Multi-antenna Global Navigation Satellite System Research Articles

Multi-Antenna Global Navigation Satellite System/Inertial Measurement Unit Tight Integration for Measuring Displacement and Vibration in Structural Health Monitoring

Large-scale engineering structures deform and vibrate under the influence of external forces. Obtaining displacement and vibration is crucial for structural health monitoring (SHM). Global navigation satellite system (GNSS) and inertial measurement unit (IMU) are complementary and widely used in SHM. In this paper, we propose an SHM scheme where IMU and multi-antenna GNSS are tightly integrated. The phase centers of multiple GNSS antennas are transformed into the IMU center, which increases the observation redundancy and strengthens the positioning model. To evaluate the performance of tight integration of IMU and multiple GNSS antennas, high-rate vibrational signals are simulated using a shaking table, and the errors of horizontal displacement of different positioning schemes are analyzed using recordings of a high-precision ranging laser as the reference. The results demonstrate that applying triple-antenna GNSS/IMU integration for measuring the displacement can achieve an accuracy of 2.6 mm, which is about 33.0% and 30.3% superior than the accuracy achieved by the conventional single-antenna GNSS-only and GNSS/IMU solutions, respectively.

Quad-channel broadband compact multi-antenna GNSS down-converter for high-reliability navigation

Abstract A high-reliability broadband high-linearity down-converter for multi-antenna global navigation satellite system (GNSS) receiver is presented in this paper. Based on direction-of-arrival estimation, the multi-antenna GNSS receiver can separate the GNSS signals from the interfering signals and suppress harmful broadband radio frequency interferences. To drive the off-chip 50 Ω resistive load and meet the stringent requirements of linearity, a quad-channel down-converter with a broadband common-gate low-noise transconductance amplifier, current-driven passive mixer and novel bridge mode transimpedance driving amplifier have been proposed to contruct the multi-antenna receiver. The operating frequency of this down-converter is from 1.15 to 1.65 GHz, covering all bands for global positioning system (GPS), Beidou navigation satellite system (BDS), global navigation satellite system (GLONASS) and Galileo. The measured results show that the proposed quad-channel down-converter achieves +38 dBm output 3rd order intercept point (OIP3) and +17 dBm OP1dB (output-referred 1 dB compression point), 9.5 dB to 12.9 dB noise figure (NF) across the variable gain of 10 dB to 27 dB and approximately 47 dB channel isolation.

Using a Moving Antenna to Improve GNSS/INS Integration Performance Under Low-Dynamic Scenarios

The integration of inertial navigation system (INS) and global navigation satellite system (GNSS) with a single antenna is widely applied in consumer-level vehicle navigation. However, it is challenging for a low-cost single-antenna GNSS/INS integrated system to provide reliable, consistent state estimation under low-dynamic scenarios (e.g., low-speed robotic applications) as the limited dynamics could lead to degradation of the system observability. We propose a novel moving-antenna GNSS/INS integration method, in which the antenna is designed to perform specific motions on the platform during vehicle maneuver, thus to improve the system observability in degraded conditions, bringing about the advantage of multi-antenna GNSS using a single antenna. It turns out that a moving antenna with a maximum speed of just 0.15 m/s would improve the system performance dramatically by applying raw GNSS carrier phase observations into the integration. In the proposed method, firstly, a moving-antenna fast initial alignment algorithm is developed, which enables the system to perform instantaneous initial alignment in static. Secondly, for GNSS/INS integration filter, the moving-antenna scheme improves the heading angle estimation accuracy by more than 50% under typical dynamic scenarios, achieving comparable performance to dual-antenna GNSS/INS integration. This work shows that it is possible and even beneficial to continuously change the inter-sensor transformation in an integrated navigation system.

