Noise and Transmission Delays in Mutual Synchronization Systems

This paper considers the effects of noise and transmission delays in a phase-averaging mutual synchronization system. The basic analytical ideas are developed with respect to a two-station system which contains first-or second-order analog phase-lock loops. From the equation describing the phase error dynamics of each system, a generalized Fokker-Planck equation is derived. It is used to obtain a good approximate analytic expression for the phase error probability density function (PDF), which is confirmed by simulation. An important quantity for such mutual synchronization systems, under random disturbances, is the variance of the frequency deviation. This may be obtained directly from a knowledge of the phase error PDF. The above development is then extended to a mutual synchronization system of arbitrary size.     

转子后总压旋态误差的研究

总压测量时,测点气流的真实总压是p~*(不考虑探针的干扰),而探针感受到的压力是p_(?)转子后旋态使气流方向有大幅度变化(如图1,在近场尾迹中可达40°),因此一般p_(?)不一定与真实压力恒等,测试系统最后得到指示压力P_(?)工程上一般要求总压的质量平均值p_m~*,而在指示端得到的是指示压力的时间平均值芦p_(H(?)),故旋态误差为     

马赫数3到7的变比热正冲波的改进解析解及近似解

作者提出的变比热正冲波改进解析解,延伸用于马赫数从3到7情况,求出过冲波后全部气动参数,按马赫数间隔为1列表给出。并附列定比热结果误差。同时提出了只取初温到终温平均比热的单比热比k_(12)近似解,平行列出结果及误差。     

Application of the Concept of Referenced Radio Navigation

This paper discusses referenced radio navigation, the concept whereby monitoring stations at known locations are used to calibrate out systematic errors in a navigation system. This concept is implemented by broadcasting calibration data to the navigating user for application as real-time corrections to the position fixes made by the user's basic navigation equipment. A method is suggested for the automatic transmission and receiver processing of the correction data. Referenced radio navigation overcomes many of the shortcomings generally associated with long-distance navigation systems, and can increase accuracy and repeatability significantly. The concept is particularly applicable to global navigation systems such as OMEGA, in which propagation or synchronization errors can contribute substantially to the system error budget.     

In-Flight Alignment and Calibration of Inertial Measurement Units?Part II: Experimental Results

This is the second part of a two-part paper which summarizes work pursued by the author in 1967 [2]. The paper describes the application of minimum-variance estimation techniques for in-flight alignment and calibration of an inertial measurement unit (IMU) relative to another IMU and/or some other reference. The first paper [1] formulates the problem, and this paper reports numerical results and analyses. The approach taken is to cast the problem into the framework of Kalman-Bucy estimation theory, where velocity and position differences between the two IMU's are used as observations and the IMU parameters of interest become part of the state vector. Instrument quantization and computer roundoff errors are considered as measurement noise, and environmental induced random accelerations are considered as state noise. In this paper, numerical results for three important IMU error parameter configurations are presented and discussed. The main results of the paper determine the effects of state and observation noise levels and the nominal trajectory on the identifications of the errors for these configurations. A discussion of the minimum number of trajectory maneuvers and of the optimal trajectory maneuvering is given.     

Position Location: Triangulation Versus Circulation

Position location algorithms, using data from electronic surveillance systems have, for the most part, been based upon statistical analysis of the points of intersection of the lines of bearing. These triangulation ion algorithms may well minimize the effect of random measurement errors on the location estimate, but few existing algorithms account for systematic (bias) errors. An algorithm based upon intersecting circles which eliminates certain types of systematic error is presented with simulation data utilized to compare the position location estimates obtained from both triangulation and circulation algorithms.     

The Effect of Random Steering Vector Errors in the Applebaum Adaptive Array

The effect of random errors in the steering vector of an Applebaum adaptive array is examined. Each component of the steering vector is assumed to have a random error component uncorrelated between elements. The array output signal-to-interferenceplus-noise ratio (SINR) is computed as a function of the error variance. It is shown that the array output SINR becomes more sensitive to steering vector errors as more elements are added to the array and as the received desired signal power becomes larger. The variance of the steering vector error that may be tolerated depends on the required desired signal dynamic range. The larger the dynamic range that must be accommodated, the smaller the error variance must be.     

飞机钣金组件数字化装配误差分析

以飞机数字化制造装配为依托,通过对飞机钣金组件在模拟量协调路线和数字量协调路线下产生误差环节的比较,着重分析了飞机钣金组件在数字化装配过程中产生的系统误差和随机误差的因素和造成误差累积的原因。针对减小在钣金零件制造路线、钣金组件装配路线、温度场变化、振动场变化、应力变化等环节的累积误差提出了改进措施。     

Random Error in ARGOS and SARSAT Satellite Positioning Systems

ARGOS and SARSAT are two satellite Doppler navigation systems in which low cost ground beacons transmit bursts of stable frequency signals. The Doppler shifted signals received by the satellite provide the positions of the beacons. The positioning error is dominated by a random component, due mainly to the short-term frequency stability of the beacon oscillator. Theoretical analysis and explicit expressions of the random errors are given.     

Further Results on Multipath Angle Error Reduction Using Multiple-Target Methods

The two-target technique proposed by the author in an earlier paper [1] for reducing radar multipath angle tracking errors has been simulated on a digital computer assuming an actual closed-loop system. When tracking with noise, the technique provides angle error performance which compares quite favorably with the expected performance given in [1] Furthermore, the large bias errors usually encountered in normal monopulse systems at low elevation angles are removed. Results of typical tracks are given, both for the method of [1], and for a modified version of the method which applies primarily to shipboard radar systems. Some results on loss of lock are also presented.     

