Autonomous Integrity Research Articles

Implementation of receiver autonomous integrity algorithm for fault detection of IRNSS

Implementation of receiver autonomous integrity algorithm for fault detection of IRNSS

Implementation and Performance Analysis of Constellation Dynamic Selection in Multi-Constellation RAIM.

Global navigation satellite system (GNSS) plays a crucial role in many fields, such as aerospace and transportation. Integrity is the measure of trust used in GNSS positioning especially in safety-critical applications. Advanced receiver autonomous integrity monitoring (ARAIM), taking full advantage of multi-constellation GNSS, shows huge potential to provide vertical navigation in civil aviation en route navigation and terminal approaches. However, the multi-constellation ARAIM also greatly exposes computational complexity and potential performance hazards in fault modes determination and fault-tolerant positioning. From the perspective of integrity risk control, rather than the pursuit of better positioning accuracy blindly for safety-critical applications, the concept of constellation dynamic selection is proposed and implemented in ARAIM and the performance analysis is discussed in this paper. Only the best two constellations which have the best vertical geometry performance are involved in ARAIM calculation anytime anywhere. The proposed method shows superiority in both integrity availability and computational complexity in both simulations and actual GNSS signal experiments. While the computational complexity is less than 10% of that using four constellations, 100% availability under LPV-200 criteria can be achieved in worldwide coverage experiment. The proposed method also overcomes the shortcomings of ARAIM with two fixed constellations and shows good robustness under depleted scenarios. Furthermore, the statistics results from observation stations proved the applicability and generality of the proposed method under current developing GNSS constellations.

A Study on Autonomous Integrity Monitoring of Multiple Atomic Clocks

Abstract A stable and reliable time keeping system depends on the integrity monitoring of the atomic frequency standard. This paper reports a scheme for autonomous integrity monitoring of multiple atomic clocks, which combines the frequency standard comparison method and the frequency jump detection method. The frequency standard comparison method uses multi-channel synchronous acquisition technology and digital frequency measurement technology to realize the precise measurement of multiple atomic frequency standards. The frequency jump detection method uses adaptive filtering to predict the relative frequency difference and give an accurate and timely alarm for the abnormal of frequency jump. The results show that the noise floor frequency standard comparator is better than 6.5×10−15 s. For a relative frequency deviation of 2.0×10−6 Hz, the probability of anomaly detection is almost 100 %. The system has high frequency measurement resolution and fast alarm of frequency jump, which can meet the real-time requirements of a time keeping system for the integrity monitoring of multiple atomic clocks.

A Slowly Varying Spoofing Algorithm Avoiding Tightly-Coupled GNSS/IMU With Multiple Anti-Spoofing Techniques

Vehicle and airborne navigation users are facing more and more complex signal interference and even spoofing. If vehicles and aircraft do not strengthen their anti-spoofing ability, their navigation performance is bound to be adversely affected. global navigation satellite system (GNSS) spoofing technology has gradually become a preferred interference method for spoofer because of its high concealment and great harm. For spoofer, user terminal increasingly adopts GNSS with inertial measurement unit (IMU): tightly-coupled GNSS/IMU, on this basis, user also configures a variety of anti-spoofing techniques to effectively deal with spoofing. Even if spoofer slowly changes user's positioning, if spoofing strategy is unreasonable, it will lead to the violation of parameter rationality of coupled filter output parameters and spoofing observation, which greatly increases the difficulty of spoofing. In view of the above problems, from the perspective of spoofer, in order to effectively counter the non cooperative target of assembling tightly-coupled GNSS/IMU by using GNSS spoofing, this paper establishes GNSS spoofing mathematical model, and proposes a slowly varying spoofing algorithm to avoid tightly-coupled GNSS/IMU with multiple anti-spoofing techniques based on the analysis of the influence mechanism of spoofing on the positioning of tightly-coupled GNSS/IMU, the algorithm proposes a measurement deviation determination method to avoid a variety of anti-spoofing techniques, which can gradually pull the positioning results of coupled system, and successfully avoid anti-spoofing techniques detection of least squares residual receiver autonomous integrity monitoring (RAIM) and parameter rationality check. The experimental results show that the algorithm can gradually change positioning of tightly-coupled GNSS/IMU within 30 s, and the north, east and down displacements basically achieve the spoofing effect, the errors with the expected offset are −0.5 m, 1.9 m and 12.7 m respectively. At the same time, the detection of the above anti-spoofing techniques is avoided. The mean value of test statistics for tightly-coupled system is reduced by 75.4% and does not exceed the alarm threshold, so as to achieve the purpose of spoofing, the effectiveness and high concealment of the spoofing algorithm are proved.

