A METHOD FOR DUAL-FREQUENCY IONOSPHERIC TIME-DELAY CORRECTING USING A C/A CODE GPS RECEIVER

The ionospheric time delay is one of the main error sources in C/A code GPS navigation and positioning applications. In this paper, a method is proposed for real-time dual-frequency ionospheric time-delay correcting using a C/A code GPS receiver, and the principle of the circuit block diagram for this method is analyzed with its feasibility theoretically demonstrated.

GPS的现代化进展及启示

目前的全球定位系统(GPS)相关信息内容多,良莠不齐,导致出现一些二手信息误导读者的问题。该文以GPS官方机构近些年公开发布的相关技术文件为依据,梳理了GPS的现代化发展历程,阐述了导航卫星上新增加的民用信号及军用信号、新一代运行控制系统、新型GPS BlockⅢ/IIIF卫星的特点,介绍了GPS Block IIIF上使用的点波束技术,并提出了几点启示。GPS是世界上第一个建成的全球卫星导航系统(GNSS),全球覆盖程度、软件应用、全球用户数量等指标都处于领先地位,它的很多技术发展方向代表当前的主流趋势。GPS建设过程中的经验教训值得我们借鉴,GPS的发展方向值得我们学习和参考。本文内容可供卫星导航行业相关人员参考。

Design and implementation of the simulation system for GPS new civil signals

In order to research on the design and implementation of a modernized GPS civil signals simulation system,a brief review of the modernized GPS signals is introduced,including the signal structure and characteristics of L2C,L5 and L1C signals.The design and implementation of the main modules of the simulation system is described in detail.The simulation system is mainly composed of parameter setting,system initialization,signal generator,noise generator,disturbance generator,signal synthesis,low-pass filter,A/D conversion and storage.The simulation results based on Matlab are then presented,and the power spectral density（PSD） of all navigation signals is analyzed.The simulation system completes the physical layer simulation of a modernized GPS new civil signal and can provide a controllable signal source for designing and testing of modernized GPS civil receivers,especially for the signal processing algorithm design of the GPS software receiver.

GPS欺骗信号对变电站时间同步装置的干扰分析与测试

当前无人机诱骗设备发射的GPS欺骗信号对变电站自动化系统的安全问题尚未明晰。为此提出了一种全球定位系统(global positioning system,GPS)欺骗信号对变电站时间同步装置的干扰评测方法,理论分析了GPS欺骗信号对变电站时间同步装置的影响。测量了无人机诱骗设备在不同发射功率下的欺骗信号功率强度及电场强度空间分布,实验验证了GPS欺骗信号对时间同步装置接收卫星质量与授时精度的影响,分析了无人机诱骗设备的发射功率以及其与时间同步装置GPS/北斗卫星导航系统(Bei-Dou system BDS)接收天线间的距离对授时精度的影响规律。结果表明:时间同步装置天线距离无人机诱骗设备10 m以外,GPS诱骗信号不会使时间同步装置进入守时状态;时间同步装置天线距离无人机诱骗设备60 m以上,GPS诱骗信号对时间同步装置的影响可忽略不计,为变电站安全稳定运行提供了参考依据。

GPS/QZSS在亚太地区实时相对定位性能分析

利用BNC(BKG NTRIP client)传输的实时观测数据,从可见卫星数、位置精度因子(position dilution of precision, PDOP)、多路径效应、信噪比和实时相对定位精度等方面对GPS和QZSS在亚太地区的定位性能进行评估和分析。结果表明,QZSS与GPS组合后,可见卫星数增加,卫星几何构型更好,可提高定位精度的可用性和可靠性;QZSS卫星多路径效应的变化规律与GPS卫星一致,且QZSS卫星各频点的多路径误差大多小于GPS卫星;GPS和QZSS卫星各频点的信噪比随高度角变化趋势基本相同;在N、E、U方向上,GPS/QZSS组合的实时相对定位精度比GPS有所提升。