Error Analysis of Space-Stable Inertial Navigation Systems

The error equations for a space-stable inertial navigation system are derived. This is done by directly perturbing the mechanization equations in the inertial frame and then transforming in open-loop fashion to the local-level frame. A rotating inertial platform and velocity and altitude damping are considered. The relations between errors in space-stable and local-level systems are noted. Numerical results are presented for certain random error sources.     

Cochannel Interference in Partially Coherent Communication

Effects of cochannel interference and synchronization error of the carrier phase on the probability of error in binary communications are considered. Several bounds on the probability of error are proposed. The bounds are easy to compute and do not require complete statistical characterization of the errors. They turn out to be simple linear combinations of error probabilities with no cochannel interferences and no phase errors. Several illustrative examples are given which show that the bounds can be tight.     

基于 Nussbaum函数的多无人机预设性能反步容错协同控制

针对多无人机协同执行任务过程中遭遇执行器增益故障下的安全飞行控制问题,设计了 1种预设性能反步容错姿态跟踪控制方案,以实现故障下的多无人机姿态同步跟踪控制。首先,定义飞行器的姿态同步跟踪误差和姿态角速率跟踪误差,分别利用预设性能函数对 2种误差进行约束,将不等式约束转化为等式约束。其次,基于转换误差设计反步容错姿态同步跟踪控制器,应用 Nussbaum函数解决由增益故障引起的未知控制增益问题。Lyapunov稳定性分析表明,姿态同步跟踪误差与姿态角速率跟踪误差稳定且收敛。仿真结果验证了控制方案的可行性以及有效性。     

Advanced Development of ESG Strapdown Navigation Systems

The fundamental problem of inertial navigation, double integration of acceleration to obtain position, is defined and discussed. Mechanizations of both space-stable and local-vertical platform systems are exhibited. The synthesis problem for an electrically suspended gyro (ESG) strapdown system is defined and discussed: readout, readout errors due to vehicle motion, synchronization of readout with system computer, alignment, correction and calibration for mass unbalance drift, and digital mechanization. Alignment, calibration, and acceleration measurement are also discussed. Sources of error involved in the electronic gimbaling including those peculiar to strapdown configuration are discussed and compared to mechanically gimbaled systems. Advanced developments required in the component and systems areas are listed, and it is shown that such development will lead to reduced complexity, higher accuracy, and increased reliability and utility for inertial systems.     

Limitations of a Variance Approximation

A common approximation for the variance of a function of two random variables is obtained via a series expansion. It is shown that for some cases the error in the approximation is quite large. This approximation is sometimes used to compare the relative merits of two alternate systems. The comparison might be erroneous if the system differences are comparable to the approximation errors.     

GPS-Based Time & Phase Synchronization Processing for Distributed SAR

Distributed synthetic aperture radar (DiSAR), including bi- and multistatic SAR, operates with distinct transmitting and receiving antennas that are mounted on separate platforms. Spatial separation has several operational advantages, such as reduced vulnerability in military applications and increased radar cross section (RCS); which may increase the capability, reliability, and flexibility of future aerospace remote sensing missions. However, in this configuration, there is no cancellation of reference oscillator phase noise as in monostatic cases. There are additional technical problems associated with temporal synchronization of the transmit and receive systems. Therefore, highly accurate time and phase synchronization must be provided. Little work on these challenges has been reported. This paper presents a Global Positioning System (GPS)-based technique for achieving successful time and phase synchronization for DiSAR. This technique offers high-frequency stability. More importantly, residual time synchronization errors may be compensated for with a high-precision range alignment method, and residual phase synchronization errors may be compensated for with a subaperture autofocus algorithm.     

Trajectory Estimation with Multi-range-rate System Based on Sparse Representation and Spline Model Optimization

The classic state methods for trajectory estimation in boost phase with multi-range-rate system include method of point-by-point manner and that of spline-model-based manner. Both are deficient in terms of model-approximation accuracy and systematic error determination thus resulting in the estimation errors well beyond the requirements, especially, concerning the maneuvering trajectory. This article proposes a new high-precision estimation approach based on the residual error analysis. The residual error comprises three components, i. e. systematic error, model truncation error and random error. The approach realizes self-adaptive estimation of systematic errors in measurements following the theory of sparse representation of signals to minimize the low-frequency components of residual errors. By taking median- and high-frequency components as indexes, the spline model-approximation is improved by optimizing node sequence of the spline function and the weight selection for data fusion through iteration. Simulation has validated the performances of the proposed method.     

滚动轴承振动的灰自助动态评估与诊断

以灰预报和自助再抽样方法为基础, 提出灰自助动态评估与诊断模型, 以评估和改进滚动轴承的振动.该模型用动态不确定度、估计区间、估计真值、平均不确定度、平均真值和系统误差测度等6个参数, 描述滚动轴承振动的基本特征.对HKRB轴承的试验表明, 该模型对随机误差的概率分布与系统误差的类型没有任何要求, 在平均不确定度为最小的条件下分离出系统误差.评估的可信度达到100%.根据灰自助动态评估结果, 还诊断出影响轴承振动的误差特征, 揭示了来自轴承零件制造的误差根源, 为实施滚动轴承振动的生产过程控制奠定了基础.      

Effect of Radar Amplitude and Phase Weighting Errors on Clutter Rejection by Burst Waveforms

This correspondence derives simple expressions for the ambiguity function X and the Q function of uniformly spaced burst waveforms that are subject to independent random errors in the transmitter and receiver pulse phase and amplitude weightings. The expressions are similar to those in [1], but have been put in more simplified form, and are valid for more general sources of error.