Thanks to the help I received during the week end, I completed the update on gr-acars. One thing I realized when working on PSK modulations (e.g RDS) is the importance of bitrate clock synchronization.
After investigating the M&M algorithm, possibly because of my misunderstanding of its implementation targeted at identifying zero-crossing of the difference of the soft bit and estimated hard bit symbol, I have attempted a very naive clock-rate synchronization on AFSK using maximum likelihood on single bits framed by different bit states (since similar successive bits are hardly affected by synchronization issues). I wanted to avoid differentiating the AFSK output since derivate is prone to noise and might make the zero-crossing identification unstable (correct ?). I would be quite interested in comments or corrections to http://jmfriedt.org/acars_clock.pdf or directions to existing literature on this issue which is far from my field of expertise. Thanks, JM -- JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, 25000 Besancon, France
