This article presents the work conducted in the R-Mode Baltic project, which aims to launch the R-Mode demonstrator in the Baltic Sea area. The article describes the concept of the Automatic Identification System (AIS) infrastructure and VHF Data Exchange System (VDES) signal utilization with respect to their potential role in the future R-Mode System. It also contains the analysis of the distance

We propose the Boerdijk–Coxeter Helix (BC Helix) model geometry as a potential node configuration for human users who are localizing within an unstructured environment. When the localization nodes are placed in Boerdijk–Coxeter Helix geometry, the nodes form a regular pattern such that the user can plant new nodes in his or her direction of travel without compromising coverage area or orientation.

Ionospheric anomalies may cause large differential range errors in Ground-Based Augmentation System (GBAS) users. To mitigate those integrity threats, worst-case ionosphere-induced position errors for potentially usable satellite geometries must be bounded by the GBAS ground facility. This mitigation method requires us to compute the worst-case range error for each satellite affected by a hypothetical

Aiming to improve the position and velocity precision of the INS/GNSS system during GNSS outages, a novel system that combines unscented Kalman filter (UKF) and nonlinear autoregressive neural networks with external inputs (NARX) is proposed. The NARX-based module is utilized to predict the measurement updates of UKF during GNSS outages. A new offline approach for selecting the optimal inputs of NARX

With the increasing number of navigation satellite constellations from multiple service providers, an emerging concept for receiver avionics is being developed which will significantly improve the current, widely available operations based on the classical Receiver Autonomous Integrity Monitoring (RAIM). This emerging concept, called Advanced RAIM (ARAIM), is envisioned to eventually provide a worldwide

This study introduces and verifies a relative navigation technique for two CubeSats in formation flying as part of the CANYVAL-C mission. Because the mission requires precision and robustness subject to restricted computational complexity, the technique employs an Extended Kalman Filter (EKF) and raw GNSS data to achieve relative navigation. The relative navigation technique is composed of two parts:

A Fault Detection and Isolation (FDI) algorithm is developed to protect against Water-Blockage (WB) pitot tube failure in the safety-critical Air Data System (ADS) used on small Unmanned Aircraft Systems (UAS). The algorithm utilizes two identical Synthetic Air Data Systems (SADS) as the basis for state estimation. Each SADS works independently with a pitot tube while sharing an IMU and GNSS receiver

Generally, GNSS-based indoor navigation systems use repeaters or pseudolites. However, these methods are vulnerable to multipath errors and require additional information, including the repeater or pseudolite position. In this study, we propose a novel one-way indoor positioning system using GNSS signal transmitters. Our system uses paired transmitters, each of which broadcasts the same set of satellite

A new global navigation concept is studied that relies on carrier Doppler shift measurements from a large LEO constellation. This system could provide an alternative to pseudorange-based GNSS. The concept uses a high-fidelity model of received carrier Doppler shift. This model is used in a point-solution batch filter that simultaneously estimates eight unknowns: the three position vector components

Reliably assessing the error in an estimated vehicle position is integral for ensuring the vehicle's safety in urban environments. Many existing approaches use GNSS measurements to characterize protection levels (PLs) as probabilistic upper bounds on position error. However, GNSS signals might be reflected or blocked in urban environments, and thus additional sensor modalities need to be considered

In this paper, we present an algorithmic framework for signal-geometry-based approaches of GNSS spoofing detection. We formulate a simple vs. simple hypothesis test independent of nuisance parameters that results in significantly reduced missed detection probability compared to prior approaches. It is highly tractable such that it can be computed online by the receiver. We employ a hypothesis iteration

Prior work established a model for uncertain Gauss-Markov (GM) noise that is guaranteed to produce a Kalman filter (KF) covariance matrix that overbounds the estimate error distribution. The derivation was conducted for the continuous-time KF when the GM time constants are only known to reside within specified intervals. This paper first provides a more accessible derivation of the continuous-time

The vulnerability of Positioning, Navigation, and Timing (PNT) services derived from Global Navigation Satellite Systems (GNSS) makes having a resilient and accurate Alternative PNT (APNT) based on high-power terrestrial radio sources necessary. The L-band is very crowded spectral real estate with GNSS, Distance Measuring Equipment (DME) and Air Traffic Control Beacon System (ATCRBS) signals occupying

Factor graph optimization (FGO) recently has attracted attention as an alternative to the extended Kalman filter (EKF) for GNSS-INS integration. This study evaluates both loosely and tightly coupled integrations of GNSS code pseudorange and INS measurements for real-time positioning, using both conventional EKF and FGO with a dataset collected in an urban canyon in Hong Kong. The FGO strength is analyzed

