WSJT-X/lib/fsk4hf/get_ft4s_bitmetrics.f90

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Fortran
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subroutine get_ft4s_bitmetrics(cd,hmod,bitmetrics,badsync)
include 'ft4s_params.f90'
parameter (NSS=20)
complex cd(0:NN*NSS-1)
complex cs(0:3,NN)
complex csymb(NSS)
complex c1(NSS,0:3) ! ideal waveforms, 20 samples per symbol, 4 tones
complex ccor(0:3,NN) ! correlations with each ideal waveform, for each symbol
complex cp(0:3) ! accumulated phase shift over symbol types 0:3
complex csum,cterm
integer icos4a(0:3),icos4b(0:3)
integer icos4c(0:3),icos4d(0:3)
integer icos4e(0:3),icos4f(0:3)
integer graymap(0:3)
integer ip(1)
logical one(0:65535,0:15) ! 65536 8-symbol sequences, 16 bits
logical first
logical badsync
real bitmetrics(2*NN,4)
real s2(0:65535)
real s4(0:3,NN)
data icos4a/0,1,3,2/
data icos4b/1,0,2,3/
data icos4c/2,3,1,0/
data icos4d/3,2,0,1/
data icos4e/0,2,3,1/
data icos4f/1,2,0,3/
data graymap/0,1,3,2/
data first/.true./
save first,one,c1,cp
if(first) then
one=.false.
do i=0,65535
do j=0,15
if(iand(i,2**j).ne.0) one(i,j)=.true.
enddo
enddo
twopi=8.0*atan(1.0)
dphi=twopi*hmod/NSS
do itone=0,3
dp=(itone-1.5)*dphi
phi=0.0
do j=1,NSS
c1(j,itone)=cmplx(cos(phi),sin(phi))
phi=mod(phi+dp,twopi)
enddo
cp(itone)=cmplx(cos(phi),sin(phi))
enddo
first=.false.
endif
do k=1,NN
i1=(k-1)*NSS
csymb=cd(i1:i1+NSS-1)
do itone=0,3
cs(itone,k)=sum(csymb*conjg(c1(:,itone)))
enddo
s4(0:3,k)=abs(cs(0:3,k))
enddo
! Sync quality check
is1=0
is2=0
is3=0
is4=0
is5=0
is6=0
badsync=.false.
ibmax=0
do k=1,4
ip=maxloc(s4(:,k))
if(icos4a(k-1).eq.(ip(1)-1)) is1=is1+1
ip=maxloc(s4(:,k+28))
if(icos4b(k-1).eq.(ip(1)-1)) is2=is2+1
ip=maxloc(s4(:,k+56))
if(icos4c(k-1).eq.(ip(1)-1)) is3=is3+1
ip=maxloc(s4(:,k+84))
if(icos4d(k-1).eq.(ip(1)-1)) is4=is4+1
ip=maxloc(s4(:,k+112))
if(icos4e(k-1).eq.(ip(1)-1)) is5=is5+1
ip=maxloc(s4(:,k+140))
if(icos4f(k-1).eq.(ip(1)-1)) is6=is6+1
enddo
nsync=is1+is2+is3+is4+is5+is6 !Number of correct hard sync symbols, 0-24
badsync=.false.
! if(nsync .lt. 8) then
! badsync=.true.
! return
! endif
do nseq=4,1,-1 !Try coherent sequences of 1, 2, and 4 symbols
if(nseq.eq.1) nsym=1
if(nseq.eq.2) nsym=2
if(nseq.eq.3) nsym=4
if(nseq.eq.4) nsym=8
nt=4**nsym
do ks=1,NN-nsym+1,nsym !87+16=103 symbols.
s2=0
do i=0,nt-1
csum=0
cterm=1
do j=0,nsym-1
ntone=mod(i/4**(nsym-1-j),4)
csum=csum+cs(graymap(ntone),ks+j)*cterm
cterm=cterm*conjg(cp(graymap(ntone)))
enddo
s2(i)=abs(csum)
enddo
ipt=1+(ks-1)*2
if(nsym.eq.1) ibmax=1
if(nsym.eq.2) ibmax=3
if(nsym.eq.4) ibmax=7
if(nsym.eq.8) ibmax=15
do ib=0,ibmax
bm=maxval(s2(0:nt-1),one(0:nt-1,ibmax-ib)) - &
maxval(s2(0:nt-1),.not.one(0:nt-1,ibmax-ib))
if(ipt+ib.gt.2*NN) cycle
bitmetrics(ipt+ib,nseq)=bm
enddo
enddo
enddo
call normalizebmet(bitmetrics(:,1),2*NN)
call normalizebmet(bitmetrics(:,2),2*NN)
call normalizebmet(bitmetrics(:,3),2*NN)
call normalizebmet(bitmetrics(:,4),2*NN)
return
end subroutine get_ft4s_bitmetrics