2015-06-15 09:04:58 +08:00
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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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[bladeRF](http://nuand.com/), HackRF, and USRP.
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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" to the Souce Files folder.
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4. Select "Release" in Solution Configurations drop-down list.
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5. Open the Property Pages dialog box and expand the Configuration Properties.
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6. Expand the C/C++ node and select the Language property page.
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7. Enable the OpenMP Support (/openmp).
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8. Build the solution.
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2015-06-19 07:51:05 +08:00
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### Building with GCC
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```
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$ gcc gpssim.c -lm -fopenmp -o gps-sdr-sim
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```
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2015-06-15 09:04:58 +08:00
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### Generating the GPS signal file
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A user-defined trajectory can be defined in a CSV file, which contains
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the Earth-centered Earth-fixed (ECEF) user positions at 10Hz.
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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 ephemers file (brdc) is a merge of the
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indiviual 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 pseudorante 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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For example;
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```
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2015-06-15 09:06:02 +08:00
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> gps-sdr-sim brdc3540.14n circle.csv gpssim.bin
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2015-06-15 09:04:58 +08:00
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```
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### Transmitting the samples with bladeRF
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The TX port of the bladeRF is connected to the GPS receiver under
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test through a DC block and a fixed 50dB attenuator.
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The simulated GPS signal file, named "gpssim.bin", can be loaded
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into bladeRF for playback as shown below:
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```
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set frequency 1575.42M
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set samplerate 4M
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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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### License
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Copyright © 2015 Takuji Ebinuma
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Distributed under the [MIT License](http://www.opensource.org/licenses/mit-license.php).
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