Noise being decode as NXDN

[devnulling]

Hi @LouisErigHerve

Just wanted to report that the NXDN improvements on this branch look great.

However, when trying to stream into this branch of dsd from GQRX, everything gets decoded as NXDN, even just noise.

[2021-06-03 21:36:33] Sync:  +NXDN96    mod: C4FM inlvl: 30% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:33] Sync:  +NXDN96    mod: GFSK inlvl: 29% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:33] Sync:  +NXDN96    mod: GFSK inlvl: 32% - RTCH - Unknown RTCH Frame
[2021-06-03 21:36:33] Sync:  +NXDN96    mod: C4FM inlvl: 30% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:33] Sync:  +NXDN96    mod: GFSK inlvl: 29% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:33] Sync:  +NXDN96    mod: GFSK inlvl: 32% - RTCH - Unknown RTCH Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: C4FM inlvl: 30% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: GFSK inlvl: 36% - RTCH - Unknown RTCH Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: C4FM inlvl: 31% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: GFSK inlvl: 30% - RTCH_C - Unknown RTCH_C Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: GFSK inlvl: 35% - RTCH - Unknown RTCH Frame
[2021-06-03 21:36:34] Sync:  +NXDN96    mod: C4FM inlvl: 31% - RTCH_C - Unknown RTCH_C Frame

[LouisErigHerve]

DSD is unstable when decoding trunked NXDN networks, I've tried to fix it several time with no success...

NXDN detection require a deep work to become more stable. One main problem is the SYNC pattern detection (FSW + LICH) : as these one are very short and contains only 1 CRC bit there are many false positive and these one also generate a lot of noise.

The FSW + LICH detection is used to set the FSK symbol decoder parameters, so any false positive detection will set bad parameters...

Any help would be welcomed...