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# gps-sdr-sim # GPS-SDR-SIM
GPS-SDR-SIM generates GPS baseband signal data streams, which can be converted
to RF using software-defined radio (SDR) platforms, such as
[bladeRF](http://nuand.com/), HackRF, and USRP.
### Windows build instructions
1. Start Visual Studio.
2. Create an empty project for a console application.
3. On the Solution Explorer at right, add "gpssim.c" to the Souce Files folder.
4. Select "Release" in Solution Configurations drop-down list.
5. Open the Property Pages dialog box and expand the Configuration Properties.
6. Expand the C/C++ node and select the Language property page.
7. Enable the OpenMP Support (/openmp).
8. Build the solution.
### Generating the GPS signal file
A user-defined trajectory can be defined in a CSV file, which contains
the Earth-centered Earth-fixed (ECEF) user positions at 10Hz.
The user specifies the GPS satellite constellation through a GPS broadcast
ephemeris file. The daily GPS broadcast ephemers file (brdc) is a merge of the
indiviual site navigation files into one. The archive for the daily file is:
[ftp://cddis.gsfc.nasa.gov/gnss/data/daily/](ftp://cddis.gsfc.nasa.gov/gnss/data/daily/)
These files are then used to generate the simulated pseudorante and
Doppler for the GPS satellites in view. This simulated range data is
then used to generate the digitized I/Q samples for the GPS signal.
For example;
```
> gps-sdr-sim brdc3540.14n circle.vsv gpssim.bin
```
### Transmitting the samples with bladeRF
The TX port of the bladeRF is connected to the GPS receiver under
test through a DC block and a fixed 50dB attenuator.
The simulated GPS signal file, named "gpssim.bin", can be loaded
into bladeRF for playback as shown below:
```
set frequency 1575.42M
set samplerate 4M
set bandwidth 2.5M
set txvga1 -25
cal lms
cal dc tx
tx config file=gpssim.bin format=bin
tx start
```
### License
Copyright © 2015 Takuji Ebinuma
Distributed under the [MIT License](http://www.opensource.org/licenses/mit-license.php).