Accuracy Study of a Single Frequency Receiver Using a Combined GPS/GALILEO Constellation

As the date of availability of GALILEO approaches, more and more interest appears to pre-evaluate the accuracy of GALILEO and combined GPS+ GALILEO receivers. The majority of simulations made are based on the general use of UERE (often presented as a function of the elevation angle of the satellite) multiplied by the GDOP (Geometric Dilution Of Precision) matrix. This is a too approximate approach to state for the real position error distributions. Therefore, the concept of an Instantaneous Pseudo Range Error (IPRE) is defined and is implemented into NAVSIM the DLR’s end to end GNSS simulator. This new module coupled with the other modules of the simulator permit to lead complete End-to-End simulations. This new functionality has the advantage to augment the field of applications and to couple the generation of errors already implemented in NAVSIM with error distributions coming from real measurements. This study is a good first approach to compare constellations between each other regarding the accuracy issue. The IPRE concept multiplies the functionalities thanks to its ability to generate real distributions of errors. The application to a combined existing constellation (GPS) for which real measurements can be used with a not yet existing constellation (GALILEO) for which only simulated data can be used is an interesting approach. These results can directly be used to test the impact of correction models, of filtering techniques, of antenna types to a combined GPS/GALILEO system thanks to the time series of IPRE and the instantaneous individual errors output from NAVSIM. The best strategy of error mitigation technique can be tested and the result can be used for receiver design before the launch of GALILEO system

Simulation of Multi-element Antenna Systems for Navigation Applications

The application of user terminals with multiple antenna inputs for use with the global satellite navigation systems like GPS and Galileo becomes more and more attraction in last 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 multipath 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 HW signal simulation tool for wavefront simulation has been developed. The signals for a number of antenna elements in a flexible user defined geometry are first generated as digital signals in baseband and then mixed up to individual RF-outputs. The paper describes the principle function of the system and addresses some calibration issues. Measurement set-ups and results of data processing with simulated signals for different applications are shown and discussed

A Multi Antenna Receiver for Galileo SoL Applications

One of the main features of the Galileo Satellite Navigation System is integrity. To ensure a reliable and robust navigation for Safety of Life applications, like CAT III aircraft landings, new receiver technologies are indispensable. Therefore, the German Aerospace Centre originated the development of a complete safety-of-life Galileo receiver to demonstrate the capabilities of new digital beam-forming and signal-processing algorithms for the detection and mitigation of interference. To take full advantage of those algorithms a carefully designed analogue signal processing is needed. The development addresses several challenging questions in the field of antenna design, frontend development and digital signal processing. The paper will give an insight in the activity and will present latest results

Propagation Problems in Satellite Navigation

The presentation provides an overview about the mechanisms of the main propagation phenomena which are relevant for satellite navigation, their magnitude, temporal and regional variation and standard methods to correct and mitigate them

MF/MC Receiver Performance Analysis under Nominal and Severe Interference Conditions

Simulations with nominal continuous wave interference, broadband noise and pulsed interference were performed for evaluation of the receiver design space of a future multi-frequency multi-constellation GBAS ground receiver. Recorded data from hardware simulations with GPS L1and Galileo E1/E5a signals plus in-band and near-band nominal interference signals according to ICAO and EUROCAE standards were analyzed with a post-processing software receiver. Additionally, results of field tests with commercial jammers (PPDs) were presented

GNSS Overview with Emphasis on Propagation Issues

Today, satellite navigation with GPS is well established and widely used. The European satellite navigation system Galileo is under development and shall become operational in 2013. The current status and planning of both Global Navigations Satellite Systems (GNSS) will be outlined where the emphasis will be on the different signals and services available with both systems. Since satellite navigation is based on measuring the signal delay between transmission at the satellite and reception by the user, the modelling and correction of the additional delay due to the propagation phenomena plays an important role for the accuracy of the derived position solution. The largest signal delay occurs within the ionosphere. The ionosphere delay can be precisely determined and nearly completed eliminated by dual frequency measurements. However, for single frequency receivers, like most commercially available GPS-receivers for the mass market, it must be corrected by modelling, and a significant error can remain. While atmospheric attenuation is negligible at the navigation frequency bands in L-band, occasionally, fast amplitude and phase scintillations can occur due to fast variations of the total electron content in the ionosphere or atmospheric turbulences. Strong scintillations occur only rarely, but then they are critical and can even lead to complete loss of the navigation signals by the receiver. The troposphere delay can be separated in a wet component due to water vapour and a dry component due to other atmospheric gases. While the dry delay can be modelled with high accuracy, the wet delay is a crucial component if accuracies in the decimetre or centimetre range are required, although it contributes normally only with 10%-20% to the total delay, because of the high temporal and spatial variability of the water vapour content in the troposphere. Due to the extreme low signal power of the satellite navigation signals when arriving at the Earth, the signals can be easily attenuated and shadowed by buildings or vegetation, e.g. in urban or rural environments or for indoor applications. In these environments multipath propagation by reflexions of the signals by buildings and other obstacles before they arrive at the user antenna can significantly degrade the ranging and positioning accuracy. Multipath propagation is difficult to correct by models, because it depends strongly on the local user environment. Different techniques exist to mitigate the effect of multipath signals partly in the signal processing of the receiver, but multipath mitigation is still the main error source in navigation besides the ionosphere error

GALANT - Galileo Antenna and Receiver Demonstrator for Safety Critical Applications

Future navigation services and performance limits provided by the upcoming Galileo satellite system will require corresponding improvements of the user navigation receiving systems. Therefore, the Institute of Communciations and Navigation of the German Aerospace Center originated the development of a Galileo Receiver Demonstrator (GALANT). The aim is to develop a complete Safety-of-Life (SoL) Galileo receiver system. For SoL applications, interference and multipath signals can cause serious performance degradations, which cannot be tolerated. Advanced signal-processing algorithms including antenna array techniques like digital beam-forming will contribute to overcome this problem by suppressing interference and multipath signals and improving the reception of useful line-ofsight satellite signals and thus enable a more accurate and reliable positioning. The first part of this paper describes the antenna array and the basic design issues. The second part is a short discussion of the front end concept utilized for the demonstrator. Subsequently, the basic digital receiver design is discussed. Finally, a brief overview of the digital beam-forming and direction finding techniques used for the demonstrator is given