Multi-antenna GNSS tight combination attitude determination in the urban environment

It is a challenging task to determine dynamic vehicle attitude using a single-frequency single-epoch multi-antenna global navigation satellite system (GNSS). In the urban environment, the number of visible satellites drops sharply due to the occlusion of trees and tall buildings, hence it is difficult to obtain the high-precision attitude of vehicles using only a multi-antenna GNSS. The GNSS tight combination algorithm selects the same reference satellite between different systems, and can effectively increase the number of observation equations after eliminating the inter-system bias, to improve the attitude accuracy of vehicles in complex environments. Compared with the loose combination algorithm, which selects reference satellites separately between different systems, the tight combination algorithm can further improve the locatable performance when there are fewer satellites. Dynamic vehicle experiments were carried out in an open environment and a complex environment, respectively, using the GPS/BDS/GALILEO three-system single-frequency and single-epoch positioning mode. The results show that the tight combination algorithm and the loose combination algorithm have the same accuracy when there are enough visible satellites in the open environment. In a complex environment, with a cut-off elevation angle of 40°, the percentage of pitch angle error, yaw angle error and roll angle error within 2° increased by 6.1%, 8.07% and 13.43%, respectively, and the ambiguity fixed rate was increased by 14.78%.

High-Rate Attitude Determination of Moving Vehicles With GNSS: GPS, BDS, GLONASS, and Galileo

We investigate the long-term performance and improvement of high-rate multiconstellation Global Navigation Satellite System (GNSS) or multi-GNSS attitude determination in a dynamical environment and evaluate how much each GNSS contributes to such an improvement with applications to land vehicle navigation. We build a multiantenna GNSS system with three nondedicated receivers and conduct two experiments with quad-constellations in GNSS-friendly and GNSS-challenged environments on January 19 and 23, 2018, respectively. A high-grade inertial measurement unit (IMU) provides a reference of comparison for dynamic attitude solutions. In the static case, the global positioning system (GPS), BeiDou navigation satellite system (BDS), and GLObal NAvigation Satellite System (GLONASS) single-constellation solutions have basically the same performance for both experiments. In the dynamic case, GPS achieves the best accuracy in the experiment on January 19, while on January 23, GPS and GLONASS achieve very similar accuracy and significantly outperform BDS in the pitch and roll components. The different dynamic performances of these single constellations are primarily attributed to their differences in observation noise level and satellite geometry strength. By combining GPS, BDS, GLONASS, and Galileo, the multi-GNSS solution performs significantly better than any single-constellation solution. The average improvements in the dynamic cases are 26.2%, 40.7%, and 36.0% on January 19 and 19.2%, 30.0%, and 36.2% on January 23 in the yaw, pitch, and roll components, respectively. The attitude solutions on January 19 are always better determined than on January 23 in the dynamic cases, which should clearly indicate the importance of combining multiple GNSS constellations and the benefit of more observed satellites and a stronger satellite geometry in GNSS-challenged environments. We also introduce the concept of “influence rate” and quantitatively analyze the contribution of each GNSS system to the combined attitude solution.

High-Accuracy Attitude Determination Using Single-Difference Observables Based on Multi-Antenna GNSS Receiver with a Common Clock

A global navigation satellite system (GNSS) receiver with multi-antenna using clock synchronization technology is a powerful piece of equipment for precise attitude determination and reducing costs. The single-difference (SD) can eliminate both the satellites and receiver clock errors with the common clock between antennas, which benefits the GNSS short-baseline attitude determination due to its lower noise, higher redundancy and stronger function model strength. However, the existence of uncalibrated phase delay (UPD) makes it difficult to obtain fixed SD attitude solutions. Therefore, the key problem for the fixed SD attitude solutions is to separate the SD UPD and fix the SD ambiguities into integers between antennas. This article introduces the one-step ambiguity substitution approach to separate the SD UPD, through which we merge the SD UPD parameter with the SD ambiguity of the reference satellite ambiguity as the new SD UPD parameter. Reconstructing the other SD ambiguities, the rank deficiency can be remedied by nature, and the new SD ambiguities can have a natural integer feature. Finally, the fixed SD baseline and attitude solutions are obtained by combining the ambiguity substitution approach with integer ambiguity resolution (IAR). To verify the effect of the ambiguity substitution approach and the advantages of the SD observables with a common clock in practical applications, we conducted static, kinematic, and vehicle experiments. In static experiments, the root mean squared errors (RMSEs) of the yaw and pitch angles obtained by the SD observables with a common clock were improved by approximately 80% and 93%, respectively, compared to double-difference (DD) observables with a common clock in multi-day attitude solutions. The kinematic results show that the dispersion of the SD-Fix in the pitch angle is two times less that of the DD-Fix, and the standard deviations (STDs) of the pitch angle for SD-Fix can reach 0.02°. Based on the feasibility, five bridges with low pitch angles in the vehicle experiment environment, which the DD observables cannot detect, were detected by the SD observables with a common clock. The attitude angles obtained by the SD observables were also consistent with the fiber optic gyroscope (FOG) inertial navigation system (INS). This research on the SD observables with a common clock provides higher accuracy.