Performance Analysis of BDS-3 SAIM and Enhancement Research on Autonomous Satellite Ephemeris Monitoring

Integrity is one of the key indicators used to characterize the performance of the global navigation satellite systems (GNSSs) and is closely related to user safety. In order to realize real-time global integrity monitoring, the BeiDou Global Navigation Satellite System (BDS-3) has realized the “satellite autonomous integrity monitoring” (SAIM) function in its satellites for the first time. BDS-3 SAIM has the monitoring functions of signal power, pseudo-range, satellite clock frequency and phase, but not the monitoring function of broadcast ephemeris. In this study, the long-term stability and distribution characteristics of BDS-3 SAIM monitoring data were analyzed by using the actual telemetry data for the first time. The results show that the SAIM monitoring data have good long-term stability and basically follow a normal distribution, which meets the design expectations. Meanwhile, in view of the fact that BDS-3 SAIM does not have the ability to independently monitor broadcast ephemerides, which may lead to the over-tolerance of BDS-3 to the probability risk of risks of integrity in the active space environment, a SAIM enhancement design for ephemeris monitoring is proposed, which integrates three relatively independent methods, with the ephemeris extrapolated from the previous cycle, and the ephemeris generated by autonomous orbit determination, inter-satellite link distance measurement data as reference data, respectively. The three methods are analyzed and verified. The results show that each of the three methods has advantages and disadvantages in terms of monitoring accuracy and resource dependence. The integration of the three methods can combine their complementary advantages and can also provide valuable as an important reference for engineering applications.

Vertical Protection Level Optimization and Availability Analysis for Advanced RAIM

With the introduction of global navigation satellite systems (GNSSs) in aviation, there has been increased dependency on GNSS position. Multi-constellation GNSS services and equipment will remain a solution for many aircraft positions in safety. Multi-constellation GNSS can improve robustness and navigation performance. Therefore, advanced receiver autonomous integrity monitoring (advanced RAIM or ARAIM) technology is being developed as an augmentation method for GNSS users under multi-constellation. ARAIM can allow increased service level globally and provide vertical guidance during the approach phase for aircrafts. Since the traditional ARAIM algorithm uses the average allocation strategy to allocate integrity and continuity risk, an allocation approach based on the particle swarm optimization (PSO) algorithm is presented in this article. Different allocation strategies for integrity and continuity risk are chosen as different particles, and the weighted sum of vertical protection level corresponding to different fault subsets is selected as the fitness function to optimize the allocation strategy and the corresponding VPL. Based on real GNSS data, the ARAIM algorithm under multi-constellation is analyzed. The experimental results demonstrate that the integrity and continuity risk allocation method based on the proposed algorithm optimizes the VPL and improves the global availability of ARAIM under multi-constellation.

