GpsSimulator

A Qt frontend for creating gps simulations and transmitting them with an SDR.

Setup

The following is a guide to exactly replicate the GPS Simulator appliance.

Setting up the software environment.

This setup guide assumes you are using a raspberry pi 4B with a user named pi. A HackRF One SDR should be plugged in to one of the USB ports, and a GPS receiver should be connected over GPIO pins.

OS Setup

Go to this link and download the Raspberry Pi OS Lite image. Write the image to a microSD card using your favorite method (dd, rufus, etc.)

Boot the raspberry pi and login (default username: pi, default password: raspberry), and enter the config screen using sudo raspi-config. Complete the following steps:

• System Options > Wireless LAN to setup wifi, and follow any propmpts.
• System Options > Boot / Auto Login and select Console Autologin.
• Interface Options > SSH and enable the SSH server.
• Interface Options > Serial Port and select No for Would you like a login shell to be accessible over serial?, and then Yes to Would you like the serial hardware to be enabled?
• Set Localisation Options if desired.
• Finally, select Finish and choose Yes to the reboot prompt.

Next, edit the file /etc/security/limits.conf and add the following line to the end of the file:

pi - rtprio - max realtime priority

Ensure you log out of the pi account and log back in before using the appliance.

Dependencies

Run sudo apt update, then install the following packages with sudo apt install <package-name>

• hackrf
• gpsd
• libgps-dev
• git
• cmake
• fluxbox
• xserver-xorg
• xinit
• qt5-default

Setup gps-sdr-sim using the following commands:

$ git clone https://github.com/osqzss/gps-sdr-sim ~/gps-sdr-sim
$ cd ~/gps-sdr-sim
$ gcc gpssim.c -lm -O3 -o gps-sdr-sim

gps-sdr-sim also requires a ephemeris file which can be aquired here: https://cddis.nasa.gov/archive/gnss/data/daily/. Grab the latest one (requires a free account) by going to the current year, current day number, the <year>n directory (e.g. 21n), then download the file named brdc<day>.<year>.gz. Decrompess the file and place it in the home directory and name it brdc_file. This file does not need to be updated.

Setup gpsd using the following commands:

$ sudo systemctl enable gpsd

And edit the DEVICES="" line of /etc/default/gpsd to be DEVICES="/dev/ttyS0".

Reboot.

HackRF One Firmware Update

The HackRF One board needs a firmware patch to function properly. Navigate to this repository and follow the instructions. This can be done on an entirely seperate computer from the raspberry pi, or the hackrf_usb.bin file can be transfered to the pi to be flashed on to the board.

Building this project

Clone and build this project into the home directory with the following commands:

$ git clone git clone https://github.com/BeyondPerception/GpsSimulator/
$ cd ~/GpsSimulator/
$ mkdir build
$ cd build
$ cmake ../
$ make gps_sim_gui_arm

Gui Setup

Unzip the file fluxbox_config.zip found in this repository's root directory, and place the folder in the home directory.

This can be done with the following command:

$ unzip ~/GpsSimulator/fluxbox_config.zip -d ~/

Additionally, add the following to the end of the ~/.profile file:

if [[ -z $DISPLAY ]] && [[ $(tty) = /dev/tty1 ]]; then
    exec startx
fi

Control Server

The GpsSimulator program exposes a port on udp 1111 which accepts commands to control the SDR. The following are the available commands.