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# GPS-SDR-SIM
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GPS-SDR-SIM generates GPS baseband signal data streams, which can be converted
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to RF using software-defined radio (SDR) platforms, such as
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[ADALM-Pluto](https://wiki.analog.com/university/tools/pluto), [bladeRF](http://nuand.com/), [HackRF](https://github.com/mossmann/hackrf/wiki), and [USRP](http://www.ettus.com/).
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### Windows build instructions
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1. Start Visual Studio.
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2. Create an empty project for a console application.
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3. On the Solution Explorer at right, add "gpssim.c" and "getopt.c" to the Souce Files folder.
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4. Select "Release" in Solution Configurations drop-down list.
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5. Build the solution.
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### Building with GCC
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```
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$ gcc gpssim.c -lm -O3 -o gps-sdr-sim
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```
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### Using bigger user motion files
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In order to use user motion files with more than 30000 samples (at 10Hz), the `USER_MOTION_SIZE`
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variable can be set to the maximum time of the user motion file in seconds. It is advisable to do
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this using make so gps-sdr-bin can update the size when needed. e.g:
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```
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$ make USER_MOTION_SIZE=4000
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```
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This variable can also be set when compiling directly with GCC:
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```
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$ gcc gpssim.c -lm -O3 -o gps-sdr-sim -DUSER_MOTION_SIZE=4000
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```
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### Generating the GPS signal file
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A user-defined trajectory can be specified in either a CSV file, which contains
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the Earth-centered Earth-fixed (ECEF) user positions, or an NMEA GGA stream.
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The sampling rate of the user motion has to be 10Hz.
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The user is also able to assign a static location directly through the command line.
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The user specifies the GPS satellite constellation through a GPS broadcast
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ephemeris file. The daily GPS broadcast ephemeris file (brdc) is a merge of the
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individual site navigation files into one. The archive for the daily file is:
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[ftp://cddis.gsfc.nasa.gov/gnss/data/daily/](ftp://cddis.gsfc.nasa.gov/gnss/data/daily/)
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These files are then used to generate the simulated pseudorange and
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Doppler for the GPS satellites in view. This simulated range data is
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then used to generate the digitized I/Q samples for the GPS signal.
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The bladeRF and ADALM-Pluto command line interface requires I/Q pairs stored as signed
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16-bit integers, while the hackrf_transfer and gps-sdr-sim-uhd.py
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support signed bytes.
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HackRF, bladeRF and ADALM-Pluto require 2.6 MHz sample rate, while the USRP2 requires
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2.5 MHz (an even integral decimator of 100 MHz).
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The simulation start time can be specified if the corresponding set of ephemerides
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is available. Otherwise the first time of ephemeris in the RINEX navigation file
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is selected.
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The maximum simulation duration time is defined by USER_MOTION_SIZE to
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prevent the output file from getting too large.
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The output file size can be reduced by using "-b 1" option to store
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four 1-bit I/Q samples into a single byte.
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You can use [bladeplayer](https://github.com/osqzss/gps-sdr-sim/tree/master/player)
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for bladeRF to playback the compressed file.
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```
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Usage: gps-sdr-sim [options]
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Options:
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-e <gps_nav> RINEX navigation file for GPS ephemerides (required)
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-u <user_motion> User motion file (dynamic mode)
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-g <nmea_gga> NMEA GGA stream (dynamic mode)
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-c <location> ECEF X,Y,Z in meters (static mode) e.g. 3967283.15,1022538.18,4872414.48
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-l <location> Lat,Lon,Hgt (static mode) e.g. 30.286502,120.032669,100
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-t <date,time> Scenario start time YYYY/MM/DD,hh:mm:ss
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-T <date,time> Overwrite TOC and TOE to scenario start time
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-d <duration> Duration [sec] (dynamic mode max: 300 static mode max: 86400)
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-o <output> I/Q sampling data file (default: gpssim.bin ; use - for stdout)
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-s <frequency> Sampling frequency [Hz] (default: 2600000)
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-b <iq_bits> I/Q data format [1/8/16] (default: 16)
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-i Disable ionospheric delay for spacecraft scenario
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-v Show details about simulated channels
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```
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The user motion can be specified in either dynamic or static mode:
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```
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> gps-sdr-sim -e brdc3540.14n -u circle.csv
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```
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```
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> gps-sdr-sim -e brdc3540.14n -g triumphv3.txt
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```
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```
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> gps-sdr-sim -e brdc3540.14n -l 30.286502,120.032669,100
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```
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### Transmitting the samples
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The TX port of a particular SDR platform is connected to the GPS receiver
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under test through a DC block and a fixed 50-60dB attenuator.
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#### BladeRF:
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The simulated GPS signal file, named "gpssim.bin", can be loaded
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into the bladeRF for playback as shown below:
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```
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set frequency 1575.42M
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set samplerate 2.6M
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set bandwidth 2.5M
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set txvga1 -25
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cal lms
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cal dc tx
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tx config file=gpssim.bin format=bin
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tx start
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```
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You can also execute these commands via the `bladeRF-cli` script option as below:
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```
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> bladeRF-cli -s bladerf.script
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```
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#### HackRF:
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```
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> hackrf_transfer -t gpssim.bin -f 1575420000 -s 2600000 -a 1 -x 0
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```
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#### UHD supported devices (tested with USRP2 only):
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```
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> gps-sdr-sim-uhd.py -t gpssim.bin -s 2500000 -x 0
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```
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#### LimeSDR (in case of 1 Msps 1-bit file, to get full BaseBand dynamic and low RF power):
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```
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> limeplayer -s 1000000 -b 1 -d 2047 -g 0.1 < ../circle.1b.1M.bin
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```
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#### ADALM-Pluto (PlutoSDR):
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The ADALM-Pluto device is expected to have its network interface up and running and is accessible
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via "pluto.local" by default.
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Default settings:
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```
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> plutoplayer -t gpssim.bin
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```
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Set TX attenuation:
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```
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> plutoplayer -t gpssim.bin -a -30.0
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```
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Default -20.0dB. Applicable range 0.0dB to -80.0dB in 0.25dB steps.
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Set RF bandwidth:
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```
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> plutoplayer -t gpssim.bin -b 3.0
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```
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Default 3.0MHz. Applicable range 1.0MHz to 5.0MHz.
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### License
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Copyright © 2015-2018 Takuji Ebinuma
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Distributed under the [MIT License](http://www.opensource.org/licenses/mit-license.php).
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Adding suppport for multi constellation
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