Research of Ionospheric Time-Delay Error Simulation in High Dynamic GPS Signal Simulator

The ionospheric time-delay is an important error source for GPS users. How tosimulate the ionospheric error is one of the key problems that need to be solved in high dynamicGPS signal simulator design. The ionospheric effects are related to the user's position. Based onthe analysis to the different ionospheric time-delay error correction methods for ground users andspace users, the approaches to calculate the ionospheric time-delay error in a high dynamic GPSsignal simulator are studied and the mathematic models are also given in this paper. The calculationproblem of eight ionospheric coefficients broadcasted in a GPS satellite message in differentapplication situations is solved. The validity of the ionospheric time-delay error calculationmethods given by this paper has been proved by simulations.

Weak GPS L1 Signal Acquisition Based on BPDC

It is difficult to achieve accurate acquisition of weak global positioning system( GPS) signals with traditional methods. A weak signal acquisition strategy based on block processing and differentially coherent( BPDC) is put forward after analyzing the advantages and disadvantages of coherent and non-coherent integration algorithms. Code phase parallel search of the pre-coherent integration is conducted by using fast Fourier transform( FFT),and the results are then differential coherent processed and block processed. BPDC method reduces computation cost compared with coherent and noncoherent( CNC) algorithm. The performance of the two algorithms is also compared based on simulated signals. The result shows that the noise suppression effect of BPDC algorithms is superior to that of traditional CNC algorithm,and the superiority of BPDC is more apparent with the reduction of carrier to noise ratio( CNR). In the case that the pre-coherent integration length is 4 ms and CNR is reduced to 28 dB-Hz,CNC algorithm cannot yet acquire signal correctly while BPDC has well acquisition performance. Therefore,for weak GPS signal acquisition,BPDC algorithm can acquire the signal with lower CNR and has better acquisition property.

复杂环境下结合EMD的GPS-IR水位反演方法

利用法国布雷斯特(Brest)港BRST测站和英国塞文大桥监测系统GNSS双频观测数据,分别在静态和高动态环境下进行GPS-IR水位反演,探究传统GNSS监测系统进行水位反演的可行性与精度.结果表明:L1波段反演精度高于L2波段;在静态场景下,GPS-IR水位反演结果与验潮站数据相关系数大于0.98,在高动态场景下,桥梁GPS-IR水位反演精度稍低.利用经验模态分解(EMD)方法对算法进行改进,提高了在桥梁复杂环境下GPS-IR水位反演结果的精度,均方根误差(RMSE)相比经典方法降低约50%.本文方法提高了GPS-IR技术在不同水域环境下的适用性,在水位监测中具有很好的应用前景.

边坡安全监测GPS-RTK信号的降噪算法研究

全球定位系统实时动态差分技术(global positioning system-real time kinematic, GPS-RTK)是解决路基边坡安全监测问题的重要手段,但GPS-RTK信号易受到多路径误差和共模误差的影响。基于小波变换(wavelet transform, WT)和主成分分析(principal component analysis, PCA)分别可以有效去除多路径误差和共模误差,提出WT-PCA算法去除信号误差。首先设置仿真信号,通过参数调优进一步提高单一算法的降噪效果。其次提出组合算法WT-PCA改进单一算法的缺陷,并与其他组合算法进行对比分析。最后,对十天高速路基边坡的GPS-RTK监测数据进行实例分析。结果表明,WT-PCA算法的信噪比和均方根误差较于WT-VMD优于66%和50%左右,算法可以有效地消除GPS-RTK信号的多路径误差和共模误差影响。提高边坡位移监测信号处理精度,进一步评估边坡结构形变及安全状态。

Hypothesis testing analysis and unknown parameter estimation of GPS signal detection

Hypothesis testing analysis and unknown parameter estimation of both the intermediate frequency(IF) and baseband GPS signal detection are given by using the generalized likelihood ratio test(GLRT) approach,applying the model of GPS signal in white Gaussian noise,It is proved that the test statistic follows central or noncentral F distribution,It is also pointed out that the test statistic is nearly identical to central or noncentral chi-squared distribution because the processing samples are large enough to be considered as infinite in GPS acquisition problem.It is also proved that the probability of false alarm,the probability of detection and the threshold are affected largely when the hypothesis testing refers to the full pseudorandom noise(PRN) code phase and Doppler frequency search space cells instead of each individual cell.The performance of the test statistic is also given with combining the noncoherent integration.

