A LoRa Multi-User Receiver based on GNU Radio

Download: GNU Radio LoRa Implementation

This is the GNU Radio software-defined radio (SDR) implementation of a LoRa receiver that can jointly decode the signal from two interfering LoRa users with the same spreading factor (SF). The implementation contains all the necessary receiver components to demodulate the colliding LoRa packets correctly even at very low SNRs.

In the GNU Radio implementation of the LoRa Tx and Rx chains the user can choose the transmission conditions of each user, such as sampling time offset (STO), carrier frequency offset (CFO), and power.

  • In the Tx chain, the implementation contains all the necessary blocks to transmit colliding LoRa packets. Each packet consists of a preamble and a payload. Each user is subject to an individual CFO, time offset and transmit power.
  • The receiver side is composed of:
    • A signal detection block that is able to detect when a LoRa packet is present.
    • A user detection block responsible of detecting and estimating the parameters of the incoming user, such as the STO, CFO, and power.
    • A synchronization block which realigns the samples to the strongest user for STO correction and applies the required CFO correction.
    • A demodulation block which recovers the symbol values of both users using a maximum-likelihood-based demodulation method.
  • The implementation can be used for experimental performance evaluation of a two-user LoRa receiver at low SNRs.

Reference

https://arxiv.org/abs/2012.08173

If you find this implementation useful for your project, please consider citing the aforementioned paper.

How to use

  • Installation:
    • Download the zip archive and extract it
    • The installation path can be set in CMakeLists.txt under #set destination.(default: home/lora_sdr)
    • Similarly to any GNU Radio OOT module, it can be build with:
      cd [path to gr-lora_sdr]/build
      cmake ../
      make
      (sudo) make install
    • The new blocks can be loaded in gnuradio-companion(GRC) by adding the following lines in home/.gnuradio/config.conf (If this file doesn’t exist you need to create it):
      [grc]
      local_blocks_path=path_to_the_downloaded_folder/gr-lora_sdr/grc
    • The custom blocks necessary for the multi-user transceiver can be found under the LoRa_mu section.
  • Usage:
    • The script /gr-lora_sdr/apps/setpaths.sh add the pythonpaths required to run the generated python files for the current shell process. It has to be adapted accordingly to the installation folder, and should be sourced with: source setpaths.sh . It can be sourced automatically on shell start by appending: source [path to the script]/setpaths.sh to ~/bashrc.sh .
    • An example of a two interfering user flowgraph can be found in the gr-lora_sdr/apps/two_users/ .
    • Set the measurement_folder variable in GRC to a desired location. (Default: gr-lora_sdr/matlab/measurement).
    • Generate the python script corresponding to the flowgraph in GRC.
    • In a terminal navigate to gr-lora_sdr/apps/two_users/
    • Execute the generated script using: ./mu_tx_rx_(simulation).py
    • A matlab script interpreting the results can be found in: gr-lora_sdr/matlab. This script compare the demodulated symbols with the reference ones, based on a frame ID present in the beginning of each payload.
  • Frequent errors:
    • “ImportError: No module named lora_sdr” under other distribution than Redhat7:
      • This issue comes probably from erroneous PYTHONPATH and LD_LIBRARY_PATH set in the script setpaths.sh.
      • The paths might need to be changed to:
        ~/lora_sdr/lib/python2.7/dist-packages
        ~/lora_sdr/lib
  • Requirements:
    • Gnuradio 3.7
    • python 2
    • cmake
    • swig
    • libvolk
    • UHD