Progress of global ARAIM availability of BDS-2/BDS-3 with TGD and ISB

Advanced RAIM (ARAIM) is an extension of Receiver Autonomous Integrity Monitoring (RAIM) by enhancing the vertical navigation capabilities, so it can be applied to higher-level precision applications. But when the observation data of the second-generation BDS (BDS-2) and the third-generation BDS (BDS-3) are combined to evaluate the ARAIM availability, the evaluation be affected by the Timing Group Delay (TGD) of different satellite signals and the Inter-system Bias (ISB) between BDS-2 and BDS-3, which is ignored by the existing literature. Therefore, in this article, we deduced the mathematical model of ARAIM and the calculation formula of Vertical Protection Level (VPL) by considering the combined influence of TGD and ISB. We used the BDS observation data and ephemeris files of 374 International GNSS Service (IGS) stations around world on July 29, 2021 to calculate the VPL of these stations and evaluate the global ARAIM availability. The results show that the number of visible BDS satellites is 8.033 and the Geometric Dilution of Precision (GDOP) is 1.721, which can meet the basic needs of global ARAIM calculations. Furthermore, when considering the combined influence of TGD and ISB, the evaluation of ARAIM availability by Multiple Hypothesis Solution Separation (MHSS) is significantly better than that without considering the combined TGD and ISB influence or their individual influence. The average VPL values at these IGS stations in four cases are 124.925 m, 13.882 m, 32.610 m and 9.962 m, and the corresponding ARAIM availability percentages are 90.839%, 95.241%, 96.751% and 99.660%, respectively. Finally, the minimum coverage of ARAIM availability based on BDS can reach 90.839%, which can meet the aviation demand for ARAIM availability in most regions and times.

Local government’s response to dissatisfaction with centralized policies: the “do-it-yourself” approach

The literature on intergovernmental relationships discusses the tension between centralization and local autonomy. However, few studies question local authorities’ response when dissatisfied with central government policies. Using Hirschman's model of exit, voice and loyalty, we explore local government's response to such dissatisfaction. Specifically, we suggest that local authorities may adopt a “do-it-yourself” approach, unilaterally engaging in semi-legal strategies to improve outcomes. This solves immediate local organizational problems, without waiting for approval. Using the Israeli case, we show how a pervasive culture of “do-it-yourself” affects local governments’ responses. We also discuss implications for the relationship between the two bodies. Points for practitioners Our findings shed light on local–central government relations, emphasizing the do-it-yourself approach. While this approach could strengthen political participation, increasing local government's involvement in public policy, it also enables local players to use semi-legal behaviors. Central government decision-makers might prevent these behaviors, strengthening administrative institutions’ enforce, regulatory enforcement and enhancing local autonomous political culture, transparency and integrity. By contrast, continuing to maintain weak formal institutions encourages the appearance of strong informal institutions.

Design of GNSS Receiver Autonomous Integrity Monitoring Platform under Ionospheric Scintillation

Abstract How to evaluate the impact of ionospheric scintillation on the availability of RAIM technology is a key problem to be solved in the field of global satellite navigation system (GNSS) security applications. Based on the relationship between ionospheric scintillation and satellite navigation signal parameters, a scheme of RAIM technology monitoring platform for satellite navigation receiver under ionospheric scintillation is proposed. Firstly, the phase screen model is used to simulate the GNSS satellite navigation signal affected by ionospheric scintillation. Then, the key module of GNSS receiver autonomous integrity monitoring platform under ionospheric scintillation is designed. Simulation results show that the designed platform can effectively simulate satellite navigation signals under ionospheric scintillation and test the effectiveness of various RAIM technology.

Development and evaluation of a generalized model of RAIM availability for single-, dual- and multi-satellite faults

Receiver autonomous integrity monitoring (RAIM) fault monitoring and identification requires first to judge the geometric distribution of currently visible satellites based on performance indicators and to determine whether it is suitable for integrity monitoring, that is, to judge the availability of the RAIM algorithm. With the rapid development of the global navigation satellite system (GNSS), the possibility of dual-satellite faults and multiple-satellite faults in GNSS navigation and positioning has greatly increased. The existing literature mainly focuses on RAIM availability evaluation for single-satellite fault or dual-satellite faults, ignoring the occurrence possibility of multiple-satellite faults, and thus there is no unified RAIM availability evaluation model. To this end, we use the characters of the quadratic matrix to derive a generalized model of RAIM availability evaluation, and the model is suitable for situations of single-, dual- and multi-satellite faults. Based on the observation data of Beidou Navigation Satellite System (BDS) from 332 International GNSS Service (IGS) stations distributed globally on 24 March 2021 and the global ephemeris file, the global RAIM availability of BDS is evaluated. The results show that the generalized model of RAIM availability evaluation has a rigorous derivation process, strong applicability and easy implementation. When the cutoff elevation angle is greater than 5°, the average number of BDS visible satellites at 332 IGS stations worldwide is 12.289 and the average geometry dilution of precision value is 8.090. This can fully meet RAIM availability evaluation and integrity monitoring requirements at most IGS stations and regions. The RAIM availability of triple-satellite faults is lower than that of dual-satellite faults, and the RAIM availability of dual-satellite faults is lower than that of single-satellite fault. For the three different faults, the RAIM availability cannot fully satisfy the four stages in aviation all over the world. Among them, the RAIM availability is highest in the en-route (oceanic/continental low density) stage for all three types of faults, which is 93.146%, 74.848%, and 67.576%, respectively, while the non-precision approach stage has the lowest RAIM availability, which is 78.193%, 13.636%, 3.333% for the three types of faults, respectively.

