WSJT-X/lib/fsk4hf/ft8b.f90

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subroutine ft8b(s,nfqso,f1,xdt,nharderrors,dmin,nbadcrc,message)
use timer_module, only: timer
include 'ft8_params.f90'
parameter(NRECENT=10)
character*12 recent_calls(NRECENT)
character message*22
real s(NH1,NHSYM)
real s1(0:7,ND)
real ps(0:7)
real rxdata(3*ND),llr(3*ND) !Soft symbols
integer*1 decoded(KK),apmask(3*ND),cw(3*ND)
max_iterations=40
norder=2
! if(abs(nfqso-f1).lt.10.0) norder=3
tstep=0.5*NSPS/12000.0
df=12000.0/NFFT1
i0=max(1,nint(f1/df))
j0=nint(xdt/tstep)
j=0
ia=i0
ib=i0+14
do k=1,NN
if(k.le.7) cycle
if(k.ge.37 .and. k.le.43) cycle
if(k.gt.72) cycle
n=j0+2*(k-1)+1
if(n.lt.1) cycle
j=j+1
s1(0:7,j)=s(ia:ib:2,n)
enddo
do j=1,ND
ps=s1(0:7,j)
where (ps.gt.0.0) ps=log(ps)
r1=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
r2=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
r4=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
rxdata(3*j-2)=r4
rxdata(3*j-1)=r2
rxdata(3*j)=r1
enddo
rxav=sum(rxdata)/(3.0*ND)
rx2av=sum(rxdata*rxdata)/(3.0*ND)
var=rx2av-rxav*rxav
if( var .gt. 0.0 ) then
rxsig=sqrt(var)
else
rxsig=sqrt(rx2av)
endif
rxdata=rxdata/rxsig
ss=0.84
llr=2.0*rxdata/(ss*ss)
apmask=0
cw=0
! cw will be needed for subtraction.
! dmin is the correlation discrepancy of a returned codeword - it is
! used to select the best codeword within osd174.
call timer('bpd174 ',0)
call bpdecode174(llr,apmask,max_iterations,decoded,cw,nharderrors)
call timer('bpd174 ',1)
dmin=0.0
if(nharderrors.lt.0) then
call timer('osd174 ',0)
call osd174(llr,norder,decoded,cw,nharderrors,dmin)
call timer('osd174 ',1)
! This threshold needs to be tuned. 99.0 should pass everything.
if( dmin .gt. 99.0 ) nharderrors=-1
endif
nbadcrc=1
message=' '
if(count(cw.eq.0).eq.174) go to 900 !Reject the all-zero codeword
if(nharderrors.ge.0) call chkcrc12a(decoded,nbadcrc)
if(nbadcrc.eq.0) then
call extractmessage174(decoded,message,ncrcflag,recent_calls,nrecent)
endif
900 continue
return
end subroutine ft8b