A multi-stage GNSS signal and data simulator

This is a GNSS signal and data simulator and generator to help the development of GNSS receiver. This program support multiple stage of simulation output:

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

Change list as below: 7/1/2021 An optimized initial version re-published on github 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 8/4/2021 Add class NavBit and LNavBit to generate GPS LNAV data stream 8/13/2021 Change format of GNSS_TIME to improve accuracy Add GetTransmitTime() method Remove obsolete file 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 9/30/2021 Add satellite signal power control support in XML Add RINEX output functions 11/25/2021 Restore CN0 field in SATELLITE_PARAM structure as stored CN0 12/8/2021 Add support for B1C and E1C 12/14/2021 Fix bug of CN0 assign incorrect value during satellite add/remove Add support for system select 1/5/2022 Add support for B-CNAV2 data stream generation 2/12/2022 Bug fix on B-CNAV1 stream generation Option to use Vel/Acc to calculated satellite position 1/23/2023 Add some variables and functions for future multi-frequency support Minor bug fix on satellite acc calculation for GEO satellite 7/28/2023 Modifications to comply with stricter syntax checking Add SignalSim.h to include all necessary header files for package users 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 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 support pilot bit generation 8/24/2023 Add Galileo I/NAV data stream generation class Add inter-signal correction (delay between different frequencies) support in XML format