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1.
Software receivers have had a discernable impact on the GNSS research community. Often such receivers are implemented in a compiled programming language, such as C or C++. A software receiver must emulate the digital signal processing (DSP) algorithms executed on dedicated hardware in a traditional receiver. The DSP algorithms, most notably correlation, have a high computational cost; this burden precludes many software receivers from running in real time. However, the computational cost can be lessened by utilizing single instruction multiple data (SIMD) operations found on modern ×86 processors. The following demonstrates how C/C++ compatible code can be written to directly utilize the SIMD instructions. First, an analysis is carried out to demonstrate why real time operation is not possible when using traditional C/C++ code is carried out. Secondly a tutorial outlines how to write and insert ×86 assembly, with SIMD operations, into C/C++ code. Performance gains achieved via SIMD operations are then demonstrated, and pseudo code outlines how SIMD operations can be employed to perform correlation. Finally, a C/C++ compatible SIMD enabled arithmetic library is added to the GPS Toolbox for use in software receivers. 相似文献
2.
Vinh T. Tran Nagaraj C. Shivaramaiah Thuan D. Nguyen Eamonn P. Glennon Andrew G. Dempster 《GPS Solutions》2018,22(1):24
The sampling frequency of a digitized intermediate frequency signal has a strong effect on the measurement accuracy of Global Navigation Satellite System (GNSS) receivers. The delay-locked loop tracking error is significant when the sampling frequency is an integer multiple of the code chipping rate, the so-called commensurate sampling frequency, and the number of distinct instantaneous residual code phases is low. This results in distortions of the correlation shape and discriminator functions that lead to a significant accuracy degradation. These effects are most pronounced when the sampling frequency is low. Notwithstanding, it is generally good for receivers to keep the sampling frequency to a minimum owing to the processing load and power consumption. It creates a challenge for existing GNSS signal processing techniques. Random, sine and sawtooth jitters have been found to mitigate these distortions considerably. A software algorithm and two hardware receiver implementations of these solutions are proposed. A register-based architecture can be directly applied to the conventional receiver architecture, while the increase in resource and power consumption is insignificant. A RAM-based design cannot only considerably minimize utilized resources but also slightly reduce the power consumption compared to the conventional architecture. 相似文献
3.
4.
Software-based global positioning system (GPS) receivers perform all the baseband signal processing and the high level functions on a general purpose processor. The heavy computational loads of the signal correlation in baseband processing make it difficult for software receivers to operate in real time. In order to improve the real-time performance, an enhanced bit-wise parallel algorithm has been developed in this study. The enhanced algorithm has been implemented and tested in a 12 channels real-time GPS software receiver. The system consists of a radio frequency front end, a data acquisition board and software that runs on a laptop with a Pentium-M 1.5 GHz processor running the Window® XP operating system. The data acquisition board packs the 2-bit intermediate frequency samples with a 2-bit in/8-bit out shift register and transfers the packed samples to laptop through a USB port. The software running on the laptop performs all the baseband and navigation processing in real time. The test results show that the enhanced algorithm significantly improves the real-time performance of the software receiver by reducing the computational operations for signal correlation by 50% compared with the existing bit-wise parallel algorithm. Furthermore, the enhanced algorithm also reduces the amount of required memory for storing data for signal correlation. 相似文献
5.
Unlike the conventional hardware approaches to GPS base band signal processing, a software GPS receiver is extremely flexible
as it comes with all the associated advantages of a software solution. With a software solution, the improvements of silicon
technology can be easily translated into better performance at smaller form factors and lower power consumption, without a
redesign and/or change to the ASIC. A general purpose Digital Signal Processor (DSP) can be used effectively for GPS signal
processing. The memory and speed resources available determine the algorithms and applications that can be effectively implemented
in the receiver. The performance of software GPS receivers will soon be difficult to be surpassed by the hardware counterparts,
as high-performance processors become available at low cost. ? 2000 John Wiley & Sons, Inc. 相似文献
6.
全球卫星导航系统(GNSS)以其全天候、操作简便、高精度等优点在测绘、航空、地质勘察、环境监测与保护等领域得到了广泛应用。为提高GNSS接收机检定设备的利用率和检定工作的效率,也为测量工作中提高GNSS接收机的使用效率提供可靠依据,文中设计了不同型号的GNSS接收机与相同型号GNSS接收机联合检测和联合数据处理的实验。实验证明,不同型号GNSS接收机联合检测具有可行性。 相似文献
7.
