[A-DX] RNEI#21 via WRMI / DRM - EasyDRF

Roger
Sonntag, 19. September 2021, 11:19 Uhr

Collage:
https://www.dropbox.com/s/ck695y1iryur5tc/2021-09-16_RNEI21_via_WRMI_EasyDRF.png?dl=0


zu EasyDRF, völlig überarbeitetes HAM-DRM mit neuem 
Fehlerschutz-Algorithmus:

http://homepages.ihug.com.au/~daz2002/tech/EasyDRF/index.html

Regarding security:
     EasyDRF does not use any network resources.
     EasyDRF does not execute or open received or transmitted files 
automatically. They must be manually selected by the user for display or 
for sending.

New features:
Work continues to improve the reliability of EasyDRF in difficult 
shortwave conditions.
Previously, EasyDRF used a repeat method to help ensure all file 
segments are decoded. This was wasteful of bandwidth, and each pass 
could still lose the same segment - making it fail.
Another common Ham-DRM application called "EasyPal" uses interleaved 
Reed-Solomon (RS) encoding to improve this situation. Unfortunately, the 
protocol extension it uses is unknown, and it still has weaknesses.
(der Programmierer hatte den Quellcode mit ins Grab genommen)

Data loss during reception is mostly caused by interference or signal 
fades taking the SNR below a usable level for some file segments. Even 
if the signal is at a usable level for most of the time, the fading can 
make decoding impossible due to these missing file segments. RS coding 
can fully correct this, up to a certain percentage of missing segments.

RS coding of the transmitted file data greatly improves the reliability 
of file transmission, but the file header information also needs to be 
made robust, as the header contains the filename and file size 
information. If this is lost, decoding is impossible.
A new scheme has been developed for EasyDRF, where a new header is 
appended to the file before RS coding and transmission. This ensures the 
new header always decodes if the file decodes successfully.
After decoding, EasyDRF removes the new header from the incoming file 
before saving it.


Other possibilities:

Save timestamped received signal quality information into a file trailer 
or separate file. This could include things like average SNR for each 
file, and the proportion of missing data segments. The file could be 
coded in Javascript and loaded into a web page for easy receiver stats 
display for experiments (such as the Shortwave Radiogram Ham-DRM 
broadcasts). This would make it easy to evaluate receiver signal quality 
from different listeners or from different areas.



roger