Position determination accuracy of a wireless communication device may be
negatively affected by a large unaccounted GPS doppler bias, which in turn may
affect GPS doppler estimations and GPS doppler measurements conducted by the wireless
communication device. The quality of GPS doppler measurements is very important
for position location, because poor quality GPS doppler measurements may prevent
the wireless communication device from acquiring satellites in the most sensitive
modes with narrow frequency ranges, which results in reduced GPS pseudorange measurement
yield. Large unaccounted GPS doppler bias also adversely affects position accuracy
because of the adverse effect on the GPS code phase measurements time propagation
to common time prior to their use in position location calculation. The same is
true in the case of unaccounted CDMA code doppler, through the adverse effect on
the AFLT code phase measurements time propagation to common time prior to their
use in a position location engine. This effect is the biggest concern in the case
of large search windows. Therefore, the present disclosure provides a method of
optimizing GPS based position location in the presence of time-varying frequency
error, including the steps of continuously measuring and/or calculating resulting
GPS doppler bias and CDMA code doppler bias and then minimizing their adverse effects
with regard to position location determination by re-centering GPS doppler search
windows based on the GPS doppler bias value, as well as using GPS doppler bias
and CDMA code doppler bias value to properly propagate GPS pseudorange and AFLT
pilot phase measurements, respectively, to common time prior to their use in a
position location engine.