The omnipresence of autonomic modulation in health and disease.

The Autonomic Nervous System (ANS) is a critical part of the homeostatic machinery with both central and peripheral components. However, little is known about the integration of these components and their joint role in the maintenance of health and in allostatic derailments leading to somatic and/or neuropsychiatric (co)morbidity. Based on a comprehensive literature search on the ANS neuroanatomy we dissect the complex integration of the ANS: (1) First we summarize Stress and Homeostatic Equilibrium - elucidating the responsivity of the ANS to stressors; (2) Second we describe the overall process of how the ANS is involved in Adaptation and Maladaptation to Stress; (3) In the third section the ANS is hierarchically partitioned into the peripheral/spinal, brainstem, subcortical and cortical components of the nervous system. We utilize this anatomical basis to define a model of autonomic integration. (4) Finally, we deploy the model to describe human ANS involvement in (a) Hypofunctional and (b) Hyperfunctional states providing examples in the healthy state and in clinical conditions.

지방정부의 성과추적평가 프레임 구성과 효과성 검증

This paper measured the efficiency of autonomous integration Chang-won city and local government in Gyeong-nam using the DEA-CCR and BCC indices. As input variables for performance measurement, the number of civil servants, appropriation budget, and area under jurisdiction were used. Output variables include local tax collection, sewage and water supply rates, road pavement rates, national basic livelihood recipients, garbage disposal, and civil complaint solving performance. The research results are presented as follows. First, the efficiency of integrated Changwon City by competency decreased overall after the integration. Second, the productivity of Jinhae and Masan after integration is low. This means that Changwon's integration performance is high, but other cities are not. Third, compared to other regions of Gyeongnam, Changwon City's capabilities are excellent. But, relative to the size of the city, autonomous capacity is inefficient by 8.1%. Autonomy capacity is highly dependent on the amount of local tax revenue. Efforts are needed to increase tax revenue in the future. In the end, in order for the integrated Changwon City to show the integrated effect, it is necessary to make efforts to strengthen its capabilities.

Code phase tracking error based autonomous integrity monitoring for GNSS/INS ultra-tightly integrated system

The ultra-tight integration of GNSS (Global Navigation Satellite System) and INS (Inertial Navigation System) may suffer from faults in GNSS, INS and integration filter. Both the faults occurred at the current epoch and at previous epochs affect the position solution deviation of ultra-tight integration at the current epoch, and the effect is reflected in GNSS code phase tracking errors. In this paper, a new autonomous integrity monitoring algorithm is proposed for the federated GNSS/INS ultra-tight integrations in which the code phases of local GNSS signal replicas for GNSS signal tracking are completely derived from the integrated navigation solution. In the proposed algorithm, GNSS code phase tracking errors are employed to construct the test statistics for fault detection through a MHSS (Multiple Hypothesis Solution Separation) method improved from the classical MHSS used in ARAIM (Advanced Receiver Autonomous Integrity Monitoring). With the improved MHSS, the proposed algorithm can account for GNSS nominal biases, multiple GNSS faults and the faults in INS and integration filter. The protection levels under multiple hypothesis are also derived. A semi-physical simulation of the federated ultra-tight integration of GPS (Global Positioning System) and INS in airplane approaching case and a vehicle-based field test of the federated ultra-tight integration of GPS, Galileo and INS are conducted to validate the proposed algorithm. The experiments show that the designed fault detection can effectively detect the occurred faults and the derived protection levels can correctly bound the caused position solution error.

