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Commands
4.4.3
ASSIGN
The ASSIGN command can fundamentally change the way that the receiver operates. Do not
alter the default settings unless you are confident that you understand the consequences.
You can use this command to assist the initial acquisition of a satellite by overriding the automatic satellite/
channel assignment and reacquisition processes with manual instructions. The command specifies the tracking
channel to use to search for a specified satellite, and if specified, at the provided Doppler frequency and
Doppler window.
The instruction remains in effect for the specified SV channel and PRN, even if the assigned satellite sets
below the horizon. If the satellite Doppler offset of the assigned SV channel exceeds that specified by the
window parameter of the ASSIGN command, the satellite may never be acquired or re-acquired.
If a manually assigned channel is commanded to return to AUTO tracking and if the assigned channel is
currently tracking a satellite another channel is also tracking, the assigned channel will immediately idle and be
reassigned to a different satellite if one is available.
To cancel the effects of ASSIGN, you must issue one of the following:
•
The ASSIGN command with the state set to AUTO
•
The UNASSIGN command
The channels are assigned by SV channel. A single SV channel is composed of the following for GPS satellite
channels:
•
one L1 CA signal channel,
•
one L1 C signal channel,
•
one L2 P(Y) signal channel,
•
one L2 C signal channel
•
one L5 signal channel
A single SBAS SV channel is composed of only one signal channel. Separate channel assignments are required
to track the L1 and L5 signals for one SBAS satellite.
Changing the ASSIGN command state to AUTO returns the SV channel control to the automatic search
algorithm. For SBAS channels, the SV channels are actually idled as they do not have an automatic search
algorithm. The search algorithm that will be used is specified by the TRACKMODE command.
Both the ASSIGN and UNASSIGN commands are accepted only when the receiver is in the Operational state.
1.
Assigning a PRN to an SV channel does not remove the PRN from the search space of the
automatic search algorithm; only the SV channel is removed. This will have the side effect
that if the PRN is assigned to one channel, the PRN may be reported on 2 channels since the
automatic search algorithm may assign another channel to track the same PRN.
2.
The Doppler fields are specified for the L1 frequency for all SV channels where multiple
signal channels are linked to the same SV channel (i.e. GPS SV channels). The Doppler will
be adjusted for the other frequencies automatically. For SV channels having only one signal
channel, the Doppler fields are specified for that specific frequency (i.e. SBAS SV
channels).
3.
GPS PRNs may only be assigned to GPS SV channels, and SBAS PRNs may only be
assigned to SBAS SV channels. Assigning a GPS PRN automatically dedicates channels to
track all signal types for that PRN while SBAS signals must be assigned individually.
WAAS G-III Reference Receiver User Manual Rev 1
Chapter 4
47
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