Single Epoch GPS Deformation Signals Extraction and Gross Error Detection Technique Based on Wavelet Transform

Wavelet theory is efficient as an adequate tool for analyzing single epoch GPS deformation signal. Wavelet analysis technique on gross error detection and recovery is advanced. Criteria of wavelet function choosing and Mallat decomposition levels decision are discussed. An effective deformation signal extracting method is proposed, that is wavelet noise reduction technique considering gross error recovery, which combines wavelet multi-resolution gross error detection results. Time position recognizing of gross errors and their repairing performance are realized. In the experiment, compactly supported orthogonal wavelet with short support block is more efficient than the longer one when discerning gross errors, which can obtain more finely analyses. And the shape of discerned gross error of short support wavelet is simpler than that of the longer one. Meanwhile, the time scale is easier to identify.

A new frequency domain search strategy in high sensitivity GPS signal acquisition circuit designing

The contradiction between the sensitivity and the frequency domain searching speed of GPS signal acquisition circuit has been discussed for a long time. The signal integration operation which enhances the sensitivity of the system also makes the frequency slots narrower, which affects the speed of the system. In this research a high sensitivity GPS signal acquisition circuit is implemented with a new frequency domain search strategy. The new strategy combines DDS sweep strategy with cyclic shifting sweep strategy which makes the TTFF (time to first fix) reduced evidently. The extra hardware resource cost of the new strategy is acceptable. The speed advantage of the new frequency domain search strategy has been verified by hardware comparison tests.

播总控校时系统GPS/BDS卫星信号接收条件改良方案研究

本文阐述了电视播出系统总控校时系统的架构与实现策略,优化了GPS、BDS卫星信号的接收条件,从而提升了校时系统的稳定性。该方案为播总控系统提供了精确且可靠的时间基准,促进了系统同步运行,确保电视信号的精准播出,为播出安全奠定了坚实基础。

GPS-RTK土地测量技术优化与测量方案创新设计研究

传统的土地测量方法往往受到地理环境、复杂地形和测量精度等问题的限制,因此需要引进更加先进和高效的测量技术。为了提高土地测量能力,引入土地测量工作中的GPS-RTK测量技术,通过多方技术改进以提高土地测量工作的效率和精准度。采用GPS-RTK技术,通过基准站、移动站和全球定位系统(GPS)卫星之间收发信号,可以在移动站实时计算出三者之间的距离,提高土地测量工作的便捷性。在信号处理方面,采用了联邦卡尔曼滤波算法,提高了土地测量工作的信号传播效率。试验结果表明,设计的土地测量工作方案的测绘性能有显著提高。

Fast Acquisition Method of GPS Signal Based on FFT Cyclic Correlation

Since the global positioning system began to operate, it has become more and more close to people’s lives, and has been applied to various fields now. In order to track and decode GPS signals, GPS signals need to be captured first. The necessary parameters of the captured GPS signal are immediately transmitted to the tracking process, and then the navigation message of the satellite can be obtained by tracking process. In this paper, the basic contents related to the signal structure of GPS system are briefly described. Then, the traditional GPS signal acquisition method based on time domain correlation method is introduced, and the GPS signal acquisition method based on FFT cyclic correlation method is discussed in this paper. By comparing the simulation results, two kinds of GPS signal acquisition methods are compared with the calculation time according to the method of controlling variables. For the two GPS signal acquisition methods, the variation of time delay error with SNR is simulated in this paper.