GNSS attitude estimation based on adaptive Kalman filtering using phase measurement

Attitude estimation using multi-antenna Global Navigation Satellite System (GNSS) has caught broad attention in recent years. The methods of indirectly calculating attitude parameters based on baseline vectors have been widely used. However, the accuracy of such methods needs to be further improved. An algorithm of directly estimating attitude parameters based on adaptive Kalman filtering (AKF) is proposed. The high-precision phase measurements are used and the system noise covariance matrix corresponding to Euler angles and angle rates is adaptively adjusted according to the maximum a posteriori estimation principle. To decrease the linearisation errors and speed the filtering convergence, a switching strategy is implemented. Namely, when the number of fixed ambiguities is equal to or more than three, the authors deem that the attitude estimate is sufficiently accurate, hence the initial state vector is constructed to start filtering. Otherwise, the attitude parameters are indirectly obtained. The static and simulation experiments are carried out. A comparative study is implemented with the two methods of indirectly calculating attitude parameters. The static and simulation results demonstrate that the proposed method has a competent performance in both accuracy and fixing success rate. The simulation results also show that the adaptability of the AKF method is nice.

A Multi-Antenna GNSS-Over-Fiber System for High Accuracy Three-Dimensional Baseline Measurement

A novel multi-antenna global navigation satellite system that uses fibers to transmit signals from multiple remote antennas to a local station with real-time microwave-photonics-based fiber length monitoring is proposed for high accuracy three-dimensional (3D) baseline measurement. In the proposed approach, microwave-photonics-based fiber length monitoring is employed to obtain the delay difference between the different GNSS channels. With the obtained delay difference information, we use the carrier-phase single-difference (SD) algorithm to calculate the 3D baseline, which is able to improve the vertical precision of the 3D baseline measurement as compared with the use of the carrier-phase double-difference (DD) algorithm. Experimental results show that the 3D baseline measurement precision using the SD algorithm is within 2 mm and the vertical positioning precision is improved by over three times compared with the approach using the conventional DD algorithm.

Multiantenna GNSS and Inertial Sensors/Odometer Coupling for Robust Vehicular Navigation

Location information is one of the most vital information required to achieve intelligence and context-awareness for Internet of Things applications such as driverless cars. However, related security and privacy threats are a major holdback. With increasing focus on the use global navigation satellite system (GNSS) for autonomous navigation and related applications, it is important to provide robust navigation solutions. Radio frequency interference, either intentional or unintentional, has a direct impact on GNSS navigation performance related to observability and accuracy. In terms of security, spoofing is the major issue of concern. This paper focuses on multiantenna GNSS and inertial navigation system (INS)-odometer integration to improve robustness, security, and privacy of navigation solutions. Multiantenna GNSS provides robustness against different interference sources and integration with INS provides continuous navigation solutions during short-term signal outages. Performance of the proposed architecture is evaluated using different user scenarios in the presence of spoofing and interference signals in real vehicular environments.

