| Pseudolite Research
In aviation,
a satellite only navigation system is not capable of meeting all requirements
for enroute navigation and precision approaches, particularly when
considering integrity and continuity. For this reason, concepts of augmentation
systems have been established. These augmentation systems can be divided
in Satellite Based Augmentation Systems (SBAS) and Ground Based Augmentation
Systems (GBAS). Aviation authorities including the
International Civil Aviation
Organization (ICAO) and the
United States Federal Aviation
Adminitstration (FAA) have been working to define the next generation
of aircraft navigation aids based on the Global Positioning System (GPS)
and other Global Navigation Satellite Systems (GNSS). The system proposed
for navigation during takeoff and landing, known as the Local Area Augmentation
System (LAAS), requires ground equipment at each airport. The LAAS ground
equipment includes an elaborate reference station to generate differential
GPS corrections, and a VHF data link transmitter to send them to nearby aircraft.
It also includes one or more GPS-band transmitters known as
Airport Pseudolites (APL).
Each
APL provides an additional GPS-like signal for nearby aircraft to use in
their navigation solutions. In general, four such solutions are needed to
achieve a basic position fix. One or more additional signals may be needed
to achieve all the elements of Required Navigation Performance (RNP) specified
by ICAO for aircraft on final approach. Simulations of satellite visibility
frequently find that the number of GNSS satellite signals available at certain
places and times is lower than the number needed for RNP. Each APL adds one
more signal to the number available. The LAAS designers have accepted the
need for one or more APLs to achieve the level of availability required by
RNP. Thus, APLs may serve as an augmentation with regard to availability
and continuity. In principle, APLs are supplementary satellites located on
the ground. However, due to effects that have to be considered and modeled
in a different way than for GNSS signals, an improvement in accuracy using
APL measurements cannot taken for granted.
The current
pseudolite reseach of the institute funded by
Deutsches Zentrum für Luft-
und Raumfahrt (DLR) focuses on two main aspects.
1. Evaluation
of all potential error sources connected with the deployment of APLs and
development of an error model.
2. Application
and validation of the error model on real flight data collected during two
experimental flight campaigns at the airport of Braunschweig
(Germany).
Point
of contact: Andreas
Teuber |