GPS现代化L1C民用信号体制分析

为了保持国际竞争力的同时满足全球范围内不断增长的PNT服务需求,美国不断进行现代化全球定位系统(GPS)的升级改造,2020年启用并播发新的民用信号L1C就是重点改造内容之一。针对新形势下日趋激烈的频谱资源竞争环境,在对GPS四个民用信号基本特征梳理归纳的基础上,阐述了L1C频点信号的选择背景及意义,分析了该信号的基本结构,重点研究了L1C信号的具体调制方式及重要特征,最后对伪码进行了详细分析,通过研究深入剖析L1C信号体制,对其他GNSS未来新体制信号的设计及工程实现有借鉴和参考价值。

Remote Sensing of Sea Surface Wind of Hurricane Michael by GPS Reflected Signals

In this paper, the propagating geometry and the w av eform of the GPS reflected signals are expatiated in detail. Furthermore, the pr inciple and the method of retrieving sea surface wind are presented. In order to test the feasibility of retrieval, the experiment data obtained by NASA in Hurr icane Michael are used. The result shows that the retrieval accuracy of wind spe ed is about 2 m/s.

Data Wipe-Off Technique for Tracking Weak GPS Signals

In this paper,the data wipe-off(DWO)algorithm is incorporated into the vector tracking loop of the Global Positioning System(GPS)receiver for improving signal tracking performance.The navigation data,which contains information that is necessary to perform navigation computations,are binary phase-shift keying(BPSK)modulated onto the GPS carrier phase with the bit duration of 20 ms(i.e.,50 bits per second).To continuously track the satellite’s signal in weak signal environment,the DWO algorithm on the basis of pre-detection method is adopted to detect data bit sign reversal every 20 ms.Tracking accuracy of a weak GPS signal is decreased by possible data bit sign reversal every 20 ms to the predetection integration time(PIT)or integration interval.To achieve better tracking performance in weak signal environment,the coherent integration interval can be extended.However,increase of the integration interval lead to decrease of the tracking accuracy by possible data bit sign reversal every 20 ms to the integration interval.When the integration interval of the correlator is extended over 20 ms in low C/No levels,the navigation DWO algorithm can be employed to avoid energy loss due to bit transitions.The method presented in this paper has an advantage to continuously estimate the navigation data bit and achieve improved tracking performance.Evaluation of the tracking performance based on the various integration intervals for the vector tracking loop of a GPS receiver will be presented.

Continuous Tracking of GPS Signals with Data Wipe-Off Method

The decentralized pre-filter based vector tracking loop(VTL)configuration with data wipe-off(DWO)method of the Global Positioning System(GPS)receiver is proposed for performance enhancement.It is a challenging task to continuously track the satellites’signals in weak signal environment for the GPS receiver.VTL is a very attractive technique as it can provide tracking capability in signal-challenged environments.In the VTL,each channel will not form a loop independently.On the contrary,the signals in the channels of VTL are shared with each other;the navigation processor in turn predicts the code phases.Thus,the receiver can successfully track signals even the signal strength from individual satellite is weak.The tracking loop based on the pre-filter provides more flexible adjustment to specific environments to reduce noise interference.Therefore,even if the signals from some satellites are very weak the receiver can track them from the navigation results based on the other satellites.The navigation data,which contains information necessary to perform navigation computations,are binary phase-shift keying(BPSK)modulated onto the GPS carrier phase with the bit duration of 20 ms(i.e.,50 bits per second)for the GPS L1 C/A signals.The coherent integration interval can be extended for improved tracking performance in signal-challenged environment.However,tracking accuracy is decreased by possible data bit sign reversal.The DWO algorithm can be employed to remove the data bit in I and Q correlation values so as to avoid energy loss due to bit transitions when the integration interval of the correlator is extended over 20 ms under the low carrier-to-noise ratio(C/No)environments.The proposed method has an advantage to provide continuous tracking of signals and obtain improved navigation performance.Performance evaluation of the tracking capability as well as positioning accuracy will be presented.