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acfloria / SatComInfrastructure

BSD 3-Clause "New" or "Revised" License
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SatComInfrastructure

Long range communication utility software for data relay and handling.

This repository provides the tools to setup a long range communication links using SatCom and/or an LTE link. The latency using the SatCom link is expected to be on average around 10-15 seconds given good signal strength but can exceed a minute with bad connection. The latency of the LTE link also depends on the signal strengths but from experience is well below 0.1 seconds.

The SatCom system is based on the Rock7 RockBLOCK Iridium modem.

Tested on Ubuntu 14.04, 16.04, and 18.04. Not tested and supported on Windows.

Architecture Overview

The following components are required for an operating satellite communication link:

The SatCom link running cost consists of a line rental and per message cost:

The cost of the LTE link depends on the data plan.

The full system architecture is shown below: Architecture

The software consists of the following modules:

The SatCom link can be simulated to test and evaluate the ground station computer and autopilot logic: Architecture with simulator

Vehicle Setup

Wiring

Connect the RockBlock module to a serial port of the Pixhawk. Due to the power requirements of the module it can only be powered over a high-power serial port as a maximum of 0.5 A at 5 V are required. If none is available/free then another power source which has the same ground level as the Pixhawk and can provide required power has to be setup. The details of the connectors and the power requirements can be found in the RockBlock documentation.

Module

The module can either use the internal antenna or an external one connected to the SMA connector. To switch between the two antennas modes the position of a small RF link cable needs to changed. If an external antenna is used always make sure that the antenna is connected to the module before powering it up to avoid damage to the module.

The default baud rate of the module is 19200. However, the iridiumsbd driver of the PX4 Autopilot requires a baud rate of 115200 so it needs to be changed using the AT commands.

  1. Connect to the module with using a 19200/8-N-1 setting and check if the communication is working using the command: AT. The response should be: OK.

  2. Change the baud rate:

    AT+IPR=9

  3. Reconnect to the model now with a 115200/8-N-1 setting and save the configuration using

    AT&W0

Now the module is ready to be used together with the PX4 autopilot.

Software

Flash the Pixhawk with the PX4 release 1.8 or newer. To activate either set the SYS_COMPANION parameter to Iridium Telemetry (115200 baud, 8N1) or add the following lines to the extras.txt on the SD card:

    # add a sleep here to make sure that the module is powered
    usleep 200000

    #driver
    if iridiumsbd start -d SERIAL_PORT
    then
        # start the iridium mavlink instance
        mavlink start -d /dev/iridium -m iridium -b 115200

        # Sleep a bit to give Mavlink time to set up
        usleep 100000

    else
        echo "WARN: Iridiumsbd driver not started, reboot"
        tune_control play -m "ML<<CP4CP4CP4CP4CP4"
    fi

where SERIAL_PORT is the serial port to which the RockBlock module is connected.

RockBlock Setup

When buying the first module on RockBlock an user account needs to be created in a first step. Log in to the account and register the RockBlock module under the My RockBLOCKs. Activate the line rental for the module and make sure that enough Credits for the expected flight duration are available on the account. When using the default settings one message per minute is sent from the airplane to the ground station.

Set up a delivery group for the message relay server and add the module to that delivery group:

Delivery Groups

Relay Server Setup

It is expected that the relay server is either using the Ubuntu 16.04 or 18.04 OS. 

allow_anonymous false
password_file /etc/mosquitto/passwd
[mqtt]

# username and password for the mqtt broker (mosquitto)
user = MQTT_USER
password = MQTT_PASSWORD

[rockblock]

# IMEI of the destination RockBLOCK modem
imei = MODULE_IMEI

# Rock7 username
username = ROCK7_USERNAME

# Rock7 password
password = ROCK7_PASSWORD

Ground Station Computer Setup

QGC computer setup

High Latency Link Settings

Verification

  1. Open a terminal on the ground station computer and change to the location of the SatComInfrastructure repository. Then start the udp2rabbit.py script:

    ./udp2mqtt.py

  2. Send a test message from RockBlock Account to the created delivery group in the Test Delivery Groups tab.

If in the terminal where the udp2mqtt.py script is running within a couple of seconds the acknowledge for a message can be observed, then the RockBlock delivery group, the relay server and the udp2rabbit script are set up correctly:

udp2rabbit message acknowledge

Running the System

  1. Start QGroundControl. Manually connect first the high latency link, the LTE link, and then the regular telemetry link:

Connect the High Latency link

  1. Open a terminal on the ground station computer and change to the location of the SatComInfrastructure repository. Then start the udp2mqtt.py script:

    ./udp2mqtt.py

  2. Power up the vehicle.

  3. Wait until the first HIGH_LATENCY2 message is received on QGC. This can be checked either using the MavLink Inspector widget or on the toolbar with the LinkIndicator. If more than one link is connected to the active vehicle the LinkIndicator shows all of them by clicking on the name of the shown link:

Link Toolbar

The link indicator always shows the name of the priority link.

  1. The satellite communication system is now ready to use. The priority link, which is the link over which commands are send, is determined the following ways:
    • If no link is commanded by the user a regular radio telemetry link is preferred over the high latency link.
    • The autopilot and QGC will fall back from the regular radio telemetry to the high latency link if the vehicle is armed and the radio telemetry link is lost (no mavlink messages received for a certain time). As soon as the radio telemetry link is regained QGC and the autopilot will switch back to it.
    • The user can select a priority link over the LinkIndicator on the toolbar. This link is kept as the priority link as long as this link is active or the user selects another priority link:

Prioritylink Selection

Troubleshooting

TODOs