93 lines
2.9 KiB
Markdown
93 lines
2.9 KiB
Markdown
# 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](https://github.com/mossmann/hackrf/wiki), 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" 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. 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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### 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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### Generating the GPS signal file
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A user-defined trajectory can be specified 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 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 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 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 command line interface requires I/Q pairs stored as signed
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16-bit integers, while the hackrf_transfer supports signed bytes.
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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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-l <location> Lat,Lon,Hgt (static mode) e.g. 30.286502,120.032669,100
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-o <output> I/Q sampling data file (default: gpssim.bin)
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-s <frequency> Sampling frequency [Hz] (default: 2600000)
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-b <iq_bits> I/Q data format [8/16] (default: 8)
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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 -b 16
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```
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```
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> gps-sdr-sim -e brdc3540.14n -l 30.286502,120.032669,100 -b 16
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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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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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For the 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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### 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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