M_DCB: Matlab code for estimating GNSS satellite and receiver differential code biases 总被引：6，自引：4，他引：2
Global navigation satellite systems (GNSS) have been widely used to monitor variations in the earth’s ionosphere by estimating total electron content (TEC) using dual-frequency observations. Differential code biases (DCBs) are one of the important error sources in estimating precise TEC from GNSS data. The International GNSS Service (IGS) Analysis Centers have routinely provided DCB estimates for GNSS satellites and IGS ground receivers, but the DCBs for regional and local network receivers are not provided. Furthermore, the DCB values of GNSS satellites or receivers are assumed to be constant over 1?day or 1?month, which is not always the case. We describe Matlab code to estimate GNSS satellite and receiver DCBs for time intervals from hours to days; the software is called M_DCB. The DCBs of GNSS satellites and ground receivers are tested and evaluated using data from the IGS GNSS network. The estimates from M_DCB show good agreement with the IGS Analysis Centers with a mean difference of less than 0.7?ns and an RMS of less than 0.4?ns, even for a single station DCB estimate. 相似文献
8.
We present a multi-constellation multi-band GNSS software receiver front end based on USRP2, a general purpose radio platform. When integrated with appropriate daughter boards, the USRP2 can be used to collect raw intermediate frequency (IF) data covering the entire GNSS family of signals. In this study, C++ class-based software receiver processing functions were developed to process the IF data for GPS L1, L2C, and L5 and GLONASS L1 and L2 signals collected by the USRP2 front end. The front end performance is evaluated against the outputs of a high end custom front end driven by the same local oscillator and two commercial receivers, all using the same real signal sources. The results show that for GPS signals, the USRP2 front end typically generates carrier-to-noise ratio (C/N 0) at 1–3 and 1–2 dB below that of the high end front end and a NovAtel receiver, respectively. For GLONASS signals, the USRP2 C/N 0 outputs are comparable to those of a Septentrio receiver. The carrier phase noise from the USRP2 outputs is similar to those of the benchmarking devices. These results demonstrate that the USRP2 is a suitable front end for applications, such as ionosphere scintillation studies. 相似文献
9.
传统的基于硬件的接收机由于芯片的封装性很难用来进行通道信号的分析研究,而基于软件无线电技术的软件接收机则很容易做到。软件接收机的跟踪通道信号统计分析可用于接收机算法的测试与比对以及卫星信号性能的分析与评估。这里搭建了GPS软件接收机L1中频数字信号处理平台,对跟踪通道输出的I、Q支路信号进行了均值、标准方差以及均方根(RMS)统计。分析了各统计值与通道对应卫星的高度角、信号强度以及噪声之间的关系。基于统计结果提出了一种估计信道信噪比的方法。最后比较了不同信号采样频率对相关三角形和导航定位解算精度的影响。 相似文献
10.
The mitigation of radio frequency interference (RFI) has a fundamental role in global navigation satellite system (GNSS) applications,
especially when a high level of availability is required. Several electromagnetic sources, in fact, might degrade the performance
of the global positioning system (GPS) and Galileo receivers, and their effects can be either in-band (i.e., secondary harmonics
generated by transmitters of other communication systems due to non-linearity distortions) or out-of-band (i.e., strong signals
that occupy frequency bandwidths very close to GNSS bands). We investigated the effects of real out-of-band signals on GNSS
receivers and analyzed the impact on the overall receiver chain in order to evaluate the impact of the interference source.
In particular, the analysis focuses on the spectrum at the front-end output, on the automatic gain control (AGC) behavior,
as well as on the digital processing stages (signal acquisition and tracking) at the analog digital converter (ADC) output.
This study refers to several experiments and data collections performed in interfered areas of downtown Torino (Italy). The
obtained results underline how digital/analog TV transmissions represent a potential interference source for GNSS applications
and might be critical for the safety of life services. 相似文献
11.
Suppression of multipath and jamming signals by digital beamforming for GPS/Galileo applications 总被引：1，自引：0，他引：1
Digital beamforming (DBF) has been studied to obtain automatic beam steering towards desired signals and simultaneous elimination
of multipath and jamming signals at GNSS receivers, which is made possible by spatial and temporal digital signal processing.
In this paper, the limitations of conventional multipath and jamming suppression techniques, which have been proven and widely
used in GPS, are investigated. Different DBF algorithms suitable for GNSS applications are investigated theoretically. New
ideas for future development of DBF are presented. The implementation of digital beamforming in FPGA/DSP for practical application
environments is also discussed.
Electronic Publication 相似文献
12.
This paper outlines the motivation for Global Navigation Satellite System (GNSS) software receivers. Features of traditional
and software-based GNSS receiver architectures are highlighted and compared, focusing on the advantages of the software design.
The choice of which architecture is advantageous, particular in the case of embedded systems, is present along with design
criteria—both for the current environment as well as what can be expected in the future.
Electronic Publication 相似文献
13.
