International Global Navigation Satellite Systems Association
IGNSS Symposium 2018
Colombo Theatres, Kensington Campus, UNSW Australia
7 – 9 February 2018
Compact multi-GNSS PPP corrections messages for
transmission through a 250 bps channel
Ken Harima
School of Science / RMIT University / Australia
T: +61-3-99253775, E: ken.harima@rmit.edu.au
Suelynn Choy
School of Science / RMIT University / Australia
T: +61-3-99252650, E: suelynn.choy@rmit.edu.au
Chris Rizos
School of Civil and Environmental Engineering/ University of New South Wales / Australia
T: +61-2-93854205, E: suelynn.choy@rmit.edu.au
ABSTRACT
Precise Point Positioning (PPP) has been a target for a lot of research over the last
few decades. The comparatively low infrastructure requirements and wide area
applicability makes the system attractive as a nation-wide positioning system.
Real-time corrections for PPP are now available through private and public entities,
and have demonstrated the feasibility of sub-decimetre-level accuracy position and
navigation using PPP. Delivery of these corrections through a satellite broadcast is
an ideal fit for a precise position infrastructure. In addition, developments in multi-
frequency PPP, multi-GNSS PPP and efforts to estimate ionospheric delays over
wide areas has the potential to reduce convergence times and expand the
applicability of PPP. However these improvements will require an increased
amount of data to be transmitted to the user. Legacy SBAS channels are limited to
250 bps and often have only one satellite available as a transmitter. The present
study explores the feasibility of delivering multi-frequency, multi-GNSS PPP
systems using a 250 bps channel. Real-time streams for PPP were re-encoded into
compact messages designed to fit into 250 bps channels used by current SBAS
downlinks. Corrections based on CNES’s CLK93 stream and JAXA’s MDC1F
streams were used base for the compact PPP messages. Corrections from the
CLK93 stream occupied about 51% of the 250 bps channel capacity once
compacted, while corrections from MDC1 occupied 52%. The original streams had
an average data rate of 6.4 kbps (CLK93) and 22.4 kbps (MDC1). Real-time PPP
solutions were computed using both the original real-time streams and the
compacted PPP streams. For the MDC1 stream the horizontal accuracy after one
hour of convergence was 4.28cm using the compact messages and 3.64cm using
the original stream. For the CLK93 stream, horizontal accuracy was 3.69cm using
the compact messages and 3.25cm using the original messages. Convergence times
were similar, between 20 and 40 minutes, for the compact and original streams. In
future versions, the remaining channel capacity on the 250 bps channel could be
used to encode a regional ionosphere model to accelerate the PPP convergence.
KEYWORDS: PPP, multi-GNSS, SBAS channels.
