WSJT-X/lib/fsk4hf/ft8b.f90

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3.7 KiB
Fortran
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subroutine ft8b(dd0,newdat,nfqso,f1,xdt,nharderrors,dmin,nbadcrc,message,xsnr)
use timer_module, only: timer
include 'ft8_params.f90'
parameter(NRECENT=10,NP2=2812)
character message*22,msgsent*22
character*12 recent_calls(NRECENT)
real a(5)
real s1(0:7,ND),s2(0:7,NN)
real ps(0:7)
real rxdata(3*ND),llr(3*ND) !Soft symbols
real dd0(15*12000)
integer*1 decoded(KK),apmask(3*ND),cw(3*ND)
integer itone(NN)
complex cd0(3200)
complex ctwk(32)
complex csymb(32)
logical newdat
max_iterations=40
norder=2
fs2=12000.0/NDOWN
dt2=1.0/fs2
twopi=8.0*atan(1.0)
delfbest=0.
ibest=0
! if(abs(nfqso-f1).lt.10.0) norder=3
call timer('ft8_down',0)
call ft8_downsample(dd0,newdat,f1,cd0) !Mix f1 to baseband and downsample
call timer('ft8_down',1)
i0=nint(xdt*fs2) !Initial guess for start of signal
smax=0.0
do idt=i0-16,i0+16 !Search over +/- half a symbol
call sync8d(cd0,idt,ctwk,0,sync)
if(sync.gt.smax) then
smax=sync
ibest=idt
endif
enddo
xdt2=ibest*dt2 !Improved estimate for DT
! Now peak up in frequency
i0=nint(xdt2*fs2)
smax=0.0
do ifr=-5,5 !Search over +/- 2.5 Hz
delf=ifr*0.5
dphi=twopi*delf*dt2
phi=0.0
do i=1,32
ctwk(i)=cmplx(cos(phi),sin(phi))
phi=mod(phi+dphi,twopi)
enddo
call sync8d(cd0,i0,ctwk,1,sync)
if( sync .gt. smax ) then
smax=sync
delfbest=delf
endif
enddo
a=0.0
a(1)=-delfbest
call twkfreq1(cd0,NP2,fs2,a,cd0)
xdt=xdt2
f1=f1+delfbest !Improved estimate of DF
call sync8d(cd0,i0,ctwk,2,sync)
j=0
do k=1,NN
i1=ibest+(k-1)*32
csymb=cmplx(0.0,0.0)
if( i1.ge.1 .and. i1+31 .le. NP2 ) csymb=cd0(i1:i1+31)
call four2a(csymb,32,1,-1,1)
s2(0:7,k)=abs(csymb(1:8))
enddo
j=0
do k=1,NN
if(k.le.7) cycle
if(k.ge.37 .and. k.le.43) cycle
if(k.gt.72) cycle
j=j+1
s1(0:7,j)=s2(0:7,k)
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
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)
endif
nbadcrc=1
message=' '
xsnr=-99.0
if(count(cw.eq.0).eq.174) go to 900 !Reject the all-zero codeword
if( nharderrors.ge.0 .and. dmin.le.30.0 .and. nharderrors .lt. 30) then
call chkcrc12a(decoded,nbadcrc)
else
nharderrors=-1
go to 900
endif
if(nbadcrc.eq.0) then
call extractmessage174(decoded,message,ncrcflag,recent_calls,nrecent)
call genft8(message,msgsent,itone)
call subtractft8(dd0,itone,f1,xdt2)
xsig=0.0
xnoi=0.0
do i=1,79
xsig=xsig+s2(itone(i),i)**2
ios=mod(itone(i)+4,7)
xnoi=xnoi+s2(ios,i)**2
enddo
xsnr=0.001
if( xnoi.gt.0 .and. xnoi.lt.xsig ) xsnr=xsig/xnoi-1.0
xsnr=10.0*log10(xsnr)-27.0
if( xsnr .lt. -24.0 ) xsnr=-24.0
endif
900 continue
return
end subroutine ft8b