伪码测距中码跟踪环的FPGA实现

码跟踪环的设计是伪码/载波相位联合测距系统的一个关键环节.分析了伪码跟踪环路的结构,利用查表法、二阶环路分别对NCO和环路滤波器等关键部分进行了设计,并给出了相应的电路结构.系统仿真与FPAG片上测试结果表明,实现了伪码准确、实时跟踪,跟踪到的伪码相位误差小于载波相位的周期长,设计的跟踪环具有一定工程应用价值.     

伪码测距雷达中的伪码跟踪环路设计

提出了一种适用于伪码测距雷达的伪码跟踪环设计方法,重点对伪码跟踪环的跟踪精度和动态性能进行了分析,讨论了一种最小跟踪误差意义下的最优环路带宽确定方法。仿真结果表明伪码跟踪环跟踪精度高,对动态运动的适应能力强。     

电离层以及多径对载波相位平滑码伪距的误差分析

当今业界主要采用载波平滑码伪距技术(Hatch 滤波器)输出平滑伪距消除多径和热噪声等带来的影响，从而减少误差和改善定位精度。由于电离层对载波和伪距的测量值作用是相反的，那么采用载波平滑码伪距技术后输出的平滑伪距就会包含这些电离层时延引入的平滑误差，从而影响定位精度，甚至危及生命安全。因此，研究电离层对载波平滑码伪距的影响十分必要和重要。通过添加电离层时间梯度模型和多径模型，对平滑滤波器的输出误差进行理论分析， 并对上述分析结果进行仿真验证，从而为选取电离层时间梯度监测门限值、选择合适滤波常数等场景提供理论基础。     

直扩/跳频测控信号伪码跟踪抗干扰性能分析

研究了直扩/跳频测控信号伪码跟踪的抗干扰性能,通过加权处理使其归结为分析干扰条件下直扩信号伪码跟踪性能。采用鉴相曲线的过零点偏移表示干扰对跟踪的影响,推导了伪码跟踪的最大干扰误差表达式。以单音信号作为输入干扰,对最大干扰误差进行了理论分析,得出了音频干扰对伪码跟踪的影响规律。仿真结果表明,理论分析与仿真结果吻合较好,验证了理论分析的正确性。     

卫星导航系统中多址干扰引起的伪码跟踪误差的分析

本文基于非相干延迟锁定环的伪码跟踪体制,研究多址干扰对伪码跟踪误差的影响,通过理论推导给出了存在多址干扰条件下最大跟踪误差的解析表达式,分析了影响多址误差的多种因素,得到了多址误差随干扰信号频率和相位的变化规律.研究结果可对进一步分析多址干扰影响和克服多址误差提供理论依据.     

GPS系统中的多径效应分析

本文研究了ＧＰＳ系统中多径效应的伪唬测量误差，先分析镜面多径信号的时间延迟和由此引起的频带扩展，然后研究在用相干和非相干延时锁定环跟踪ＰＮ码信号时多径信号对Ｓ曲线的影响和由此带来的伪距测量误差（多径误差）以及减小多径误差的方法。     

压制干扰对GPS接收机码跟踪环的性能影响分析

压制干扰是GPS接收机面临的重要的人为威胁之一,对伪码跟踪的跟踪测距精度产生影响,甚至导致伪码跟踪环失锁。干扰对伪码跟踪环的影响模型涉及许多因素,建模比较困难。以常用的非相干超前减滞后功率延迟锁定环为例,建立了码跟踪环在宽带噪声干扰、窄带干扰和点频干扰下的跟踪误差模型,比较了压制干扰对C/A码和P(Y)码跟踪环性能的不同影响。通过对不同干扰方式下C/A码和P(Y)码跟踪误差的仿真,得出了对C/A码和P(Y)码跟踪环性能影响较大的干扰方式和干扰频率,为GPS接收机干扰方法和抗干扰措施的选择提供了理论依据。     

