Page | 1 March 4, 2019
APN-073 Rev E
APN 073:
RTK ASSIST &
RTK ASSIST PRO
Page | 2 March 4, 2019
Contents
RTK ASSIST Overview .................................................................................................................................... 3
How It Works ................................................................................................................................................ 3
RTK ASSIST ..................................................................................................................................................... 4
RTK ASSIST PRO ............................................................................................................................................. 5
Operating Modes .......................................................................................................................................... 6
Requirements for using RTK ASSIST & RTK ASSIST PRO ................................................................................ 6
RTK ASSIST & RTK ASSIST PRO Subscriptions ................................................................................................ 8
Verifying RTK ASSIST ..................................................................................................................................... 8
Enable L-Band Tracking ................................................................................................................................. 9
Configuration for RTK ASSIST ...................................................................................................................... 11
Logs and Commands ................................................................................................................................... 11
Where to go for Support ............................................................................................................................. 12
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RTK ASSIST
RTK ASSIST Overview
NovAtel’s RTK ASSIST
TM
and RTK ASSIST PRO
TM
empower RTK users to seamlessly operate with
centimetre level accuracy during RTK correction signal outages caused by radio connectivity issues or
wireless or cellular signal disruptions. RTK users can continue their operation without being impacted by
signal outages, leading to increased productivity. RTK ASSIST and RTK ASSIST PRO are supported through
NovAtel’s satellite-based correction services and thus do not require any local infrastructure. RTK
ASSIST is currently available for OEM6
®
and OEM7
®
product lines and RTK ASSIST PRO is available on
OEM7
®
, for eligible hardware and firmware models.
How It Works
RTK ASSIST and RTK ASSIST PRO work by using the precise GNSS correction data delivered by the
geostationary (GEO) satellites
1
to maintain centimetre level accuracy in the absence of RTK corrections.
These corrections are received through L-Band tracking and subsequently used by the position engine to
maintain centimetre level accuracy.
Figure 1: Global Coverage Map for Correction Delivery
1
GNSS correction service is provided by TerraStar.
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RTK ASSIST
RTK ASSIST operates seamlessly in the background for up to twenty minutes from the onset of an RTK
outage. After that, the position type will transition to the next most accurate available. Datum
differences or biases are automatically compensated for when transitioning between position types. The
algorithm is designed to facilitate smooth transitions during RTK outages. However, as with any carrier
phase-based positioning, there is a possibility that a position jump may occur due to an incorrect
ambiguity fix. The positioning solution will transition back to using RTK corrections once connection has
been re-established with the correction source.
As the RTK ASSIST technology uses the precise correction data delivered via geostationary satellites, any
obstructions (i.e., buildings, grain tanks, tree lines) can potentially degrade or block the satellite signals.
Depending on the L-Band signal blockage duration, the position error will increase over time. If L-Band
signals are lost for more than 2 minutes, RTK-level accuracies cannot be maintained and RTK ASSIST will
disengage. The resulting position type will be determined by the accuracy level of the solution at the
time RTK ASSIST becomes inactive.
The RTK ASSIST functionality will engage if there is L-Band tracking and the GNSS receiver has had at
least one RTK fix prior to the outage.
Users can expect centimetre level accuracy during the RTK outage when using RTK ASSIST. However, the
accuracy will degrade as the outage duration increases but will stabilize (approximately 4 cm RMS). If
the RTK outage occurs in the first 30 minutes of operation, further degradation (approximately 20 cm
RMS) may be observed.
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Figure 2: Summary of How RTK ASSIST Works
Figure 2: Summary of How RTK ASSIST Works shows the basic flow structure
that RTK ASSIST will follow. If an outage occurs while in RTK mode, RTK ASSIST will engage. At this point,
if RTK returns before the 20 minute time period, RTK will resume as normal. However, if RTK corrections
do not return, the next most accurate position type will be used (SBAS, PSRDiff etc.) until corrections are
re-established.
RTK ASSIST PRO
Similar to RTK ASSIST, RTK ASSIST PRO will operate seamlessly in the background, however without limit
after the onset of an RTK outage. RTK ASSIST PRO leverages multi constellation support to provide highly
accurate and reliable positioning in RTK correction outages.
RTK ASSIST PRO also provides standalone centimetre level positioning in areas where RTK is no longer
practical or beneficial. Standalone positioning is provided at the TerraStar-C PRO level. When operating
without an initial RTK fix the user may require nudging to handle datum offsets. Please refer to APN-061
for information on TerraStar-C PRO.
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Operating Modes
RTK ASSIST operates in two different modes: Coast and Full Assist.
Coast:
Coast is available as soon as the RTK ASSIST corrections are received from the L-Band satellite. In this
position mode, error growth during the RTK outage is slightly greater when compared to Full Assist
mode. When in this mode, RTK will not resume following a full GNSS signal outage until after RTK
corrections are restored.
