Novatel OM-20000041 E Comparison Of R T-2 And RT-20, 232 MiLLennium GP SCard Software Version 4.50 Command Descriptions Manual Rev 1, Figure E-8 RT-20 Re-initialization Process

E Comparison Of R T-2 And RT-20
232 MiLLennium GP SCard Software Version 4.50 Command Descriptions Manual Rev 1
and reference model information is lost. The timeout threshold for RTK differential corrections is 30
seconds, but for Type 1 pseudorange corrections, the timeout is 60 seconds. Therefore, when the RT-20
can no longer function because of this timeout, the pseudorange filter can produce differential positions
for an additional 30 seconds (provided RTCM Type 1 messages were transmitted along with the Type 59
messages) before the system reverts to single point positioning. Furthermore, once the link is re-
established, the pseudorange filter produces an immediate differential position while the RTK filter takes
an additional 14 seconds to generate its positions. The reference models require 7 reference observations
before they are declared useable, and this will take 14 seconds, based on a 1/2 Hz differential correction
rate. The reference model must be healthy before solutions are logged to the low latency logs, so there is
a delay in the use of real time carrier positioning to the user once the link has been re-established. The
RTK logs (RTCA/B, RTKA/B AND BSLA/B) use matched observations only (no extrapolated observations),
and these will be available after three reference observations are received, but will have about 1.5 seconds
latency associated with them.
Figure E-8 RT-20 Re-initialization Process
The RTK system is based on a time-matched double difference observation filter. This means that observations at
the remote site have to be buffered while the reference station observation is encoded, transmitted, and decoded.
Only two seconds of remote observations are saved, so the reference station observation transmission process has
to take less than 2 seconds if any time matches are to be made. In addition, only remote observations on even
second boundaries are retained, so reference station observations must also be sent on even seconds if time matches
are to be made.
REFERENCE
REMOTE
1234567
Reference
Doppler Start generating
RTKA/B logs
Models
Ready Generate
RTKA/B
logs
RTCM59 messages
required following
RESETRT20 reference phase
models and and
PRTKA/B