Satellite Constellation Geometry Research Articles

Detection of GNSS antenna oscillatory motion and multipath conditions via exploitation of multipath-induced SNR variations

The multipath effect is well known as one of the dominant error sources in most high-precision GNSS applications, as its site-dependent and fast-changing nature render it challenging to model and mitigate using differencing techniques. However, in this study, we present a novel approach of using the multipath effect of GNSS signal in the case of oscillatory motion of a GNSS antenna to determine the characteristics of the oscillatory motion by utilizing the signal-to-noise (SNR) ratio measurements of the GNSS signals and without applying the positioning solution or the use of other sensors. The proposed method is based on the hypothesis that for a short time period, while the multipath conditions remain constant and the satellites are approximately at the same position, an oscillation-type motion of the antenna should generate changes in multipath, expressed as oscillatory pattern variations in the SNR measurements of the satellites. This approach can be used to identify the multipath parameters and extract characteristics of the oscillatory motion of the GNSS antenna. The SNR-based modeling of cm-level antenna oscillations was demonstrated in simulated and field experiments. The benefits of this method include immunity to poor satellite constellation geometry, adaptability to changing multipath geometry and fast processing time. This approach could potentially, under conditions, contribute to GNSS reflectometry (GNSS-R) applications, where the oscillatory motion of the GNSS antenna generates the same effect as the satellite motion-induced multipath, limiting simultaneously the observation periods and the amount of data to be processed.

System for the planning of a linear object GNSS measurement campaign implemented in motion and including DTM or DSM

The GNSS measurement campaign of the linear object requires solving the optimisation problem to determine the receiver's movement that ensures the DOP values in the subsequent points of the route are as low as possible for the pre-defined time frame. The aim of this article is to present an original system for the planning of a linear object GNSS measurement campaign implemented in motion and including DTM or DSM. This program is unique to current GNSS measurement planning softwares because the existing solutions enable the analysis of the satellite constellation geometry exclusively for particular coordinates and at a given time, without taking into account the terrain model and its land cover. The results of simulation tests obtained using the proposed system should be considered as reliable because they are similar to the results of real tests carried out during the mobile GNSS measurements on a tram line.

Testing of Software for the Planning of a Linear Object GNSS Measurement Campaign under Simulated Conditions

The precision of a linear object measurement using satellite techniques is determined by the number and the relative position of the visible satellites by the receiver. The status of the visible constellation is described by the Dilution Of Precision (DOP). The obtained geometric coefficient values are dependent on many variables. When determining these values, field obstacles at the receiver location and satellite positions changing with time must be taken into account. Carrying out a series of surveys as part of a linear object Global Navigation Satellite System (GNSS) measurement campaign requires the optimisation problem to be solved. The manner of the inspection vehicle’s movement should be determined in such a way that the surveys are taken only within the pre-defined time frames and that the geometric coefficient values obtained at subsequent points of the route are as low as possible. The purpose of this article is to develop a software for the planning of a linear object GNSS measurement campaign to implemented in motion and taking into account the terrain model and its coverage. Additionally, it was determined how much the developed program improves DOP values on the planned route under simulated conditions. This software has no equivalent elsewhere in the world, as the current solutions for the planning of a GNSS measurement campaign, e.g., Trimble GNSS Planning, GNSS Mission Planning, or GPS Navigation Toolbox, allow the satellite constellation geometry to be analysed exclusively for specific coordinates and at a specific time. Analysis of the obtained simulation test results indicates that the campaign implementation in accordance with the pre-determined schedule significantly improves the quality of the recorded GNSS data. This is particularly noticeable when determining the position using the Global Positioning System (GPS) and GLObal NAvigation Satellite System (GLONASS) satellite constellations at the same time. During the tests conducted on the road along a three-kilometre-long route (tram loop) in Gdańsk Brzeźno, the average value of the obtained Position Dilution Of Precision (PDOP) decreased by 22.17% thanks to using the software to plan a linear object GNSS measurement campaign. The largest drop in the geometric coefficient values was noted for an area characterised by a very large number of field obstacles (trees with crowns and high buildings). Under these conditions, the PDOP value decreased by approx. 25%. In areas characterised by a small number of field obstacles (single trees in the vicinity of the track, clusters of trees and buildings located along the track), the changes in the PDOP were slightly smaller and amounted to several percent.

Monitoring the response of Severn Suspension Bridge in the United Kingdom using multi‐GNSS measurements

The application of GPS in bridge monitoring aims to determine accurately and precisely the response of the deck and towers of the bridge and estimate the main response characteristics (amplitude and modal frequencies). The main requirement of GPS monitoring is a high level of accuracy and availability of fixed solutions, which ensure the reliable operation of GPS and result in the precise estimation of the bridge's response. However, the derived GPS time series of bridge monitoring can be contaminated by noise, due to the performance of the GPS satellite(s), the geometry of the GPS satellite constellation and the potential obstructions due to the bridge elements, which can even lead to GPS solution of poor accuracy and/or precision and result in reduced efficiency of the performance of the GPS monitoring. This study investigates the potential contribution of other Global Navigation Satellite Systems (GNSS) constellations for a more robust and reliable displacement time series solution, derived from multi-GNSS records. More specifically, a novel method is developed to derive the optimal combination of GNSS records to determine the GNSS displacement time series based on checks of parameters which reflect the geometry of the satellite constellation and the quality of the GNSS satellites signals. The method is applied in monitoring of the Severn Suspension Bridge, in the United Kingdom, and it is revealed the enhancement in the GNSS monitoring performance of the bridge response for specific time intervals for various locations on the bridge's support towers, suspension cables and deck.

