FT4,FT8 and RX diversity

WSJTX patch to implement diversity for FT4 and FT8 mode is available here.
WSJTX version 2.1.2: description: FT4FT8-DIV PDF file
Source and configuration files: ZIP file
Windows executable file: WSJTX 2.1.2 EXE file

Diversity reception is common in all modern radio communications. FT8 mode of WSJTX is extremely popular on HAM shortwave bands and we need better reception techniques to deal with interference and other obstacles contributing to weak signal reception.

Better FT4/8 decoding is achieved using diversity, by combining two or more RX signal sources. 2 to 5 dB S/N can be gained, enough to make some QSOs possible.

Time diversity, also called incremental redundancy, combines two consecutive even/odd samples.
Space diversity combines two samples when two coherent receivers are used.
Frame diversity is also implemented.

Since time and space diversity both adds up to seven passes to FT4/8 decoder leading to longer decoding time, a fast CPU Code was tested on Linus with 3.8 GHz i7 CPU and works fine. Results are excellent: S52D made several QSOs that would not be possible with standard FT8 decoder. Benefits are seen on empty band with only few decodes, as well as on crowded 20m band. Usually 5 % more messages are decoded using either time or space diversity.

Old vesrion for WSJTX 2.0.0:
FT8-DIV PDF file
Code and other files: ZIP file for WSJTX 2.0.0