Position and velocity reliability testing in degraded GPS signal environments

This paper evaluates the potential capacity of Receiver Autonomous Integrity Monitoring (RAIM) algorithms for Global Positioning System (GPS) and GPS Aided GEO Augmented Navigation (GAGAN) to support approach and landing phases of flight with vertical guidance. As the traditional RAIM does not support vertical guidance, Advanced RAIM (ARAIM) with potential to achieve worldwide coverage of vertical guidance, is used. These algorithms have focused on the Horizontal Protection Level (HPL) and Vertical Protection Level (VPL). User position is computed by detecting and excluding faults within the navigation solution and position accuracies are also provided. It is found that using RAIM, Position Dilution of Precision (PDOP) mean was good (1.5674) and Position Error (PE) was estimated to be 9.4042m with Fault Detection and Exclusion (FDE) implementation. While on the other hand, to increase horizontal and vertical accuracies, Advanced RAIM algorithm is implemented using GPS and GAGAN data. In case of GPS, Horizontal Protection Error (HPE) mean is 32.8541m and Vertical Protection Error (VPE) mean is 19.9901m. In case of GAGAN, HPE mean is 2.7190m and VPE mean is 3.3010m, thus achieving 95 percent accuracy requirement.

In this article, the problem of detecting and excluding faulty global navigation satellite systems (GNSSs) measurements at the receiver end is formulated as a parameterized quadratic programming (PQP) problem. Compared to the existing fault detection and exclusion (FDE) methods, which mostly rely on exhaustive search, the PQP method is computationally efficient for finding the outliers even when the number of outliers is moderate or large. In the context of multiconstellation GNSS where the probability of multiple simultaneous faults is increased, the PQP method is ideal for the task of fault exclusion since the computation time does not increase with the number of fault hypotheses. It is noted that this article addresses the computational load due to the exclusion function only. The integrity risk bound and continuity risk bound are of fundamental importance to assess the performance of FDE algorithms for safety-critical applications. With the aim to benefit safety-critical applications, the PQP method is integrated with the integrity risk bound and the continuity risk bound derived for FDE using Chi-squared receiver autonomous integrity monitoring (RAIM). It is emphasized that the integration of the PQP method and the integrity and continuity risk bounds do not make the PQP method a practical integrity monitoring method. This is because the computation of the integrity risk bound is still combinatorial and the resulting integrity risk bound is rather conversative. Instead, the integration allows for the opportunity to refine the PQP method so that it can be considered a practical integrity monitoring method. In particular, improvements to reduce the computational load for the Chi-squared RAIM FDE integrity risk bound calculation can readily be applied to the integrity risk bound calculation for the PQP method. Also, further research on PQP parameter tuning can be pursued to tighten the integrity risk bound.

Currently, global navigation satellite system (GNSS) receivers can provide accurate and reliable positioning service in open-field areas. However, their performance in the downtown areas of cities is still affected by the multipath and none-line-of-sight (NLOS) receptions. This paper proposes a new positioning method using 3D building models and the receiver autonomous integrity monitoring (RAIM) satellite selection method to achieve satisfactory positioning performance in urban area. The 3D building model uses a ray-tracing technique to simulate the line-of-sight (LOS) and NLOS signal travel distance, which is well-known as pseudorange, between the satellite and receiver. The proposed RAIM fault detection and exclusion (FDE) is able to compare the similarity between the raw pseudorange measurement and the simulated pseudorange. The measurement of the satellite will be excluded if the simulated and raw pseudoranges are inconsistent. Because of the assumption of the single reflection in the ray-tracing technique, an inconsistent case indicates it is a double or multiple reflected NLOS signal. According to the experimental results, the RAIM satellite selection technique can reduce by about 8.4% and 36.2% the positioning solutions with large errors (solutions estimated on the wrong side of the road) for the 3D building model method in the middle and deep urban canyon environment, respectively.

The satellite transmits carrier signal to Global Positioning System (GPS) receivers suffered signal degradation in varied environmental conditions, from space through atmosphere to ground, especially due to the effects of multipath fading. In order to investigate the error performance of GPS signal transmission over multipath fading situations, a vector delay-locked tracking loop structure is applied to GPS receiver with the support of the Kalman filtering algorithms in this paper. The vector delay-locked tracking loop system is supported with receiver autonomous integrity monitoring (RAIM) and fault detection and exclusion (FDE) algorithm to prevent signal unlocked situation. Simulations of the satellite signal to GPS receiver over the multipath fading noise are investigated under three channel conditions: the additive Gaussian white noise (AWGN), Rayleigh fading noise, and Rician fading noise. The extended Kalman filter (EKF) algorithm is applied to improve the system performance. Analysis for various combinations of the above mentioned algorithms is studied and compared.

