M17_Implementations

Various implementations

Woj's implementation (/SP5WWP)

Overview

Written in C, it has all the components described by the protocol's specification of the stream mode:

• convolutional encoder with soft Viterbi decoder (utilizing fixed point arithmetic),
• Golay encoder with soft decoder (fixed point),
• bit interleaver and randomizer,
• cyclic redundancy check (CRC) validation,
• callsign decoder

There's no support for any encryption yet.

Building

Simply cd to the directory of interest and make

Capabilities

Two executables are available:

• m17-coder-sym is used to convert a raw binary data bitstream to symbols. Symbol stream has to be filtered with an appropriate filter before transmission, see the specification document for details.
• m17-decoder-sym decodes a stream of floats at stdin, one sample per symbol. After a valid syncword is detected, decoding process starts. The program expects a stream of synchronized symbols at the input. See the /grc/symbol_recovery.grc file for details.
• m17-packet-encode is a handy tool for generating baseband (or a symbol stream, if needed) for M17 packets. The program expects a limited stream of raw data at the stdin. The number of bytes is set with the -n parameter, range 1 to 798.

Testing

Both the encoder and the decoder can be tested simultaneously. The test setup should look as follows:
GRC flowgraph -> fifo1 -> m17-coder-sym -> fifo2 -> m17-decoder-sym -> stdout
To perform a simple test, GNURadio 3.10 is required.

Run the following commands:

mkfifo fifo1
mkfifo fifo2

This should create 2 named pipes: fifo1 and fifo2. The first one is used for the "transmitted" raw bitstream from GNURadio. The other one is used for the "receiver" part - the symbol stream.

Start gnuradio-companion, open the .grc file included in this repo (/grc/m17_streamer.grc) and change the name of the named pipe to fifo1 (at the File Sink block - the rightmost one). Change the location of it if needed.

Open up 2 consoles and run:
Console 1:

cat fifo1 | ./m17-coder-sym > fifo2

Console 2:

cat fifo2 | ./m17-decoder-sym

Hit the Execte the flow graph button in GNURadio and watch it roll.

Console 2 should show similar results, with the Frame Number advancing each frame: