高动态载波锁相环设计和性能分析

常规的二阶载波跟踪环路由于环路带宽的限制,无法满足接收机高动态条件下的环路跟踪,为了解决环路的高动态应力引起的噪声响应对环路带宽的要求,需要合并动态应力到误差跟踪控制信号才能满足高动态的性能要求。本文从载波跟踪二阶环路的结构入手,对利用外界速度辅助的三阶环路进行动态稳定性和稳定误差性能进行仿真计算和性能分析,结果表明这种有外界速度辅助的三阶载波锁相环路可以改善信号跟踪环路的动态应力性能。     

FPLL载波跟踪环仿真及高动态GPS信号测试

针对高动态环境下普通GPS接收机跟踪环路容易失锁的问题,考虑到锁频环动态性能好、锁相环跟踪精度高的特点,实现了二阶锁频环辅助三阶锁相环的载波跟踪环(FPLL)。根据FPLL结构原理和误差分析理论,提出了一种FPLL环路的码相位和载波相位精度分析方法。借助GPS软件接收机平台,在Matlab环境下仿真实现了FPLL载波跟踪环,并利用Spirent GSS7700仿真器采集高动态GPS模拟信号对FPLL环路进行了测试。测试结果和精度分析表明,在导航信号的载噪比为40dB-Hz,加速度为26g,加加速度为9g/s的条件下,该高动态跟踪环路能够达到码相位1.31m(1σ),载波相位为4.24×10-3 m/s(1σ)的跟踪精度。     

超紧组合中不同精度IMU对GNSS信号跟踪性能的提升

详细推导了惯性测量单元(IMU)精度与全球导航卫星系统(GNSS)接收机信号跟踪环路误差之间的数学模型,分析了IMU辅助的高动态载波跟踪环路误差精度,比较了不同精度IMU辅助GNSS信号捕获性能,证明了分析推导的正确性和合理性,指出了惯性卫星超紧组合导航系统对IMU的精度要求。     

基于矢量跟踪的GNSS／SINS相干深组合系统研究

为满足组合导航系统在高动态环境下的性能要求,设计基于矢量跟踪的GNSS／SINS相干深组合导航方法。利用矢量跟踪环路将所有可视卫星的跟踪和导航解算融为一体,增强通道间的辅助;高动态对载波跟踪影响更大,在通道预滤波中将码环载波环分别用独立的滤波器处理,组合滤波中采用通道间差分降低滤波状态维数,提高计算效率。引入惯导的加速度辅助本地信号参数预测,较精确地测量卫星视线方向的加速度,减小接收机在高动态时段的剩余动态,提高本地信号参数的预测精度。基于矢量跟踪软件接收机搭建相干深组合仿真系统,实验表明该方法在高动态等环境下能提高信号跟踪性能,改善系统的精度、可靠性。      

基于卡尔曼滤波的GPS高动态载波跟踪环路设计

针对高动态环境会使接收机接收信号载频上产生很大的多普勒频移及其变化率,普通的GPS载波跟踪环无法保证可靠的跟踪等问题,通过综合分析传统的二阶叉积自动频率控制环(CPAFC)辅助三阶锁相环(PLL)的高动态载波跟踪环路,以及卡尔曼滤波器在动态跟踪中的优势与劣势,该文设计了一种基于卡尔曼滤波的二阶CPAFC辅助三阶PLL的GPS高动态载波跟踪环路。通过仿真分析证明,新的环路能更好地适应动态性,整体跟踪性能更好;并且在信噪比较低的情况下,环路优势更明显。     

