WSJT-X/lib/demod64a.f90

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subroutine demod64a(s3,nadd,afac1,mrsym,mrprob,mr2sym,mr2prob,ntest,nlow)
! Demodulate the 64-bin spectra for each of 63 symbols in a frame.
! Parameters
! nadd number of spectra already summed
! mrsym most reliable symbol value
! mr2sym second most likely symbol value
! mrprob probability that mrsym was the transmitted value
! mr2prob probability that mr2sym was the transmitted value
implicit real*8 (a-h,o-z)
real*4 s3(64,63),afac1
integer mrsym(63),mrprob(63),mr2sym(63),mr2prob(63)
if(nadd.eq.-999) return
afac=afac1 * float(nadd)**0.64
scale=255.999
! Compute average spectral value
ave=sum(s3)/(64.*63.)
i1=1 !Silence warning
i2=1
! Compute probabilities for most reliable symbol values
do j=1,63
s1=-1.e30
psum=0.
do i=1,64
x=min(afac*s3(i,j)/ave,50.d0)
psum=psum+s3(i,j)
if(s3(i,j).gt.s1) then
s1=s3(i,j)
i1=i !Most reliable
endif
enddo
if(psum.eq.0.0) psum=1.e-6
s2=-1.e30
do i=1,64
if(i.ne.i1 .and. s3(i,j).gt.s2) then
s2=s3(i,j)
i2=i !Second most reliable
endif
enddo
p1=s1/psum !Symbol metrics for ftrsd
p2=s2/psum
mrsym(j)=i1-1
mr2sym(j)=i2-1
mrprob(j)=scale*p1
mr2prob(j)=scale*p2
enddo
nlow=0
do j=1,63
if(mrprob(j).le.5) nlow=nlow+1
enddo
ntest=sum(mrprob)
return
end subroutine demod64a