mCU IQ Modulation

At Libre Space Foundation we are devoted to developing and supporting open-source space technologies. OpenSatCom is an inspiring initiative backed by the European Space Agency and Libre Space Foundation. Within the scope of this initiative, a series of testings, projects and sub-activities will be explored in order to further enhance and support open software and hardware technologies in Satellite Communications. mCU IQ Modulation is one such project developed as a sub-activity within the OpenSatCom initiative. This project has been focusing on exploring three main areas:

  1. Investigating the usage of off-the-shelf SoCs (with embedded DACs) to generate a digital radiofrequency signal, given an IQ bit stream.
  2. Exploring the use case of spread-spectrum SATCOM applications.
  3. Evaluating the results of the experimental design.

The main architecture used to validate the target project is illustrated in the diagram:

The experiments conducted spanned over testing DACs and DACs in DMA mode using STM32Cube for the firmware SDK on top of PlatformIO. As far as the hardware is concerned, our first approach was to design a custom shield for the NUCLEO-L476RG. It included all the elements necessary for the development, including signal storing and unbalanced to balanced conversion. The hardware itself consists of two parts:

  • The analog section, built to convert single-ended signals from DACs into balanced signals for input to the modulator.
  • And a MicroSD card holder connected with the SPI interface of Nucleo ST board.

During the final stage of this first experiment, we attempted to generate a series of flowgraphs and signals to better perceive the results delivered. This way we were able to provide end-to-end validation.

If you want to get a closer look at the firmware and hardware used, the tests conducted, the results delivered as well as the next steps and what will be investigated in the future, feel free to download the report.

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