Myriam Foucras Jérôme Leclère Cyril Botteron Olivier Julien Christophe Macabiau Pierre-André Farine Bertrand Ekambi 《GPS Solutions》2017,21(2):293-306
In global navigation satellite system (GNSS) receivers, the first signal processing stage is the acquisition, which consists of detecting the received GNSS signals and determining the associated code delay and Doppler frequency by means of correlations with a code and carrier replicas. These codes, as part of the GNSS signal, were chosen to have very good correlation properties without considering the effect of a potential received Doppler frequency. In the literature, it is often admitted that the maximum GPS L1 C/A code cross-correlation is about ?24 dB. We show that this maximum can be as high as ?19.2 dB when considering a Doppler frequency in a typical range of [?5, 5] kHz. We also show the positive impact of the coherent integration time on the cross-correlation and that even a satellite with Doppler outside the frequency search space of a receiver impacts the cross-correlation. In addition, the expression of the correlation is often provided in the continuous time domain, while its implementation is typically made in the discrete domain. It is then legitimate to ask the validity of this approximation. Therefore, the purpose of this research is twofold: First, we discuss typical approximations and evaluate their regions of validity, and second, we provide characteristic values such as maximums and quantiles of the auto- and cross-correlation of the GPS L1 C/A and Galileo E1 OS codes in the presence of Doppler, for frequency ranges up to 50 kHz and for different integration times. 相似文献
14.
In a spoofing environment, a Global Navigation Satellite System (GNSS) receiver must employ anti-spoofing techniques for obtaining a normal navigation solution from the GNSS signal. We propose a new method for identifying spoofing signals using the norm of the difference of baseline vectors (NDB) obtained from multiple receivers. The main focuses of this research are to reduce the initial time required to identify the spoofing signal and to mitigate the physical constraints on multiple antennas placement. First, the multi-correlators of each receiver track both GNSS and spoofing signals simultaneously and classify them into two signal groups. Then, the baseline vectors are generated from the double-differenced carrier phase measurements of the classified signal groups, and the NDB is calculated. If the target positions of the spoofing signal groups are almost the same, the NDB has a fairly small value when the base position of the selected baseline vectors is calculated from one of the GNSS groups and the rover positions of the baseline vectors are calculated from each spoofing group of the multiple receivers. Using the NDB, a hypothesis is established, and a hypothesis test is conducted for identifying the spoofing signal. The performance of the proposed test statistics is analyzed with respect to the distance between the GPS antennas and the tuning parameter. Our experimental results show that the proposed method effectively performs spoofing identification with a short baseline. Additionally, the method exhibits a very low probability of fault detection and fast response time. This means that the immediate anti-spoofing can work properly in spoofing environments. 相似文献
15.
Thomas Hobiger Tadahiro Gotoh Jun Amagai Yasuhiro Koyama Tetsuro Kondo 《GPS Solutions》2010,14(2):207-216
Off-the-shelf graphics processing units provide low-cost massive parallel computing performance, which can be utilized for
the implementation of a GPS software receiver. In order to realize a real-time capable system the crucial stages of the receiver
should be optimized to suit the requirements of a parallel processor. Moreover, the receiver should be capable to provide
wider correlation functions and provide easy access to the spectral domain of the signals. Thus, the most suitable correlation
algorithm, which forms the core part of each receivers should be chosen and implemented on the graphics processor. Since the
sampling rate of the received signal limits the real-time capabilities of the software radio it is necessary to determine
an optimum value, considering that the precision of the observable varies with sampling bandwidth. We are going to discuss
details and present our single frequency multi-channel implementation, which is capable of operating in real-time mode. Our
implementation differs from other solutions by the wideness of the correlation function and allows simple handling of data
in the spectral domain. Comparison with output from a commercial hardware receiver, which shares the antenna with the software
radio, confirms the consistency and accuracy of our development. 相似文献
16.
随着北斗三号卫星导航系统(BDS-3)的全面建成,湖北省北斗地基增强系统需要进行整网软硬件升级与改造,以实现对BDS-3卫星的兼容. 本文详细介绍了此次升级的内容:包括72台True CORS R1接收机的板卡硬件升级与固件包升级,增加对BDS-3的支持;TrueNET平台的软件升级;升级之后进行了接收机回归测试及系统精度测试:开展了新增频点的数据质量分析及双差质量分析,以及对RINEX原始文件进行了卫星数、高度角等分析;接收机软件研发完成后进行了整机性能测试,各项指标均满足要求;系统精度测试结果标明:网络实时动态(RTK)定位精度水平优于3 cm,垂直优于5 cm;差分全球导航卫星系统(DGNSS)定位精度水平优于1 m,垂直优于2 m. 相似文献
17.
