4 SBF Reference
The list of SBF blocks available on your receiver can be found in Appendix A.
4.1.3
SBF Block Time Stamp (TOW and WNc)
Each SBF header is directly followed by a time stamp, which consists of two fields:
and
Parameter Type Units & Scale Do-Not-Use
Description
Factor
Value
u4
0.001 s
4294967295 Time-Of-Week : Time-tag, expressed in whole milliseconds from the beginning
of the current GPS week.
u2
1 week
65535
The GPS week number associated with the
is a continuous week count
(hence the "c"). It is not affected by GPS week rollovers, which occur every 1024
weeks.
By definition of the Galileo system time,
WNc
is also the Galileo week number
plus 1024.
In the SBF time stamps, the definition of the week always follows the GPS convention even if
the block contains data for another constellation. This means that WNc 0, TOW 0 corresponds
to Jan 06,1980 at 00:00:00 UTC.
If the time-of-week or the week number is unknown, which is typically the case for a few sec-
onds after start-up, the corresponding field is set to its Do-Not-Use value (see section 4.1.7). It
does not mean that the SBF block is unusable, but simply that the receiver could not time-tag
it. It is typical that the
TOW
field becomes valid before the WNc field.
The interpretation to give to the time stamp is block-dependent. Three types of time stamps
are possible:
•
Receiver time stamp
: this type of time stamp is used for the SBF blocks containing
synchronous data, i.e. data generated at a given epoch in the receiver time scale.
Examples of such blocks are the measurement and PVT blocks (
and
). The time stamp is always a multiple of the output interval as specified
by the
command (see also section 4.1.8). As soon as the receiver time
is aligned with the GNSS time, the receiver time stamp is guaranteed to never decrease
in successive SBF blocks.
•
SIS time stamp
: it is used for asynchronous blocks containing navigation message data
from the signal-in-space. The time stamp corresponds to the time of transmission of
the end of the last navigation bit used to build the SBF block. It always follows the GPS
convention, as explained above.
•
External time stamp
: this type of time stamp is used for SBF blocks triggered by external
asynchronous events, such as the
block.
For the blocks with a SIS or an external time stamp, there is no strict relation between the
time stamp of the SBF blocks and their order of transmission. For example, the SBF stream
may contain a
block with ephemeris parameters received one hour in the past (i.e.
the time stamp is one hour in the past) followed by another block with a current receiver time
stamp.
4.1.4
Sub-blocks
Some blocks contain sub-blocks. For example, the
block contains
N
SatInfo
sub-blocks, each sub-block containing data for one particular satellite. Unless the
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Страница 147: ...3 Command Line Reference PVTMode Static StandAlone SBAS DGPS RTKFloat RTKFixed Cartesian1 COM1 147 ...
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