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@PHDTHESIS{Circiu:793914,
author = {Circiu, Mihaela-Simona},
othercontributors = {Meurer, Michael and Dovis, Fabio},
title = {{I}ntegrity aspects for dual-frequency dual-constellation
ground based augmentation system ({GBAS})},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2020-07268},
pages = {1 Online-Ressource (xxviii, 252 Seiten) : Illustrationen,
Diagramme},
year = {2020},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2020},
abstract = {For navigation in aviation, high performance requirements
in terms of integrity, accuracy, continuity, availability,
and robustness against interference need to be achieved. The
Global Navigation Satellite System (GNSS) alone is not
sufficiently accurate and cannot provide precision approach
with the required integrity. The Ground Based Augmentation
System (GBAS), a development of local-area differential GNSS
aims at providing precision approach guidance meeting all of
these requirements under low-visibility conditions. GBAS
provides differential corrections and integrity monitoring
of GNSS, which are broadcast via a Very High Frequency (VHF)
radio data link, termed as Very High Frequency Data
Broadcast (VDB). The system is currently under development
with single-frequency single-constellation Global
Positioning System (GPS) L1 stations being already in use.
Several studies have shown that ionospheric anomalies that
cause large spatial gradients pose a significant threat to
this system [1, 2, 3]. With the increasing number of
satellites broadcasting signals on a second Aeronautical
Radio Navigation Service (ARNS) frequency (L5/E5a)
available, the dual-frequency processing becomes a promising
option for the next generation aviation users. The use of
the signals in a second frequency band can remove the effect
of the ionosphere which is one of the dominant sources of
errors for the single frequencies user. However, it also
yields many different options for processing. Until today
there is no clear concept defined on how to use the new
signals in a future Dual-Frequency Dual-Constellation (DFDC)
GBAS to provide better performance compared to the existing
system. This thesis provides essential contributions to the
development, standardization and implementation of a future
DFDC GBAS. The new service type shall be able to provide
sufficient availability, integrity and continuity to be
usable globally. Relevant contributors to the error budget
are reviewed, characterized and modeled in an appropriate
way. The thesis is structured as follows. First, it provides
a detailed overview of the existing integrity concept for
the single frequency GBAS. The goal of this review is to set
the framework and identify the aspects needed in the
development of the DFDC GBAS. Next, the thesis discusses the
modifications needed when evolving to a DFDC system. The use
of the signals from a second frequency band and second
constellation enable many different processing modes. In
this thesis, the proposal and the selection of the
processing modes for a DFDC GBAS is based on upgrading the
existing GBAS, but maintaining the main characteristics
(e.g. maintaining the existing VDB link). This concept adds
several constraints, such as backwards compatibility to the
existing single frequency system and the limited remaining
VDB capacity. Taking into account all the constraints, the
mostpromising processing modes are presented and discussed.
Based on the selected modes, the thesis discusses the
modifications to the integrity concept and identifies the
different aspects that need to be taken into account for
each of the processing modes, which is the main contribution
on this part. This includes the need for the new ground
multipath error models, new airborne multipath models and
consideration of the satellite code biases in the integrity
concept. Each of these aspects are discussed in the thesis
and summarized next including the main contributions. The
first error source considered is the multipath and noise
errors in the ground reference receivers. Until now,
performance analysis of the ground multipath errors using
the GPS L1 Coarse/Aquisition (C/A) signal has been studied.
In this thesis, the performance analysis of the new signals
from the Galileo satellites in the E1 and E5a frequency
bands and GPS L5 signals as measured by the experimental
GBAS test bed available at Deutsches Zentrum für Luft- und
Raumfahrt e.V. (DLR) is presented. The results show that the
raw noise and multipath level of Galileo signals and of the
GPS L5 signals are smaller than that of GPS L1. The new
signals are also less sensitive to the choice of
carrier-smoothing time constant. As the Galileo
constellation has different ground track repeatability from
GPS, the applicability of the existing methods for the
derivation of the ground multipath models is investigated in
the thesis. The impact of different effects factor
influencing the multipath models such as the smoothing time
constant and the receiver parameters are studied.
Furthermore, dual-frequency ground multipath error models
are derived that differ from the combination of single
frequency models. Another important source of error to be
considered in a future DFDC GBAS is the airborne multipath.
With the removal of the ionospheric error, the airborne
multipath error becomes a dominant source of error. The
current models are defined only for GPS L1 100 seconds
smoothing time constant and no models are available for the
new signals broadcast by GPS satellites on L5 band and
Galileo satellites. This thesis contributes to the
development of the airborne multipath models for the new
signals. The work proposes an improved methodology for the
derivation of the multipath models for aviation using
measurements from flight tests. The improvements include a
proposal of a new method for the estimation of the carrier
phase ambiguities, the separation of the receiver antenna
errors from the multipath errors and an overbounding for the
non-Gaussian distribution of the data. The removal of the
antenna errors constitutes one of the main changes from the
existing models. Until now, the receiver antenna errors were
modeled together with the multipath errors. However, the
results from this thesis show that these errors have
different behavior than the multipath errors and thus a
decomposition of these two errors is suggested. Different
factor of influence on the airborne multipath, including
airframe structure and antenna performance, the receiver
bandwidth and correlator spacing and the smoothing time
constant are investigated and discussed in this thesis. A
third aspect relevant for DFDC GBAS that is discussed in the
thesis is the satellite code biases. These biases differ
between satellites and depend mainly on the GNSS receiver
hardware (e.g. bandwidth and correlator spacing). If the
ground reference stations and airborne receiver use
different configurations, a residual error remains affecting
the GBAS user. These biases can be calculated based on
measurements from a high gain antenna. Initial estimates of
the satellites code biases are used in this thesis to
investigate the impact of the differential satellite code
bias on a GBAS user. The results show that the residual
errors are not negligible and vary from few centimeters to
decimeters. The errors are especially important for the
dual-frequency processing modes that combine the errors from
different frequencies. Thus, they will affect the GBAS user
and need to be taken into account in the integrity budget.
The thesis proposes different concepts to include them in
the integrity budget of the DFDC GBAS. Finally, the thesis
presents an assessment of the expected nominal performance
of different processing modes for future DFDC GBAS. The
evaluations are based on measurements from flight trials
conducted on DLR’s Airbus A320 aircraft. The error models
developed in the thesis are used as input for the study.
This work contributes to the tradeoff studies needed for a
selection of an optimal processing mode for DFDC GBAS.},
cin = {614710},
ddc = {621.3},
cid = {$I:(DE-82)614710_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2020-07268},
url = {https://publications.rwth-aachen.de/record/793914},
}
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