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。     

Single GPS receiver time-relative positioning with loop misclosure corrections

Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about 40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under 20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the horizontal components and 29 cm for the vertical component with dual frequency data.     

GPS接收机数字码跟踪环性能研究

从数字码跟踪环的角度研究了高动态体制下GPS接收机性能，对伪码捕获和跟踪过程建立了数学模型；推导出伪码捕获的检测概率和虚警概率，提出改进的双Dwell搜索方法；对高阶DDLL的动态跟踪性能及输入随机噪声影响进行了定量分析。通过MATLAB及Simulink动态仿真结果表明，双Dwell搜索方法能显著缩短平均捕获时间；可根据具体应用环境，选择不同的环路参数，以优化码跟踪环的特性。     

Precision spacecraft navigation using a low-cost GPS receiver

Within the PROBA-2 microsatellite mission, a miniaturized single-frequency GPS receiver based on commercial-off-the-shelf (COTS) technology is employed for onboard navigation and timing. A rapid electronic fuse protects against destructive single-event latch-ups (SEL) and enables a quasi-continuous receiver operation despite the inherent sensitivity to space radiation. While limited to single-frequency C/A-code tracking with a narrow-band frontend, the receiver is able to provide precision navigation services through processing of raw GPS measurements on ground as well as a built-in real-time navigation system. In both cases, ionospheric path delays are eliminated through a combination of L1 pseudorange and carrier phase measurements, which also offers a factor-of-two noise reduction relative to code-only processing. By comparison with satellite laser ranging (SLR) measurements, a 0.3-m (3D rms) accuracy is demonstrated for the PROBA-2 reduced dynamic orbit determinations using post-processed GPS orbit and clock products. Furthermore, the experimental onboard navigation system is shown to provide real-time position information with a 3D rms accuracy of about 1?m, which notably outperforms the specification of the Standard Positioning Service (SPS). In view of their lower hardware complexity, mass budget and power requirements as well as the reduced interference susceptibility, legacy C/A-code receivers can thus provide an attractive alternative to dual-frequency receivers even for demanding navigation applications in low Earth orbit.     

基于SoC的导航接收机闭环跟踪环路设计与实现

在传统基于FPGA+DSP架构的导航接收机中,跟踪模块处于开环处理模式,存在实时性和可靠性差的问题,同时现场可编程逻辑门阵列(FPGA)和数字信号处理(DSP)之间大量的数据通信导致了 IO资源和功耗的增加.基于片上系统(SoC)架构提出了 一种卫星导航接收机的闭环跟踪环路方案,整个跟踪处理过程在FPGA内实现了完整的...     

基于GPS单频接收机的精密单点定位研究

介绍了利用单频GPS接收机进行精密单点定位的数学模型及解算方案,并采用选权拟合法得到比较准确的状态参数初值及其方差-协方差,加快了卡尔曼滤波的收敛。算例结果表明,利用精密卫星星历及卫星钟改正数并采用单频观测值,半个小时后的定位精度可达1~2分米的水平。     

利用双手持式GPS接收机编制旅游图的尝试

介绍了利用双手持式GPS接收机进行旅游图空间地理信息采集的方法，指出了目前旅游图编制存在的一些技术问题，提出了旅游图革新的几点想法。     

Improved GRACE kinematic orbit determination using GPS receiver clock modeling

Kinematic positions of Low Earth Orbiters based on GPS tracking are frequently used as pseudo-observations for single satellite gravity field determination. Unfortunately, the accuracy of the satellite trajectory is partly limited because the receiver synchronization error has to be estimated along with the kinematic coordinates at every observation epoch. We review the requirements for GPS receiver clock modeling in Precise Point Positioning (PPP) and analyze its impact on kinematic orbit determination for the two satellites of the Gravity Recovery and Climate Experiment (GRACE) mission using both simulated and real data. We demonstrate that a piecewise linear parameterization can be used to model the ultra-stable oscillators that drive the GPS receivers on board of the GRACE satellites. Using such a continuous clock model allows position estimation even if the number of usable GPS satellites drops to three and improves the robustness of the solution with respect to outliers. Furthermore, simulations indicate a potential accuracy improvement of the satellite trajectory of at least 40 % in the radial direction and up to 7 % in the along-track and cross-track directions when a 60-s piecewise linear clock model is estimated instead of epoch-wise independent receiver clock offsets. For PPP with real GRACE data, the accuracy evaluation is hampered by the lack of a reference orbit of significantly higher accuracy. However, comparisons with a smooth reduced-dynamic orbit indicate a significant reduction of the high-frequency noise in the radial component of the kinematic orbit.     

Real-time kinematic positioning of LEO satellites using a single-frequency GPS receiver

Due to their low cost and low power consumption, single-frequency GPS receivers are considered suitable for low-cost space applications such as small satellite missions. Recently, requirements have emerged for real-time accurate orbit determination at sub-meter level in order to carry out onboard geocoding of high-resolution imagery, open-loop operation of altimeters and radio occultation. This study proposes an improved real-time kinematic positioning method for LEO satellites using single-frequency receivers. The C/A code and L1 phase are combined to eliminate ionospheric effects. The epoch-differenced carrier phase measurements are utilized to acquire receiver position changes which are further used to smooth the absolute positions. A kinematic Kalman filter is developed to implement kinematic orbit determination. Actual flight data from China’s small satellite SJ-9A are used to test the navigation performance. Results show that the proposed method outperforms traditional kinematic positioning method in terms of accuracy. A 3D position accuracy of 0.72 and 0.79 m has been achieved using the predicted portion of IGS ultra-rapid products and broadcast ephemerides, respectively.     

Determination of the ionospheric foF2 using a stand-alone GPS receiver

The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities.     

