Cross-talk statistics and impact in interferometric GNSS-R

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a statistical analysis of the crosstalk phenomenon in interferometric Global Navigation Satellite Systems Reflectometry (iGNSS-R). Crosstalk occurs when the Delay-Doppler Map (DDM) of a tracked satellite overlaps others fromundesired satellites. This study is performed for ground-based and airborne receivers and for a receiver onboard the International Space Station (ISS) such as the upcoming GNSS Reflectometry, Radio Occultation and Scatterometry onboard ISS experiment. Its impact on ocean altimetry retrievals is analyzed for different antenna arrays. Results show that for elevation angles higher than 60 degrees, crosstalk can be almost permanent from ground, up to 61% from airborne receivers at 2-km height, and up to similar to 10% at the ISS. Crosstalk can only be mitigated using highly directive antennas with narrow beamwidths. Crosstalk impact using a seven-element hexagonal array still induces large errors on ground, but reduces to centimeter level on airborne receivers, and is negligible from the ISS.Peer ReviewedPostprint (author's final draft

SNR degradation in GNSS-R measurements under the effects of radio-frequency interference

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Radio-frequency interference (RFI) is a serious threat for systems working with low power signals such as those coming from the global navigation satellite systems (GNSS). The spectral separation coefficient (SSC) is the standard figure of merit to evaluate the signal-to-noise ratio (SNR) degradation due to the RFI. However, an in-depth assessment in the field of GNSS-Reflectometry (GNSS-R) has not been performed yet, and particularly, about which is the influence of the RFI on the so-called delay-Doppler map (DDM). This paper develops a model that evaluates the contribution of intra-/inter-GNSS and external RFI effects to the degradation of the SNR in the DDM for both conventional and interferometric GNSS-R techniques. Moreover, a generalized SSC is defined to account for the effects of nonstationary RFI signals. The results show that highly directive antennas are necessary to avoid interference from other GNSS satellites, whereas mitigation techniques are essential to keep GNSS-R instruments working under external RFI degradation.Peer ReviewedPostprint (author's final draft

FLAMINGO – Fulfilling enhanced location accuracy in the mass-market through initial GalileO services

This paper discusses FLAMINGO, an initiative that will provide a high accuracy positioning service to be used by mass market applications. The status and future for the initiative are discussed, the required accuracies and other location parameters are described, and the target applications are identified. Finally, the currently achieved accuracies from today’s Smartphones are assessed and presented. FLAMINGO (Fulfilling enhanced Location Accuracy in the Mass-market through Initial GalileO services), part funded through the European GNSS Agency, is a collaborative venture comprising NSL (as lead organization), Telespazio France, University of Nottingham, Rokubun, Thales Alenia Space France, VVA, BQ, ECLEXYS and Blue Dot Solutions. The initiative is developing the infrastructure, solutions and services to enable the use of accurate and precise GNSS within the mass-market, thereby operating predominantly in an urban environment. Whilst mass-market receivers are yet to achieve accuracies below one metre for standard positioning, the introduction of Android raw GNSS measurements and the Broadcom dual frequency chipset (BCM47755), has presented the devices such an opportunity. FLAMINGO will enable and demonstrate the future of high accuracy positioning and navigation information on mass-market devices such as smartphones and Internet of Things (IoT) devices by producing a service delivering accuracies of 50cm (at 95%) and better, employing multi-constellation, PPP and RTK mechanisms, power consumption optimisation techniques. Whereas the Galileo High Accuracy Service targets 10cm precision within professional markets, FLAMINGO targets 30-50cm precision in the mass-market consumer markets. By targeting accuracies of a few decimetres, a range of improved and new applications in diverse market sectors are introduced. These sectors include, but are not limited to, mapping and GIS, autonomous vehicles, AR environments, mobile-location based gaming and people tracking. To obtain such high accuracies with mass market devices, FLAMINGO must overcome several challenges which are technical, operational and environmental. This includes the hardware capabilities of most mass-market devices, where components such as antennas and processors are prioritised for other purposes. We demonstrate that, despite these challenges, FLAMINGO has the potential to meet the accuracy required. Tests with the current Smartphones that provide access to multi-constellation raw measurements (the dual frequency Xiaomi Mi 8 and single frequency Samsung S8 and Huawei P10) demonstrate significant improvements to the PVT solution when processing using both RTK and PPP techniques

Neumann-Hoffman Code Evasion and Stripping Method for BeiDou Software-defined Receiver

