Software Receiver Research Articles

Analysis of Single Frequency GPS Receiver Under Delay and Combining Spoofing Algorithm

Global position system (GPS) has become a satellite based critical international navigation and timing system. Navigation has a significant effect in our daily life. Hence, such a commonly used system is an interesting goal for criminal utilizing. Trusting GPS navigation, need spacious knowledge to inadvertent and intentional interferences. The position deviation in GPS, which is subject to spoofing, is analyzed in this paper. Serious research into spoofing has been carried out in recent years. One of the basic requirements and major challenges in designing anti-spoofing methods and evaluating a successful GPS spoofing countermeasure is collection of actual spoofing data used to verify the proposed protection algorithm. Since actual spoofing data is acquired through an expensive spoofer-receiver device, preparing genuine spoofing data without expensive spoofing devices, including extra software or hardware, can be helpful in the development of anti-spoofing studies. In this paper, after providing a refined assessment of existing approaches, a new practical and low-cost technique is proposed that helps to generate a set of spoofing data only with the employment of software receiver and a set of real GPS measurements. In this way, a new kind of spoofing data is resulted by utilizing delay and mixing procedure. This data will be generated in victim receiver antenna, if a spoofer-receiver device is used in practice. After explanation of the spoofing algorithm, its influence on the GPS receiver is studied in details, and then validation of proposed method is proved by appropriate tests.

CSC Code Discriminator: Theoretical Analysis of Performance

This paper presents the theoretical development and analysis of a novel DLL discriminator robust to multipath errors, called the Combination of Squared Correlators (CSC). The CSC discriminator features a simple implementation based on four (complex) static correlators per channel, without falling into the wide family of patented architectures.In this paper, the theoretical analysis of the properties of the CSC architecture is developed in a well structured context: (i) definition of the discrimination rule; (ii) theoretical analysis in the absence of noise; (iii) theoretical noise tracking jitter analysis; and, (iv) multipath error envelope analysis. In all cases, the CSC results are compared to those of the Strobe discriminator, which is the natural benchmark.The promising performance of the CSC discriminator inserted in a complete software receiver is also proved in a heavy multipath scenario, expressly simulated to stress the code tracking loop robustness. Copyright © 2015 John Wiley & Sons, Ltd.

Improvement of signal synchronization in GPS software receiver

In GPS receivers, navigation bit allocation is performed throughout the process of signal tracking and detection. In the process of signal tracking, the locally generated signal must be synchronized with the received signal. The Costas phase-locked loop (PLL) behavior, which is often used for signal synchronization, is characterized by dominant tracking error sources. The resulting phase tracking errors are significant in the presence of weak signals, i.e. signals with the low signal-to-noise ratio (SNR). In order to improve the signal synchronization and enable signal tracking by the receiver, we here proposed the usage of a non-data-aided (NDA) phase estimator. Based on the practical processing of the GPS signals, it is shown that the applied NDA algorithm is more resistant to sudden changes in frequency (phase) of the input signal than the previously considered phase discriminator in the Costas PLL. Also, we have shown that the solution analyzed here exhibits more stable operation in signal tracking for a low SNR.

Regionally based alarm index to mitigate ionospheric scintillation effects for GNSS receivers

AbstractAn approach to mitigate the effect of ionospheric scintillation on GNSS (Global Navigation Satellite System) users in the European region using TEC (total electron content) at 1 Hz rate is presented. The TEC in the study is derived using raw GPS (Global Positioning System) observations obtained from the EUREF networks. The study also presents derivation of a geographic mesh‐map warning of the expected standard deviation of phase jitter in receiver carrier tracking loops, information which would help to mitigate scintillation effects in GPS software receivers.

Overcoming the challenges of BeiDou receiver implementation.