Several layers of defense can be implemented in a Global Navigation Satellite System (GNSS) receiver to improve its performance in the presence of interference. These layers include the use of pre-correlation mitigation techniques, post-correlation quality indicators to screen measurements and Fault Detection and Exclusion (FDE) at the position solution level. This paper provides a characterization of the interaction between these layers of interference mitigation and measurement quality check. Data collected in the presence of increasing power jamming levels have been processed using different interference mitigation techniques, including Robust Interference Mitigation (RIM) and the Adaptive Notch Filter (ANF). A Software Defined Radio (SDR) approach has been adopted and measurements were generated considering five interference mitigation techniques. Position solutions were then computed using the Forward-Backward approach for Receiver Autonomous Integrity Monitoring (RAIM). Signals from GPS, Galileo and Beidou were processed and both single and dual constellation solutions were analysed. The analysis shows that interference mitigation allows the receiver to track a higher number of signals, even in the presence of high jamming levels. This increased measurement availability is then effectively exploited by RAIM techniques that provide reliable solutions. Measurements from several constellation further improve the reliable availability of the position solutions.

The Advanced Receiver Autonomous Integrity Monitoring (ARAIM) provides an Aircraft‐Based Augmentation System function for aircraft Global Navigation Satellite System equipment. Currently, the consideration of temporal correlations of test statistics is an important update to the ARAIM baseline algorithm. However, due to the tight budgets of integrity and continuity, the updated ARAIM Fault Detection and Exclusion (FDE) is not satisfactory in availability coverage. The baseline algorithm is based on equal allocation of integrity and continuity, which causes ARAIM to be susceptible to faults and satellite outages. An availability optimisation of ARAIM FDE based on dynamic budget allocation is proposed, aiming to make full use of the prior knowledge provided by the Integrity Support Message (ISM). The contribution of each solution separation test in the ARAIM FDE to the total continuity and integrity risks is estimated, and the continuity and integrity allocation constraints are obtained. The impacts of faults and satellite outages on availability are analysed, and a predictive Protection Level (PL) for ARAIM FDE is proposed for use as an objective function for optimising risk allocation. Then, a risk allocation method based on the multiplier penalty function method is proposed. The performances of the baseline algorithm and the proposed method under the maximum Number of Effective Samples are simulated. For dual‐constellation H‐ARAIM, the optimised Horizontal PL (HPL) is 40% lower than that of the baseline algorithm on average, and the average number of critical satellites supporting RNP 0.3 is less than 1 worldwide. For the three‐constellation V‐ARIAM, the optimised HPL is 27% lower than that of the baseline algorithm on average, and the optimised Vertical PL (VPL) is 18% lower. The proposed method has high availability coverage and can better respond to the requirements for high‐performance navigation services.

On the enhanced detectability of GPS anomalous behavior with relative entropy

Integrity Monitoring (IM) for navigation systems is critical to ensure the safety of auto-driving vehicles. It refers to accurately raising alarms to a user when navigation positioning errors exceed the performance limitation. Although Receiver Autonomous Integrity Monitoring (RAIM) methods have been widely applied for Global Navigation Satellite System (GNSS) observations via a consistency checking algorithm, the integrity performance for auto-driving would suffer from a large degradation due to the low satellite visibility with signal occlusions and Non-Line-of-Sight (NLOS) receptions in urban environments. To alleviate this problem, the Fifth-generation (5G) communication signals are used as an auxiliary urban navigation source to increase the number of observations, and then an IM method for the integration of GNSS/5G (G5GIM) is proposed to improve the integrity performance. Specifically, the positioning reference signals of the 5G system in urban canyons are modeled to enrich the observations of the vehicle navigation, followed by the Horizontal Protection Level (HPL) estimation method and the fault detection algorithm for the integration of GNSS and 5G observations. Experimental results on the simulation and UrbanNav datasets show that the proposed G5GIM method significantly outperforms the existing GNSS RAIM method in terms of HPL reduction, fault detection rate and positioning accuracy improvement.

Traditional positioning methods, such as conventional Real Time Kinematic (cRTK) rely upon local reference networks to enable users to achieve high-accuracy positioning. The need for such relatively dense networks has significant cost implications. Precise Point Positioning (PPP) on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks, hence providing significant cost benefits especially in remote areas. This paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer ambiguities. Integrity monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method. A new method to detect and exclude GPS base-satellite failures is developed. A base-satellite is a satellite whose measurements are differenced from other satellite’s measurements when using between-satellite-differenced measurements to estimate position. The failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing modes. The results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static cases. In the kinematic processing cases, failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites.

Current cooperative positioning with global navigation satellite system (GNSS) for connected vehicle application mainly uses pseudorange measurements. However, the positioning accuracy offered cannot meet the requirements for lane-level positioning, collision avoidance and future automatic driving, which needs real-time positioning accuracy of better than 0.5 m. Furthermore, there is an apparent lack of research into the integrity issue for these new applications under emerging driverless vehicle applications. In order to overcome those problems, a new extended Kalman filter (EKF) and a multi-failure diagnosis algorithm are developed to process both GNSS pseudorange and carrier phase measurements. We first introduce a new closed-loop EKF with partial ambiguity resolution as feedback to address the low accuracy issue. Then a multi-failure diagnosis algorithm is proposed to improve integrity and reliability. The core of this new algorithm includes using Carrier phase-based Receiver Autonomous Integrity Monitoring method for failure detection, and the double extended w test detectors to identify failure. A cooperative positioning experiment was carried out to validate the proposed method. The results show that the proposed closed-loop EKF can provide highly accurate positioning, and the multi-failure diagnosis method is effective in detecting and identifying failures for both code and carrier phase measurements.