Full Assist:
Full assist provides the lowest position error growth during RTK correction outages and makes it possible
for RTK to resume even if there are complete GNSS signal outages during the RTK ASSIST period. This
mode requires a convergence period of approximately 30 minutes from navigation start.
Requirements for using RTK ASSIST & RTK ASSIST PRO
The RTK ASSIST functionality requires the receiver to be enabled for both RTK positioning and L-Band
tracking. These requirements can be checked against the model of the receiver and determine that
options for L-Band and RTK are both enabled.
OEM6
The firmware requirement for RTK ASSIST is 6.710 (OEM060710RN0000) or later.
Based on the OEM6 model structure, firmware Option 4 must be RTK (i.e., “R”), the firmware Option 2
must be “2” or higher, and the firmware Option 3 should be “L” or “J”. For example:
• OEM628-D2L-R0G-TT0
• OEM628-D2J-RPR-TTN
• SM6L-D2L-RPG-0T0
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Figure 3: OEM6 Model Structure & Firmware Model Options for RTK ASSIST
The “L” or “J” option enables L-Band tracking, and the “R” option allows the receiver to use RTK ASSIST
service. However, the user must configure the receiver to track the L-Band signal (see Enable L-Band
Tracking ) and a RTK ASSIST subscription must be purchased and activated before the receiver will start
using the corrections and providing RTK ASSIST functionality.
To use the RTK ASSIST service, the channel configuration options for dual-frequency (L1 & L2) tracking
must be included in the model, as well a minimum of GPS+GLONASS tracking. To allow for this, the first
two firmware options must be a minimum of “D” and “2” as shown in the examples and Figure 3 above.
OEM7
The firmware requirements for RTK ASSIST is 7.02 (OM7MR0200RN0000) or later.
The firmware requirements for RTK ASSIST PRO on OEM7 is 7.05 (OM7MR0500RN0000) or later.
Dual frequency is represented by the “D” or “F” in the 2
nd
character. The “R” model is required for RTK in
the 4
th
character. As stated above, GPS + GLONASS tracking should be enabled for optimal performance
of the system.
• OEM729-DFN-RNN-CBN
Figure 4: OEM7 Model Structure and Firmware Model Options for RTK ASSIST
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RTK ASSIST & RTK ASSIST PRO Subscriptions
To purchase a RTK ASSIST subscription, contact your NovAtel dealer or sales office
2
. NovAtel Customer
Support can provide free 3 or 5-day trial RTK ASSIST subscriptions for test and demonstration purposes
3
.
Users cannot subscribe to both RTK ASSIST and TerraStar subscriptions simultaneously.
The receiver’s NovAtel Product Serial Number (PSN) or TerraStar Product Activation Code (PAC) is
needed to obtain a subscription. Before contacting your NovAtel sales office, obtain the PSN for the
receiver you wish to activate using the command “LOG VERSION”.
To verify an RTK ASSIST subscription, users can use the TERRASTARINFO log as demonstrated below:
LOG TERRASTARINFO
< TERRASTARINFO COM1 0 87.0 FINESTEERING 1919 247530.423 02000020 a7ce 32768
"QU075:2185:6222" PAYG 00000800 0 0 0 LOCAL_AREA 51.11639 -114.03806 2
Bits
Mask
Description
0-8
Reserved
9
TerraStar-C
10
TerraStar-L
11
RTK ASSIST
12
RTK ASSIST PRO
13
TerraStar-C PRO
12-31
Reserved
Table 1: TERRASTARINFO bit mask description
The bit mask (0x00000800) indicates that the receiver has a TerraStar RTK ASSIST service.
Verifying RTK ASSIST
Users can check the status of their RTK ASSIST solution by looking at the RTKASSISTSTATUS log
4
LOG RTKASSISTSTATUS
2
http://www.novatel.com/where-to-buy/sales-offices/
3
Contact support@novatel.com for more details. Maximum of 3 test subscriptions will be provided per receiver.
4
Users can find the relevant logs and commands in the user manual for their product.
OEM6: http://www.novatel.com/assets/Documents/Manuals/om-20000129.pdf
OEM7: http://docs.novatel.com/OEM7/Content/Home.htm
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< RTKASSISTSTATUS COM1 0 68.0 FINESTEERING 1919 166861.000 00040020 80fe 46774
ACTIVE COAST 1085.0 21.0
ACTIVE: The active keyword indicates that RTK ASSIST is engaged and currently providing positioning.
This field will report INACTIVE when not being used.
1085.0: This is the time remaining (seconds) in the RTK ASSIST mode before transitioning to the next
most accurate available positioning mode. The maximum is 20 minutes (1200 seconds) for RTK ASSIST,
and unlimited for RTK ASSIST PRO.
