QZS's PRN number and the future of MADOCA

category: gnss
tags: madoca qzss

QZS’s PRN number

Receiving the signal from the quasi-zenith satellite (QZS) 1 replacement in the alert off state, I confirmed the delivery of the high-precision augmentation signal of MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis). The PRN (pseudo random noise) number was 206. I think I’ve heard this PRN 206 somewhere.

Navigation satellite receivers identify satellites by PRN number or SVID (space vehicle identification) number. And I’m sure many people think of satellites from the numbers displayed on their receivers. For example, PRN 194 or SVID 2 (J02) is the satellite signal of QZS-2. Since adding 10 of 184 gives 194, PRN 184 represents a SLAS (submeter level augmentation service) signal of QZS-2. Since subtracting 10 of 194 gives 184, one can imagine that PRN 204 represents the MADOCA signal of QZS-2 easily.

PRN 193 (J01) was assigned to QZS-1, PRN 194 (J02) was assigned to QZS-2, PRN 199 (J07) was assigned to QZS-3 (Geostationary satellite), PRN 195 (J03) was assigned to QZS-4, and PRN 196 (J04) was assigned to QZS-1R (replacement).

PRN numbers when the full constellation of seven satellites

The PRN number of QZS-5 will be assigned to 197 (J05), but it is slightly irregular after that (Table 3.2.1-1 on page 25 of the interface specification IS-QZSS-PNT-004). The PRN number for QZS-6 is planned to be 200 (J08), and that for QZS-7 is scheduled to be 201 (J09). After full constellation of the quasi-zenith satellite system, the signal in the L1 frequency band is changed from L1 C/A (coarse acquisition) to L1 C/B (coarse acquisition with binary offset carrier?), for preventing code pull-in at the wrong timing. Therefore, the PRN number will be changed.

Therefore, I summarized the relationship between the satellite and the PRN number written in the IS-QZSS-PNT-004, SLAS specification IS-QZSS-L1S-004, and CLAS specification IS-QZSS-L6-004 by the PRN number. PNT indicates the position, navigation, and timing signal, CLAS indicates the centimeter level augmentation service, MDC indicates the MADOCA distribution signal, and parentheses indicate future plans.

PRNsatellite and signal
187(not determined yet)
188(not determined yet)
190(not determined yet)
191(not determined yet)
193J01PNT, J01CLAS
194J02PNT, J02CLAS
195J03PNT, J03CLAS
196J04PNT, J04CLAS
197(J05PNT, J05CLAS)
198(J06 non standard code)
199J07PNT, J07CLAS
200(J08PNT, J08CLAS?)
201(J09PNT, J09CLAS?)
202(J10 non standard code)
203(J04PNT L1 C/B)
204J02MDC (J05PNT L1 C/B)
205J03MDC (J08PNT L1 C/B)
206J04MDC (J09PNT L1 C/B)
208(MDC? non standard code)
212(MDC? non standard code)

SLAS signals are not broadcast from QZS-5 and later. Also, the question mark in PRN 200, 201, 207-212 shows uncertain because there is no description of SVID in IS-QZSS-L6-004, and the PRN numbers are guessed from the past PRN allocation.

What I felt painful in the assignment of PRN numbers 204-206 is the same PRN number will be assigned to different satellites.

It would be very easy to understand if the PRN number of the L1 C/B signal could be the PRN number of the L1 C/A signal plus 10. If PRN 187, PRN 188, etc. can be used for PNT, I think that these can be used for L1 C/B.

MADOCA broadcast from QZS

The MADOCA distribution broadcast by QZS’s L6E signal is a technical demonstration. Anyone can use it for free. On the other hand, MADOCA which is distributed in NTRIP format on the Internet is a commercial paid service.

When switching from the L1 C/A signal to the L1 C/B signal, the MADOCA in L6E signal, which currently has PRN numbers 204 to 206, has been upgraded, and the PRN number may change accordingly. The change to the L1 C/B signal is expected around 2024.