Demand side load shift has re-emerged as an important tool to solve the problems accompanying the restructuring of power systems, such as capacity shortage, transmission congestion, electricity price volatility and possible reduced system reliability. A methodology to determine demand side load shift is developed to enhance reliability and to reduce nodal price volatility of restructured power systems. In restructured power systems, the conventional same for all customers electricity price is replaced by nodal prices. Electricity prices will interact mutually with demands. This interaction is known as demand response. Demand response is modeled using demand-price elasticity matrix which includes self- and cross-elasticities. The demand side load shifts under N-2 random system contingencies are determined using demand-price elasticity. Then the overall stochastic demand side load shift is calculated using the determined demand side load shifts under random contingencies and their probability. Reliability enhancement and nodal price reduction of restructured power systems due to stochastic demand side load shift are investigated using optimal power flow (OPF) and reliability evaluation techniques. A small but comprehensive reliability test system, RBTS, is used to illustrate the concepts, and simulation results show that stochastic demand side load shift is an efficient tool to reduce nodal price volatility and enhance system and nodal reliability of restructured power systems.

When equipment manufacturers conduct reliability enhancement testing, customer process development, and engineering testing, the resource investment needed to support all three efforts can be significant. FSI International operates a unique equipment reliability enhancement program that allows simultaneous process development, reliability and engineering testing. The program groups all three test objectives with the following advantages: 1) Greater operating efficiency gained by multi-tasking a single lab tool; 2) Considerable capital and operating expense savings; and 3) Accelerated learning cycles and quality improvement. The FSI program is based on SEMI E10-92, the Motorola IRONMAN equipment test philosophy, and customer equipment evaluation guidelines. The main principle of the FSI reliability program is continuous 24-hour operation of the tool. Process data is collected at regular intervals and system reliability is tracked continuously. The original program goals were system MTBF/spl ges/1000 hrs. and total system uptime exceeding 99%, while maintaining the tool for engineering and customer application work. The advantages of continuous testing are twofold. First, the equipment design becomes more robust and better able to meet future customer process requirements. Second, a database is created that characterizes the machine on a long-term basis and allows better process predictions to be made. The paper details the testing methodology adopted for this reliability program. It reviews the troubleshooting and corrective action procedure, the status of the program, and summarize the results.

Due to poor signal-strength, multi-path effects, and a lack of adequate visible satellite vehicles (SV), GPS receivers do not work indoors. This work addresses these challenges by using a mechanically steerable, high-gain directional antenna as the front-end of the GPS receiver along with a robust signal processing technique to acquire satellites in indoor environments. Our experiment on a local warehouse shows that, the system is capable of acquiring 5 or more SVs (which is a requirement for instant GPS technique [4]), whereas a Garmin device barely sees 3, and the system is capable of estimating indoor locations with 3--18 m errors when compared to the ground truth.

Increasing redundant paths in transmission grids has always been thought to be a tool to enhance service reliability. However, network equations by intertwining power flows through redundant paths impose more limits on systems with more redundancy. Accordingly, autonomous removing of a few lines may relief capacity limit violations in some contingency events thereby enhancing service reliability. This paper aims to study impacts of manual removing of transmission lines on composite system reliability. For doing so, the existing model is extended to consider optimal transmission switching (OTS) as a remedial action. The model minimizes total damage cost imposed by load curtailments. The extended model is formulated in mixed integer linear programming (MILP) format that can be easily solved via commercial solvers. The model is applied to likely contingencies wherein violations in capacity limits are encountered. Then, the results along with occurrence probability of the contingencies are taken into use to calculate load point and system oriented reliability indices. Simulation results on the modified reliability test system (MRTS) demonstrate great enhancements in service reliability when OTS is realized.

This paper presents a bistatic 60 GHz frequency-modulated continuous-wave (FMCW) radar system for non-contact heart rate monitoring, utilizing high-gain Fabry–Perot cavity (FPC) antennas at both the transmitter and receiver. Each FPC antenna integrates a partially reflective surface (PRS) and a metallic ground plane to form a resonant cavity. Compared to conventional patch arrays of the same aperture, the FPC antenna improves the antenna gain from 4.1 dBi to 8.1 dBi at the transmitter and from 3.9 dBi to 7.8 dBi at the receiver, resulting in an overall link budget enhancement of approximately 7.9 dB. This dual high-gain configuration theoretically increases the maximum detection range by a factor of 2.48. The proposed radar system was implemented and experimentally validated under indoor conditions using both calibration targets and human participants. Active measurement results confirm that the bistatic radar equipped with FPC antennas extends the reliable heart rate detection distance by approximately 2.27 times compared to a conventional system, closely matching the theoretical prediction. These results confirm the practicality and effectiveness of FPC antennas in extending both the range and reliability of millimeter-wave vital sign detection systems.