your position is our focus
4.4.6 How to change between protocols
1.
Reconfiguring
a
port
from
one
protocol
to
another
is
a
two-step
process.
First
of
all,
one
needs
to
assign
the
on
each
port.
4.5 Acquisition
At
system
power
up
the
ANTARIS
®
4
GPS
Software
executes
the
initial
acquisition
code.
This
part
of
the
GPS
Software
defines
three
different
strategies:
•
Coldstart
•
Warmstart
•
Hotstart
Depending
on
the
amount
of
valid
orbital
information
available,
the
receiver
chooses
the
fastest
possible
startup
scenario.
Before
the
receiver
can
calculate
a
position
fix
it
must
must
acquire
and
track
GPS
signals.
Acquisition
is
the
process
of
‘locking’
onto
the
signal.
The
SV
search
and
acquisition
time
highly
depends
on
the
h
signal
levels
are
preferred.
After
acquisition,
the
receiver
will
have
to
synchronize
to
the
data
stream,
and
download
orbit
data
from
the
ded.
g
is
If
orbit
data
has
been
downloaded
before,
and
the
receiver
is
calculating
position
fixes,
it
can
continue
to
do
so
even
when
the
signal
level
falls
below
the
minimum
signal
level
that
would
be
required
for
data
decoding.
preferred
protocol(s)
to
a
port.
One
port
can
handle
several
protocols
at
the
same
time
(e.g.
NMEA
and
UBX).
By
default,
all
ports
are
configured
for
UBX
and
NMEA
protocol
so
in
most
cases,
it’s
not
necessary
to
change
the
port
settings
at
all
(UBX-CFG-PRT
or
"PUBX,41"
messages).
2.
Activate
certain
messages
signal
level.
For
best
performance
hig
50Bits/s
data
stream.
This
can
only
be
done
down
to
a
certain
signal
level
(~25-30dBHz).
If
the
signal
level
falls
below
that
threshold,
downloading
data
is
halted,
and
can
only
be
resumed
once
the
signal
level
is
above
the
threshold,
again.
A
first
position
fix
can
only
be
achieved
if
orbit
data
for
a
sufficient
number
of
satellites
has
been
deco
Trackin
the
process
of
maintaining
lock
on
a
previously
acquired
signal.
Minimum Acquisition Time
depends on Signal Level
Acquisition
Sync/
Confirm
Download
Ephemeris
Tracking
typ
:
27
secs
18..36 secs
Start
Receiver
First
Position
Time
(TTFF)
Cha
nn
el
s
ve
l
M
ini
m
a
l Si
gna
l Le
Minimum Sync/ Download Level
~25.30 dBHz, continously
Figure 73: GPS Signal Acquisition
4.5.1 Coldstart
Strategy
In
Coldstart,
the
receiver
searches
all
valid
SV
numbers,
from
1
to
32,
in
a
predefined
order.
As
soon
as
SVs
are
found,
they
are
transferred
to
tracking
and
ephemeris
decoding
starts.
This
process
takes
between
18
to
36
wi
Once
there
t
SVs
with
valid
ephemeris,
position
fixes
are
calculated
and
output.
seconds
th
good
sky
view,
but
can
take
much
longer
otherwise.
are
sufficien
GPS
Modules
-
System
Integration
Manual
(SIM)
(incl.
Reference
Design)
Receiver
Description
GPS.G4-MS4-05007-A1
Page 89