Global Navigation Satellite System (GNSS)-based positioning is experiencing rapid changes. The existing GPS and the GLONASS systems are being modernized to better serve the current challenging applications under harsh signal conditions. These modernizations include increasing the number of transmission frequencies and changes to the signal components. In addition, the Chinese BeiDou Navigation Satellite system (BDS) and the European Galileo are currently under development for global operation. Therefore, in view of these new upcoming systems the research and development of GNSS receivers has been experiencing a new upsurge. In this article, the authors discuss the main functionalities of a GNSS receiver in view of BDS. While describing the main functionalities of a software-defined BeiDou receiver, the authors also highlight the similarities and differences between the signal characteristics of the BeiDou B1 open service signal and the legacy GPS L1 C/A signal, as in general they both exhibit similar characteristics. In addition, the authors implement a novel acquisition technique for long coherent integration in the presence of NH code modulation in BeiDou D1 signal. Furthermore, a simple phase-preserved coherent integration based acquisition scheme is implemented for BeiDou GEO satellite acquisition. Apart from the above BeiDou-specific implementations, a novel Carrier-to-Noise-density ratio estimation technique is also implemented in the software receiver, which does not necessarily require bit synchronization prior to estimation. Finally, the authors present a BeiDou-only position fix with the implemented software-defined BeiDou receiver considering all three satellite constellations from BDS. In addition, a true multi-GNSS position fix with GPS and BDS systems is also presented while comparing their performances for a static stand-alone code phase-based positioning.

Double Stage NCO-Based Carrier Tracking Loop in GNSS Receivers for City Environmental Applications

A double stage NCO (numerically controlled oscillator)-based tracking loop with a new frequency discriminator is proposed to track the carrier frequency of the GNSS signal in signal degraded environments. The structure can be easily implemented and modified with conventional GNSS receivers, and the new frequency discriminator has absolute linearity in a wide pull in range. The principle and performance of the method are described and analyzed in detail. Simulation and field test with a software receiver show that this method can effectively track a weak signal compared with other presented methods in an open loop.

Optimization Method of Coherent Accumulation Operation Based on SIMD Architecture

With SIMD functional unit as part of a wide range of application acceleration, how to effectively use this architecture to optimize the application to become a hot spot compiler optimization. This paper discusses the SIMD instructions and pipeline optimization methods. After using MMX instructions and pipeline optimization, real-time to achieve a strong guarantee pure software receiver.

Application of SIMD Technology in the Coherent Integration Accumulation Multiplication Optimization

In this paper, the problem of real-time software GPS receiver process faced propose a new SIMD instruction based on coherent integration accumulate operations program optimization methods. After using MMX instructions and pipeline optimization, complete the 1s coherent integration of data needed to calculate the cumulative 0.7s, computation using only 6.5% of the ordinary SISD instructions, real-time to achieve a strong guarantee pure software receiver.

An Optimized Acquisition Algorithm in GPS Software Receiver

An Optimized Acquisition Algorithm in GPS Software Receiver

Applied Technology in "GNSS if Signal Acquisition System" and Software Receiver Design

The paper completed the software and hardware design of GNSS intermediate frequency signal acquisition system under Linux operating system, realized the GNSS software receiver under Linux. Basing on QT C++ graphical user interface application development framework and Qwt plug-in, the software and data graphical display interface was also accomplished. By caching the data of RF module and controlling read and write signals of CY7C68013A through FPGA, the high-speed data transmission function was completed. The test results show that the data transmission rate of this data acquisition system can reach more than 200 Mbps, software receiver satisfies the requirement of positioning accuracy, has good flexibility and higher adaptability, and the algorithm of which was easy to be expanded and upgraded.

