GNSS has been evolving dramatically in recent years. There are currently 6 GNSS constellations, which are GPS (United State), GLONASS (Russia), BeiDou (China), Galileo (EU), QZSS (Japan), and IRNSS (India). The number of navigation satellites is currently over 115 and expected to go to over 150 by 2020. As the GNSS systems gradually evolve, the number of both constellations and satellites used for positioning increase, which would result in obtaining accurate position information. However, in a point of augmentation system, a large amount of data is required to support the correction messages for the available satellites of all the constellations. Because a bandwidth for the correction messages is generally limited, sending or scheduling the correction messages might be an important issue in a near future. In this study, we analyze the relationship between the size of bandwidth and Real Time Kinematics (RTK) performance. Multiple Signal Messages (MSM), the only Radio Technical Commission for Maritimes (RTCM) correction message which supports multi-constellation GNSSs, has been used for this analysis. Instead of the conventional method that broadcasts all the message at the same time, we assigned the MSM broadcasting interval for each constellation as 5 second. A test for this study was conducted on the roof of Sejong University under an open sky environment. RF signal was logged to a LabSat 3 instrument through a Trimble geodetic antenna. The RF signal was then reradiated to a Trimble NetR9 receiver with various type of MSM messages, and then we compared the accuracy of RTK position fed the scheduled MSM correction with that of unscheduled correction. We also did the same comparison for a poor DOP condition and analyzed the effect of the limited bandwidth.

Keywords: GPS, RTK, correction, MSM, RTCM