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SignalSim

A multi-stage GNSS signal and data simulator

This is a GNSS signal and data simulator and generator to help the development of GNSS receivers.

This program supports multiple stages of simulation output:

  1. Reference trajectory of receiver (as standard reference result)
  2. Observation (helps to debug and test PVT program)
  3. Baseband correlation result (combined with local channel configuration parameters, helps to debug baseband tracking and control program)
  4. Digital IF result (helps to debug baseband process algorithm)
  5. A realtime GNSS signal simulator (with hardware signal interpolation and up converter)

System Capabilities

SignalSim provides comprehensive support for multi-constellation GNSS simulation with the following capabilities:

Constellation Support

  • GPS: Full constellation of 32 satellites
  • BeiDou (BDS): Complete constellation of 63 satellites
  • Galileo: Full constellation of 36 satellites
  • GLONASS: Complete constellation of 24 satellites

Technical Specifications

  • Constellation: Support GPS, BDS, GLONASS and Galileo, QZSS/IRNSS interface reserved for future expansion
  • Multiple frequency bands: Support for L1/L2/L5, B1/B2/B3, E1/E5/E6, G1/G2
  • Data formats: RINEX 2/3/4 support for observation and navigation data
  • Configuration: JSON-based scenario configuration
  • Signal generation: Digital IF samples with configurable sampling rate and bit depth

SignalSim is designed for both educational and professional use, with commercial licensing available for advanced features.

Signal Support and Testing Status

The following table shows the current testing status of various GNSS signals in SignalSim:

Key Components

IFdataGen

The IF Data Generator component creates GNSS Intermediate Frequency (IF) sample files that can be used with RF front-ends or GNSS software-defined radio applications. For detailed information on building and using this component, see the IFdataGen README.

JsonObsGen

The JSON Observation Generator creates GNSS observation data based on JSON configuration files. This component replaced the older XML-based generator.

Library Core

The core libraries provide fundamental GNSS data processing capabilities including:

  • Ephemeris and almanac parsing
  • Navigation bit stream generation
  • Satellite signal modeling
  • RINEX file handling
  • Trajectory calculation

Change List

2025

  • 6/18/2025

    • Fix bug of access out of array boundary in BCNAV1 data stream compose
    • Update IFdataGen VS2022 project file
    • Add VS2022 project file to JsonObsGen

  • 6/6/2025

    • Add configs folder with examples .json files for multiple constellations.
    • Explain how to set center frequency and bandwidth for each constellation in the IFdataGen GNSS_Signal_Calculations.
    • Expand unit and integration tests for signal generation and update the test matrix accordingly.
    • Update IFdataGen README with new examples and configuration guidance.

  • 5/14/2025

    • Rewrite BCNAV1/2/3 navigation data stream generation method (ephemeris generation completed, almanac in next release)
    • Rename PrnCode to PrnGenerate
    • Add variable valid in struct GPS_ALMANAC and redefine contents of variable flag

  • 5/6/2025

    • Relocate shared RINEX data files from /XmlObsGen to root
    • Relocate SatIfSignal.h and SatIfSignal.cpp from IFdataGen/ to inc/ and src/

  • 4/22/2025

    • Enhanced documentation with updated main README.md
    • Added CMakeLists.txt to support IFdataGen builds
    • Fixed initial bugs in IFdataGen.cpp implementation
    • Implemented command-line support for JSON configuration files
    • Created detailed README.md in IFdataGen folder with demo instructions and usage examples
    • Integrated EphData folder into IFdataGen Folder

  • 3/11/2025

    • Demo program to generate IF signal is added with sample .json config file
    • Most common signals are supported but with only limited verification
    • Following signals will be only available with commercial license: L1P/L2P, E5 AltBOC, TMBOC, ACEBOC, QMBOX, LEX CSK
    • Multi-thread version which runs dozen times faster only available with commercial license

  • 1/28/2025

    • Bug fix and improvements on almanac data stream composition
    • Fix bug on possible incorrect week number in data stream of I/NAV and F/NAV if almanac of some satellite missing
    • Fix bug on incorrect week number set in data stream
    • Second parameter of function CompleteAlmanac() uses UTC time
    • Add BDS GEO satellite ephemeris to almanac conversion
    • Add GLONASS satellite ephemeris to almanac conversion

  • 1/15/2025

    • Rearrange some definitions and declarations
    • Change FREQ_INDEX_XXX definitions to SIGNAL_INDEX_XXX for better discrimination of signals at same frequency
    • Key word extension in JSON for future IF data generation support

2024

  • 10/20/2024

    • Add JSON format scenario control file to replace XML format
    • Add JsonParser.cpp/JsonParser.h to read JSON data structure from file
    • Add JsonInterpreter.cpp/JsonInterpreter.h to translate JSON data structure to scenario control
    • Add a JsonObsGen project that has the same output using test_obs2.json (same parameters as test_obs2.xml used in XmlObsGen project)

  • 10/5/2024

    • CMakeLists.txt added to XmlObsGen folder to guide how to build project using cmake
    • Minor fixes