利用多相关器的伪码测距多址干扰抑制算法性能分析

伪码跟踪多相关器技术广泛应用于导航接收机抗多径和导航信号质量监测。论文通过对比分析多径和多址信号对导航信号相关峰畸变的影响,揭示了多相关器技术可用于多址干扰抑制。通过仿真分析了多址误差随期望接收信号与干扰信号功率差和载波多普勒频率差的变化规律,并与传统的并行多址干扰对消方法进行了对比。仿真结果表明当多址干扰信号功率差小于10dB时,ELS和Double-delta与单级并行干扰对消方法的性能相当,但是实现复杂度大大降低。      

大误差条件下单频干扰引起的伪码跟踪误差研究

单频干扰能够引起较大的伪码跟踪误差,基于小误差条件的跟踪误差分析会失效。在大误差条件下,由于码环鉴相器不再工作在线性区域,利用鉴相器输出的二阶泰勒展开式代替一阶线性化近似,该文给出了单频干扰下伪码跟踪误差的解析表达式。通过数值分析和仿真实验分析验证了在单频干扰下伪码跟踪误差随干扰起始相位、干扰频率和干信比的变化特性。结果表明:当干扰引起的伪码跟踪误差较大时,基于鉴相器线性化的理论预测的准确性显著下降,而基于鉴相器二阶泰勒近似的理论分析能够准确预测大误差条件下的伪码跟踪误差,在跟踪误差不超过0.34 chip时,理论分析误差不超过20%。     

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。     

器件的非理想化对光纤陀螺精度的影响

为了提高开环光纤陀螺的测量精度,研究了干涉式开环光纤陀螺系统中元器件的非理想化对陀螺精度的影响.根据光纤陀螺系统的结构特点,给出了陀螺系统不同元器件的矩阵模型,导出了开环陀螺的输出表达式,重点分析了光源偏振度和输出光功率波动、耦合器分光比波动以及系统中光纤尾纤熔接点对轴误差造成的偏振误差.研究结果表明,在诸多影响因素中,光源波动对陀螺系统的影响最大,耦合器分光比波动次之,熔接点对轴误差的影响最小.     

New computation approaches for open-loop SSTDMA network synchronization

This paper presents two new open-loop synchronization algorithms for computing the satellite position. One is based on a three-rotational co-ordinate transformation, the other is based on a numerical iteration method. A detailed comparison of these two algorithms with other available algorithms is given with respect to accuracy of the computed separation distances between ground stations and the satellite, sensitivity to measurement and implementation errors, computation speed, and implementation complexity.     

Impulse response modeling of indoor radio propagation channels

If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming of the channel's transfer functions. It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations; a modified Poisson distribution shows a good fit to the arrival time of the multipath components; amplitudes are lognormally distributed over both local and global areas, with a log-mean value that decreases almost linearly with increasing excess delay; for small displacements of the receiving antenna, the amplitude of the multipath components are correlated; the amplitudes of adjacent multipath components of the same impulse response function show negligible correlations; and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antenna separation     

基于相关法飞行时间三维感知的误差机理研究

飞行时间测量是三维感知系统的重要原理之一。近年来随着半导体技术的发展,基于信号相关法的飞行时间测量系统以其无活动部件、高集成度、低功耗的优势,在三维成像领域迅速发展。文中系统研究了基于信号相关的飞行时间测量技术的数学原理,分析了其误差来源及其数学模型,并进行了横向对比。研究结果表明:飞行时间成像系统的光源误差、多路径误差和环境光是制约测量精度和适用范围的主要因素。     

