An open-source GNSS Direct Position Estimation Plug-in Module for Two-Step Positioning SDRs, integrated into SoftGNSS v3.0 by Borre et al. (2007)
Intelligent Positioning and Navigation Laboratory (IPNL) / PNT Signal Processing Laboratory
The Hong Kong Polytechnic University
DPE_module v1.0 is to be formally introduced at the upcoming Institute of Navigation GNSS+ 2024 (ION GNSS+ 2024) conference. https://www.ion.org/gnss/abstracts.cfm?paperID=13473
DPE_module v1.0 is a Direct Position Estimation (DPE) plug-in module that can be integrated into existing two-step positioning (2SP) MATLAB SDRs. 2SP information, namely tracking code phase, signal transmission time, receiver local time, satellite position from Least Squares, satellite clock bias, and Least Squares position solution, are used as input for the plug-in module.
Programmed in a user-friendly language, MATLAB, DPE_module v1.0 is aimed for better understanding and familiarity of a practical implementation of DPE. In this repository, DPE_module v1.0 is integrated into the SoftGNSS MATLAB GPS L1 C/A 2SP SDR from Borre et al. (2007), which is based on Scalar Tracking Loop (STL). But integration of DPE_module v1.0 is not restricted to an STL-based receiver and can be integrated with other 2SP architectures, such as Vector Tracking Loop (VTL). Additionally, the GNSS constellation is not restricted to GPS L1 C/A, but is also integrable with SDRs working with other BPSK-modulated GNSS signals.
DPE_module v1.0 would use the grid-based method, by which of establishing a set of candidate position, velocity, and time (PVT) and obtaining the correlations from each satellite before finally non-coherently summing them up to obtain the candidate position with the highest signal correlation, which would be the PVT estimate of DPE. Position as well as receiver clock bias estimate from 2SP are also used as initialization for the grid of candidate position. An illustration is provided below (Vicenzo et al. 2024)
Instead of iteratively computing the signal correlations per every candidate position, our DPE plug-in module pre-calculates the correlations per every pre-determined chip spacing or code phase. This implementation was previously used by previous research on collective detection, which is another name for DPE, to save computational time (Axelrad et al., 2009; Cheong et al., 2011).
Parts of SoftGNSS v3.0 have been adapted to allow the DPE_module v1.0 to be integrated into it.
The software presented in this repository is a SoftGNSS v3.0 that has been integrated with DPE_Module v1.0, and using it follows the same steps as running a regular SoftGNSS v3.0. Modifications were made to SOftGNSS v3.0 to also run on 16-bit samples (int16/short data).
When running with 16-bit data samples, use int16 in settings.dataType (instead of short). On the other hand, use schar in settings.dataType (instead of int8) when running with 8-bit data samples.
Further information on using the software can be found in the original SoftGNSS v3.0 readme readme - SoftGNSS.txt and ppt GPS_L1_CA_SDR.pdf.
All DPE_module v1.0 parameters can be edited from initSettings.m, which are listed below.
-
settings.candPVT_spacing= Grid spacing for the latitude-longitude-height estimation (Default = 1 meter) -
settings.DPE_latlong_span= Span of latitude and longitude search space (Default = ±30 meters) -
settings.DPE_height_span= Span of height search space (Default = ±50 meters) -
settings.DPE_clkBias_span= Span of clock bias search space (Default = ±20 meters) -
settings.DPE_nonCohInt= DPE non-coherent integration time (Default = 1 ms) to improve the performance of DPE as the satellite correlations would be more filtered -
settings.DPE_plotCorrelogram= Output the correlograms, plotted at the estimated DPE height -
settings.gt_llh= Ground truth coordinates in geodetic coordinates to output the positioning errors from both DPE and 2SP -
settings.chipspacing_dpe_precalc= Chip spacings between the pre-calculated correlations (Default = chips/sample)
DPE_module v1.0 was developed with MATLAB2022a and it is recommended to run the program with the same version or later. Running the program with other MATLAB versions has yet to be tested. No additional MATLAB toolbox is required i.e., it can run with just the basic MATLAB package and no additional toolboxes.
Dependencies of the underlying SoftGNSS v3.0 can be found in its readme file readme - SoftGNSS.txt
DPE_module v1.0 was written by Sergio Vicenzo, inspired by the multicorrelator-based DPE (Corr-DPE) written by HaoSheng Xu and Bing Xu, which was previously introduced in (Vicenzo et al. 2023).
Sergio Vicenzo is currently a PhD student at the Department of Aeronautical and Aviation Engineering, The Hong Kong Polytechnic University. He received first-class honours in Bachelor of Engineering in Aviation Engineering from the same university in 2022. He is supervised by Assistant Professor Bing Xu, and co-supervised by Associate Professor Li-Ta Hsu. His research interests include GNSS urban navigation and positioning with direct position estimation.
Email: seergio.vicenzo@connect.polyu.hk
I, Sergio Vicenzo, hereby do not claim ownership nor any responsibility for the SoftGNSS v3.0 software by Prof. Borre and Prof. Akos and the llh2xyz.m script by Prof. Todd Walter. All changes made to the SoftGNSS v3.0 software have been labelled appropriately and its GNU license kept intact in each code file, in accordance to GNU General Public License. No changes were made to the llh2xyz.m script and its copyright statement is kept intact.
No copyright infringement is intended from any of the MATLAB scripts provided in this GitHub repository.
Axelrad P, Donna J, Mitchell M (2009) Enhancing GNSS acquisition by combining signals from multiple channels and satellites. In: Proc. ION GNSS 2009, Institute of Navigation, Savannah, Georgia, USA, September 22 – 25, 3117-3128
Borre K, Akos DM, Bertelsen N, Rinder P, Jensen SH (2007) A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach. Birkhäuser, Boston, Massachusetts.
Cheong JW, Wu J, Dempster AG, Rizos C (2011) Efficient Implementation of Collective Detection. In: Proc. IGNSS Symposium 2011, International Global Navigation Satellite Systems Society, Sydney, New South Wales, Australia, November 15-17.
Vicenzo S, Xu B, Dey A, Hsu L-T (2023) Experimental Investigation of GNSS Direct Position Estimation in Densely Urban Area. In: In: Proc. ION GNSS+ 2023, Institute of Navigation, Denver, Colorado, USA, September 19 – 23, 2906-2919.
Vicenzo S, Xu B, Xu H, Hsu L-T (2024) GNSS direct position estimation-inspired positioning with pseudorange correlogram for urban navigation. GPS Solutions 28(2). https://doi.org/10.1007/s10291-024-01627-5
This repository is still under development. I apologise if some information is incomplete or if you encounter any problems...
Last Updated: 13 May 2024