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5G Broadcast - TV and Radio Services

MBMS Modem - Measurements & GPS

This tutorial shows how to have the MBMS Modem log signal-quality measurements (CINR, BLER, MCS and related values) to a CSV file, optionally tagged with GPS position and time. This is useful for drive tests and coverage analysis.

note

This page covers measurement logging with position data. If instead you want to discipline the system clock from GPS (for accurate timestamps), see GPS Time Synchronization for rt-mbms-modem. The two are related but separate: this page reads GPS position/time into the measurement file; that page feeds GPS time to the system clock via chrony.

Configuring a GPS mouse​

MBMS Modem relies on GPSD (https://gpsd.gitlab.io/gpsd/) for GPS data acquisition. GPSD is the GPS daemon that reads the receiver and makes position and time available to other programs.

Please follow the setup instruction for gpsd to configure it for your GPS receiver: https://gpsd.gitlab.io/gpsd/installation.html

Usually, this should boil down to:

  • sudo apt install libgps-dev gpsd
  • Checking which (virtual) serial port your GPS mouse uses, once you plug it in (e.g. /dev/ttyACM0)
  • Setting this device in /etc/default/gpsd:
# Devices gpsd should collect to at boot time.
# They need to be read/writeable, either by user gpsd or the group dialout.
DEVICES="/dev/ttyACM0"
# Other options you want to pass to gpsd
GPSD_OPTIONS=""
  • Adding gpsd to the dialout group: sudo usermod -a -G dialout gpsd
  • Checking if everything works with one of the client applications, e.g. cgps (can be installed with sudo apt install gpsd-clients). This should show position data.

Logging measurement data to a CSV file​

Configuration for measurement file​

Is in /etc/5gmag-rt.conf:

  measurement_file: {
    enabled: true;
    file_path: "/tmp/modem_measurements.csv";
    interval_secs: 10;
    gpsd:
    {
      enabled: true;
      host: "localhost";
      port: "2947";
    }
}

You can modify the location of the created file here, set the interval in which measurement lines are written to it, and enable/disable GPS.

File format​

The created file is in semicolon-separated CSV format.

The columns contain:

  1. system timestamp
  2. latitude
  3. longitude
  4. gps timestamp
  5. CINR
  6. PDSCH MCS
  7. PDSCH BLER
  8. PDSCH BER
  9. MCCH MCS
  10. MCCH BLER
  11. MCCH BER
  12. First MCH index
  13. First MCH MCS
  14. First MCH BLER
  15. First MCH BER

If there are more MCHs, they are appended at the end of the line:

  1. Second MCH Index

  2. Second MCH MCS

  3. Second MCH BLER

  4. Second MCH BER

Example output​

Each line is one measurement interval. Reading the first row against the column list above:

  • 2021-02-26T15:09:54 = system timestamp
  • 48.392428 / 16.104939 = latitude / longitude
  • 2021-02-26T15:09:54 = GPS timestamp
  • 22.847839 = CINR (dB)
  • 4 / 0.000000 / 0.000000 = PDSCH MCS / BLER / BER
  • 2 / 0.000000 / - = MCCH MCS / BLER / BER (a - means the value was not available for that interval)
  • 0 / 9 / 0.000000 / - = first MCH index / MCS / BLER / BER
2021-02-26T15:09:54;48.392428;16.104939;2021-02-26T15:09:54;22.847839;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:00;48.392428;16.104939;2021-02-26T15:10:00;27.173386;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:05;48.392428;16.104939;2021-02-26T15:10:05;26.828796;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:11;48.392428;16.104939;2021-02-26T15:10:11;23.722340;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:17;48.392428;16.104939;2021-02-26T15:10:17;24.914352;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:22;48.392428;16.104939;2021-02-26T15:10:22;26.893414;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:28;48.392428;16.104939;2021-02-26T15:10:28;22.102150;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;
2021-02-26T15:10:34;48.392428;16.104939;2021-02-26T15:10:34;22.894867;4;0.000000;0.000000;2;0.000000;-;0;9;0.000000;-;

Next steps​