gps-sdr project taken from

Gogs 8742394768 Changes to work with gps-sdr. 5 months ago
extclk d8eab7ede7 HackRF TCXO 7 years ago
player 03db365cb7 LimeSuite bug workaround for LimeSDR mini 4 years ago
rtk 8cee8d2dfa RTK example 7 years ago
satgen a55476985d Generating NMEA GGA with SatGen v3 Software 7 years ago
.gitignore 4b16857401 Add the option to define a custom user motion size 4 years ago
LICENSE fe6ed116cc Update LICENSE 7 years ago
Makefile 23c1e4456d Add missing dependency to Makefile 2 years ago c7245bc740 Upate URL to Ephemeris data 2 years ago
bladerf.script 10acc03d50 Add bladerf.script, and update 7 years ago
brdc3540.14n ad465dbc29 Created 7 years ago
circle.csv ad465dbc29 Created 7 years ago
getopt.c d1e8f91569 Initial commit 7 years ago
getopt.h d1e8f91569 Initial commit 7 years ago e4f2c1b25b Update for compatibility with Python 3 and GNU Radio 3.8 2 years ago
gpssim.c 8742394768 Changes to work with gps-sdr. 5 months ago
gpssim.h 4b16857401 Add the option to define a custom user motion size 4 years ago
rocket.csv ddaa7b2e52 Generated by MatRockSim 7 years ago
satellite.csv ea2d5455c8 Update satellite trajectory 7 years ago
triumphv3.txt 8c9db505d2 Generated by SatGen v3 software 7 years ago
u-center.png ad465dbc29 Created 7 years ago
ublox.jpg ad465dbc29 Created 7 years ago


GPS-SDR-SIM generates GPS baseband signal data streams, which can be converted to RF using software-defined radio (SDR) platforms, such as ADALM-Pluto, bladeRF, 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" and "getopt.c" to the Souce Files folder.
  4. Select "Release" in Solution Configurations drop-down list.
  5. Build the solution.

Building with GCC

$ gcc gpssim.c -lm -O3 -o gps-sdr-sim

Using bigger user motion files

In order to use user motion files with more than 30000 samples (at 10Hz), the USER_MOTION_SIZE variable can be set to the maximum time of the user motion file in seconds. It is advisable to do this using make so gps-sdr-bin can update the size when needed. e.g:

$ make USER_MOTION_SIZE=4000

This variable can also be set when compiling directly with GCC:

$ gcc gpssim.c -lm -O3 -o gps-sdr-sim -DUSER_MOTION_SIZE=4000

Generating the GPS signal file

A user-defined trajectory can be specified in either a CSV file, which contains the Earth-centered Earth-fixed (ECEF) user positions, or an NMEA GGA stream. The sampling rate of the user motion has to be 10Hz. The user is also able to assign a static location directly through the command line.

The user specifies the GPS satellite constellation through a GPS broadcast ephemeris file. The daily GPS broadcast ephemeris file (brdc) is a merge of the individual site navigation files into one. The archive for the daily file can be downloaded from: Access to this site requires registration, which is free.

These files are then used to generate the simulated pseudorange 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.

The bladeRF and ADALM-Pluto command line interface requires I/Q pairs stored as signed 16-bit integers, while the hackrf_transfer and support signed bytes.

HackRF, bladeRF and ADALM-Pluto require 2.6 MHz sample rate, while the USRP2 requires 2.5 MHz (an even integral decimator of 100 MHz).

The simulation start time can be specified if the corresponding set of ephemerides is available. Otherwise the first time of ephemeris in the RINEX navigation file is selected.

The maximum simulation duration time is defined by USER_MOTION_SIZE to prevent the output file from getting too large.

The output file size can be reduced by using "-b 1" option to store four 1-bit I/Q samples into a single byte. You can use bladeplayer for bladeRF to playback the compressed file.

Usage: gps-sdr-sim [options]
  -e <gps_nav>     RINEX navigation file for GPS ephemerides (required)
  -u <user_motion> User motion file (dynamic mode)
  -g <nmea_gga>    NMEA GGA stream (dynamic mode)
  -c <location>    ECEF X,Y,Z in meters (static mode) e.g. 3967283.15,1022538.18,4872414.48
  -l <location>    Lat,Lon,Hgt (static mode) e.g. 30.286502,120.032669,100
  -t <date,time>   Scenario start time YYYY/MM/DD,hh:mm:ss
  -T <date,time>   Overwrite TOC and TOE to scenario start time
  -d <duration>    Duration [sec] (dynamic mode max: 300 static mode max: 86400)
  -o <output>      I/Q sampling data file (default: gpssim.bin ; use - for stdout)
  -s <frequency>   Sampling frequency [Hz] (default: 2600000)
  -b <iq_bits>     I/Q data format [1/8/16] (default: 16)
  -i               Disable ionospheric delay for spacecraft scenario
  -v               Show details about simulated channels

The user motion can be specified in either dynamic or static mode:

> gps-sdr-sim -e brdc3540.14n -u circle.csv
> gps-sdr-sim -e brdc3540.14n -g triumphv3.txt
> gps-sdr-sim -e brdc3540.14n -l 30.286502,120.032669,100

Transmitting the samples

The TX port of a particular SDR platform is connected to the GPS receiver under test through a DC block and a fixed 50-60dB attenuator.


The simulated GPS signal file, named "gpssim.bin", can be loaded into the bladeRF for playback as shown below:

set frequency 1575.42M
set samplerate 2.6M
set bandwidth 2.5M
set txvga1 -25
cal lms
cal dc tx
tx config file=gpssim.bin format=bin
tx start

You can also execute these commands via the bladeRF-cli script option as below:

> bladeRF-cli -s bladerf.script


> hackrf_transfer -t gpssim.bin -f 1575420000 -s 2600000 -a 1 -x 0

UHD supported devices (tested with USRP2 only):

> -t gpssim.bin -s 2500000 -x 0

LimeSDR (in case of 1 Msps 1-bit file, to get full BaseBand dynamic and low RF power):

> limeplayer -s 1000000 -b 1 -d 2047 -g 0.1 < ../circle.1b.1M.bin

ADALM-Pluto (PlutoSDR):

The ADALM-Pluto device is expected to have its network interface up and running and is accessible via "pluto.local" by default.

Default settings:

> plutoplayer -t gpssim.bin

Set TX attenuation:

> plutoplayer -t gpssim.bin -a -30.0

Default -20.0dB. Applicable range 0.0dB to -80.0dB in 0.25dB steps.

Set RF bandwidth:

> plutoplayer -t gpssim.bin -b 3.0

Default 3.0MHz. Applicable range 1.0MHz to 5.0MHz.


Copyright © 2015-2018 Takuji Ebinuma
Distributed under the MIT License.