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diff --git a/supervision.tex b/supervision.tex new file mode 100644 index 0000000..4c5923c --- /dev/null +++ b/supervision.tex @@ -0,0 +1,90 @@ +% LICENSE: see LICENCE +\section{Supervision of Transmitted Ensembles} +\subsection{Introduction} +We have seen a way to monitor the transmission infrastructure (or at least some +of its essential parts) in chapter \ref{monitmunin} about munin monitoring. +These monitoring elements give an indication about ODR-DabMux and ODR-DabMod +health from within the infrastructure itself, and may not be able to inform you +about some issues happening outside of the software tools. + +Monitoring the transmitted signal from an external place can complement the +internal monitoring and broaden the supervision coverage. In the end, we can +only consider the broadcast system being in an operational state if a receiver +can play all programmes, and being able to verify this automatically by placing +a receiver in the field is the only way to ensure this. + +In this chapter, we will see one way to achieve this. + +\subsection{Welle.io Software-Defined Receiver} +The welle.io\footnote{Project page: \url{http://welle.io}, sources on: +\url{https://github.com/AlbrechtL/welle.io}} project offers an SDR DAB receiver +that can run both with a graphical user interface for ease of use, and as a +command-line tool that can be used for automated systems. +The command-line tool called \texttt{welle-cli} presents an HTTP API that makes +ensemble parameters and audio content available to third party tools. Until this +tool becomes part of a released version, checkout the \texttt{next} branch and +compile it using CMake, as described in the readme. Execute it directly from the +build folder, so that it also can access the \texttt{index.html} file. + +welle-cli can present the ensemble data in more than one way, but we will focus +on the HTTP interface. It is enabled with the \texttt{-w 7979} option, which +will run the HTTP server on port 7979. Select the channel to receive, e.g.~10A, with +\texttt{-c 10A}. +When you point your browser to \url{http://localhost:7979}, you will get a +simple web-page that shows a subset of the data available through the API. When +pressing a Play button, \texttt{welle-cli} will start decoding the selected +sub-channel and stream it to the browser as an MP3 stream.\footnote{MP3 is used +because it is the only compressed audio format that is supported in all +browsers. The AAC or MP2 audio inside the ensemble is re-encoded by +\texttt{welle-cli} using the LAME encoding library.} + +Several options are available for decoding the programmes: use \texttt{-D} to +decode all audio and PAD simultaneously. This requires a powerful PC. Use +\texttt{-C} to decode the audio in a carousel, i.e.~one-by-one. When using +\texttt{-CP} the decoder remains up to 80s on a programme, but switches +programmes once a slide was correctly decoded. Compared to \texttt{-C} alone, +this improves the likelihood of decoding slideshow at the expense of a lower +audio level update rate. + +While this web-page already has some utility as-is, it mainly serves as an +illustration of what can be done with the API, where the real value of +\texttt{welle-cli} resides. The API is, for the moment, quite simple: +\begin{itemize} + \item \texttt{/mux.json} contains most information in JSON format. From + this JSON you can extract the list of services, the ensemble parameters, + TII decoding and other information. + \item \texttt{/mp3/SID} will give you a live mp3 stream of the primary + component of the given service id. + \item \texttt{/fic} will send a data stream containing the FIC. This can be + saved to file and analysed offline with other tools, among which + etisnoop (using its \texttt{-I} option). etisnoop is also able to do + live analysis of the FIC, e.g. with + \verb+curl -s http://localhost:7979/fic|etisnoop -I /dev/stdin+ + whose YAML output can in turn be processed further. + \item \texttt{/channel} will return the currently tuned channel on + receiving a GET request, and set the channel and restart the receiver on + receiving a POST. +\end{itemize} + +Other HTTP URLs give back information that needs to be processed further. +See the script code inside \texttt{index.html} to understand how to work with +it. + +\begin{itemize} + \item \texttt{/spectrum} will send a sequence of float values that + show the spectrum power density of the signal. + \item \texttt{/nullspectrum} will send a sequence of float values that + show the spectrum power density of the NULL symbol, where the TII + carriers are visible. + \item \texttt{/constellation} will send a sequence of complex float I/Q + values corresponding to the demodulated constellation points. + \item \texttt{/impulseresponse} will send a sequence of float values that + represent the measured channel impulse response. +\end{itemize} + +An example integration into a monitoring system is given in the +\texttt{welle-cli-munin.py} script. This munin plugin fetches the +\texttt{mux.json} and converts the audio levels in a format that munin can +graph. In this way, an entire ensemble can be monitored at once. + +% vim: spl=en spell tw=80 et |