BDS-3 Integrity Risk Modeling and Probability Evaluation

Focusing on the global integrity monitoring performance of the BDS-3, the integrity failure model and effect analysis (IFMEA) of the system space segment and the ground control segment were carried out, and the system integrity risk tree model was established according to the IFMEA results. To evaluate the system’s integrity risk probability more reasonably, this paper establishes an abnormal event prediction model with a Bayesian method, based on actual operation data, under a situation in which the BDS-3 just opened service. With statistical analysis results of system anomalies since 27 December 2018—which is the date the BDS-3 began providing basic service—according to the anomaly prediction model, the system’s integrity risk probability under the 95% confidence limit was calculated to be approximately 0.9e-7/h, meeting the design index requirements of 1e-7/h. The analysis results also show that the main risk factors affecting the integrity of BDS-3 are ‘pseudorange measurement anomaly’ and ‘miss-detection of satellite autonomous integrity monitoring’. The results are important references with practical engineering significance for improving the integrity performance of BDS-3.

Performance Evaluation of a Quorum Sensing based Scheme in Multi-Agent Task Development

Robotics is positioned today as a fundamental tool in industrial and commercial development, where machines interact directly with humans. There is a vast variety of tasks that require autonomous, robust, and high-performance systems. Among these tasks can benefit from the autonomous integration of multiple elements, known as multi-agent systems. These schemes have interesting advantages over the single robot solution centered on the high degree of robustness achieved and the lower cost. The control of these multi-agent systems turns out to be of great complexity and is an active field of robotics research. The motion coordination schemes are complex and require a certain level of processing and communication. In this paper, a decentralized coordination scheme for low-cost robot groups based on local interaction is evaluated. The algorithm uses bacterial Quorum Sensing (QS) as a behavioral model, a scheme under which certain actions are triggered by the agents conditioned to the population density in the region they cover. The algorithm is tested in navigation tasks for different conditions of the design parameters. Among the parameters evaluated are environment dependence, system size, and QS threshold. The development times of the tasks were statistically analyzed, and a strong dependence of the environment on the total time required was found (a well-structured and small environment concerning the system improves the performance considerably), as well as the design of the robot in terms of QS threshold and sensors.

Kalman Filter-Based Integrity Monitoring for GNSS and 5G Signals of Opportunity Integrated Navigation

A Kalman filter-based receiver autonomous integrity monitoring algorithm (RAIM) is proposed to exploit sequential measurements from global navigation satellite systems (GNSS) and cellular 5G signals of opportunity (SOPs), to ensure safe vehicular navigation in urban environments. To deal with frequent threats caused by multipath and non-line-of-sight conditions, an innovation-based outlier rejection method is introduced. Next, a fault detection technique based on solution separation test is developed, and the quantification of protection levels is derived. Experimental results of a ground vehicle traveling in an urban environment, while making pseudorange measurements to GPS satellites and cellular 5G towers, are presented to demonstrate the efficacy of the proposed method. Incorporating 5G signals from only 2 towers is shown to reduce the horizontal protection level (HPL) by 0.22 m compared to using only GPS. Moreover, the proposed method is shown to reduce the HPL and vertical protection level (VPL) by 84.42% and 69.63%, respectively, over the snapshot advanced RAIM (ARAIM).

Robust Modeling of GNSS Orbit and Clock Error Dynamics

<h3>Abstract</h3> In this paper, we develop new stochastic orbit and clock error models for positioning, fault detection, and integrity monitoring over time. GPS and Galileo orbit and clock data are evaluated and ranging errors are analyzed and modeled over time. This work is intended for time-sequential safety-critical navigation systems including global navigation satellite systems (GNSSs) integrated with inertial navigation systems (INSs) and Kalman filter implementations of Advanced Receiver Autonomous Integrity Monitoring (ARAIM).