This study proposes three novel integrity monitoring algorithms based on Bayesian Receiver Autonomous Integrity Monitoring (BRAIM). Two problems of integrity monitoring for land-based applications for GNSS challenging environments are explored: requirements for sufficient measurement redundancy and the presence of large biases. The need for measurement redundancy was mitigated by using BRAIM. This

Extensive ionospheric studies were conducted to support the initial phase of system design approval for the existing SLS-4000 GBAS installed at Antonio Carlos Jobim International Airport (formerly Galeão International Airport) (GIG) in Rio de Janeiro, Brazil. This paper focuses on determining the broadcast value of the standard deviation of vertical ionospheric gradients (or ) that is required to bound

China is developing its BeiDou Satellite-Based Augmentation System (BDSBAS) in accordance with international standards, and it has provided initial Single Frequency (SF) and Dual-Frequency Multi-Constellation (DFMC) services since July 2020. This paper gives a comprehensive introduction to BDSBAS from the aspects of its general design, system time datum, coordinate reference system and signal characteristics

The availability of orbit information with high precision and low latency is a key requirement for many Earth-observation missions, predominantly in the field of radio occultation. Traditionally, precise orbit determination solutions of low-Earth orbit (LEO) satellites are obtained offline on ground after downloading GNSS measurements and auxiliary spacecraft data to the processing center. The latency

Precise point positioning (PPP) uses precise satellite orbits, clock corrections and biases derived from a global network of reference stations to enable accurate positioning worldwide. Natural Resources Canada's Canadian Spatial Reference System (CSRS) PPP is a free Web service offering automated PPP processing. A critical factor limiting the adoption of PPP in many applications is the convergence

Filtering-based indoor positioning using ultra wideband (UWB) requires known velocity to predict prior position in the prediction stage. Velocity can be obtained from an inertial measurement unit (IMU) sensor or the posterior state vector at the previous time stamp. Both methods have limitations when using them in practice. This paper proposes two novel velocity determination approaches, which use

The GNSS performance is significantly degraded in urban canyons because of the signal interferences caused by buildings. Besides the multipath and non-line-of-sight (NLOS) receptions, the diffraction effect frequently occurs in urban canyons, which will severely attenuate the signal strength when the satellite line-of-sight (LOS) transmitting path is close to the building edge. It is essential to evaluate

A navigation concept is being developed that relies on passive one-way ranging using pseudorange and beat carrier-phase measurements of high-frequency (HF) beacon signals that travel along non-line-of-sight paths via ionosphere refraction. This concept is being developed as an alternative to GNSS positioning services. If the set of signals that reaches a user receiver has sufficient geometric diversity

Welcome to the Spring 2021 issue of NAVIGATION. We present the latest research articles (papers) that have successfully completed the thorough review process managed by our associate editors and their expert reviewers. The topics span the broad range of PNT research from GNSS interference mitigation to better positioning of low Earth orbit satellites. And we feature an article on ION's GNSS software‐defined

The past several years have seen a proliferation of software‐defined radio (SDR) data collection systems and processing platforms designed for or applicable to satellite navigation (satnav) applications. These systems necessarily produce datasets in a wide range of different formats. To correctly interpret this SDR data, essential information such as the packed sample format and sampling rate is needed

This paper builds on the machine learning research to propose two new algorithms based on optimizing the Adaptive Neuro Fuzzy Inference System (ANFIS) with a dual‐polarization antenna to predict pseudorange errors by considering multiple variables including the right‐hand circular polarized (RHCP) signal strength, signal strength difference between the left‐hand circular polarized (LHCP) and RHCP outputs

Due to the small size of Micro Aerial Vehicles, they are well suited for various indoor applications, especially search/rescue operations. Most of these operations are performed in unknown 3D environments. Real‐time map construction and vehicle's localization are essential tasks. Various approaches provide solutions for 3D‐map representation. However, these approaches require expensive embedded systems

In the Global Navigation Satellite System (GNSS) L5/E5a interference environment, RTCA DO‐292 proposes a model to compute the degradation due to the presence of interference signals, such as Distance Measuring Equipment/TACtical Air Navigation (DME/TACAN), Joint Tactical Information Distribution System/Multifunctional Information Distribution System (JTIDS/MIDS), etc., and due to the application of

The benefits of GNSS have created dependencies on navigation in modern day aviation systems. Many of these systems operate with no backup navigation source. This makes the capabilities supported by precise navigation vulnerable. This paper investigates a contemporary approach to terrain‐referenced navigation (TRN), used to preserve an aircraft's navigation solution during periods of GNSS denial. Traditionally

Large ionospheric gradients acting between a Ground Based Augmentation System (GBAS) reference station and an aircraft on approach could lead to hazardous position errors if undetected. Current GBAS stations provide solutions against this threat that rely on the use of “worst‐case” conservative threat models, which could limit the availability of the system.

