基于多帧相位增强的米波雷达低仰角目标DOA估计方法

针对米波雷达低仰角目标的DOA估计问题,该文提出一种新的基于多帧相位特征增强方法,所提方法可以有效解决低仰角条件下阵列接收信号中直达信号相位特征模糊问题,进而提高DOA估计精度。通过学习多帧原始数据的相位分布特征与理想环境下直达波信号的相位分布特征之间的复杂映射关系,有效削弱多径信号引起的相位误差,将增强后的相位信息与原始的幅度信息进行数据重组,并利用已有的超分辨算法进行DOA估计。通过计算机仿真实验和实测数据验证,该文所提方法在DOA估计性能以及泛化能力上优于基于物理驱动的MUSIC算法以及数据驱动的基于特征反演和基于支持向量回归的两种估计方法。     

基于混合模型的强直达波与多径杂波消除

针对非合作无源相干定位中强直达波与多径杂波对目标散射信号的强抑制特点,提出了采用AR与MA的混合模型消除直达波与多径杂波的新方法。文中推导了采用AR模型和MA模型对多径信道建模的正则方程,提出了采用混合模型消除直达波与杂波的迭代算法。理论与仿真结果表明该方法对直达波与多径杂波的消除是非常有效的。     

雷达低空目标跟踪的偏差补偿算法研究

在单脉冲测角体制下,由于多径效应的影响,极大地降低了雷达目标的跟踪精度,甚至丢失该目标.本文主要通过理论分析和对实际环境的计算仿真,分析了岸、海基雷达跟踪低空运动目标时俯仰角测量误差大小及其产生原因.针对固定偏差补偿法在实际应用中的不足,提出了从复单脉冲比中估计反射路径与直接路径信号的相对相位的算法,从而实现联合相位的动态补偿,并在跟踪滤波中利用估计相位作为阀值来去除尖峰误差,在仿真中获得了良好的跟踪结果.     

基于前向搜索的GNSS长距多径信号判别技术

卫星导航接收机中的多径信号,尤其是长距多径信号会造成伪码的错误捕获与跟踪,带来很大的伪距测量误差,甚至定位失效。针对这一问题,利用卫星导航系统中独有的直达信号相对于多径信号具有最超前码相位的特性,在导航信号捕获跟踪之后,继续通过相关峰前向搜索的方法来判别直达信号与多径信号,在剔除多径分量之后获得准确的伪距测量值。在此基础上讨论了长距多径信号的搜索区间,给出了新的接收机处理架构,从而为卫星导航中长距多径信号的去除与精确定位的实施提供了重要参考。     

一种基于改进的Rake模型的GNSS接收机抗多径新技术

传统的GNSS接收机只跟踪一路信号,它是直达和多径成分的合成信号,利用该信号进行定位运算必然会产生多径误差.本文提出了一种用于GNSS接收机的抗多径新技术,它基于改进的Rake模型,将合成信号中的直达和多径成分分离,并对它们分别保持跟踪,在跟踪直达信号的指峰(Finger)中,将其他指峰所跟踪的多径成分从合成信号中减去...     

多径环境中被动雷达导引头测向性能分析

对多径效应下被动雷达导引头相位模型进行了理论推导,并通过仿真,分析了多种频率、速度、攻击角条件下被动雷达导引头测角受到的多径影响情况。仿真试验表明,大攻击角下多径影响较小。     

射线跟踪模型及其在3G网络规划中的应用

一、射线跟踪模型 射线跟踪是一种被广泛用于移动通信和个人通信环境中的预测无线电波传播特性的技术,可以用来辨认出多径信道中收发之间所有可能的射线路径.一旦所有可能的射线被辨认出后,就可根据电波传播理论来计算每条射线的幅度、相位、延迟和极化,然后结合天线方向图和系统带宽就可得到接收点的所有射线的相干合成结果.     