Performance Analyses of a RAIM Algorithm for Kalman Filter with GPS and NavIC Constellations.

This paper evaluates the performance of an integrity monitoring algorithm of global navigation satellite systems (GNSS) for the Kalman filter (KF), termed KF receiver autonomous integrity monitoring (RAIM). The algorithm checks measurement inconsistencies in the range domain and requires Schmidt KF (SKF) as the navigation processor. First, realistic carrier-smoothed pseudorange measurement error models of GNSS are integrated into KF RAIM, overcoming an important limitation of prior work. More precisely, the error covariance matrix for fault detection is modified to capture the temporal variations of individual errors with different time constants. Uncertainties of the model parameters are also taken into account. Performance of the modified KF RAIM is then analyzed with the simulated signals of the global positioning system and navigation with Indian constellation for different phases of aircraft flight. Weighted least squares (WLS) RAIM used for comparison purposes is shown to have lower protection levels. This work, however, is important because KF-based integrity monitors are required to ensure the reliability of advanced navigation methods, such as multi-sensor integration and vector receivers. A key finding of the performance analyses is as follows. Innovation-based tests with an extended KF navigation processor confuse slow ramp faults with residual measurement errors that the filter estimates, leading to missed detection. RAIM with SKF, on the other hand, can successfully detect such faults. Thus, it offers a promising solution to developing KF integrity monitoring algorithms in the range domain. The modified KF RAIM completes processing in time on a low-end computer. Some salient features are also studied to gain insights into its working principles.

Integrity Risk Under Temporal Correlation for Horizontal ARAIM

Integrity requirements for safety-critical global navigation satellite system applications, such as in civil aviation for the nonprecision approach through precision approach, are defined in a per hour or per approach (i.e., 150s) basis by the International Civil Aviation Organization. This article presents a novel methodology for mapping such operational requirements to the specific risk at an algorithmic level for advanced receiver autonomous integrity monitoring (ARAIM), in particular horizontal ARAIM (H-ARAIM). We thoroughly evaluated the actual risk over time by performing extensive first-order Gauss Markov Process Monte Carlo runs for the propagation of time-correlated position errors and test statistics over one hour exposure time and accounting for multiple events of loss of integrity over the time interval. A comparison of the risk over time and the risk for a single epoch leads to the number of effectively independent samples. The current integrity equation was modified using the number such that a specific risk requirement is allocated to a single sample for the determination of the protection level. This study also examined the impact of the modified risk allocation on the existing fault detection and exclusion algorithm by conducting H-ARAIM availability simulations and by comparing the results based on the newly proposed method with that obtained using the existing single sample-based risk allocation. In our preliminary assessment, little impact on the global availability (availability loss of approximately up to 1%) of the inflated terms of the integrity equation due to the number of valid samples was found.

Vestibular-autonomic interactions: beyond orthostatic dizziness.

This review aims to summarize the current literature describing vestibular-autonomic interactions and to describe their putative role in various disorders' clinical presentations, including orthostatic dizziness and motion sensitivity. The vestibular-autonomic reflexes have long been described as they relate to cardiovascular and respiratory function. Although orthostatic dizziness may be in part related to impaired vestibulo-sympathetic reflex (orthostatic hypotension), there are various conditions that may present similarly. A recent clinical classification aims to improve identification of individuals with hemodynamic orthostatic dizziness so that appropriate recommendations and management can be efficiently addressed. Researchers continue to improve understanding of the underlying vestibular-autonomic reflexes with recent studies noting the insular cortex as a cortical site for vestibular sensation and autonomic integration and modulation. Work has further expanded our understanding of the clinical presentation of abnormal vestibular-autonomic interactions that may occur in various conditions, such as aging, peripheral vestibular hypofunction, traumatic brain injury, and motion sensitivity. The vestibular-autonomic reflexes affect various sympathetic and parasympathetic functions. Understanding these relationships will provide improved identification of underlying etiology and drive improved patient management.