The full deployment of China's BeiDou navigation satellite system (BDS) was finalized in June 2020. To support safety‐critical applications, the system must provide assured signal‐in‐space (SIS) performance. As one of the key steps forward for BDS, this paper characterizes the SIS range errors (SISREs) for both the regional (BDS‐2) and the global (BDS‐3) systems from the integrity perspective. Following

This paper describes a novel approach for reducing the kinematic position and time errors on a GPS receiver in low Earth orbit. For dual‐frequency GPS receivers, point solution errors are dominated by signal‐in‐space ranging errors, which introduce sharp discontinuities in the position and time estimates when GPS visibility changes. These discontinuities may be calculated and removed, greatly reducing

GNSS positioning relies on orbit and clock information, which is predicted on the ground and transmitted by the individual satellites as part of their broadcast navigation message. For an increased autonomy of either the space or user segment, the capability to predict a GNSS satellite orbit over extended periods of up to two weeks is studied. A tailored force model for numerical orbit propagation

The advent of assisted GPS/GNSS can reduce the time to first fix (TTFF) dramatically and still provide sufficient positioning accuracy. However, many applications utilize GNSS for timing and assisted GPS/GNSS does not always provide the accurate nanosecond synchronization. Accurate timing is challenging for assisted GNSS due to the lack of diversity in the solution over short time periods. The relatively

Theoretical results conclude that Direct Position Estimation (DPE)‐based Global Navigation Satellite System (GNSS) receivers can achieve more robust localization than their conventional two‐step counterparts. However, compared to conventional approaches, there is a much smaller body of work for DPE, and DPE receiver implementations are highly experimental. This work surveys DPE techniques from the

Signal generation in the GPS III satellites employs weighted voting to combine the baseband P(Y) signal with both components of the baseband L1C signal on the in‐phase part of the L1 carrier. Weighted voting employs majority voting with pseudorandom time multiplexing of pure signals, producing a constant‐envelope real‐valued combination of the three biphase inputs with different useful received powers

Long term evolution (LTE) signals have the potential for use in positioning, especially in challenging environments. The time‐of‐arrival (TOA)‐based technique supported by LTE is attractive due to its high positioning accuracy. However, it is vulnerable to multipath propagation effects in typical LTE channels. This paper will summarize several existing advanced TOA estimators for LTE signals, i.e.

Global navigation satellite system (GNSS) signals are vulnerable to radio frequency interference (RFI) and spoofing. RFI detection has become trivial with many detection algorithms available and built into GNSS receivers; this is not the case with spoofing. GNSS spoofing can involve generating false GNSS signals with one or more altered components of GNSS satellite transmissions: radio frequency (RF)

Marine navigation systems have very accurate sensors, such as 0.01deg/hr gyro drift stability and 0.1mg/year accelerometer bias stability. Common calibration methods and equipment do not meet the accuracy required. In this paper, a systematic method for calibration of an inertial measurement unit (IMU) for marine applications is proposed which is not based on the accuracy of the calibration turn table

The Extended Kalman Filter (EKF) is currently a dominant sensor fusion method for mobile devices, robotics, and autonomous vehicles. Its performance heavily depends on the selection of EKF parameters. Therefore, the optimal selection of parameters is a critical factor in EKF design and use. In this paper, a methodical and efficient method of EKF parameter tuning is presented. The tuning framework uses

The future of deep space exploration depends upon technological advancement towards improving spacecraft's autonomy and versatility. This study aims to examine the feasibility of autonomous orbit determination using advanced accelerometer measurements. The objective of this research is to ascertain specific sensor requirements to meet pre‐defined mission navigation error budgets. Traditional inertial

High spatio‐temporal variability of atmospheric water vapor affects microwave signals of Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR). A better knowledge of the distribution of water vapor improves both GNSS‐ and InSAR‐derived data products. In this work, we present a collocation framework to combine and retrieve zenith and (relative) slant tropospheric

Precise measurements of signal phase are essential for Global Navigation Satellite System (GNSS) position estimates. However, propagation through the earth's ionosphere imposes frequency‐dependent phase errors. The frequency dependence is exploited to correct phase errors proportional to total electron content (TEC) divided by frequency. Scintillation causes additional stochastic errors, which can

Precise point positioning (PPP) service is of great significance for BDS. The design and implementation of the service are presented. The PPP‐B2b signal of the service is constructed, which is efficient multiplexed with other signal components, and achieves compatibility between two service phases. A customized message format that can augment all visible satellites of four core constellations in mainland

Modern Global Navigation Satellite System (GNSS) receivers have to withstand significant levels of interference in order to operate under harsh conditions, such as in the presence of jamming and of other Radio Frequency (RF) threats. A possibility is to implement pre‐correlation interference mitigation techniques that operate directly on the samples provided by the receiver front‐end. This paper provides