© 2016 The Royal Institute of Navigation. The acquisition and tracking strategies of the BeiDou navigation satellite signals are affected by the modulation of Neumann-Hoffman code (NH code), which increases the complexity of receiver baseband signal processing. Based on the analysis of probability statistics of the NH code, a special sequence of incoming signals is proposed to evade the bit transitions caused by the NH code, and an NH Code Evasion and Stripping method (NCES) based on the NH-pre-modulated code is proposed. The NCES can be applied in both 20-bit NH code and 10-bit NH code. The fine acquisition eliminates the impact of NH code on the traditional tracking loop. These methods were verified with a BeiDou PC-based software-defined receiver using the actual sampled signals. Compared with other acquisition schemes which try to determine or ignore the NH code phase, the NCES needs fewer incoming signals and the actual runtime is greatly reduced without sacrificing much time to search in the secondary code dimension, and the success rate of acquisition is effectively improved. An extension of Fast Fourier Transform (FFT)-based parallel code-phase search acquisition gives the NCES an advantage in engineering applications

Performance and requirements of GEO SAR systems in the presence of Radio Frequency Interferences

Geosynchronous Synthetic Aperture Radar (GEO SAR) is a possible next generation SAR system, which has the excellent performance of less than one-day revisit and hundreds of kilometres coverage. However, Radio Frequency Interference (RFI) is a serious problem, because the specified primary allocation frequencies are shared by the increasing number of microwave devices. More seriously, as the high orbit of GEO SAR makes the system have a very large imaging swath, the RFI signals all over the illuminated continent will interfere and deteriorate the GEO SAR signal. Aimed at the RFI impact in GEO SAR case, this paper focuses on the performance evaluation and the system design requirement of GEO SAR in the presence of RFI impact. Under the RFI impact, Signal-to-Interference-plus-Noise Ratio (SINR) and the required power are theoretically deduced both for the ground RFI and the bistatic scattering RFI cases. Based on the theoretical analysis, performance evaluations of the GEO SAR design examples in the presence of RFI are conducted. The results show that higher RFI intensity and lower working frequency will make the GEO SAR have a higher power requirement for compensating the RFI impact. Moreover, specular RFI bistatic scattering will give rise to the extremely serious impact on GEO SAR, which needs incredible power requirements for compensations. At last, real RFI signal behaviours and statistical analyses based on the SMOS satellite, Beidou-2 navigation satellite and Sentinel-1 A data have been given in the appendix

Implementation of a Radio Frequency Fingerprint Detector Based on GNSS Signals

Geolocation is one of the most significant manifestations of the current development of information technologies and it is used for multiple applications, such as mobile networks, military systems, or in the stock market. For that reason, it is important to verify the source of this type of signals, as they could be susceptible to being tricked by spoofing attacks, namely fake transmitters. This thesis is based on the development of a GNSS signal type classifier based on radio frequency (RF) fingerprinting methods that will determine if a signal belongs to an authorized transmitter or if it comes from a non-authorized GNSS signal generator/repeater. First, a total of 620 signals have been recorded in lab environments, follows: 40 different scenarios of real GNSS signal (with antennas located on the roof of the university) and 580 scenarios of the generated signal (using a GNSS signal generator). Each of the scenarios contains different types of signals (different GNSS constellations and/or bands, different satellites, etc.). Then, using a MATLAB-based simulator, the recorded signal is read, a certain time-frequency transform is applied (in this case the discrete Wavelet Transform), and an image of the wavelet transform of each sample is saved. These images include the features of the signal's RF fingerprinting. Next, a machine learning algorithm called SVM, also designed in MATLAB, is used. This algorithm classifies two or more different signal classes, and finally evaluate the classification accuracy. We used 80% of the images in each category for training and the remaining 20% for testing. Finally, a confusion matrix is obtained showing the accuracy obtained by the SVM algorithm in the testing phase. The analysis of the results has shown that the SVM classification algorithm can be a very effective model for the identification of GNSS transmitters through the use of fingerprinting features. It has been observed that when the Spectracom scenario is configured with more than one satellite, accuracy is lower compared to being configured with only one. This is because the signal obtained when more than one satellite is configured is more similar to the signal obtained from the antenna in comparison to the single satellite configuration, and for that reason, SVM has more difficulty in classifying it correctly. Another observation is that accuracy is also reduced when more than two categories are classified at the same time compared to a binary classification. Despite this, the accuracy is very high in the scenarios used, with 99.47% being the lowest value obtained and 100% the highest. Therefore, this implementation of RF fingerprinting methods is very promising in the context of determining whether a signal belongs to the actual GNSS satellite constellation or to a signal generator with a high level of accuracy

Passive detection of moving aerial target based on multiple collaborative GPS satellites

