Global Positioning System Reference
In-Depth Information
satellite elevation of 2º are described in [25]. The models in [25] are a function of
satellite elevation and height. Note that these models require more computation
time than the analytical models. One example of a three-parameter fractional form
is the UNBabc model. The
a
,
b
, and
c
parameters for the dry component mapping
function are given by:
(
)
a
=
118972
.
−
0026855
.
h
+
010664
.
cos
φ
1000
,
d
b
c
=
00035716
.
d
=
0082456
.
d
The
a
,
b
, and
c
parameters for the wet component mapping function are given by:
(
)
a
=
061120
.
−
0035348
.
h
+
001526
.
cos
φ
1000
,
w
b
c
=
00018576
.
w
=
0062741
.
w
7.2.5 Receiver Noise and Resolution
Measurement errors are also induced by the receiver tracking loops. In terms of the
DLL, dominant sources of pseudorange measurement error (excluding multipath,
which will be discussed in Section 7.2.6) are thermal noise jitter and the effects of
interference. The C/A code composite receiver noise and resolution error contribu-
tion will be slightly larger than that for P(Y) code because the C/A code signal has a
smaller RMS bandwidth than the P(Y) code. Typical modern receiver 1
values for
the noise and resolution error are on the order of a decimeter or less in nominal con-
ditions (i.e., without external interference) and negligible compared to errors
induced by multipath.
Receiver noise and resolution errors affect carrier phase measurements made by
a PLL. PLL measurements errors in nominal conditions are on the order of 1.2 mm
(1
σ
) when tracking the P(Y) code.
Extensive treatment of DLL and PLL errors is provided in Section 5.6. The effects of
interference on DLLs and PLLs are discussed in Section 6.2.
σ
) when tracking the C/A code and 1.6 mm (1
σ
7.2.6 Multipath and Shadowing Effects
One of the most significant errors incurred in the receiver measurement process is
multipath. Multipath errors on both pseudorange and carrier-phase measurements
were discussed in detail in Section 6.3. As described in that section, multipath errors
vary significantly in magnitude depending on the environment within which the
receiver is located, satellite elevation angle, receiver signal processing, antenna gain
pattern, and signal characteristics. Within this chapter, as an example, we will use
typical 1-sigma multipath levels in a relatively benign environment of 20 cm and 2
cm, respectively, for a wide bandwidth C/A code receiver's pseudorange and
carrier-phase measurements.
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