一种SINS/GPS深组合导航系统技术问题分析

为了满足高动态用户及强干扰条件下的应用需求,提出了一种基于卫星信号矢量跟踪的SINS/GPS深组合导航方法,设计了基于FPGA硬件平台的实施方案。利用组合卡尔曼滤波器反馈回路取代了传统接收机中独立、并行的跟踪环路,能够同时完成所有可视卫星信号的跟踪和导航信息处理;通过矢量跟踪算法对所有可视卫星信号进行集中处理,能够增强跟踪通道对信号载噪比变化的适应能力,从而提高接收机在强干扰或信号中断条件下的跟踪性能;根据SINS导航参数和星历信息推测GPS伪码相位和多普勒频移等参数,用以辅助卫星信号的捕获和跟踪,能够大大缩短接收机的搜索捕获时间,并增强接收机在高动态条件下的跟踪性能。基于矢量跟踪的深组合方法不仅在GPS信号短暂中断期间,能够保证系统的导航精度和可靠性,而且在强干扰环境中能够维持较好的伪码相位和载波频率跟踪性能。     

GPS信号跟踪的多径影响分析与仿真

多径信号是GPS定位的主要误差源之一。码和载波跟踪环是GPS接收机的重要组成部分，它们直接决定了接收机的性能，因此当前多径消除技术研究的核心即是从跟踪环内部着手研究。本文仔细分析了GPS接收机信号跟踪环以及多径信号对跟踪精度的影响，对伪距码与载波相位多径误差进行了比较，并且通过仿真结果和图表阐明了码和载波相位多径误差之间的协同关系。     

正交复用二进制偏移载波双环跟踪技术

针对正交复用二进制偏移载波信号(QMBOC)跟踪时存在的多零点模糊问题,首先比较了模糊消除的常用方法,并对双环跟踪方法进行了理论分析,在此基础上利用二进制偏移载波信号(BOC(1,1))的双环跟踪环路对QMBOC信号进行了跟踪,同时将副载波联合环路纳入双环跟踪方法作研究对比.仿真结果表明,在载噪比高于24dB·Hz的环境下,BOC(1,1)的双环跟踪误差趋近于0,小于联合跟踪方法下的跟踪误差,实现了良好的处理效果.     

一种改进扩展卡尔曼滤波算法的GPS多径抑制应用

在用EKF算法消除微弱GPS卫星信号中的噪声,并估计出多径幅度与码相位时延的码跟踪环中,由于各种误差的存在,从而降低了环路的跟踪性能。针对这一问题,该文在EKF算法的基础上提出了一种LSEKF算法,该LSEKF算法用最小二乘估计的原理对EKF算法所用的采样观测点进行修正,构造出一组无偏、均方误差和最小与空间分布确定的新型采样观测点,用来进行后续的滤波估计。仿真结果表明,相比EKF算法,LSEKF算法拥有更高的伪码跟踪精度,而且收敛速度更快,跟踪门限也更低。     

多径效应的动态特性对码跟踪环路的影响分析

接收机与卫星之间的相对运动,使得多径效应存在动态特性。针对卫星轨道的不同,分析多径效应对测距误差的影响,着重讨论静止接收机接收GEO卫星信号时出现的固有多径现象,仿真分析多径信号的衰落频率对码跟踪环路的影响。仿真结果表明,当衰落频率接近或大于码环路带宽时,多径对码跟踪精度的影响会在一定程度上被滤除;不同的卫星轨道导致多径效应的动态特性存在差异,会使测距误差在时域上表现出短时快变和长时缓变两种特征。为研究多径效应产生机理与卫星轨道因素的相关性提供了验证途径。     

An all-pass filter for compensation of ionospheric dispersion effects on wideband GNSS signals

Compared with the traditional GPS L1 C/A BPSK-R(1) signal, wideband global navigation satellite system (GNSS) signals suffer more severe distortion due to ionospheric dispersion. Ionospheric dispersion inevitably introduces additional errors in pseudorange and carrier phase observations that cannot be readily eliminated by traditional methods. Researchers have reported power losses, waveform ripples, correlation peak asymmetries, and carrier phase shifts caused by ionospheric dispersion. We analyze the code tracking bias induced by ionospheric dispersion and propose an efficient all-pass filter to compensate the corresponding nonlinear group delay over the signal bandwidth. The filter is constructed in a cascaded biquad form based on the estimated total electron content (TEC). The effects of TEC accuracy, filter order, and fraction parameter on the filter fitting error are explored. Taking the AltBOC(15,10) signal as an example, we compare the time domain signal waveforms, correlation peaks, code tracking biases, and carrier phase biases with and without this all-pass filter and demonstrate that the proposed delay-equalization all-pass filter is a potential solution to ionospheric dispersion compensation and mitigation of observation biases for wideband GNSS signals.     