  • 10/1/2024

    • New CNavBit class for CNAV bit stream generation
    • Expand URA index range to support corresponding data field in CNAV
    • L2CM and L5I signal use CNAV data modulation

  • 9/21/2024

    • Add Galileo E5a F/NAV data modulation support
    • Bug fix of group delay and signal modulation phase in B2b signal

  • 6/5/2024

    • Add almanac word (word 7~10) to Galileo E1 data stream
    • Add Reed-Solomon encoded ephemeris (word 17~20) to Galileo E1 data stream
    • Bug fixes on E1 ephemeris word and TOW composition

  • 2/29/2024

    • Enable almanac read and data stream generation containing almanac subframe/string
    • Change function parameter of SetAlmanac() in NavBit and all derived classes
    • Add functions to read almanac file in Almanac.cpp
    • Add array to store almanacs in CNavData class
    • Add functions to read almanac files and convert ephemeris to almanac in CNavData class
    • Ephemeris to almanac conversion for GLONASS and BDS GEO satellites will be added in future version
    • The time parameter of FindEphemeris() and FindGloEphemeris() definition changes to follow corresponding system
    • Add almanac subframe/string generation for D1/D2, LNAC and GNAV data stream

  • 1/6/2024

    • Add GPS L1C CNAV2 navigation stream generation class
    • Fix bugs in BDS D1/D2 navigation stream generation
    • Add L1C/L5/E6 support into CSatelliteSignal class
    • Observation support multi-frequency in structure and RINEX output

2023

  • 11/27/2023

    • Change BCNavBit to virtual class and derive three classes for B-CNAV1/2/3 data stream
    • Combine iode2/iode3 to iode in ephemeris structure
    • Add B-CNAV2 and B-CNAV3 support in CSatelliteSignal
    • Modify GetTravelTime() and GetCarrierPhase() to use correct group delay

  • 11/13/2023

    • Add support to RINEX 4 format navigation file
    • Modify Rinex.cpp to support RINEX 4 format data set
    • Expand and modify GPS_EPHEMERIS structure to support ephemeris from different navigation data format
    • Calculate clock/delay for different frequency with corresponding parameters

  • 10/28/2023

    • Replace UnscaleDouble and roundi/roundu with UnscaleInt/UnscaleUint
    • Add UnscaleLong/UnscaleULong to better support data fields longer than 32bit (C-NAV and BC-NAV)

  • 9/19/2023

    • Add complex_number class
    • Add E5 support
    • Add dummy F/NAV data stream generation
    • Satellite signal generation allows NULL pointer for data bit to generate all 0 modulation data

  • 8/30/2023

    • Add GLONASS satellite parameter and raw measurement calculation
    • Add GLONASS slot/freq output to RINEX file
    • Add GLONASS GNAV data stream composition
    • Leap second correction in CSatelliteSignal
    • Update the PDF file for design description

  • 8/24/2023

    • Add Galileo I/NAV data stream generation class
    • Add inter-signal correction (delay between different frequencies) support in XML format

  • 8/15/2023

    • Add pilot bit generation function
    • Remove pilot bit generation in NavBit and CSatelliteSignal class
    • GetFrameData() method in NavBit (and derived classes) no longer supports pilot bit generation

  • 8/9/2023

    • Add a new class CSatelliteSignal to get data/pilot modulation
    • Add a new NavBit derived class D1D2NavBit to generate BDS2 data stream
    • Call to GetFrameData() in NavBit class will be obsolete in the future

  • 7/28/2023

    • Modifications to comply with stricter syntax checking
    • Add SignalSim.h to include all necessary header files for package users

  • 1/23/2023

    • Add some variables and functions for future multi-frequency support
    • Minor bug fix on satellite acc calculation for GEO satellite

2022

  • 2/12/2022

    • Bug fix on B-CNAV1 stream generation
    • Option to use Vel/Acc to calculate satellite position

  • 1/5/2022

    • Add support for B-CNAV2 data stream generation

2021

  • 12/14/2021

    • Fix bug of CN0 assign incorrect value during satellite add/remove
    • Add support for system select

  • 12/8/2021

    • Add support for B1C and E1C

  • 11/25/2021

    • Restore CN0 field in SATELLITE_PARAM structure as stored CN0

  • 9/30/2021

    • Add satellite signal power control support in XML
    • Add RINEX output functions

  • 8/30/2021

    • Fix bug of TOW add extra 1 when put into LNAV data stream
    • Fix bug of not put in week number in LNAV data stream
    • Use complete GNSS time to get LNAV data stream

  • 8/13/2021

    • Change format of GNSS_TIME to improve accuracy
    • Add GetTransmitTime() method
    • Remove obsolete file

  • 8/4/2021

    • Add class NavBit and LNavBit to generate GPS LNAV data stream

  • 7/5/2021

    • Add XML format trajectory output
    • Add support to load BDS ionosphere parameter in RINEX header
    • Add support to load GPS/BDS/Galileo UTC parameters in RINEX header
    • Add support to load BDS/Galileo ephemeris in RINEX file
    • Optimize XML file content interpreter

  • 7/1/2021

    • An optimized initial version re-published on github

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