Passive localization is an important part of intelligent surveillance in security and emergency applications. Nowadays, Global Navigation Satellite Systems (GNSSs) have been widely deployed. As a result, the satellite signal receiver may receive multiple GPS signals simultaneously, incurring echo signal detection failure. Therefore, in this paper, a passive method leveraging signals from multiple GPS satellites is proposed for moving aerial target detection. In passive detection, the first challenge is the interference caused by multiple GPS signals transmitted upon the same spectrum resources. To address this issue, successive interference cancellation (SIC) is utilized to separate and reconstruct multiple GPS signals on the reference channel. Moreover, on the monitoring channel, direct wave and multi-path interference are eliminated by extensive cancellation algorithm (ECA). After interference from multiple GPS signals is suppressed, the cycle cross ambiguity function (CCAF) of the signal on the monitoring channel is calculated and coordinate transformation method is adopted to map multiple groups of different time delay-Doppler spectrum into the distance−velocity spectrum. The detection statistics are calculated by the superposition of multiple groups of distance-velocity spectrum. Finally, the echo signal is detected based on a properly defined adaptive detection threshold. Simulation results demonstrate the effectiveness of our proposed method. They show that the detection probability of our proposed method can reach 99%, when the echo signal signal-to-noise ratio (SNR) is only −64 dB. Moreover, our proposed method can achieve 5 dB improvement over the detection method using a single GPS satellite

Evaluating the differences and accuracies between GNSS applications using PPP

Global Navigation Satellite Systems (GNSS) are satellite systems with global coverage. There are currently several GNSS systems in operation today including the United States NAVSTAR Global Positioning System, Russian GLONASS, Chinese Beidou and the European Union’s Galileo system. The Galileo and Beidou systems are currently undergoing upgrading in order to achieve more sustainable and comprehensive worldwide exposure, ultimately providing users with a broader option of systems and wider more reliable coverage. In recent years, in addition to the GPS constellation, the ability to utilise extra satellites made available through the GLONASS and Beidou systems has enhanced the capabilities and possible applications of the precise point positioning (PPP) method. Precise Point Positioning has been used for the last decade as a cost-effective alternative to conventional DGPS-Differential GPS with an estimated precision adequate for many applications. PPP requires handling different types of errors using proper models. PPP precision varies with the use of observations from different satellite systems (GPS, GLONASS and mixed GPS/GLONASS/Beidou) and the duration of observations. However, the fundamental differences between GPS, GLONASS, Beidou and Galileo and the lack of a fully tested global tracking network of multi-Global Navigation Satellite Systems necessitate the evaluation of their combined use. More studies are required in order to confirm the reliability and accuracy of the results obtained by the various methods of PPP. This is outside the scope of this paper. This research paper will evaluate and analyse the accuracy and reliability between different GNSS systems using the Precise Point Positioning technique with emphasis on the function and performance of single systems compared with combined GNSS systems. A methodology was designed to ensure accurate and reliable results have been achieved. Solutions generated from identical data will be compared for bias, accuracy and reliability between single standalone GPS and combined GNSS systems. This study focused on the performance of these systems over a twenty four hour observation period, decimated into 1, 2, 6, 12 and 24 hours. The study found that the reliability and performance of GNSS systems over standalone GPS was insignificant over a twenty four hour period. In fact, where satellite availability and constellation are at a premium, standalone GPS systems can produce equivalent quality results compared with combined GNSS. Having said this, the combined GNSS systems achieved quicker convergence times than standalone systems. With limited access and availability to resources, in particular GNSS receivers, the results can be seen as preliminary testing enhancing the knowledge of GNSS users. Nonetheless, this dissertation covers a wide range of topics and field testing providing relevant reliable data on the accuracy, precision and performance of both standalone and combined Global Navigation Satellite Systems

Validation of BeiDou Observations

This study presents validation of BeiDou measurements in un-differenced standalone mode and experimental results of its application for real data. A reparameterized form of the unknowns in a geometry-free observation model was used. Observations from each satellite are independently screened using a local modeling approach. Main advantages include that there is no need for computation of inter-system biases and no satellite navigation information are needed. Validation of the triple-frequency BeiDou data was performed in static and kinematic modes, the former at two continuously operating reference stations in Australia using data that span two consecutive days and the later in a walking mode for three hours. The uses of the validation method parameters for numerical and graphical diagnostics of the multi-frequency BeiDou observations are discussed. The precision of the system’s observations was estimated using an empirical method that utilizes the characteristics of the validation statistics. The capability of the proposed method is demonstrated in detection and identification of artificial errors inserted in the static BeiDou data and when implemented in a single point positioning processing of the kinematic test