基于GPS单频软件接收机的捕获与跟踪算法实现

在分析基于软件无线电全球定位系统（GPS）接收机结构的基础上,研究了GPS单频软件接收机的捕获和跟踪算法,并基于MATLAB平台在PC上仿真了GPS单频软件接收机样机。信号捕获采用基于快速傅里叶变换（FFT）的并行码相位搜捕算法;信号跟踪联合使用超前滞后非相干延迟锁定环和科斯塔斯环的跟踪环结构。采用实测数据对信号捕获、跟踪算法进行了分析和验证。结果表明：仿真的GPS单频软件接收机具备基本的基带信号处理功能。     

AItBOC信号码跟踪性能研究

通过分析A1tBOC（15,10）信号的功率谱密度、自相关函数,得出该信号在码跟踪性能上的理论优势,并根据Betz码跟踪评估理论仿真分析了接收机前端带宽、相关器间隔、环路鉴别器类型、载噪比以及全频带和单边带两种接收方式对该信号码跟踪精度的影响,并且通过与BPSK（10）、BOC（15,10）和单边带AltBoc（15,10）信号对比,得出AltBOC（15,10）信号在码跟踪精度上的优势,为AltBOC接收机设计提供理论依据。     

载波/多普勒平滑伪距在Android手机中的定位实现

针对Android手机GNSS伪距定位精度较低的问题,利用手机端观测信息,通过载波相位/多普勒平滑伪距改善手机端伪距观测值的质量,从而达到提高定位精度的效果。首先给出了Android手机GNSS原始观测量的获取方法,然后推导了载波相位平滑伪距和多普勒平滑伪距算法模型,并设计合理有效的试验对算法的精度进行评定。试验结果表明：在手机端静态定位中载波相位和多普勒平滑算法均可提高原始伪距的定位精度,且多普勒平滑算法表现更优;在手机端动态定位中多普勒平滑算法可获得比原始伪距更优的定位精度,但是载波相位平滑算法较原始伪距更差;由于硬件的制约手机端周跳和信号失锁严重,占比超过50%,载波相位在手机端的可用性较低;多普勒平滑算法的最优平滑时间常数小于等于10 s,具有实时动态定位的巨大潜力。     

Effects of building materials on UHF ranging signals

Positioning and tracking inside buildings using wireless location methods has recently received considerable attention. One method is the estimation of the time of arrival of satellite or terrestrial-based radio frequency signals in order to produce ranges from the transmitter to the receiver. This paper investigates the effect of walls made of various construction materials on the penetration of ranging signals. In the tests conducted, a GPS pseudo-satellite transmits a pseudorandom noise code at a carrier frequency of 1.57542 GHz. After penetrating walls made of plywood, gyprock and cinder blocks, the signal is received by a GPS receiver which measures the carrier phase and the pseudorange between the transmitter and receiver using code correlation. Compared to measurements obtained with no walls present, the effect on the measurements is determined. The results indicate that the carrier phase measurement is superior to the pseudorange in terms of noise, stability, and the magnitude of the effect of the walls on the range obtained. Ranges based on the carrier phase only change by a few centimeters. Given that the integer number of cycles of the phase can be determined and phase lock is maintained, the carrier phase measurement shows considerable promise for indoor ranging.     