21.0: The corrections age reported in the RTKASSISTSTATUS log should typically be below 30 seconds. If
the age exceeds this value, then L-Band tracking is likely being degraded. The most likely cause of
degraded L-Band tracking is obstructions between the antenna and the L-Band satellite.
An alternative way to see if RTK ASSIST is active for users using the BESTPOS log is to look at Field #20
(Extended Solution Status) to see if bit four is active.
Enable L-Band Tracking
To enable L-Band tracking, the “ASSIGNLBANDBEAM” command is used. The factory default setting for
“ASSIGNLBANDBEAM” is “IDLE”, which means that the receiver will not track an L-Band signal unless
configured to do so.
To enable L-Band tracking, the “AUTO” setting is recommended in most cases. Specifically:
Figure 5: BESTPOS Extended Solution Status
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ASSIGNLBANDBEAM AUTO
The auto setting allows the GNSS receiver to automatically track the signal from the highest elevation
TerraStar satellite for the best performance. To determine which TerraStar signal is the best to use in a
particular location, the receiver must have a position solution available.
To verify the L-Band tracking status, the “LBANDTRACKSTAT” log can be used. For example:
<LBANDTRACKSTAT COM1 0 80.5 FINESTEERING 1835 140789.000 00000020 29fd 13306
< 1
< "98W" 1539902500 1200 974c 00c2 0 345.395 42.398 3.5073 71580.844 1363392 1168
1085 173150784 136010 0.0038
This log reports the L-Band tracking status of the TerraStar signal. Some helpful fields are highlighted
above and described below:
• 98W: This is the name of the TerraStar beam or transmitting satellite being tracked.
• 00c2: This is the “Tracking Status Word”. A tracking status of “00c2” indicates that the receiver
is tracking and locked onto the TerraStar signal.
• 42.398: This is the C/No or “Carrier to Noise Density Ratio” (in dB-Hz). The C/No is typically
about 40-45 dB-Hz in ideal conditions. A low C/No can result in missed corrections and
correspondingly degraded performance.
• 71580.44: This is the “Lock Time” (in seconds). This field can be monitored to ensure that the
L-Band signal is being tracked continuously without any loss of lock.
While the TerraStar signal can be tracked even without a subscription, the receiver will not decode and
use the TerraStar service data until a valid subscription has been activated.
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Configuration for RTK ASSIST
To enable RTK ASSIST on a receiver with a valid model and subscription, use the commands provided
below.
LOG TERRASTARINFO (Indicates a valid RTK ASSIST subscription)
ASSIGNLBANDBEAM AUTO (Enables L-Band tracking)
RTKASSIST ENABLE (On by default – users can verify by logging the command)
RTKASSISTTIMEOUT SUBSCRIPTION_LIMIT (Use the maximum amount of time possible)
LOG RTKASSISTSTATUS (Users can verify that RTKASSIST is working when there is no RTK correction
signal)
Logs and Commands
All logs and commands described below can be found in documentation for OEM6 and OEM7 in their
respective firmware manual
OEM6: http://www.novatel.com/assets/Documents/Manuals/om-20000129.pdf
OEM7: http://docs.novatel.com/OEM7/Content/Home.htm
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Where to go for Support
To help answer questions and/or diagnose any technical issues that may occur, the NovAtel Support
website is a first resource: www.novatel.com/support/
Remaining questions or issues, including requests for test subscriptions or activation resends, can be
directed to NovAtel Support by visiting www.novatel.com/support/contact/. To enable the online form
and submit a ticket, first select a "Product Line" and then an associated "Product" from the list.
However, before contacting Support, it is helpful to collect data from the receiver to help investigate
and diagnose any performance-related issues. In those cases, if possible, collect the following list of logs
(the LOG command with the recommended trigger and data rate is included):
LOG VERSIONA ONCE
LOG RXSTATUSA ONCHANGED
LOG RAWEPHEMB ONCHANGED
LOG ALMANACB ONCHANGED
LOG IONUTCB ONCHANGED
LOG GLORAWEPHEMB ONCHANGED
LOG GLORAWALMB ONCHANGED
LOG GLOCLOCKB ONCHANGED
LOG RANGEB ONTIME 1
LOG BESTPOSB ONTIME 1
LOG LBANDTRACKSTATB ONTIME 1
LOG TERRASTARINFOA ONCHANGED
LOG TERRASTARSTATUSA ONCHANGED
LOG RXCONFIGA ONCE
LOG RTKASSISTSTATUSA ONTIME 1
The data described above can be collected using a terminal program that supports binary data logging,
or NovAtel’s CONNECT utility can be downloaded and installed from the NovAtel website:
www.novatel.com/support/info/documents/809.
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