This two year project will set the framework for the development of an operational Analysis Centre Software (ACS) which will be a precursor of an operational National Positioning Infrastructure (NPI) to be funded under the Australian government’s NPI initiative from around 2016.

The ACS will implement a new precise positioning technique (PPP-RTK) developed in the CRCSI that will enable real-time positioning services across Australia and its maritime jurisdictions with improved accuracy and timeliness. It will bring together the physical infrastructure of AuScope with the techniques and algorithms developed in the CRCSI to deliver an NPI for the benefit of the Australian community.

The development of an ACS will assist both AuScope and the CRCSI to maximise the utilisation of the government’s investment in infrastructure and research.

This project is interlinked with Project 1.18 Near real-time tropospheric zenith delay estimation using GPS.

Australia’s National PNT

Australia’s Satellite Utilisation Policy provides a vision for Australia’s use of space and space-related technologies including providing strategies to enable Australia to meet its national priorities through space and to ensure Australia meets its future space-related education and innovation needs. The Policy emphasises the importance of space based navigation and timing as components of Australia’s smart infrastructure and social, economic and national security.

Annexed to the Policy is the National Positioning Infrastructure (NPI) Plan. This Plan proposes improved governance of the national positioning infrastructure, additional investment in ground infrastructure to deliver accurate and reliable positioning information to users across Australia and the development of a sovereign capability for GNSS product generation and integrity monitoring through an Analysis Centre Software (ACS) capability.

The ACS Project

The 1.14 program is the 1st phase (definition phase) in the creation of the ACS. It shall provide a definition of the user and software requirements together with the definition of the ACS preliminary design. Full implementation of the ACS with a new precise positioning technique (PPP-RTK) developed in projects 1.01 and 1.19 will enable real-time positioning services across Australia and its maritime jurisdictions with improved accuracy and timeliness. The ACS is heavily dependent on algorithms and prototype source code from pre-defined outputs of a broad range of CRCSI positioning programs.

Notably it is interlinked with:

  • 1.01 Precise Positioning
  • 1.11 High Accuracy Real-time Positioning Utilising the Japanese Quasi-Zenith Satellite System (QZSS) Augmentation System
  • 1.18 Near Real Time Tropospheric Zenith Delay Estimation using GPS.
  • 1.19 Multi-GNSS PPP-RTK Network Processing
  • 1.21 Ionosphere modelling to support ambiguity resolution for PPP-RTK.
  • Satellite Delivery of Augmented Positioning Data in Australia
  • BeiDou precise orbit and attitude modelling for PPP-RTK

The objective of the ACS project is to setup the ground for the development of a multi-GNSS, multi-frequency network processing platform (see Figure 1). It shall deliver as output the numerical estimation and quality indicators of the network parameters for the GNSS satellites and CORS network stations receivers that the users require to position themselves in a Precise Point Positioning in real-time and off-line mode.


Chart 1
Figure 1: ACS project : from the GNSS satellites, to ground stations, to the ACS to the user

The ACS mission

Importantly the ACS will allow sovereign control over how a future NPI will process and deliver precise positioning products to the users. Specifically it will promote Australia’s unique, state-of-the-art modelling and analyses software systems for multi-GNSS parameter estimation and quality control.

In order to take the full advantage of the multi constellation GNSS environment, and Australia’s exclusive geographical position in the Southern hemisphere (Figure 2) the ACS requires the implementation of advanced and sophisticated algorithms.

Chart 2

Figure 2: Full number of GNSS constellations visible above Australia

It shall provide to the users in Australia the necessary information that will allow them to enable the following positioning modes:

  1. PPP: Classical PPP with float ambiguities where only orbits and clocks of the GNSS satellites are provided. This approach is prone to accuracies of a few decimetres
  2. PPP-AR: PPP with ambiguity resolution (AR) where orbits, satellite clocks and satellite un-calibrated signal delays are provided. This approach is proven to provide accuracies of a few centimetres but the lack of regional augmentation information generates large convergence (time to first fix) rates up to several tenths of minutes if not hours
  3. PPP-RTK: PPP with ambiguity resolution (AR) with regional augmentation where orbits, satellite clocks, satellite un-calibrated signal delays and atmospheric corrections are provided. This is the so-called PPP-RTK mode where the convergence rates are minimal (few seconds or minutes) and the position accuracies reach up to a few centimetres (Figure 3).

 

Chart 3Figure 3: PPP-RTK solution for MOBS station (Melbroune). The Blue time-series represents the PPP float solution. The green time-series represent the PPP-AR with rapid convergence solution using Slant Total Electron Content information.


For this purpose, the ACS shall produce State Space Representation (SSR) messages of stages I, II and III.

The principle of the SSR concept is to provide information on the status of individual GNSS error sources. According to the RTCM 10403.2 standards the SSR Messages are developed in three major stages:

Stage I. Messages for precise orbits, satellite clocks and satellite code biases. Enables classic PPP mode using IGS products (Table 1)
Stage II. Messages for vertical TEC (VTEC) for single frequency receivers.
Stage III. Messages for slant TEC, troposphere and satellite phase biases. This message shall enable PPP-AR with rapid convergence i.e. PPP-RTK (Table 2)

Table 1 : Stage 1 RTCM SSR message types

Message Type

Message Name

1057

SSR GPS Orbit Correction

1058

SSR GPS Clock Correction

1059

SSR GPS Code Bias

1060

SSR GPS Combined Orbit and Clock Corrections

1061

SSR GPS URA

1062

SSR GPS High Rate Clock Correction

1063

SSR GLONASS Orbit Correction

1064

SSR GLONASS Clock Correction

1065

SSR GLONASS Code Bias

1066

SSR GLONASS Combined Orbit and Clock Corrections

1067

SSR GLONASS URA

1068

SSR GLONASS High Rate Clock Correction

 

Table 2 : Stage 3 RTCM SSR message types

Message Type

Message Name

1264

SSR Ionosphere Spherical Harmonics

1265

SSRSatellite GPS Phase Bias

1266

SSR Satellite GLONASS Phase Bias

1267

SSRSatellite Galileo Phase Bias

1268

SSRSatellite QZSS Phase Bias

1269

SSRSatellite SBAS Phase Bias

1270

SSRSatellite BDS Phase Bias

1264

SSR Ionosphere Spherical Harmonics

 

 

 

 

 

Project Team

Dr Stavros Melachroinos
Email: Stavros.Melachroinos@ga.gov.au