On 02/01/2016 15:03, Ed Wilson wrote: > I wonder how this performance translates to JT65 and JT9; I can see > improvement, but nothing as good as -30 dB.
Hi Ed, the performance of each decoder is discrete. I will try and summarize: The WSPR-2 decoder in WSJT-X has several performance improvements over the WSPR application. It was the first to use two pass decoding with signal subtraction after the first pass, this is the main reason you can receive multiple spots on the same DF. Steve K9AN authored these changes with assistance from Joe K1JT for integration into WSJT-X. JT65 decoding is undergoing a major rewrite and the current development source is the result of that, it too uses 2 pass with intermediate signal subtraction decoding. It also incorporates an advanced soft decision decoding (basically very well informed guessing) for the signals that cannot be decoded simply from the encoded FEC parity data. This last part replaces KVASD and is currently able to achieve ~0.5dB resolution improvements over KVASD. Steve originated that latest soft decision algorithm and both Joe and Steve have fine tuned it to the current state. JT9 had a round of improvements for the v1.5 release but since then not much has happened. The two signal subtraction mechanism could be applied there too but the benefit would be smaller since JT9 signals are much less likely to overlap until the bands reach higher occupancy. Overall WSPR-2 is the most sensitive of the three on HF, this is due to the shorter message and slower symbol rate which allows more averaging to dig deeper into the noise. Occasional -30dB reports occur with JT65 and JT9 but these are rare and beyond the expected range. JT65 and JT4 in WSJT-X will eventually use experience based decoding which is basically using existing known information like known active callsigns to do more targeted guessing of decodes, this allows deeper searches for successful decodes to be completed in a fraction of the time that a exhaustive search would take. These experienced based methods allow JT65 to gain a few more dB resolution approaching -30dB. 73 & HNY Bill G4WJS. ------------------------------------------------------------------------------ _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
