| Pseudolite Research
APL
Error Modeling
Using
APL data requires to be aware of some special features. For example, signal
dynamics are much higher than for satellite signals. APL signals have to
be acquired in a distance of tens of miles, but also in the vicinity of the
airport. This phenomenon is refered to as near-far problem and requires a
careful configuration and setting of the whole system. Furthermore, it has
to be taken into account that there might be no direct line-of-sight between
(the negative elevated) APL and a top-mounted aircraft antenna.
The
investigated potential errors are:
-
The
tropospheric component is due to the diverging signal paths of APL and satellite
signals, the signal creeping component is due to signal reception without
line-of-sight induced by the conducting surface of the fuselage, and the
reference receiver bias component is due to remaining problems with the near-far
problem. The error model provides corrections for APL code and phase
measurements.
Analytical
determination of the signal creeping effect on the pseudorange regarding
a Dornier Do 128 aircraft in relation to the roll angle PHI and the geometrical
angle ALPHA which is the azimuth difference between the longitudinal axis
of the aircraft and the direction to the APL.
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