Effects of the 2012–2013 solar maximum on GNSS signals in Brazil

To investigate the effects of equatorial ionospheric scintillation on GNSS signal tracking performance during the current solar maximum a research project was established between the Brazilian Institute of Geography and Statistics (IBGE), the University of the State of Rio de Janeiro (UERJ), and the Position, Location and Navigation (PLAN) Group of the Department of Geomatics Engineering, University of Calgary (UofC). This was done using intermediate frequency (IF) data processed with a software receiver and code and carrier phase data obtained using a standard geodetic receiver located at the same site. The main benefit of using a software receiver is flexibility. IF data was collected daily from 8 to 12 p.m. local time (11 p.m. to 3 a.m. UTC) using a dual-frequency front-end at IBGE facilities in Rio de Janeiro, from June 2012 to March 2013, whenever scintillation occurred. Four observation sessions were selected for processing along with another one with no scintillation, for comparison. The front-end antenna was located only 5 m away from a standard receiver antenna of the Brazilian active geodetic network, to allow a comparison of the two solutions under the same conditions. In the observation domain, the software receiver produced no actual cycle slips and only up to 4 % of missing L2 observations, indicating that the state-of-the-art acquisition and tracking algorithms used are resistant to equatorial ionospheric scintillation, whereas for the hardware receiver up to 288 cycle slips were detected and 13 % of L2 observations missing over a 4-h session under strong scintillation. The latter represents an improvement of a factor of 3 over the performance of another hardware receiver used at the same site 10 years ago during the previous solar maximum. In the position domain, Precise Point Positioning solutions using L1 code observations gave very similar results for the software and hardware receivers in all sessions, with the ionosphere being responsible for degrading coordinate accuracies up to a factor of 12. The best positioning accuracies were those given by dual-frequency solutions, at the centimeter to a few decimeters level in kinematic mode.

A Visual Simulation Method for 2-D Complex Situation of Electromagnetic Environment

As the complex situation of electromagnetic environment is difficult to be analyzed and simulated visibly, interface program is developed based on the calculation module of Wireless Insite2.5 software. Equipments such as communication, radar, electronics resists and other radio devices are studied to build accurate theoretic models. Moreover, a method for creating software receivers quickly in MATLAB is proposed and other equipment models are created automatically just based on the parameters of equipments in the same way. Then, situations of time, frequency and energy-domain are calculated successfully with using Wireless Insite2.5. Complex 2-D situation of electromagnetic environment is displayed in the 2-D map by using MATLAB map display technology. At last, Display and query visualization for complex situation of electromagnetic environment is realized by designing a visual data query tool of mouse.

A fully software Global Navigation Satellite System reflectometry (GNSS-R) receiver for soil monitoring

Global Navigation Satellite System reflectometry (GNSS-R) is an emerging technique used for the remote sensing of soil surfaces. In this work, a bistatic radar equation method was implemented for soil moisture remote sensing using GNSS-R. Both direct and reflected GPS signals were collected by a fully software receiver mounted onboard an aircraft. The reflected signal was processed with an open loop approach, obtaining delay-Doppler maps (DDMs) and the corresponding delay waveforms. Signal to noise ratio (SNR) time series were estimated from non-coherently integrated delay waveforms. To take into account variations in system parameters from nominal values, a calibration was performed in regard to signals reflected from a water lake. Finally, a retrieval process to estimate the permittivity of soil surfaces from the evaluated SNR was applied and the results showed good correlation with the status of field flooding.

Oscillator Frequency Offset Impact on Software GPS Receivers and Correction Algorithms

Software-based Global Positioning System (GPS) receivers have been recognized as an effective research platform in recent years. The impact of oscillator frequency offset on hardware receiver and software receiver signal processing is contrasted based on a refined signal model and cross correlation function (CCF) analysis. Several online clock error correction algorithms are presented to produce unbiased measurements and clock error estimates with known and unknown front end frequency plans and with and without signal tracking and navigation solutions for single- and dual-frequency receivers on both static and dynamic platforms. The CCF formulation and the clock correction performance are validated using simulated signals and real single- and dual-frequency GPS data. The raw frequency error measurements with 0.02 s time resolution for an oven controlled crystal oscillator (OCXO) using real GPS signal report an Allan deviation (ADEV) of 1.3E-11 and a standard deviation of 1.56E-11.

Using fuzzy logic control for the robust carrier tracking loop in a Global Positioning System/Inertial Navigation System tightly integrated system

The noise bandwidth is an important parameter on the Global Positioning System (GPS) tracking loop; the larger the bandwidth the better the high dynamic performance, but the thermal noise suppression capability is reduced. In a GPS/Inertial Navigation System (INS) tightly integration system, the GPS receiver’s carrier phase lock loops (PLLs) are aided by the Doppler shift from the INS, which can reduce user most dynamics. So the noise bandwidth can be narrowed to decrease the thermal noise tracking errors. However, due to the inertial sensor errors, the external INS-derived Doppler shift information are not completely accurate, therefore a Doppler-aiding error-induced phase error source must exist. The part of tracking error is derived in this paper. Other error sources are still present, so the bandwidth of PLLs cannot be set arbitrarily. This paper applies one artificial intelligence technique, the fuzzy logic controller (FLC), to calculate the PLL noise bandwidth on-line. Simulation results prove that the proposed FLC-based software receiver does achieve a superior tracking ability over conventional tracking loops in complicated conditions. In addition, the proposed algorithm works in the real-time mode and can be used in many practical applications.

