Japan’s CLAS positioning service receives major upgrade

Japan’s Quasi-Zenith Satellite System (QZSS) CLAS received a major enhancement on Nov. 30. QZSS CLAS (centimeter-level augmentation service) is the satellite-based nationwide open PPP-RTK service in Japan, providing centimeter positioning accuracy within one minute.

With the introduction of a new, highly efficient atmospheric correction message, the number of available satellites will be increased to 17 for those using CLAS. GPS, Galileo and QZS satellites in view will be corrected by the QZS L6 signal.

“The performance is expected be improved considerably, especially in urban areas,” said Rui Hirokawa, the deputy general manager, Space Systems Department of Mitsubishi Electric Corporation, Kamakura Works, in an email to GPS World.

Compact SSR — a highly efficient RTCM-compatible open specification for PPP/PPP-RTK — is applied to QZS CLAS. Compact SSR is accepted as a PPP-RTK standard in the 3GPP LTE positioning protocol (LPP) and the mobile communication standard for LTE/5G, with plans for it to be applied to the Galileo High-Accuracy Service (HAS).

Detailed information about the augmentation system upgrade is described in the ION GNSS+ 2020 paper, “Open Format Specifications for PPP/PPP-RTK Services: Overview and Interoperability Assessment,” by Rui Hirokawa and Ignacio Fernández-Hernández.

Since July 1, CLAS has been broadcasting a trial signal compliant with IS-QZSS-L6-003 using the L6D signal of QZS-3, which increases the number of augmented satellites to a maximum of 17 for more stable positioning accuracy.

On Nov. 30 (JST), the official broadcast of the augmentation information began from all four QZS satellites (QZS-1, 2, 3 and 4).

To continue using CLAS after Nov. 30, it may be necessary to update the receiver’s F/W to comply with IS-QZSS-L6-003. Please contact the manufacturer of the CLAS receiver for further information. Read more in this National Space Policy Secretariat notice.