Manuel Cuntz

Development of Robust Safety-of-Life Navigation Receivers

This paper summarizes the development of safety-of-life receivers for global navigation satellite systems. Two receiver systems have been successfully fabricated, integrated, and tested by means of field experiments. Implementation issues of these two systems are described in this paper. The third generation of this receiving system is based on a dual-band approach with antennas that are able to separate two frequency bands using two outputs. Measured results show that high isolation between the two bands can be achieved.

Antenna and RF front end calibration in a GNSS array receiver

The use of spatial-domain signal processing for mitigation of interference signals in receivers of global navigation satellite systems (GNSS) allows for improvement of the overall system performance. To fully benefit from the use of adaptive antenna arrays, the individual signal processing paths in such a multi-antenna system should be thoroughly calibrated. The focus of this paper is on the specifics of such calibration in receivers for satellite navigation systems (e.g. GPS and coming Galileo). The design goals of the antenna and RF front end for GNSS receivers are reviewed. The architecture of a GNSS array receiver for safety-of-life applications with high robustness against radio interference is presented. The practical solutions for the antenna array and RF front-end calibration along with the field test results demonstrating their performance are outlined.

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.

Development of robust safety-of-life navigation receivers at the german aerospace center (DLR)

This paper summarizes the development of safety-of-life receivers for global navigation satellite systems (GNSS) that has been being conducted at the Institute of Communications and Navigation of the German Aerospace Center (DLR). Two receiver systems have already been successfully fabricated, integrated and tested by means of field experiments. Implementation issues of these two systems are described in this contribution. Details about the third generation of DLRs receiving system, which is currently under development, are also briefly discussed.

ADIBEAM: Design and experimental validation of a robust beamforming platform for Galileo reference ground stations

The increase in navigation accuracy demanded by EGNOS and Galileo and their future evolution encourages the study and design of advance receiver architectures. In that direction, the ADIBEAM project focuses on the design of high accuracy ground stations, specifically GNSS Reference Stations, in order to improve its robustness in front of multipath and interference errors with the goal of achieving centimeter level tracking accuracy. The adoption of antenna arrays and digital beamforming at the ground reference station receivers is one of the most promising approaches to cope with errors induced by multipath and interference. This paper proposes an innovative design of a ground based tracking station. In particular, the architecture proposed is based on the use of an antenna array and digital beamforming techniques, considering both adaptive and deterministic methods. The work carried out here considers the ground based tracking system, including the characterization of the system components (antennas, RF chains, calibration techniques, GNSS software receiver and digital beamforming), and the development of a software based experimentation platform representative of the proposed design for a hardware prototype. The sensitivity to perturbations and the extreme difficulty to perfectly control and calibrate all the components of the system, especially regarding the antenna array implementation, requires that the proposed design take into consideration not only the benefits of the possible solutions but also their feasibility for a real implementation. In summary, this paper will present the design proposed and the Experimentation Platform used for its validation.

Self-contained calibration determination by jointly solving the attitude estimation and calibration problem in the steering vector domain

Antenna calibration is a mandatory requirement to determine the attitude of a multi-antenna receiver. Moreover, knowing the antenna attitude can vastly improve detection and mitigation of spoofers and / or Radio Frequency Interferences (RFIs). In todays receivers the time-varying phase offset introduced by the active elements like amplifiers, downconverters as well as various filters and unequal cable lengths are usually calibrated using a pilot signal, which is injected in the antenna signal. This method, however, does not only complicate the manufacturing process, but also increases the complexity of the receiver architecture and power consumptions. New approaches developed recently use GNSS live signals for calibration. These methods are established based on the fact that for each incoming GNSS signal the direction of arrival (DOA) is exactly known by means of the ephemeris data, which is transmitted from each satellite. In order to estimate the calibration phases, the DOAs of the received satellite signals are compared with their corresponding expected DOAs, which are determined based on the ephemeris data. The problem, however, lies in the fact, that the expected DOAs are given in the East-North-Up (ENU) coordinate frame, whereas the measured DOAs are given in the local coordinate frame and are additionally affected by the unknown phase offsets to be calibrated. The proposed algorithm therefore solves the attitude estimation and calibration problem jointly. This paper proposes a novel algorithm and validates it using measurement data.

Comparison of SAGE and classical multi-antenna algorithms for multipath mitigation in real-world environment

The performance of the Space Alternating Generalized Expectation Maximisation (SAGE) algorithm for multipath mitigation is assessed in this paper. Numerical simulations have already proven the potential of SAGE in navigation context, but practical aspects of the implementation of such a technique in a GNSS receiver are the topic for further investigation. In this paper, we will present the first results of SAGE implementation in a real world environment.

Navigating in the Galileo test environment with the first GPS/Galileo multi-antenna-receiver

Array processing is a very promising technology for mitigation and detection of radio interference in receivers of satellite navigation systems. This paper presents early results of a multi-antenna receiver measurement campaign in Berchtesgaden GATE.

Jamming and Spoofing in GPS/GNSS Based Applications and Services – Threats and Countermeasures

GPS positioning and time synchronization have become crucial for a large variety of services and applications. Especially for safety-critical applications and infrastructure networks a reliable and robust service of GPS is essential. However, the availability of cheap jamming devices has recently demonstrated the threat for GPS applications. GPS jamming is no longer only a hypothetical threat, it is already present and will become increasingly dangerous for GPS users. For this reason the German Aerospace Center (DLR) developed strategies to cope with these threats and to retain a valid position solution even in harsh interference environments.