Performance Trades for Multiantenna GNSS Multisensor Attitude Determination Systems

We present various performance trades for multiantenna global navigation satellite system (GNSS) multisensor attitude estimation systems. In particular, attitude estimation performance sensitivity to various error sources and system configurations is assessed. This study is motivated by the need for system designers, scientists, and engineers of airborne astronomical and remote sensing platforms to better determine which system configuration is most suitable for their specific application. In order to assess performance trade-offs, the attitude estimation performance of various approaches is tested using a simulation that is based on a stratospheric balloon platform. For GNSS errors, attention is focused on multipath, receiver measurement noise, and carrier-phase breaks. For the remaining attitude sensors, different performance grades of sensors are assessed. Through a Monte Carlo simulation, it is shown that, under typical conditions, sub-0.1-degree attitude accuracy is available when using multiple antenna GNSS data only, but that this accuracy can degrade to degree level in some environments warranting the inclusion of additional attitude sensors to maintain the desired level of accuracy. Further, we show that integrating inertial sensors is more valuable whenever accurate pitch and roll estimates are critical.

Analysis of Multi-Antenna GNSS Receiver Performance under Jamming Attacks.

Although antenna array-based Global Navigation Satellite System (GNSS) receivers can be used to mitigate both narrowband and wideband electronic interference sources, measurement distortions induced by array processing methods are not suitable for high precision applications. The measurement distortions have an adverse effect on the carrier phase ambiguity resolution, affecting the navigation solution. Depending on the array attitude information availability and calibration parameters, different spatial processing methods can be implemented although they distort carrier phase measurements in some cases. This paper provides a detailed investigation of the effect of different array processing techniques on array-based GNSS receiver measurements and navigation performance. The main novelty of the paper is to provide a thorough analysis of array-based GNSS receivers employing different beamforming techniques from tracking to navigation solution. Two beamforming techniques, namely Power Minimization (PM) and Minimum Power Distortionless Response (MPDR), are being investigated. In the tracking domain, the carrier Doppler, Phase Lock Indicator (PLI), and Carrier-to-Noise Ratio (C/N0) are analyzed. Pseudorange and carrier phase measurement distortions and carrier phase position performance are also evaluated. Performance analyses results from simulated GNSS signals and field tests are provided.

Concepts, Development, and Validation of Multiantenna GNSS Receivers for Resilient Navigation

Array processing proved itself in the last decades as a powerful approach to suppress harmful radio frequency interference. However, the interference mitigation in the spatial domain can also lead to the attenuation and loss of the desired Global Navigation Satellite System (GNSS) signals that are not sufficiently separated by their directions of arrival from the interfering signals. In order to overcome this effect, this paper proposes an approach to combine array processing and vector tracking in a single receiver. Formerly, the vector tracking loops have been shown to deliver superior performance in scenarios with blocked line-of-sight signals due to aiding of the affected signals during the outage. Since vector tracking loops are susceptible to faked GNSS signals, the proposed receiver architecture also includes a spoofing detection based on the direction-of-arrival estimation. The paper presents the technical concept and details about the realization of the array-based receiver that was developed at the German Aerospace Center (DLR). The techniques used to mitigate brute-force radio frequency interference and to detect spoofing signals are described. Experimental results obtained with these techniques in field are discussed.

Alternative Algorithm for Determining the Attitude Parameters of a Moving Platform Using Multi-Antenna GNSS Sensors

This case study aims to demonstrate a multi-antenna Global Navigation Satellite System (GNSS) technique and quality evaluation approach that can be used to determine the attitude parameters for a moving platform. First, considering the highly dynamic behavior of a moving platform, a noniterative parameter determination approach was introduced. A rigorous error analysis approach was then established to give explicit indications on the obtained attitude parameters. Based on the numerical results from both simulated and real datasets, it has been illustrated that the proposed approach is capable of giving efficient and reliable attitude parameter estimates independently without the need for auxiliary information. Consequently, the multi-antenna GNSS system can serve as an immediate resolution for the attitude determination of moving platforms in modern day applications.

A General Multivariate Formulation of the Multi-Antenna GNSS Attitude Determination Problem

Global Navigation Satellite System (GNSS) carrier phase ambiguity resolution is the key to high precision positioning, navigation and attitude determination. In this contribution we present a general formulation for the multi-antenna GNSS attitude determination problem. This multivariate formulation provides a general framework for solving various GNSS attitude determination problems. With the use of this formulation we show how the constrained integer least-squares carrier phase ambiguities and corresponding attitude matrix can be solved.