Positioning Performance Limits of GNSS Meta-Signals and HO-BOC Signals.

Global Navigation Satellite Systems (GNSS) are the main source of position, navigation, and timing (PNT) information and will be a key player in the next-generation intelligent transportation systems and safety-critical applications, but several limitations need to be overcome to meet the stringent performance requirements. One of the open issues is how to provide precise PNT solutions in harsh propagation environments. Under nominal conditions, the former is typically achieved by exploiting carrier phase information through precise positioning techniques, but these methods are very sensitive to the quality of phase observables. Another option that is gaining interest in the scientific community is the use of large bandwidth signals, which allow obtaining a better baseband resolution, and therefore more precise code-based observables. Two options may be considered: (i) high-order binary offset carrier (HO-BOC) modulations or (ii) the concept of GNSS meta-signals. In this contribution, we assess the time-delay and phase maximum likelihood (ML) estimation performance limits of such signals, together with the performance translation into the position domain, considering single point positioning (SPP) and RTK solutions, being an important missing point in the literature. A comprehensive discussion is provided on the estimators’ behavior, the corresponding ML threshold regions, the impact of good and bad satellite constellation geometries, and final conclusions on the best candidates, which may lead to precise solutions under harsh conditions. It is found that if the receiver is constrained by the receiver bandwidth, the best choices are the L1-M or E6-Public Regulated Service (PRS) signals. If the receiver is able to operate at 60 MHz, it is recommended to exploit the full-bandwidth Galileo E5 signal. In terms of robustness and performance, if the receiver can operate at 135 MHz, the best choice is to use the GNSS meta-signals E5 + E6 or B2 + B3, which provide the best overall performances regardless of the positioning method used, the satellite constellation geometry, or the propagation conditions.

Estimation Of Global Positioning System Measurement Errors For GAGAN Applications

The Global Positioning System (GPS) has been in use for providing positioning, navigation and timing (PNT) services in many parts of the world. There are several errors that affect the positional accuracy of GPS. Prominent among them are ephemeris errors, satellite and receiver clock errors, multipath errors, signal propagation errors such as ionospheric delay, tropospheric delay, and instrumental biases of the satellite and receiver. In this paper, prominent estimation techniques to characterize various GPS measurement errors are reviewed. The GPS data in the Receiver INdependent EXchange (RINEX) format obtained from a Dual frequency GPS receiver is used in this analysis. Among all the errors, ionospheric delay is found to be the most dominant. However, these delay measurements are affected by the satellite and receiver instrumental biases. The instrumental biases exist as the signals at the two GPS frequencies experience different delays inside the satellite and receiver hardware. For estimation of the instrumental biases Extended Kalman filter(EKF) technique is adopted. The user equivalent range error (UERE) obtained due to all the error sources is of the order of few metres. After accounting for various errors, the estimation accuracy is significantly improved.The positional accuracy of the GPS Aided GEO Augmented Navigation (GAGAN) system is basically dependent on ranging errors and the satellite constellation geometry(1). The lineof-sight ionospheric measurements derived from the Global Positioning System (GPS) observables are corrupted by the instrumental biases present in both the GPS satellites and the receivers. The instrumental bias and Total Electron Content (TEC) results (Hyderabad GAGAN station (78.47°E, 17.45°N)) obtained using theExtended Kalman filter technique are presented in this paper. In this work the main focus is towards development of an improved error free approach for aircraft navigation. The existing navigation solutions are based on iterative algorithms and require an initial estimate of the receiver position for computing the navigation solution which is not possible in all conditions. Accurate, reliable and cost effective navigation solution algorithms that suit the Indian geographic area and area of application are proposed in this work. A non-iterative point solution approach algorithm computes the navigation solution based on the available satellite positions and pseudorange measurements(3). The improvement in GPS system has given a feasibility of automated operation of satellite based augmenting system in aircraft navigation can augment GAGAN and improves the positional accuracy of the user. In this paper a communication approach , high, accurate processing using EKF scheme is proposed for GPS aided geo augmented navigation (GAGAN) application. The effectiveness of the proposed approach for higher performance is evaluated under variable conditions.

A Study on GDOP for Vector-Based Tracking Loop GPS/INS Receiver

Geometric Dilution of Precision (GDOP) value will become larger when the number of visible satellites is less than four or the geometry of satellite constellation is poor, a GDOP Chimney Peak phenomenon is also easy to emerge [, the positioning accuracy of GPS receiver will be affected seriously. A vector-based tracking loop GPS/INS receiver design method is proposed in this paper. The current position of receiver is given by INS, Line-of-Sight (LOS) unit vectors between receiver and satellites will be built, which are transmitted into vector tracking loop, the relationship between LOS and GDOP is introduced in detail. Pseudorange and pseudorange-rate are used as measurements to design navigation filter. The simulation results demonstrate that proposed vector tracking method can avoid GDOP Chimney Peak phenomenon, position Root Mean Square error is less than 10 meters.