ION GNSS+2022, the most famous global technology conference for GNSS technologies, products and services, has been held in Colorado for five days. ION GNSS+ brings together leaders in GNSS and positioning, navigation and timing to present new research, introduce new technologies, discuss current policies, display products and exchange views. ION GNSS + used online meeting this year, including Session C1: New Technologies, Opportunities and Challenges, to share the eight new technology trends. Among them, Allystar shared the issue of BeiDou B2b and IGS-SSR PPP on Allystar GNSS Chip, which attracted attention from all walks of life.

The authors are Altti Jokinen, Marco Mendonça,Gary Hau, Ryan Yang and Yi-Fen Tseng from Allystar.

After the BeiDou and GALILEO satellite systems are online, the precision of the GNSS receiver has improved in recent years. The need for high-precision positioning is also increasing in different areas, especially in professional applications such as precision agriculture and marine navigation. And Precise Point Positioning (PPP) is one of the most anticipated solutions in the coming years. Currently, PPP is mainly available for high-end geodetic receivers, which are expensive and bulky. In this context, this presentation focuses on bringing PPP to a broader range of users by running the PPP solution on the tiny and affordable multi-frequency GNSS chip from Allystar. 

The BeiDou satellite system is operated and built by China, and it’s currently (26 January 2022) composed of 44 healthy satellites. The system consists of three types of satellites: Medium Earth orbits (MEO) providing global service, Inclined Geosynchronous Orbits (IGSO), and Geosynchronous Equatorial Orbit (GEO) providing regional service in Asia. The development of BeiDou has progressed fast and there are now more BeiDou than GPS or Galileo satellites. The BeiDou system is also the first satellite constellation to provide operational continent-wide PPP correction service broadcast over the satellites. 

BeiDou B2b-PPP corrections are broadcast on the BeiDou-3 GEO satellites that cover most of the Asian continent. The BeiDou B2b-PPP corrections are freely available and can be received over the B2b signal. Orbit, clock, and code-bias corrections are currently provided, which enables real-time float ambiguity PPP. There are currently three BeiDou GEO satellites broadcasting the same set of corrections, providing redundancy if some of the satellites are blocked by trees or buildings, if there are interference, or other signal strength issues are present.

For the PPP use case, Allystar receiver tracks the BeiDou B1i, B1C and B2a and GPS L1 and L5 signals that are used for positioning and BeiDou B2b from the GEO satellites that are used for receiving corrections. It is necessary to track the B1C signal in addition to B1i, since the B2b-PPP corrections are referring to the B1C (CNAV1) ephemeris. In addition, CNAV1 provides more advanced global ionosphere model. The CNAV1 ionosphere models employs spherical harmonics to model the ionospheric delay and it is shown in the literature that it typically provides more accurate estimates of ionospheric delay than conventionally used Klobuchar based models.

Allystar GNSS receiver run a-state-of-the-art PPP engine on the chip. The PPP engine uses Kalman filter to estimate states such as position, tropospheric wet delay and carrier-phase ambiguities. the tropospheric hydrostatic delay is corrected using the UNB3m model, while the ionospheric delay is corrected initially by the BeiDou CNAV ionosphere model and it is also estimated using dual-frequency observations. Site-displacement and satellite phase wind-up effects are corrected by the relevant models.

Real-time PPP performance using the B2b-PPP corrections is demonstrated in this paper using data collected in Hong Kong. This test includes continuous performance and PPP convergence analysis. It is shown that PPP using B2b corrections can provide decimeter level performance or better after initial convergence.

Utilization of the RTCM State Space Representation (SSR) format corrections in Allystar receiver is also demonstrated in this paper. The corrections are produced by Centre National d'Études Spatiales (CNES, French space agency) in the famous scientific demonstrator PPP-Wizard (Precise Point Positioning With Integer and Zero-difference Ambiguity Resolution Demonstrator) and are accessible via the International GNSS Service (IGS) for scientific applications. They are delivered using TCP/IP and subsequently applied to GPS L1/L5, Galileo E1/E5A, BeiDou B1i and GLONASS G1 signals. RTCM-SSR based corrections are an option for users located outside the BeiDou B2b coverage area or asking for a better accuracy, Geoflex being the operator of this PPP-CNES© Technology for commercial applications.

In conclusion, it is demonstrated that real-time PPP is feasible using cost-efficient 3x3 mm Allystar GNSS chip. It is also shown that free BeiDou B2b PPP corrections and RTCM SSR sold by Geoflex, a pure agnostic PPP operator dedicated to serve mass-market applications at the right price, can provide an accurate solution for many applications. This product is suitable for users requiring higher accuracy than conventional Single Point Positioning (SPP) solution.