Global Positioning System Reference
In-Depth Information
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Many software packages implement a fixed value for the ratio of the best and the
second-best solutions, e.g.,
v
T
Pv
2nd smallest
∆
∆
>
3
(7.207)
v
T
Pv
sm
to decide on discernibility. The explanations given above lend some theoretical justi-
fication to this commonly used practice, at least for a high degree of freedom. Other
discrimination tests are proposed in Wang et al. (1998).
7.9 REAL-TIME RELATIVE POSITIONING
[29
Transmitting the pseudorange and/or the carrier phase observations from a reference
station to a moving receiver allows the latter to compute its location in real time. On-
site computations allow for real-time quality assurance of kinematic applications and
precise navigation to a known location. Various approaches have become available
that apply to local areas, regions, or even the globe. Local area approaches generally
aim to transmit sufficiently accurate information to allow a mobile user to fix ambi-
guities and therefore determine its position at the centimeter level with respect to the
reference station. There are various options available for transmitting the data, i.e.,
cell phones, dedicated ground transmitters, geostationary satellites, and the Internet.
Lin
—
2.2
——
Sho
*PgE
7.
9.1 Carrier Phase and Pseudorange Corrections
[29
Tr
ansmitting corrections is less of a telemetry load than transmitting the raw obser-
va
tions, because the dynamic range of the corrections is small. For every satellite
p
ob
served at station
k
, we determine an integer number
K
k
,
int
P
k,b
(
1
)
int
1
λ
p
k,b
(
1
)
− Φ
c
λ
K
k
2
I
k,P
(
1
)
N
k
(
1
)
T
GD
=
=
−
+
λ
(7.208)
(
1
)
1
λ
δ
1
λ
δ
p
k,P
(
1
)
p
k,
+
−
Φ
us
ing the observed pseudoranges and carrier phases at some initial epoch, and then
co
mpute the carrier phase range
p
k
(t)
at subsequent epochs as
Θ
p
k,b
(t)
p
k,b
(t)
K
k
Θ
= Φ
+ λ
(7.209)
The numerical value of the carrier phase range is close to that of the pseudorange,
differing primarily because of the ionosphere, as can be seen from the right side of
(7.208). The discrepancy for the carrier phase range at epoch
t
is