一种消除多径误差的外场天线测试技术

多径效应在机载天线的外场测试中会严重影响测试精度。针对该问题,提出了一种能够消除多径误差且简单易行的测试方法。该方法考虑多径信号的产生机理和矢量叠加原理,对直达和反射信号的组合进行测试,通过数据处理得出直达波信号强度,用于天线增益和方向图计算。利用该方法对机载VHF/UHF天线开展了外场测试,测试结果与仿真曲线吻合良好,证明了该方法的有效性。该测试方法可用于机载航电系统的总体设计与试验验证工作。     

宽带数据采集系统的相位噪声分析

研究了宽带数据采集系统的相位噪声、信号频率和信噪比之间的关系。根据相位噪声的计算模型,推导出多载频信号和宽带信号相位抖动信噪比的计算方法,通过噪声的频谱可以看出,独立时钟相位的抖动噪声是均匀分布在整个采样频谱中的,过采样和滤波可有效改善其信噪比。理论结果表明线性调频信号的相位噪声可用宽带信号的模型计算,当信号的带宽较小时,完全可由单频信号的计算公式得出近似的结果。最后,仿真结果验证了该SNR算法的有效性。     

基于抛物方程的电波相位预测方法

针对大气波导和不规则地形等复杂环境下的电波传播相位预测,研究了基于抛物方程(PE)的相位计算方法,并通过与理想导体平面上自由空间条件下几何光学双射线模型计算的传播相位对比,对该相位计算方法进行了验证.在此基础上,利用PE方法计算的幅度和相位,研究了大气波导对脉冲信号传播的影响.     

Altitude Measurement Based on Terrain Matching in VHF Array Radar

The multipath signal and direct signal lying within a beamwidth of a receiving antenna are highly correlated, which degrades the performance of DOA in a VHF array radar. Especially on rough terrain, the reflection centers of elements are not at the same horizontal plane; thus the variation of indirect wave path difference from each element with respect to the target’s depression angle is not linear. In this paper, we assume the two-path-component data model, with one direct component and one indirect component related to the ground reflection. This paper builds a highly deterministic multipath signal model which takes the curvature of the signal path and the terrain parameters of the reflection region into account based on the sphere model, gives calculation methods of the reflection coefficient and lengths of the direct path and indirect path, and proposes a synthetic steering vector super-resolution algorithm. The results for both simulated and measured data show that this method provides excellent performance in resolving the DOA problem in a multipath environment compared to the data model that only considers the flat-earth model.     

Modeling of the TOA-based distance measurement error using UWB indoor radio measurements

Time of arrival (TOA) estimation used with ultra wideband (UWB) transmission is currently the most popular technique for accurate indoor geolocation. Due to severe indoor multipath conditions, these techniques often suffer from significant inaccuracy in location estimation. In this paper, we introduce a model for the error in estimated distance as measured from the estimated TOA of the direct path (DP) in a typical multipath indoor environment. The TOA estimation error has two components, (1) the errors caused by the multipath dispersion affecting any signal path and (2) the errors caused by undetected direct path (UDP) conditions. The statistical behavior of this error is also a function of the system bandwidth. The empirical data from UWB indoor measurements in an office building are used to design a model for the distance measurement error. This model relates the behavior of the two components of the TOA estimation error to the bandwidth of the system.     

多径衰落的数学模型及分析

多径效应是影响低仰角测控系统正常工作的重要因素。介绍了多径效应产生的机理,建立了多径衰落的数学模型。无线电信号在收发天线间传播时,存在直射路径和多条反射路径,当直射信号和反射信号相互抵消时就会产生多径效应。依据建立的数学模型,分析了多径衰落产生的条件和对系统影响的程度。多径衰落产生的位置由地面站天线高度、飞行器飞行高度和二者之间的距离决定,多径衰落深度主要由地面对电波的反射系数决定。在上述分析的基础上,提出了避免和减小多径衰落对系统影响的几种措施。     

