Communication Systems Engineering with GNU Radio

3Communicating with External Software (Python, Networking, ZeroMQ, MQTT)

While GNU Radio is well suited for processing continuous data streams, using external software might sometimes be efficient either because existing decoding tools have already been developed and are suited for processing the output of GNU Radio blocks, or for batch processing datasets when continuous streams are not needed (e.g. RAdio Detection And Ranging [RADAR] target signals), or when tuning the radio frequency frontend or processing parameters prior to implementing a dedicated GNU Radio block (out-of-tree [OOT] module). These three cases will be addressed in this section:

1. using first in first out (FIFO) file systems provided, for example, by Unix mkfifo to connect a pseudo-file output to the standard input, as will be demonstrated with the multimon software [Elias Önal, 2023] for decoding POCSAG sentences,
2. using Internet protocol (IP) datagram (user datagram protocol [UDP]) or connected (transmission control protocol [TCP]) communication [Fall and Richard Stevens, 2011] by running a dedicated thread next to the GNU Radio scheduler, allowing to access, for example, the dataflow control variable for the flowgraph,
3. using the XML-RPC (remote process control) to access the variables driving a GNU Radio flowchart and benefiting from a description of the remote function being called rather than a custom protocol as described earlier,
4. using the ZeroMQ and message queuing telemetry transport (MQTT) overlays ...