This paper presents a new modified Single Block Zero‐Padding (mSBZP) Partial Correlation Method (PCM) Parallel Code Search (PCS) algorithm for effective acquisition of weak GNSS tiered signal using coherent processing of its secondary code (SC) component. Two problems are discussed: acquisition of primary codes with a longer period using FFT blocks of limited length, and the utilization of PCS in the

Pedestrian navigation with handheld sensors is still particularly complex. Pedestrian Dead Reckoning method is generally used, but the estimation of the walking direction remains problematic because the device's pointing direction does not always correspond to the walking direction. To overcome this difficulty, it is possible to use gait modeling based approaches. But, these methods suffer from sporadic

This paper develops novel covariance and square‐root factor formulations of a consider‐neglect Kalman filter for navigation applications. The proposed filter partitions system parameters into three distinct categories: those to be estimated by the filter, those whose contribution to the system are considered without being explicitly estimated, and those with sufficiently low effect on the system such

All‐source navigation has become increasingly relevant over the past decade with the development of viable alternative sensor technologies. However, as the number and type of sensors informing a system increases, so does the probability of corrupting the system with sensor modeling errors, signal interference, and undetected faults. Though the latter of these has been extensively researched, the majority

In this paper, we propose a machine‐learning‐based approach to automatically detect a satellite oscillator anomaly. A major challenge is to differentiate an oscillator anomaly from ionospheric scintillation. Although both scintillation and oscillator anomalies cause phase disturbances, their underlying physics are different and, therefore, show different carrier‐frequency dependency. By using triple‐frequency

We propose a Simultaneous Localization and Mapping (SLAM)‐based Integrity Monitoring (IM) algorithm using GPS and fish‐eye camera to compute the protection levels while accounting for multiple faults in GPS and vision. We perform graph optimization using GPS pseudoranges, pixel intensities, vehicle dynamics, and satellite ephemeris to simultaneously localize the vehicle, GPS satellites, and key image

Clock synchronization is critical for synchronous pseudolite systems. Wireless synchronization methods are desirable for their flexibility in system deployment, and most of them build a tree topology of time information flow based on master‐slave synchronization between pseudolites. A slave pseudolite can receive signals broadcast by multiple pseudolites; however, existing methods usually utilize one

Recently, the joint design of the GNSS message structure and the associated channel‐coding scheme have been investigated as a means to reduce the Time‐To‐First‐Fix (TTFF) and particularly the time to retrieve the Clock and Ephemerides Data (CED). In this context, a new method to co‐design the navigation message and the channel‐coding scheme structure is proposed in this paper. This new co‐design enables

The in‐motion alignment for the underwater strapdown inertial navigation system is still a challenging problem due to various disturbances in the underwater environment. In this paper, a novel in‐motion alignment method, based on the Lie group representation, is developed. In this method, the process model is rewritten using the Lie group of the constant attitude matrix between two inertial frames

Ionospheric scintillation is the physical phenomena affecting radio waves coming from the space through the ionosphere. Such disturbance is caused by ionospheric electron‐density irregularities and is a major threat in Global Navigation Satellite Systems (GNSS). From a signal‐processing perspective, scintillation is one of the most challenging propagation scenarios, particularly affecting high‐precision

Distance measuring equipment (DME) has been a cornerstone of aviation navigation for the last 70 years. While GNSS is taking an increasingly important role in civil aviation, DME can still play an important role in a robust aviation infrastructure in the foreseeable future. Advanced concepts have been developed to improve DME performance and capabilities. One concept is a DME‐based pseudolite that

The former Galileo Commercial Service (CS) will provide a High Accuracy Service (HAS) and a Commercial Authentication Service (CAS). The first will disseminate free Precise Point Positioning (PPP) corrections through the E6‐B signal whereas the second will provide authentication capabilities through the E6‐C pilot component that will be encrypted. For this reason, improved processing strategies for

In the BeiDou Navigation Satellite System (BDS) B1 band, a single‐sideband complex binary offset carrier (SCBOC) modulation is employed to combine the legacy and the modernized B1 signals into an asymmetric‐wideband composite signal for the backward compatibility. However, SCBOC modulation has only been regarded as a means to achieve the co‐existance between B1I and B1C signals, whose high‐precision

As the dependence of Global Navigation Systems (GNSS) increases, so does a growing demand for GNSS accuracy in urban environments. This research aims to improve navigation in these environments by integrating non‐line‐of‐sight signals, building models, and measured signal to noise ratios in ways not typically used in GNSS positioning. We propose a technique of combining elements of shadow matching

This research investigates the mutual interference between a GNSS signal refracted through the atmosphere and the same signal reflected from the surface below. For low‐altitude occultations, the reflected signal can be present as multipath when tracking the direct signal. This poses a problem when making remote sensing measurements using GNSS‐RO or GNSS‐R techniques. Here, this issue is addressed in

No abstract is available for this article.