Application of successive interference cancellation to the GPS pseudolite near-far problem

Ground-based transmitters called pseudolites have been proposed to augment the basic Global Positioning System (GPS) in environments where satellite visibility is limited. One difficulty in their use is the so-called near-far problem, where in close proximity to the ground transmitter, the pseudolite signal can be orders of magnitude stronger than the satellite signals. This large range of signal levels prevents a conventional receiver from simultaneously detecting both types of signals. This paper describes the application of a signal processing technique, known as successive interference cancellation (SIC), to the acquisition and tracking of weak satellite signals in the presence of a nearby pseudolite and possible multipath reflections of this pseudolite signal. The SIC architecture is implemented on simulated and experimental near-far data sets. The results are compared with a conventional detector and improvements in acquisition and tracking performance are illustrated.     

基于阶次小波包的转子加速阶段振动故障研究

针对发动机转子在加速阶段的振动信号为非稳态、且该阶段的振动信号无法直接使用谱分析等技术处理的问题,提出了利用改进的阶次跟踪分析技术对信号进行等角度重采样,将时域非稳态信号转换为角域稳态信号,然后对信号进行小波包分析及能量特征向量提取。结果表明,利用阶次小波包方法可以很好地处理变速振动信号,效果好于直接使用小波包分析非稳态的时域信号,计算后的结果可用于进一步的数据处理。     

减速器振动信号的经验模态分解

时域同步平均是直升机减速器诊断技术的基础,目前这种方法依赖于转速传感器提供相位同步信号。探讨了应用经验模态分解代替时域同步平均分析减速器振动信号的方法。构建了一个减速器振动信号模型,提取了故障特征信号。对经验模态分解过程进行了理论推导,证明经验模态分解可以分离出故障特征信号,给出了信号分离的充分条件。将这种方法应用于直升机减速器的两种故障(点蚀和裂纹)振动数据,结果表明经验模态分解正确地分离出了故障特征信号,信号特征更为显著。     

小波变换的原理及其在噪声材料超声评价中的应用

从信号自理的角度给出了小波变换的工程理解。小波变换可以看作从原始信号中不断抽取细节,最终只留下信号主干的过程。用小波变换对噪声材料粗晶奥氏体不锈钢中人工缺陷的超声Ａ型信号处理的结果表明,在对小波系数合理解释的情况下,小波换能有效地提高信噪比。     

基于时频脊线和阶次分析的转子故障诊断

为解决采用在转子升降速过程中产生的非平稳信号难以进行故障诊断的问题,提出一种基于2维时频脊线和阶次分析的转子故障诊断方法。采集转子升降速信号,采用2维时频分布的峰值脊线提取法获得信号脊线特征,结合脊线特征与等角度重采样技术依次获得信号角度域、角-阶域和阶次域图像,将信号阶次域内的特征参数作为故障敏感特征,输入人工神经网络诊断模型,对转子信号的故障类型进行分类。利用实测信号验证所提方法的实际应用效果,并与传统特征提取法的结果进行对比。结果表明:阶次分析方法的测试准确率约为99.8%,标准差小于0.09%,均优于传统特征提取法。基于时频脊线和阶次分析的转子故障诊断方法具有更高的诊断准确率,在非平稳信号特征提取过程中具有很好的可行性和准确性。     

An Optical Technique for Simultaneous Beamforming and Cross-Correlation

This paper presents a method of greatly simplifying the processing of received signals from antenna arrays through the use of a coherent optical system for signal processing. It is shown that a coherent optical system is ideally suited for carrying out beamforming operations. Several other advantages of coherent optics for this application are also discussed. A major result is a technique for forming several unambiguous beams simultaneously by correlating the signals from two linear arrays. The coherent optics technique permits this operation to be carried out with extreme simplicity.     

一种容腔效应标定技术及其在高频响动态探针中的应用

介绍一种容腔效应标定方法,以理论模型推导与实验验证相结合的方式,完成了对高频响动态探针的动态标定,并通过ARMAX(自动回归滑动平均)模型辨识得到了容腔的传递函数.结果表明该方法简单可行,能够很好地通过探针的动态响应信号来确定探针容腔的传递函数,从而确定测量信号和真实信号之间的关系,对今后考虑容腔效应的动态标定提供了参考.      

Stretch: A Time-Transformation Technique

Stretch is a passive, linear, time-variant technique for performing temporal operations on many classes of signals. The technique employs three dispersive networks and a mixer. Signal slowdown, speedup, or time reversal can be attained by choice of network slopes. These temporal operations are performed within a signal "window," and the duration of the window is determined by the network time-bandwidth products. Both heuristic argumentation and rigorous analysis are presented, as are the results of a simple laboratory experiment.     

余度飞行控制系统的仿真研究

 余度技术是提高飞行自动控制系统可靠性的有效手段。本文通过对一种三余度控制系统的仿真研究,评述了信号选择器、比较器与主备式余度舵机的性能要求,分析了它们在故障的瞬态、故障监控的覆盖与减少误切除等方面的效果。     

Ground-multi path mitigation via polarization steering of GPS signal

Multipath (MP) is the dominant error source in Global Positioning System (GPS) code-based position solutions requiring high accuracy. A technique is introduced here to mitigate error due to ground-reflected MP signals. The technique uses two orthogonal dipoles to capture the direct GPS signal and the ground-reflected GPS signal. Adjusting the amplitude and phase of the received voltage between the two dipoles can reduce the impact of MP error. Theoretical derivations of this technique are performed for a GPS signal upon reflection from dry soil, seawater, and fresh water. The theoretical results are verified with a real world experiment on the aforementioned surfaces. GPS pseudo-range (PR) and carrier-to-noise ratio (C/No) measurements for specific satellites are used to verify the predicted theoretical results.     

