Quality Control of Ionospheric Corrections for Adoption of Wide Area Augmentation at the Low Latitude Regions

Takeyasu Sakai, Takahiro Aso, Kazuaki Hoshinoo, Ken Ito

Abstract:	QZSS (quasi-zenith satellite system) is a Japanese satellite navigation program with a regional service coverage. The orbits for QZS (quasi-zenith satellite) are 24-hour elliptic orbit inclined 43 degrees in order to broadcast radiosignals from high elevation angle into urban canyons. With a full constellation of QZSS, one of QZSS satellites always exists at around the zenith so that it helps the first acquisition of navigation signals and quick start of GNSS receiver as well as it provides both GPS-like and SBAS-like ranging signals. The first QZSS satellite, QZS-1 “Michibiki”, was launched successfully on 11th Sept. 2010 from Tanegashima Space Center, Japan, and settled to the intended inclined elliptic orbit. By the end of November, initial functional checkout for satellite bus and mission equipment was completed without any major problems. Since then, technical validation experiments have been conducted by some participating organizations. QZSS is broadcasting GPS augmentation information on the GPS L1 frequency for experiments. For this purpose L1-SAIF (submeter-class augmentation with integrity function) signal has been developed based on SBAS standard. The ENRI has been responsible for development of L1-SAIF Master Station (L1SMS). The facility was successfully developed and tested with expected performance. Following initial functional checkout, the initial experiment has been conducted successfully using a combination of QZS-1 on orbit and L1SMS. L1-SAIF signal achieves the intended accuracy smaller than 1 meter in an RMS manner at the mainland of Japan. Ionosphere disturbance sometimes, however, degrades the position accuracy, especially at the southwestern islands of Japanese territory. From an operational point of view, positioning accuracy should be uniform over the service area. In order to improve ionospheric correction information, a possible way is quality control of ionospheric corrections. It is possible to introduce monitoring the quality of ionospheric corrections in real time; In the current implementation, the quality of ionospheric corrections generated by planar fitting is examined only by chi-square test. Here the authors introduce additional monitoring and quality control into ionospheric corrections. The MCS of wide area augmentation monitors the consistency of ionospheric corrections with measurements from the ground network, and if inconsistency is detected, it attributes the associate ionospheric corrections with large uncertainty to be deweighted in user receivers or ‘not monitored’ status not to be used. In order to investigate this idea, the authors have upgraded the L1-SAIF Master Station to be capable of monitoring ionospheric corrections generated by itself. The expected performance is examined via experiments at the southwestern islands of Japan, and it is shown that this strategy has a potential of 10% improvement of position accuracy at the low latitude region.
Published in:	Proceedings of the 2015 International Technical Meeting of The Institute of Navigation January 26 - 28, 2015 Laguna Cliffs Marriott Dana Point, California
Pages:	353 - 363
Cite this article:	Sakai, Takeyasu, Aso, Takahiro, Hoshinoo, Kazuaki, Ito, Ken, "Quality Control of Ionospheric Corrections for Adoption of Wide Area Augmentation at the Low Latitude Regions," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 353-363.
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