🛰️ Python GPS receiver

This project implements a software-defined GPS L1 receiver in Python. It covers the full signal processing chain required to extract navigation messages from raw real-valued samples, based on the standard GPS signal structure and BPSK modulation.

📦 Features

• Reads raw real-valued data from .dat file (int16 format)
• Signal spectrum visualization (optional)
• Satellite acquisition using correlation techniques
• Carrier and code tracking loop (DLL + PLL)
• Digital demodulation (BPSK)
• Navigation message decoding

🚀 Quick Start

Requirements

• Python3.7 or higher
• pip3
• numpy
• scipy
• matplotlib (optional, for plotting)

Install dependencies:

pip3 install -r requirements.txt

Input data

To test the receiver, you will need raw sample data recorded from a GPS L1 signal. This receiver processes only the real (in-phase) component of the signal – not complex I/Q data. Make sure the file contains signed 16-bit integers (int16) representing real-valued samples.

If you don't have your own recordings, you can use public datasets as a starting point and extract only the real part if needed. Sample data can be downloaded e.g. from gnss-sdr project page on SourceForge. Alternatively (on Linux or WSL), use this wget command in your terminal:

wget https://sourceforge.net/projects/gnss-sdr/files/data/2013_04_04_GNSS_SIGNAL_at_CTTC_SPAIN.tar.gz

Note: If the estimated download time is too long, you can also download the data using Google Colab and then copy it to your Google Drive after mounting the drive in Colab Notebook.

Then unpack the archive:

tar -zxvf 2013_04_04_GNSS_SIGNAL_at_CTTC_SPAIN.tar.gz

Finally, run the script to extract only the real component of the signal:

python3 prepare_data.py

▶️ Usage

In the main.py file, adjust the sampling frequency fs to match your input data. A default value of 4 MHz is provided for compatibility with the gnss-sdr dataset. You can also enable or disable plotting by setting the plot boolean variable. Then run:

python3 main.py

📈 Output

1. Signal spectrum visualization

2. Correlation surface received in the signal acquisition phase

3. Carrier frequency tracking

4. Code-phase offset correction over time

5. BPSK constellation diagram

6. BPSK symbols

📄 Results

1. Acquisition results

----------------- Acquisition results -----------------
  1) Detected satellite PRN ID: 1
  2) Doppler offset: 7000.0
  3) Code-phase offset: 3988

2. Decoding results

Note: Values are raw binary fields decoded from the NAV message, without applying scaling factors from ICD-GPS-200.

----------------- Satelite number: 12 -----------------
                     (Subframe 5)
  1) Eccentricity: 9361
  2) Almanac reference time: 144
  3) Orbital inclination: 6870
  4) Rate of right ascension: 690
  5) Root of semi major axis: 6222754
  6) Longitude of ascension node: 6754408
  7) Argument of perigee: 16245516
  8) Mean anomaly at reference time: 5461369
  9) Clock bias: 133
  10) Clock drift: 1

----------------- Satelite number: 13 -----------------
                     (Subframe 5)
  1) Eccentricity: 10777
  2) Almanac reference time: 111
  3) Orbital inclination: 58976
  4) Rate of right ascension: 691
  5) Root of semi major axis: 6222393
  6) Longitude of ascension node: 4614217
  7) Argument of perigee: 11235851
  8) Mean anomaly at reference time: 3973047
  9) Clock bias: 1910
  10) Clock drift: 0

----------------- Satelite number: 14 -----------------
                     (Subframe 5)
  1) Eccentricity: 14148
  2) Almanac reference time: 111
  3) Orbital inclination: 60194
  4) Rate of right ascension: 64837
  5) Root of semi major axis: 6222489
  6) Longitude of ascension node: 12240192
  7) Argument of perigee: 11360731
  8) Mean anomaly at reference time: 3638923
  9) Clock bias: 232
  10) Clock drift: 0

----------------- Satelite number: 15 -----------------
                     (Subframe 5)
  1) Eccentricity: 11286
  2) Almanac reference time: 111
  3) Orbital inclination: 219
  4) Rate of right ascension: 64801
  5) Root of semi major axis: 6222491
  6) Longitude of ascension node: 4274620
  7) Argument of perigee: 439308
  8) Mean anomaly at reference time: 11761330
  9) Clock bias: 119
  10) Clock drift: 2047