With the advent of new global navigation satellite systems (GNSSs) and new signals, GNSS users will rely more on them to obtain higher-accuracy positioning. Evil waveform monitoring and assessment are of great importance for GNSS to achieve its positioning, velocity, and timing service with high accuracy. However, the advent of new navigation signals introduces the necessity to extend the traditional analyzing techniques already accepted for binary phase-shift keying modulation to new techniques. First, the well-known second-order step thread model adopted by the International Civil Aviation Organization is introduced. Then the extended new general thread models are developed for the new binary offset carrier modulated signals. However, no research has been done on navigation signal waveform symmetry yet. Simulation results showed that, waveform asymmetry may also cause tracking errors, range biases, and position errors in GNSS receivers. It is thus imperative that the asymmetry be quantified to enable the design of appropriate error budgets and mitigation strategies for various application fields. A novel evil waveform analysis method, called waveform rising and falling edge symmetry (WRaFES) method, is proposed. Based on this WRaFES method, the correlation metrics are provided to detect asymmetric correlation peaks distorted by received signal asymmetry. Then the statistical properties of the proposed methods are analyzed, and a proper deformation detection threshold is calculated. Finally, both simulation results and experimentally measured results of Beidou navigation satellite system (BDS) M1-S B1Cd signal are given, which show the effectiveness and robustness of the proposed thread models. 相似文献
18.
Tropospheric delay gradients from numerical weather prediction models: effects on GPS estimated parameters 总被引：3，自引：1，他引：2
Several numerical weather prediction (NWP) models provide information on the 3D state of the neutral atmosphere which has
enabled GNSS researchers to have improved a priori information of the delay induced in the GNSS signals. However, the quality
of weather models on the one hand and computational difficulties on the other, are motivations to develop an algorithm based
partly on NWP models, while still estimating the remaining residual delay through GNSS processing strategies. An algorithm
has been developed to estimate horizontal delay gradients from Meteorological Service of Canada NWP models. The GNSS software
“Bernese” has also been modified to handle these gradients, as well as zenith delay and mapping functions based on NWP models
in phase and code observation equations. Month-long precise point positioning results show strong correlation between north–south
hydrostatic gradients and latitude differences, with significant but less strong correlation with the height and zenith total
delay parameters. The longitude components were not sensitive to the implementation of gradients. High precision GNSS applications
such as long term geodynamics studies, realization of terrestrial reference frames and climatology and consequential interpretations
may be affected by ignoring the asymmetry of the neutral atmosphere. In addition to estimating the gradients, implementing
a priori information on gradients in the processing software may have an impact on estimated results and consequential interpretations. 相似文献
19.
High accurate global navigation satellite systems (GNSS) require to correct a signal delay caused by the troposphere. The delay can be estimated along with other unknowns or introduced from external models. We assess the impact of the recently developed augmentation tropospheric model on real-time kinematic precise point positioning (PPP). The model is based on numerical weather forecast and thus reflects the actual state of weather conditions. Using the G-Nut/Geb software, we processed GNSS and meteorological data collected during the experiment using a hot-air balloon flying up to an altitude of 2000 m. We studied the impacts of random walk noise setting of zenith total delay (ZTD) on estimated parameters and the mutual correlations, the use of external tropospheric corrections, the use of data from a single or dual GNSS constellation and the use of Kalman filter and backward smoothing processing methods. We observed a significant negative correlation of the estimated rover height and ZTD which depends on constraining ZTD estimates. Such correlation caused a degraded performance of both parameters when estimated simultaneously, in particular for a single GNSS constellation. The impact of ZTD constraining reached up to 50-cm differences in the rover height. Introducing external tropospheric corrections improved the PPP solution regarding: (1) shortened convergence, (2) better overall robustness, particularly, in case of degraded satellite geometry, (3) less adjusted parameters with lower correlations. The numerical weather model-driven PPP resulted in 9–12- and 5–6-cm uncertainties in the rover altitude using the Kalman filter and the backward smoothing, respectively. Compared to standard PPP, it indicates better performance by a factor of 1–2 depending on the availability of GNSS constellations, the troposphere constraining and the processing strategy. 相似文献
20.
Hybrid GPS + GLONASS 总被引：1，自引：0，他引：1
The hybridization of GPS with GLONASS has formed a first stage in GNSS development. We examine the performance of the hybrid
system in the position domain for both code and carrier phase cases. Several major differences exist between GPS and GLONASS;
most significant is GLONASS's signal frequency diversity, which can lead to measurement bias, particularly so when a pair
of receivers are operating at different temperatures. Unless signal frequency diversity is addressed either on-receiver or
at the data processing stage, positioning errors can occur at the centimeter level. We outline the difficulties of combining
observations from the two systems and discuss how these may be overcome. ? 1999 John Wiley & Sons, Inc. 相似文献