Achim Hornbostel

DME/TACAN interference mitigation for GNSS: algorithms and flight test results

The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm.

Simulation of Multi-Element Antenna Systems for Navigation Applications

The application of user terminals with multiple antenna inputs for use with the global navigation satellite systems like Global Positioning System (GPS) and Galileo has attracted more and more attention in the past years. Multiple antennas may be spread over the user platform and provide signals required for the platform attitude estimation or may be arranged in an antenna array to be used together with array processing algorithms for improving signal reception, e.g., for multi-path and interference mitigation. In order to generate signals for testing of receivers with multiple antenna inputs and corresponding receiver algorithms in a laboratory environment, a unique hardware signal simulation tool for wavefront simulation has been developed. The signals for a number of antenna elements are first generated in a flexible user defined geometry as digital signals in baseband and then mixed up to individual RF-outputs. This paper describes the principle functionality of the system and addresses some calibration issues. Measurement setups and results of data processing with simulated signals for different applications are shown and discussed.

Autonomous satellite state determination by use of two-directional links

Results of study contract of the European Space Agency (ESA) with respect to achievable improvements of emphemeris and clock state determination as well as of integrity by use of intersatellite links and board-autonomous measurements to ground reference stations are presented. Simulation and analyses for two different aspects were performed. The first aspect was the determination of the satellite state using intersatellite links and a conventional ground network. In the second aspect, additional two-way ground-referenced links were added and the performance analysis was repeated for such a configuration with emphasis on autonomous measurements on board the satellites.

Compact antenna array receiver for robust satellite navigation systems

A compact navigation receiver comprising a decoupled and matched four-element L1-band antenna array with an inter-element separation of a quarter of the free-space wavelength is presented in this paper. We investigate the impact of the decoupling and matching network on the robustness of the navigation receiver. It is observed that in order to achieve high robustness with a compact antenna array, it is necessary to employ a decoupling and matching network, particularly in case of three spatially separated interferers. Furthermore, we study the influence of the polarization impurity of the compact planar antenna array on the equivalent carrier-to-interference-plus-noise ratio (CINR) of the receiver when impinged with different numbers of diametrically polarized interference signals. It is shown that the higher-order modes possess strong polarization impurity, which may halve the available degrees-of-freedom for nulling in the presence of linear-polarized interferers, using a conventional null-steering algorithm. We verify the robustness of the designed compact receiver by means of a complete global-navigation-satellite-system demonstrator. It is shown that the maximum jammer power that is allowed us to maintain the CINR above 38 dBHz with three interferers can be improved by more than 10 dB if a decoupling and matching network is employed.

Realization of an End-to-End Software Simulator for Navigation Systems

The paper presents the DLR-NavSim tool. This tool was developed for simulation future civil navigation satellite systems like GNSS-2 or Galileo. In the introduction the aim, the problems, and the principal set-up of the simulation tool are described. In the second chapter a detailed description of the two different levels is presented. Also described are the mean influences on a navigation system, which are realised within this tool in one of the two levels. The third chapter depicts some preliminary results of each level simulation to demonstrate the capacity of the DLR-NavSim tool for navigation satellite systems.

Land mobile multipath channel reduction effects on a real GNSS receiver

One of the current limitations to evaluate the impact of a realistic multipath environment over a GNSS receiver is the high number of multipath rays that are needed to model the channel in a HW RF constellation simulator. That makes necessary the application of reduction techniques to decrease the number of channels per satellite to be simulated. The initial evaluation of two reduction techniques based on the solution of optimization problems is presented for an urban vehicle scenario, focusing the study on the evaluation of the multipath effect over code pseudorange measurements.

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.

GNSS receiver performance assessment with a realistic aeronautical channel model

A multipath model for the aeronautical channel, which was derived from a channel measurement campaign, has been implemented into hardware simulators. The way of implementation is described in detail and simulation results obtained with a GNSS receiver and showing the impact of multipath are presented.