Can you build a communication and location extension for our product

Our customer has an existing device built around an embedded computer. They ask us to design and build a communication and localization subsystem so that they can extend the applicability of their product.

Design requirements:

  • GPRS link

    Built around a Sierra Wireless 3G module. Requires three different physical SIM slots that can be selected under control of the embedded computer.

  • GNSS localisation

    Global Navigation Satellite System location solution based on a ublox UC530 GPS module

  • Iridium satellite communication backup link

    Iridium satcom in case the 3G coverage is not sufficient

  • AIS receiver

    For monitoring ship positions and navigation headings

  • Flexible antenna selection

    All critical RF communications have both on-board and external antennas, the antenna selection has to be under software control

  • Robust power supply

    The device is powered over ethernet, the communication module we design must have robust separate regulators on-board.

Since the application needs to interface to an embedded computer and multiple communication channels are required to be operated in parallel, we decide to build an USB-hub on-board our design. This way, a single high-speed USB link requiring only a single USB connection to the computer can cater for all communication channels.

The hub has 4 downstream client ports that connect to:

  • an Sierra Wireless AirPrime MC module for 3G communication
  • an SRT Marine Krypton AIS receiver
  • an Iridium 9602 satellite modem
  • an NXP ARM Cortex M3 processor running an AT-based control protocol

The ARM processor then interfaces to various on-board sensors, the GNSS receiver module, all antenna switches and the SIM card selection.

Power is provided through DC-DC convertors that regulate the PoE input net to the required on-board voltage rails.


Detail of the 3G antenna switch section