Examples of DOP values:
PDOP:
1.7
PDOP:
4.3
PDOP:
12.6
DOP
value
is
ok
for
good
GPS
performance
DOP
value
is
acceptable
for
a
good
GPS
performance
DOP
too
high
(all
the
satellites
are
in
a
straight
line),
this
will
degrade
the
GPS
performance
Figure 4: Examples of DOP values
1.4.2 Multipath
Direct
Direct
Shadowing
Multipath
Figure 5: A multi-path environment
A
multi-path
environment
exists
if
GPS
signals
arrive
at
the
antenna
directly
from
the
satellite,
(line
of
sight,
LOS)
and
also
from
reflective
surfaces,
e.g.
water
or
building
walls.
If
there
is
a
direct
path
in
addition
to
the
reflected
path
available,
the
receiver
can
usually
detect
the
situation
and
compensate
to
some
extent.
If
there
is
no
direct
line
of
sight,
but
only
reflections,
the
receiver
is
not
able
to
detect
the
situation.
Under
these
multipath
conditions
the
range
measurement
to
the
satellite
will
provide
incorrect
information
to
the
navigation
solution,
resulting
in
a
less
accurate
position.
If
there
are
only
a
few
satellites
in
sight,
the
navigation
solution
might
be
wrong
by
several
hundred
meters.
If
there
is
a
LOS
available,
the
effect
of
multi-path
is
actually
twofold.
First,
the
correlation
peak
will
be
distorted
which
results
in
a
less
precise
position.
This
effect
can
be
compensated
for
by
advanced
receiver
technology
such
as
the
ANTARIS
®
4
t
patented
multipath
mitigation
scheme.
The
second
effect
relates
to
the
carrier
phase
relation
of
the
direct
and
reflected
signal,
the
received
signal
strength
is
subject
to
an
interference
effect.
The
two
signals
may
cancel
each
other
(out
of
phase)
or
add
to
each
other
(in
phase).
Even
if
the
receiver
remains
stationary,
the
motion
of
the
satellite
will
change
the
phase
relation
between
direct
and
reflected
signal,
resulting
in
a
periodic
modulation
of
the
C/N
0
measured
by
the
receiver.
GPS
Modules
-
System
Integration
Manual
(SIM)
(incl.
Reference
Design)
GPS
Fundamentals
GPS.G4-MS4-05007-A1
Page 15