Development of a PC-Based Software Receiver for the Reception of Beidou Navigation Satellite Signals

Beidou is the Global Navigation Satellite System (GNSS) being developed in China, with the aim to provide a global navigation service that is similar to the Global Positioning System (GPS) and Galileo navigation systems. In this paper, it is demonstrated that through the flexibility and re-configurability of a PC-based software receiver in which the baseband operations are realized in terms of software, it is possible to acquire, track, and demodulate Beidou satellite signals even when only a limited amount of information is known. Further, with the Beidou interface control document now available, the proposed PC-based software receiver can be easily adapted to perform navigation functions. This research lays the foundation for the further development of navigation receivers and exploration of multi-GNSS applications.

ソフトウェアGNSS受信機の開発( GPS/GNSS研究会)

ソフトウェアGNSS受信機の開発( GPS/GNSS研究会)

Weak signal acquisition method for GPS software receiver

For high sensitivity and operation efficiency in weak signal acquisition of Global Positioning System(GPS) software receiver,a differential coherent accumulated acquisition algorithm based on Fast Fourier Transform(FFT) was proposed.The limitation of coherent integration time was overcome by block accumulation of demodulated GPS intermediate frequency data.Based on FFT frequency shift characteristics,a Doppler circular frequency search was used to achieve low computation instead of frequency compensation search.The loss in frequency was resolved by different down conversions.Compared to the original incoherent accumulation,Signal-to-Noise Ratio(SNR) was improved by differential coherent accumulation of coherent results.The weak signal in a-39 dB poor SNR environment was successfully acquired in experiments.High sensitivity and operation efficiency of the proposed algorithm were confirmed by the experimental results.

Receiver-channel based adaptive blind equalization approach for GPS dynamic multipath mitigation

Aiming at mitigating multipath effect in dynamic global positioning system (GPS) satellite navigation applications, an approach based on channel blind equalization and real-time recursive least square (RLS) algorithm is proposed, which is an application of the wireless communication channel equalization theory to GPS receiver tracking loops. The blind equalization mechanism builds upon the detection of the correlation distortion due to multipath channels; therefore an increase in the number of correlator channels is required compared with conventional GPS receivers. An adaptive estimator based on the real-time RLS algorithm is designed for dynamic estimation of multipath channel response. Then, the code and carrier phase receiver tracking errors are compensated by removing the estimated multipath components from the correlators’ outputs. To demonstrate the capabilities of the proposed approach, this technique is integrated into a GPS software receiver connected to a navigation satellite signal simulator, thus simulations under controlled dynamic multipath scenarios can be carried out. Simulation results show that in a dynamic and fairly severe multipath environment, the proposed approach achieves simultaneously instantaneous accurate multipath channel estimation and significant multipath tracking errors reduction in both code delay and carrier phase.

Differential coherent algorithm based on fast navigation-bit correction for airborne GNSS-R software receivers

Signals from the Global Navigation Satellite System (GNSS) scatter over the sea surface resulting in relatively low Signal-to-Noise Ratios (SNR). A differential coherent algorithm is given here to improve the SNR and reduce the performance degradation due to the Squaring-Loss and the navigation-bit effect. The algorithm uses fast navigation-bit correction for Delay-Doppler Maps (DDM) in airborne Global Navigation Satellite Signal Reflectometry (GNSS-R) software receivers. The system model is introduced with an analysis of the statistical properties with simulations to support the theoretical analysis. Field experiments with real airborne receivers then demonstrate the effectiveness of this algorithm. Comparisons with test results show that this algorithm offers a significant SNR gain over conventional algorithms.