ASPeCT: Unambiguous sine-BOC(n,n) acquisition/tracking technique for navigation applications

This article presents a new tracking technique for sine-BOC(n,n) (or Manchester encoded) ranging signals, which is most likely to be a part of the new European Global Navigation Satellite System (GNSS), Galileo, signal plan. When traditional sine-BOC(n,n) tracking is considered, although offering excellent performance compared with current signals, it has the main drawback of potentially giving biased measurements. The new method presented herein allows the removal of this threat while maintaining the same level of performance. An adapted version of this technique can also be used for acquisition purposes     

Limitations of Series-Fed Arrays in Broadband Communications

The purpose of this paper is to investigate the signal distortion which results when long, series-fed arrays are used for communication. It is shown that under certain conditions the antenna array can be considered a linear filter, the response of which is a function of frequency as well as spatial coordinates. The distortion accompanying the transmission as measured by the least mean-square difference between the transmitted and the received signals is derived. This expression is evaluated for the case of a uniformly excited array and a rectangular band-pass signal spectrum. In the absence of noise the transmitted signal can be completely recovered in the receiver by employing the proper linear filter. In the presence of noise the signal cannot, of course, be completely recovered. However, a technique for minimizing the distortion, in this case using a pre-filter and a post-filter, is investigated.     

Multiple-Tone Signals and Detection Probabillities

An analysis technique is presented for multiple-tone signals insystems employing noncoherent integration of a square-law detectoroutput. It is shown how the characteristic function for the teststatistic can be found from the easily determined "coherent"characteristic function defined in the two-dimensional signal space.This result is applied to two detection problems, the detection of multiple-tone signals in Gaussian noise and the detection of a Gaussian signal in multiple-tone plus Gaussian noise interference.The detection curves are compared to an approximation that is often used in practice to estimate performance. It is found that detection performance in the presence of multiple-tone interferences can be significantly different from that in the presence of Gaussian noise alone.     

HF multipath passive single site radio location

This paper considers the problem of passive geolocation for the case of HF multipath propagation. A new technique is developed for the estimation of interpath time delay applying the multiple signal classification (MUSIC) superresolution spectral estimation method. The technique samples the signals received by two spatially separated antennas to compute the normalized MUSIC cepstrum. The method is applied to experimental data in a preliminary proof-of-concept analysis     

信号周期分段处理法诊断单级传动齿轮副故障

为了诊断单级传动齿轮副故障,本文提出信号周期分段处理的方法。首先同步整周期采集振动信号,然后对采集的振动信号做时域平均,进行降噪和凸显故障脉冲的处理。利用周期分段处理法,将振动平均信号等距分段,分别对各段信号进行频谱分析。比较各段信号的时域波形和频谱的异同,可以准确诊断出单级传动齿轮副中同步齿轮故障位置,且还能诊断出非同步齿轮故障位置。数字仿真试验以及模拟故障实验结果都证实了信号周期分段处理法诊断齿轮故障的可行性和有效性;它为诊断单级传动齿轮副故障提供一种有效手段。      

Phase-Coded Interrupted CW Signals and Processors

High resolution radars require signals with large time-bandwidth product such as CW signal and coherent pulse train (CPT). We discuss a phase-coded interrupted CW (ICW) signal which is the combination of CW signal and CPT. Phase codes used here are with perfect periodic autocorrelation. The periodic ambiguity function of ICW signals is studied including single-carrier signal and multi-carrier signal. It is interesting that the gate function has different effects on two signals and contributes to a multi-carrier ICW signal which yields nearly perfect autocorrelation. Meanwhile we also suggest an efficient receiver approach to ICW signals, which can reduce the computational burden of the processor and utilize the good properties of P3 and P4 codes.     

Composite Bound on Arrival Time Estimation Errors

Time of arrival (TOA) estimation of narrowband signals is a problem of considerable practical interest in radar and sonar applications. A new technique is presented to analyze the mean square error (MSE) performance of TOA estimation schemes, based on recently developed lower bound. We obtain a complete characterization of the MSE as a function of the signal and noise parameters. The results are given in a simple closed-form analytical expression.     

多分辨率分析及其在图像分解和编码中的应用

多分辨率分析是信号处理特别是图像处理的一种新的有效方法，可以在不同尺度上给出信号的信息。在分析其理论的基础上，将其应用在图像的分析的编码中，最后给出了处理结果。     

Adaptive digital beamforming for angle estimation in jamming

A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams     

The Effect of Hard Limiting in the Presence of Large Out-of-Band Interfering Signals

The effect of hard limiting on the phase of a test signal was investigated when large out-of-band interfering signals are present at the input to the limiter. First a single and then two discrete interfering signals were considered. The interfering signals and the test signal are restricted to narrow but separated bands. The test signal is recovered after limiting by narrowband filtering. The analysis of the single interfering signal is essentially the same as that performed by Cahn.1 In this correspondence experimental evidence is presented to verify the analysis and, in addition, the case of two interfering signals is considered.