vii berichte von fachinstituten an universitäten und technischen

366 Fachinstitute an Universitäten und Hochschulen
navigation. The so called BaiCES simulator is based on the
commercial simulation environment, ML-Designer, from
the Mission Level Design GmbH.
This simulation infrastructure enables the user to build up
a simulation application graphically, by drag and drop
models from the model library into the simulation build up
window and connecting their in- and output ports. Each
model represents a certain partition of a GNSS System, like
the satellite orbit, the satellite signal, the receiver, the user
environment (terrain data) or the positioning algorithm. A
model library was developed which consists mainly of the
algorithms which were implemented in existing GNSS
simulation tools in the past. The main advantage of this
approach is the enormous flexibility and transparency to the
user of this simulator. The model library can be extended
at any time to include new models or new research results
in satellite navigation.
C-NAV Study
Although not considered for the first generation of European
Galileo satellites, the (additional) use of C-band frequencies
is currently topic of an ESA study which started in late 2007
and is to be completed by 2008. The Institute was already
involved in a similar study a couple of years ago funded by
national institutions. A future C-band signal could use the
frequency of 5.019 GHz, thus offering a bandwidth of 20
MHz in a frequency band not yet overloaded by other signal
sources. Application of C-Band navigation signals provides
both advantages and drawbacks. At C-band, the increased
free space loss represents the most significant issue.
Increased signal attenuation due to foliage attenuation and
in case of heavy rain can also be considered as drawbacks.
However, small ionospheric effects and technological
progress will likely balance some of the disadvantages from
a long term point of view. The main intention of this study
is to provide an analysis of the effects of C-band frequencies
on the navigation process and to define appropriate signals
and emission procedures to overcome the inherent
drawbacks of C-band, investigate the current state of
hardware technology suitable for C-band navigation, and
to define services for a C-band GAILLEO system.
Gnss Receiver Development
GNSS Hardware Receiver
An experimental dual frequency (L1 C/A and L2 civil
signal) real-time kinematic (RTK) receiver is currently
developed at the Institute of Geodesy and Navigation in
collaboration with FhGIIS (Frauenhofer Institute for
Integrated Circuits) and IfEN GmbH. This investigation is
funded within the scope of a research project in contract with
DLR (German Aerospace Centre). The development
includes a large number of paper studies to investigate
existing RTK receiver designs, new boundary conditions
due to the Galileo system and due to GPS modernization.
Also new possibilities to integrate the internet, low cost INS
and GIS into the RTK receiver have been explored. The
most exciting part of the project is the development of a
breadboard receiver using a wideband L1 CA/L2CS frontend.
Signal processing is performed by a FPGA card
plugged into a PC and by a software correlator. RTK
positions are calculated by fixing the integer ambiguities
using the LAMBDA method. The positioning software runs
under the Windows Operating System and has interfaces
to the FPGA and the software correlator. By using this dual
correlator approach, software and hardware correlation
techniques can be directly compared.
ipexSR – a PC based GNSS Software Receiver
The ipexSR (Institute of Geodesy and Navigation PC-based
Experimental Software Receiver) is a GNSS receiver
realized completely in software (Visual C++/Assembler)
capable of tracking GPS and GNSS signals in real-time or
post-processing. It implements various tracking and
positioning techniques, including the CRUSR (Cramer-Rao
Under Sampling Receiver) technology and has been
developed since 2002. The receiver accepts on input IF
samples taken from hard disc (post-processing mode) or
from a National Instruments ADC card (real-time). The
ipexSR performs all tasks of a conventional hardware
receiver, like acquisition, tracking and positioning. It also
includes a signal monitor which analyzes the GNSS signals
present in the IF data stream. At the moment the ipexSR has
been validated for GPS C/A code signals and will be
updated in 2004 to track the GPS L2 civil signal and Galileo
type signals. The S/W receiver development is one of the
major current research interests at the Institute of Geodesy
and Navigation as is features a number of benefits for the
scientific community.
GNSS software receiver
The software-based receiver technology approach also plays
an important role for research in the field of indoorpositioning
– which is described in the next few paragraphs
in more detail – as it is a very flexible and extendable
method.
Sensor Fusion
In-Door-Positioning
The institute plays a vital role within the project “Galileo/
GPS Indoor Navigation & Positionierung (INDOOR)”
funded by the German Aerospace Centre (DLR) and
coordinated by IfEN GmbH. The total number of seven
partners in the INDOOR consortium represents the branches
of industry, SME, research institute, and university and aim
to enforce the role of the German economy on a future user