一种新的BOC调制无模糊跟踪鉴别器设计

建立了导航接收机码跟踪延迟锁定环的数学模型,讨论了DP和EMLP鉴别器在不同信号、不同前端滤波器带宽的鉴别曲线特性,阐述了BOC调制模糊跟踪产生的原因。针对BOC调制信号的模糊跟踪问题,从BOC调制的机理出发,将BOC调制分成伪码和副栽波两部分分析,阐述了一种新的鉴别器设计。实验表明：新鉴别器设计,鉴别曲线线性跟踪区域斜率最高为9,可实现BOC调制的无模糊跟踪。     

Algorithm for carrier-adjusted DGPS positioning and some numerical results

This paper derives a DGPS positioning algorithm, referred to as the algorithm for carrier-adjusted DGPS positioning. This algorithm can be applied by a DGPS user when code and carrier observations are available and when the dynamic behaviours of both mobile positions and receiver-clock biases can and cannot be modelled. Since the algorithm directly uses code and carrier observations, the stochastic model of observations has a simple structure and can be easily specified. When the dynamic behaviour of mobile positions can be modelled, the algorithm can provide recursive solutions of the positions, on the other hand, when the behaviour cannot be modelled, it can provide their instantaneous solutions. Furthermore, the algorithm can integrate with a real-time quality-control procedure so that the quality of the position estimates can be guaranteed with a certain probability. Since in the use of the algorithm there always exist redundant observations unless the position parameters are inestimable, the quality control can even be performed when only four satellites are tracked. Using the algorithm and real GPS data collected at a 100-km baseline, this contribution investigates how DGPS positioning accuracies vary with the type of observables used at reference and mobile stations, and how important it is to choose an elevation-dependent standard deviation for code observations in DGPS data reduction. It was found that using carrier observations along with code observations is more important at the reference station than at the mobile station. Choosing an elevation-dependent standard deviation for code observations can result in better positioning accuracy than choosing a constant standard deviation for code observations. For the 100-km baseline, half-metre single-epoch positioning accuracy was achieved when dual-frequency data was used at both reference and mobile stations. The positioning accuracy became better than 0.75m when the types of observable used at the mobile station were replaced by L1 code and carrier. Received: 9 April 1996 / Accepted: 6 February 1997     

GPS navigation data bit decoding error during strong equatorial scintillation

Strong equatorial scintillation is often characterized by simultaneous fast phase changes and deep amplitude fading. The combined effect poses a challenge for GNSS receiver carrier tracking performance. One of the consequences of the strong scintillation is increased navigation message data bit decoding error. Understanding the rate of the data bit decoding error under equatorial scintillation is essential for high accuracy and high integrity applications. We present the statistical relationship between the data bit decoding error occurrences and the intensity of amplitude scintillation based on the processing of intermediate frequency GPS scintillation data collected on Ascension Island in March 2013. A third-order phase lock loop (PLL) is implemented to process the data and to access the data bit error typically expected in conventional receivers. A Kalman filter-based PLL is also used to process the same data to demonstrate that the data bit decoding error can be reduced through advanced carrier tracking designs.     

Double-filter model with modified Kalman filter for baseband signal pre-processing with application to ultra-tight GPS/INS integration

In federated design of ultra-tight GPS/INS integrated system, the baseband signal pre-processing is completed in a single pre-filter assigned for each channel. As the state space model of this single pre-filter includes the code tracking errors coupled with carrier tracking errors, ionospheric errors and normalized signal amplitude, the carrier tracking process may be destroyed. Also, the measurement noises are not independent any longer after passing through the code and carrier discriminators. Therefore, we propose a double-filter-based pre-filter model that distributes the carrier and code tracking into two independent filters: a conventional pre-filter, where the normalized signal amplitude is excluded from the state space and tracks only the code signal, and a 3-dimension state filter, tracking the carrier signal. The measurement information from both filters is a scalar quantity, which removes most of the noise correlation. To further improve the performance of the double-filter-based pre-filter model, we propose a modified Kalman filter algorithm. Simulation and field tests have been conducted, and the performance analysis has been done for the following configurations in a vector-tracking mode: double-filter model with modified Kalman filter, double-filter model with conventional Kalman filter and traditional single-filter model. The preliminary analysis indicates that the double-filter model with modified Kalman filter shows the best performance in tracking and navigation domains, while the traditional single-filter model shows a sub-optimal performance.