This commits introduces a significant redesign of the AX.25 decoding
block. Due to the poor AX.25 sync flag, the decoders exhibited too many
false alarms. To deal with this problem, we introduced the quadrature
demod filter block, that tried to measure the SNR based on the running
variance of the signal. The problem with that was that the user should
have to fine tune two parameters, the one related with the amplitude of
the incoming signal and the second one related with the window that the
calculations should take place. This solution worked until now, but we
can always increase the performance.
The new AX.25 decoder stores the bitstream in a queue and always tries
to exlpoit possible valid frames in the queue. If now sync flags have
been encountered, the queue is flushed. After a valid frame extraction,
bits corresponding to this frame are also deleted from the queue.
This technique requires more memory and CPU, but it increases a lot the
decoding performance.
The AX.25 decoder is now decoding the received frames.
Also, the module now provides a UDP message source block. This block
will be responsible to receive UDP packets and transform them into PMT
messages for further processing in the GNU Radio flowgraph. As the
communication with the satnogs-client will be done in the same host, we
do not have to care about packet loss.
Furthermore, the module now provides and a debug message source block
for easy debugging.
Manolis Surligas
Manolis Surligas