Spectrum Analyzer for LibreRouter June Updates

What I have been working on

During the past weeks, I had the chance to work on the spectrum analyzer in the following topics:

  • During the BattleMesh, I has the chance to engage with several developers that are working on topics related:
    • Felix Fietkau is one of the developers of the ath9k module, and we had a conversation to understand better the inner workings of the driver, and what the output of the module will serve me for the Spectrum Analyzer functionality
    • Paul Fuxjäger from FunkFeuer, with whom we discussed some potential uses of the module, along with other collaborations that could arise in the future related with the module.
  • I engaged with the FFT_eval project’s source code, that is used to decode radio i/q signals into easily representable values, and added a JSON output for the data. Instead of continue our own fork of the project, I did this in the mainstream project, promoting one codebase. The merge request is currently pending: https://github.com/simonwunderlich/FFT_eval/pull/13 . Many thanks to Gui Irribarren and BrainSlayer from the DD-WRT project to provide most of this implementation.

Once I engaged with the LibreMesh projects, I understood that one of the purposes of having the Spectrum Analyzer was to be able to do a Frequency Survey in the TVWS spectrum. This is very valuable because one of the proposals of using this part of the spectrum is through a regional database of usage, where you can ask for permission to use a frequency and the database needs to authorize you.

So, my other job has been to seek for current implementations of TVWS Database and, in particular, the PAWS protocol (an IETF draft proposal for TVWS Databases). I managed to found a team that is working on this (Prof. Karandikar from the IITB of Mombay and his OpenPAWS project) and we are talking to see if we can collaborate.

That’s a rougth report on what has been happening during the last weeks.

What I’ll be working on

I’ll describe the architecture that I expect to implement in the upcoming weeks.

With the help of ubus, I will be working on an event based architecture that involves the following parts:

The yellow parts are the new parts.

A brief description of the parts involved:
* Spectral Scan Manager: It manages ath9k states, recovers i/q data from the atheros modules and hands them over through ubus
* Spectral Scan Decoder: FFT_eval wrapper that will receive Spectral Scan Manager i/q data and turn it into JSON
* Spectral Analysis Collector: A configurable daemon that will collect the Spectral Scan Decoder data for further analysis. This collection could be kept in memory or sent to a secondary server (like the OpenPAWS server)
* Visualization Module: Will access the information handed by the Decoder or the Collector (depending which information we would like to access) and visualize it in a Waterfall graph.
* Spectrum Availability CLI Interface: This is a potential proposal (if time allows) to have a simpler interface that can be accessed from command-line. Could implement something similar to this: https://wiki.mikrotik.com/wiki/Manual:Spectral_scan

For the next week, I’ll implement the Spectral Scan Manager, the Spectral Scan Decoder wrapper, and a simple visualization.

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