS)are used as pilot signals for carrier phase-based TOA estimation,respectively.Finally,to quantify the accuracy of our multipath tracking SDR,indoor field tests are carried out in a conference environment,where an LTE base station is installed for commercial use.Our test results based on CRS show that,in the static test scenarios,the TOA accuracy measured by the 1-σerror interval is about 0.5 m,while in the mobile environment,the probability of range accuracy within 1.0 m is 95%.

Improved estimation of rotor position for sensorless control of a PMSM based on a sliding mode observer

This work proposes a new strategy to improve the rotor position estimation of a permanent magnet synchronous motor(PMSM) over wide speed range. Rotor position estimation of a PMSM is performed by using sliding mode observer(SMO). An adaptive observer gain was designed based on Lyapunov function and applied to solve the chattering problem caused by the discontinuous function of the SMO in the wide speed range. The cascade low-pass filter(LPF) with variable cut-off frequency was proposed to reduce the chattering problem and to attenuate the filtering capability of the SMO. In addition, the phase shift caused by the filter was counterbalanced by applying the variable phase delay compensation for the whole speed area. High accuracy estimation result of the rotor position was obtained in the experiment by applying the proposed estimation strategy.

基于四阶累积量的自适应参数型多径时延估计

在存在多通道信号干扰及背景噪声的情况下,本文提出了一种基于四阶累积量的自适应参数型时间延时估计方法。该方法能准确地进行多径传输情况下的时间延时估计,有效地抑制相关高斯噪声的影响. 仿真结果说明了方法的有效性。该时间延时估计方法可用于声纳及雷达系统的目标定位。

自适应参数型多径时延估计方法的研究

在考虑多通道非平稳信号干扰及背景噪声的情况下 ,提出了基于自适应参数型时间延时估计方法。该方法能准确地进行多径传输情况下的时间延时估计 ,有效地抑制干扰和噪声的影响。仿真结果说明了该方法的有效性。

LMS自适应时延估计法在被动定位系统中的应用研究

小均方 (LMS)自适应时延估计法不依赖于输入信号和噪声的统计先验知识而可以跟踪动态或时变的环境和参数 ,算法亦比较简单。计算机仿真和湖试数据分析表明 ,将LMS自适应时延估计法应用于被动定位系统 ,可以获得较高的定位精度。另外 ,对影响被动定位精度的因素进行了分析。

基于合成时空谱的多目标运动分析

针对水下多目标的检测与定位问题 ,提出了一种基于合成时空谱的多目标运动分析方法 .该方法可对多个弱目标同时实现检测、定位、跟踪和运动分析 ,避免了多目标跟踪中的数据关联、轨迹交叉等信号处理难点 ,提高了算法的适用性 .研究利用遗传算法的小生境技术 ,实现了多目标的运动参数估计 .仿真结果表明 ,在低信噪比情况下 ,对强度不等、轨迹交叉的

An enhanced mixed modulated Lagrange explicit time delay estimator with noisy input

The mixed modulated Lagrange explicit time delay estimation （MMLETDE） algorithm provides an efficient time delay estimation between narrowband or sinusoidal signals. However, it does not explicitly consider the additive measurement noise at the input, which actually exists in practice. Aiming at this issue, an enhanced MMLETDE algorithm is proposed for noisy inputs based on the unbiased impulse response estimation technique, assuming that the noise power ratio is known a priori. Simulation results show that for narrowband signals or sinusoids over a wide frequency range, the proposed algorithm with a small filter order performs well in moderate and high noise scenarios.

不确定性系统的自适应鲁棒跟踪控制(英文)

针对存在未知干扰和未建模动态等不确定性的系统的自适应鲁棒跟踪控制问题进行了探讨 .首选将e1 优化控制器的有限拍设计方法结合给出了最优鲁棒稳态跟踪控制器的设计方法 .然后利用集员辨识的思想 ,将名义模型的参数和未建模动态及干扰的大小作为未知参数 ,提出了一种递推参数估计方法 .最后将上述研究结果结合起来提出了一种自适应鲁棒跟踪控制策略 ,证明了自适应算法的全局收敛性并给出了鲁棒跟踪性能指标的一下较紧的上界 .与现有的结果相比 ,本文提出的自适应控制具有非保守的鲁棒稳定性 。

基于三阶累积量的自适应参数型多径时延估计

在存在背景噪声干扰的情况下 ,本文提出了一种基于三阶累积量的自适应参数型多径时延估计方法。该方法能准确地进行多径传输情况下的时间延时估计 ,有效地抑制相关噪声干扰的影响 ,仿真结果说明了该方法的有效性。

一种基于多径消除的自适应时延估计算法

多径信号和背景噪声严重影响自适应时延估计算法性能,为克服此问题,提出了一种基于多径消除的自适应时延估计算法。该算法先通过2个FIR滤波器消除多径信号的影响,再利用自适应时延估计器来准确地进行时间延迟估计。与现有算法相比,新算法的收敛速度较快,不需要真实时延的先验信息,且在有背景噪声的影响下也能得到准确的时延估计。计算机仿真验证了新算法的有效性。

自适应短波通信系统跳频信号时差定位方法

短波通信在拓宽应用广泛性与普适性的同时,也存在信号跳频与难以监管问题。以自适应短波通信系统为研究对象,提出一种跳频信号时差定位方法。分析自适应短波通信系统的天波传输信道电离层特性、短波传播形式与跳频信号特点,利用离散频谱与傅里叶基,构建基于平坦衰落信道的跳频信号定位模型,根据架构的模型似然函数与互相关函数矩阵,获取目标方位定位最大似然估计,实现跳频信号时差定位。采用三个信号接收站与一个控制处理中心构成自适应短波通信系统,经过外场试验环境,展开信号源信号与无人机遥控跳频信号的时差定位试验,依据对比实验结果可知,所提方法能够有效定位目标信号,且定位精度具有显著的优越性,验证了方法的正确性与可行性,并为日后的研究工作提供了一定的参考价值。

基于混合优化的自适应加速稳健PnP算法

根据目前摄像机位姿估计应用的实时性要求,针对RPnP算法在利用最小二乘误差求解时无法得到唯一解的问题,提出了一种改进自适应加速RPnP算法。在计算误差最小二乘时加入更多的限制条件,确定了输出解的唯一性;随后计算对应的摄像机外参数,代替每个极小值重投影误差的计算和比较过程,节省了大量位姿求解的时间;最后自适应地将原算法和改进后的算法相结合,使得输出结果最优化。实验证明,该方法可以大大降低算法的时间复杂度,并且运行时间受点数影响极小,可以较好地应用于实时性要求高的场景。

A novel repetition space-time coding scheme for mobile FSO systems

Considering the influence of more random atmospheric turbulence, worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output （MIMO） free space optics （FSO） communica- tion systems, this paper establishes a channel model for the mobile platform. Based on the combination of Alamouti space-time code and time hopping ultra-wide band （TH-UWB） communications, a novel repetition space-time coding （RSTC） method for mobile 2x2 free-space optical communications with pulse position modulation （PPM） is devel- oped. In particular, two decoding methods of equal gain combining （EGC） maximum likelihood detection （MLD） and correlation matrix detection （CMD） are derived. When a quasi-static fading and weak turbulence channel model are considered, simulation results show that whether the channel state information （CSI） is known or not, the coding sys- tem demonstrates more significant performance of the symbol error rate （SER） than the uncoding. In other words, transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas. CMD has almost the same effect of signal combining with maximal ratio combining （MRC）. However, when the channel correlation increases, SER performance of the coding 2×2 system de- grades significantly.