NLOS GPS signal detection using a dual-polarisation antenna

The reception of indirect signals, either in the form of non-line-of-sight (NLOS) reception or multipath interference, is a major cause of GNSS position errors in urban environments. We explore the potential of using dual-polarisation antenna technology for detecting and mitigating the reception of NLOS signals and severe multipath interference. The new technique computes the value of the carrier-power-to-noise-density (C/N ₀) measurements from left-hand circular polarised outputs subtracted from the right-hand circular polarised C/N ₀ counterpart. If this quality is negative, NLOS signal reception is assumed. If the C/N ₀ difference is positive, but falls below a threshold based on its lower bound in an open-sky environment, severe multipath interference is assumed. Results from two experiments are presented. Open-field testing was first performed to characterise the antenna behaviour and determine a suitable multipath detection threshold. The techniques were then tested in a dense urban area. Using the new method, two signals in the urban data were identified as NLOS-only reception during the occupation period at one station, while the majority of the remaining signals present were subject to a mixture of NLOS reception and severe multipath interference. The point positioning results were dramatically improved by excluding the detected NLOS measurements. The new technique is suited to a wide range of static ground applications based on our results.     

GPS接收机时钟控制方法

对多种GPS接收机长时间的静态观测数据,用单点定位算法,计算GPS接收机每一个历元的接收机坐标和钟差,分析计算钟差的变化规律,并了解在完成GPS接收机的定位和时钟的校准后,去如何控制其时钟。     

Design of an adaptive GPS vector tracking loop with the detection and isolation of contaminated channels

GPS Solutions - In vector tracking loop (VTL), the relativity among received signals is exploited to deeply integrate the entire information within signal processing channels. However, the tracking...     

Use of a reduced IMU to aid a GPS receiver with adaptive tracking loops for land vehicle navigation

A reduced inertial measurement unit (IMU) consisting of only one vertical gyro and two horizontal accelerometers or three orthogonal accelerometers can be used in land vehicle navigation systems to reduce volume and cost. In this paper, a reduced IMU is integrated with a Global Positioning System (GPS) receiver whose phase lock loops (PLLs) are aided with the Doppler shift from the integrated system. This approach is called tight integration with loop aiding (TLA). With Doppler aiding, the noise bandwidth of the PLL loop filters can be narrowed more than in the GPS-only case, which results in improved noise suppression within the receiver. In this paper, first the formulae to calculate the PLL noise bandwidth in a TLA GPS/reduced IMU are derived and used to design an adaptive PLL loop filter. Using a series of vehicle tests, results show that the noise bandwidth calculation formulae are valid and the adaptive loop filter can improve the performance of the TLA GPS/reduced IMU in both navigation performance and PLL tracking ability.     

Design and implementation of an adaptive code discriminator in a DSP/FPGA-based Galileo receiver

In the design of a global navigation satellite system receiver, the tracking performance depends on the code tracking loop and the associated discriminator. An adaptive code discriminator under a multi-correlator architecture has been designed based on a multi-objective principle to achieve a balance among various, sometimes conflicting, design objectives. With the proposed optimization approach and adaptive logic, concerns of large pull-in region and small steady-state error can be addressed. The proposed scheme is implemented in a digital signal processor/field programmable gate array board and an experiment is conducted to process GIOVE-A signals. The test results reveal the advantages of the proposed code tracking architecture and discriminator design.     

Local deformation monitoring using GPS in an open pit mine: initial study

High-performance GPS RTK software has been developed within the Geodetic Research Laboratory (GRL) at the University of New Brunswick (UNB). This software was initially designed for gantry crane auto-steering. Due to limitations with classical geodetic deformation monitoring techniques, the Canadian Centre for Geodetic Engineering (CCGE) at UNB has decided to augment its fully automated deformation monitoring system with GPS. As a result, the GRL and CCGE have combined efforts to achieve the required precision. As a first step, tests of the GPS real-time kinematic (RTK) software have been carried out at Highland Valley Copper Mine in British Columbia, Canada. An open-pit mine environment places certain constraints on the achievable accuracies attainable with GPS. Consequently, the software has been modified to meet the needs of this particular project and data have been post-processed for analysis. This paper describes the approach taken at UNB to address high precision requirements in a constrained signal availability environment. Technical and scientific aspects of the UNB software, especially in handling two predominant errors (residual tropospheric zenith delay and multipath) at the mine, are discussed. Results of tests that have been carried out at the mine are presented.     

GPS signal acquisition using the repeatability of successive code phase measurements

This paper introduces a new method for GPS signal acquisition, which is based on the repeatability of successive code phase measurements and the M-of-N search algorithm. The performance of the proposed method in terms of probability of signal detection is similar to that of traditional methods, except that the calculation of the probability of detection does not rely on the noise distribution or the Carrier-to-Noise ratio (C/N₀). The code phase repeatability-based method is presented along with equations for probability of detection and probability of false detection. If the distribution of the noise is known, it also provides an estimate of the C/N₀. The proposed method is illustrated for coherent and non-coherent acquisition and C/N₀ estimation.     

基于B1C新信号的BDS/INS深组合改进的跟踪环路设计

针对北斗卫星导航系统/惯性导航系统(BDS/INS)的深组合定位系统,提出了一种利用惯性导航系统(INS)辅助B1C正交分量的信号跟踪算法,以解决定位过程中信号较弱致深组合定位系统失锁的问题. 该算法使用了考虑INS数据的卡尔曼滤波算法,并同时利用导频分量和数据分量构成本地码,对信号进行跟踪. 由该算法对实测数据计算,并利用传统算法进行对比,可以得出在弱信号的环境下跟踪环路较为稳定,伪距精度较高.