实用中低精度光纤陀螺的信号处理设计

开环光纤陀螺系统直接从探测器的电信号解算出光纤陀螺的Sagnac相移，具有结构简单、全光纤、成本低廉等优点。所以开环光纤陀螺是满足中低精度应用要求的比较理想的方式。为了在开环光纤陀螺结构中满足大动态范围和高测量精度的要求，系统的信号处理方案利用多次谐波分析的数据处理方法，并且结合高阶契比雪夫FIR滤波器、自适应最佳采样速度设定、频谱分析技术、数字相关处理等数字信号处理技术，实现了2deg/h的精度。本文除了介绍上述设计方法外，并且通过对实验结果的对比测试分析，提出进一步提高光纤陀螺精度和稳定度的途径和设想。     

Use of Deeply Integrated GPS/INS Architecture and Laser Scanners for the Identification of Multipath Reflections in Urban Environments

This paper investigates the constructive use of multipath reflections of Global Positioning System (GPS) signals for navigation in urban environments. Urban navigation applications are generally characterized by a significant presence of multipath signals. In order to maintain reliable and accurate navigation capabilities, it is critical to distinguish between direct signal and multipath. At the same time, multipath reflections can be exploited as additional measurements for those cases where the number of direct path satellites is insufficient to compute the navigation solution. The paper develops a method for the identification of multipath reflections in received satellite signals: i.e., multipath is separated from direct signal and a line-of-site between the GPS receiver and a multipath reflecting object is determined. Once multipath reflections are identified, they can be used constructively for navigation. The method presented in the paper exploits an open-loop batch-processing GPS receiver, laser scanner and inertial navigation system (INS) to identify multipath reflections in received satellite signals. Experimental GPS, inertial and laser scanner data collected in real urban environments are applied to demonstrate identification of multipath reflections.     

A Multipath Detection Scheme for CDMA Systems With Space–Time Spreading

Space-time spreading (STS) is an appealing open-loop transmit diversity scheme, which has recently been included into the cdma2000 standard. It has been shown that the performance of the STS scheme is highly sensitive to fading coefficient estimation errors, particularly when the channel is highly time dispersive. In practical systems, channel estimation is normally performed after the multipath components are resolved, which suggests that improving multipath detection reduces such estimation errors. Motivated by this, we address, in this paper, the problem of multipath detection in STS-based code division multiple access (CDMA) systems. We first extend the conventional energy-based multipath detection scheme (EMDS) to cope with the spatial channel structure. We derive approximate expressions for the probability of detection and probability of false alarm. It is shown that the errors produced by the conventional scheme in detecting the potential multipath components severely impact the performance of the receiver. To improve upon the EMDS, we introduce and analyze an improved multipath detection scheme (IMDS) based on the estimation of the interference power in the individual resolved multipath components. The efficacy of the proposed scheme stems from the fact that the interference in each potential path is estimated and subtracted before that path is detected. We also present a simple and realizable version of the proposed IMDS detection scheme. Our results show that the proposed scheme not only improves the bit-error-rate performance significantly but also utilizes the pilot power much more efficiently.     

磁光调制法测量玻璃内应力

为了实现玻璃内应力的高精度测量,提出了一种磁光调制的新方法,建立了基于磁光调制的内应力测量系统.首先,根据偏振光的穆勒矩阵描述方式推导了该系统的测量模型,通过分离被测信号的直流、基频和各次谐波分量,并利用归一化的方法,消除了光强波动对测量结果的影响,并根据处理接收到的各信号分量得到玻璃内应力方向和应力双折射大小.通过测量玻璃的不同位置验证了该方法的有效性,内应力方向的测量精度为5,应力双折射的测量精度低于0.5 nm/cm,且系统具有稳定性高、精度高等特点.     

低仰角多目标测量系统能力分析与对策

提出了利用4个以上地面测量站,通过合理的布站,形成多目标测量系统,完成落区多目标子母弹测量,即同时测量目标至各站的距离,从而计算各目标在空中的位置。主要针对落区低抛子母弹地面平坦开阔,多径对测量的影响是主要因素,并采取适当的改善措施,以提高测距精度,通过对低抛子弹测量信道余量的估算,进一步说明有足够的信道余量,克服多径衰落。