IEEE - Aerospace and Electronic Systems - April 2021 - 9

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under international civil aviation organization (ICAO)
standardization in the project team terrestrial data
link (PT-T) [9], LDACS is the future aeronautical
datalink for applications related to the safety and
regularity of flight for terrestrial long-range communications [10].
The objective of this article is to demonstrate an
experimental in-flight implementation of GBAS using the
LDACS as datalink 1) to multiply the available bandwidth, 2) to increase the service range, and 3) to introduce
state-of-the-art broadcast cyber-security using timed efficient stream loss-tolerant authentication (TESLA) [11].
The flight trials discussed in this article were cofunded by
the German national research project migration towards
integrated COM/NAV avionics (MICONAV) and took
place in March and April 2019. During MICONAV also
other experiments were performed that are not discussed
in this article.

METHODOLOGY
The main purpose of the experiments was to demonstrate the
ability of LDACS to provide a secure datalink for GBAS.
For this purpose, we implemented a terrestrial LDACS
ground station and GBAS reference station [see Figure 2(a)
and (b)], as well as a software-based GBAS receiver. We

Figure 1.
DLRs research aircraft Falcon 20-E5 (D-CMET) used in the
experiments.

APRIL 2021

mounted the receiver on a research aircraft [see Figures 1 and
2(c)] and flew the setup in the vicinity of the ground station.

EXPERIMENTAL SETUP
The experimental setup consisted of one LDACS aircraftstation and one LDACS ground station. The GBAS ground
station was colocated with the LDACS ground station.
Figure 3 shows the complete experimental setup in detail:
The GBAS ground station receives GNSS data with a Tallysman TW 3972 antenna, processes it using a JAVAD
Sigma unit, and passes it to the GBAS ground processing
software. The processed GBAS data are passed on to the
ground station PC and authenticated with the TESLA protocol before it is transmitted in a message format specific to
the experiment. If desired, TESLA authentication can be
turned off as indicated in the red box at the center of the diagram. The ground PC is connected to the LDACS groundstation radio via user datagram protocol(UDP)/internet
protocol (IP). In the aircraft-station, received messages are
processed in the reverse order to verify GBAS correction
data. The correction data are then used by the GBAS software in the aircraft to calculate GBAS position, velocity,
and time (PVT) and protection levels.

LDACS DATALINK SETUP
The LDACS aircraft-station was configured for bidirectional communication as specified in [9] and [12]. In addition to LDACS radio equipment, the aircraft-station
integrated a Ubuntu 18.04 LTS Linux computer for
LDACS and GBAS airborne data processing, and several
measurement and storage devices, such as a Rubidium
clock, a spectrum analyzer, and an I/Q data recorder. Several of these parts are identified in Figure 2(c).
The LDACS ground station as well as the GBAS
ground station and antennas were installed on top of an
office building at the German Aerospace Center (DLR)

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IEEE - Aerospace and Electronic Systems - April 2021

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