RTCM3 MSM QZSS L1C/B support

[info@…]

Have noticed Trimble Alloy and Septentrio PolaRx5 RTCM3 MSM streams now including a new signal that appears to be 1E. Septentrio note in their 5.7.0 firmware update that the QZSS L1C/B signal can now be enabled in RTCM3 MSM streams. This mapping has been added to the RTKLIB fork see ​https://github.com/rtklibexplorer/RTKLIB/blob/main/src/rtcm3.c#L106 Made a similar addition to a local BNC build and it appears to be logging the RTCM streams to rinex files as expected - it did need local skeleton files that added the 1E signal. Noted some header defaults in src/rinex/rnxobsfile.cpp and signal priorities, and should QZSS 1E be added to these, it does not seem necessary for logging as stream to rinex.

Index: src/RTCM3/RTCM3Decoder.cpp
===================================================================
--- src/RTCM3/RTCM3Decoder.cpp	(revision 10930)
+++ src/RTCM3/RTCM3Decoder.cpp	(working copy)
@@ -356,12 +356,12 @@
 static struct CodeData qzss[RTCM3_MSM_NUMSIG] = {
         {0.0, 0},
         {GPS_WAVELENGTH_L1, "1C"},
+        {GPS_WAVELENGTH_L1, "1E"},
         {0.0, 0},
         {0.0, 0},
         {0.0, 0},
         {0.0, 0},
         {0.0, 0},
-        {0.0, 0},
         {QZSS_WAVELENGTH_L6, "6S"},
         {QZSS_WAVELENGTH_L6, "6L"},
         {QZSS_WAVELENGTH_L6, "6X"},

[stuerze]

Hallo,

in principle it would not be a problem to add the line with respect to the signal mapping for the L1CB signal. But there is an unresolved issue regarding the PRN numbers:

For the expanded QZSS constellation with 11 satellites, the PRN range should be extended as well. Currently, there are three options regarding PRN assignment under discussion because there are PRN numbers for L1C, L2C and L5 signals on the one hand and on the other hand some of the QZSS satellites transmits the L1C/B signals using a PRN number that differs from those used for the L1C, L2C and L5 signals.

And as soon this is not resolved it doesn’t make sense from my point of view to add the signal mapping for L1CB signal.

Do you agree?

Best regrads, Andrea

[info@…]

PRN J08 is the highest in the current IGS satellite meta data, also the highest with current nav data, and with this change BNC did convert a RTCM3 MSM stream to rinex including J08.

See also ​https://qzss.go.jp/en/overview/services/sv03_signals.html

Currently seeing L1C/B from J04 (SVN J005 / QZS-1R) and J08 (SVN J007 / QZS-6)

QZS-5 deployment failed: ​https://global.jaxa.jp/press/2025/12/20251222-2_e.html

QZS-7 deployment is pending: ​https://global.jaxa.jp/press/2026/06/20260615-1_e.html

The RTCM3 MSM encoding is not so limited.

When BNC is being used to simply log RTCM3 and convert to RINEX, can't see a reason for it to vary the handing for particular PRNs. For the PPP processing there may well be issues, is there going to be an ISB that needs to be accounted for, but that seems a separate matter.

There are lots of other examples of satellites with varying signals within constellations. e.g. Hard coding PRNs into software appears to have caused issues after the recent BDS-2 decommission, where software might have baked in special handing for PRNs less than 19, e.g. is there a Trimble Alloy reporting the expected signals for BDS satellites with PRNs less than 19 and might that be a firmware issue and is there even a firmware available to address this yet, and is your mobile phone handling the change as expected.

If you know the provenance of this signal addition then that might be relevant, is it in a recent standard update, is it a de-facto standard, and were other signals added such as 1Z and 1Bs. The standard process seems to be lagging on the signal id assignments, and not only for MSM, there is also the SSR and IGS-SSR signal assignments, it's affecting interoperability - just trying to help.

[stuerze]

The signal addition is a planned update within the RTCM Version 3 Standard. It was discussed and successful iteroperability tested within the RTCM Committee SC-104 - more specifically, within the QZSS working group. But from that QZSS working group it is aspierd to also include the satellite ID extension, along with the L1C/B incorporation, in the next revision of the RTCM Version 3 document. For both a CDV is requiered to make it part of the Version 3 standard. Hence, I can add it before CDV and release but its standardization is not completed so far.

[stuerze]

I have added L1C/B (RINEX code: '1E') in QZSS Signal ID Mapping. It will be available with the next release of BNC