Fluorescent light interaction with personal communication signals

Personal communication systems within office buildings are designed on the premise of slow (<10 Hz) amplitude and phase variations. The ubiquitous presence of fluorescent lights in that environment introduces variations at twice the line frequency, however, when propagation is via multipath reflections from such fixtures and when the direct path is blocked. The mechanisms responsible for these effects are the time-varying dielectric properties of the ionized gas in the tube, which cause the path length and strength of multipath components to be variable. Measurements in an office showed peak-to-peak variations up to 3 dB and 90°     

A new spatial path persistency model for TOA-based indoor geolocation

Analysis of the persistency and birth/death of multipath components of the channel impulse response is essential for performance evaluation of indoor geolocation algorithms using indirect paths for ranging. The use of indirect paths via multipath diversity is particularly important for situations where the direct path gets blocked. In this letter, we propose a statistical model for the spatial behavior of the persistency of multipath components as a mobile moves inside a building. Based on empirical data from a measurement calibrated ray tracing algorithm we show that the persistency in a typical building is modeled by log-logistic distribution rather than commonly assumed exponential distribution and path birth can be modeled as a Poisson distribution.     

相对时延的码片内的多径分离

本文首先通过分析多径传播对单频信号和调制信号的影响,指出在扩频方式下,存在进一步分离码片内多径的可能性。然后基于导出的相关解扩输出的解析表达式,在忽略噪声的理想条件下,求解码片内多径的问题可以近似转化为对一线性方程组的求解。最后对接收滤波器输出为矩形脉冲序列和三解脉冲序列两种情况进行了仿真,仿真结果表明,码片内多径的幅值、相应能够被精确地分离出来,多径时延的估计误差为信号的采样间隔。     

Location Error Analysis of an Active RFID‐Based RTLS in Multipath and AWGN Environments

In this paper, we analyze the location accuracy of real‐time locating systems (RTLSs) in multipath environments in which the RTLSs comply with the ISO/IEC 24730‐2 international standard. To analyze the location error of RTLS in multipath environments, we consider a direct path and indirect path, in which time and phase are delayed, and also white Gaussian noise is added. The location error depends strongly on both the noise level and phase difference under a low signal‐to‐noise ratio (SNR) regime, but only on the noise level under a high SNR regime. The phase difference effect can be minimized by matching it to the time delay difference at a ratio of 180 degrees per 1 chip time delay (Tc). At a relatively high SNR of 10 dB, a location error of less than 3 m is expected at any phase and time delay value of an indirect signal. At a low SNR regime, the location error range increases to 8.1 m at a 0.5 Tc, and to 7.3 m at a 1.5 Tc. However, if the correlation energy is accumulated for an 8‐bit period, the location error can be reduced to 3.9 m and 2.5 m, respectively.     

多径效应对信号接收及方向测量的影响

在论述L阵干涉仪和圆阵相关法测向体制误差形成的基础上,基于电磁波传播的多 径效应,建立了地空无线链路四径传输模型,并将单个多径分量用时延相同的多径簇来描述 ,分析了多径分量和多径簇对单个天线接收信号相位和不同天线接收信号互相关系数造成的 影响。仿真结果表明,多径条件下接收信号的波形、频谱和相位谱较直射信号都将发生显 著的变化,多径效应对俯仰角造成的测量误差要大于对方位角造成的测量误差。     

海面多路径效应对被动微波测角的影响分析

在拦截超低空目标时,海面多路径效应会严重影响被动制导型舰空导弹的测角精度。首先阐述海面多路径效应产生机理,然后结合旋转式相位干涉仪的测角原理,通过建立海面多路径镜面反射几何模型,给出了双天线直达信号和镜面反射信号表达式。在此基础上,选取典型超低空弹道,根据仿真结果代入多路径计算模型,分析超低空弹道多路径效应对测角精度的影响。仿真结果表明,海面多路径效应对被动微波体制导引头测角影响显著,为下一步研究抑制多路径影响措施提供了重要参考。