WSJT-X/lib/mskrtd.f90

160 lines
4.6 KiB
Fortran
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subroutine mskrtd(id2,nutc0,tsec,ntol,nrxfreq,line)
! Real-time decoder for MSK144.
! Analysis block size = NZ = 7168 samples, t_block = 0.597333 s
! Called from hspec() at half-block increments, about 0.3 s
parameter (NZ=7168) !Block size
parameter (NSPM=864) !Number of samples per message frame
parameter (NFFT1=8192) !FFT size for making analytic signal
parameter (NPATTERNS=4) !Number of frame averaging patterns to try
character*3 decsym !"&" for mskspd or "^" for long averages
character*22 msgreceived !Decoded message
character*22 msglast !!! temporary - used for dupechecking
character*80 line !Formatted line with UTC dB T Freq Msg
complex cdat(NFFT1) !Analytic signal
complex c(NSPM) !Coherently averaged complex data
complex ct(NSPM)
integer*2 id2(NZ) !Raw 16-bit data
integer iavmask(8)
integer iavpatterns(8,NPATTERNS)
integer npkloc(10)
integer nav(6)
real d(NFFT1)
real pow(8)
real xmc(NPATTERNS)
logical first
data first/.true./
data nav/1,2,3,5,7,9/
data iavpatterns/ &
1,1,1,1,0,0,0,0, &
0,0,1,1,1,1,0,0, &
1,1,1,1,1,0,0,0, &
1,1,1,1,1,1,1,0/
data xmc/2.0,4.5,2.5,3.5/ !Used to label decode with time at center of averaging mask
save first,t03,t12,nutc00,pnoise,nsnrlast,msglast
if(first) then
t03=0.0
t12=0.0
nutc00=nutc0
pnoise=-1.0
first=.false.
endif
fc=nrxfreq
!!! Dupe checking should probaby be moved to mainwindow.cpp
if( nutc00 .ne. nutc0 ) then ! reset dupe checker
msglast=' '
nsnrlast=-99
nutc00=nutc0
endif
tframe=float(NSPM)/12000.0
line=char(0)
msgreceived=' '
max_iterations=10
niterations=0
d(1:NZ)=id2
rms=sqrt(sum(d(1:NZ)*d(1:NZ))/NZ)
if(rms.lt.1.0) return
fac=1.0/rms
d(1:NZ)=fac*d(1:NZ)
d(NZ+1:NFFT1)=0.
call analytic(d,NZ,NFFT1,cdat) !Convert to analytic signal and filter
! Calculate average power for each frame and for the entire block.
! If decode is successful, largest power will be taken as signal+noise.
! If no decode, entire-block average will be used to update noise estimate.
pmax=-99
do i=1,8
ib=(i-1)*NSPM+1
ie=ib+NSPM-1
pow(i)=dot_product(cdat(ib:ie),cdat(ib:ie))*rms**2
if( pow(i) .gt. pmax ) then
pmax=pow(i)
endif
enddo
pavg=sum(pow)/8.0
! Short ping decoder uses squared-signal spectrum to determine where to
! center a 3-frame analysis window and attempts to decode each of the
! 3 frames along with 2- and 3-frame averages.
np=8*NSPM
call msk144spd(cdat,np,ntol,nsuccess,msgreceived,fc,fest,tdec)
if( nsuccess .eq. 1 ) then
tdec=tsec+tdec
decsym=' & '
goto 999
endif
! If short ping decoder doesn't find a decode, then 4-, 5-, and 7-frame averages
! spanning the first 7 frames of the block.
do iavg=1,NPATTERNS
iavmask=iavpatterns(1:8,iavg)
navg=sum(iavmask)
ndf=nint(7.0/navg)
npeaks=2
call msk144sync(cdat(1:8*NSPM),8,ntol,ndf,iavmask,npeaks,fc,fest,npkloc,nsyncsuccess,c)
if( nsyncsuccess .eq. 0 ) cycle
do ipk=1,npeaks
do is=1,3
ic0=npkloc(ipk)
if(is.eq.2) ic0=max(1,ic0-1)
if(is.eq.3) ic0=min(NSPM,ic0+1)
ct=cshift(c,ic0-1)
call msk144decodeframe(ct,msgreceived,ndecodesuccess)
if(ndecodesuccess .gt. 0) then
tdec=tsec+xmc(iavg)*tframe
decsym=' ^ '
goto 999
endif
enddo !Slicer dither
enddo !Peak loop
enddo
msgreceived=' '
! no decode - update noise level used for calculating displayed snr.
if( pnoise .lt. 0 ) then ! initialize noise level
pnoise=pavg
elseif( pavg .gt. pnoise ) then ! noise level is slow to rise
pnoise=0.9*pnoise+0.1*pavg
elseif( pavg .lt. pnoise ) then ! and quick to fall
pnoise=pavg
endif
return
999 continue
! successful decode - estimate snr !!! noise estimate needs work
if( pnoise .gt. 0.0 ) then
snr0=10.0*log10(pmax/pnoise-1.0)
else
snr0=0.0
endif
nsnr=nint(snr0)
!!!! Temporary - dupe check. Only print if new message, or higher snr.
if( msgreceived .eq. msglast .and. nsnr .le. nsnrlast ) return
msglast=msgreceived
nsnrlast=nsnr
if( nsnr .lt. -8 ) nsnr=-8
if( nsnr .gt. 24 ) nsnr=24
write(line,1020) nutc0,nsnr,tdec,nint(fest),decsym,msgreceived,char(0)
1020 format(i6.6,i4,f5.1,i5,a3,a22,a1)
return
end subroutine mskrtd