WSJT-X/lib/ft4/ft4_decode.f90

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Fortran
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subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
use packjt77
include 'ft4_params.f90'
parameter (NSS=NSPS/NDOWN)
character message*37
character c77*77
character*61 line
character*37 decodes(100)
character*120 data_dir
character*17 cdatetime0
character*6 mycall,hiscall,hhmmss
complex cd2(0:NMAX/NDOWN-1) !Complex waveform
complex cb(0:NMAX/NDOWN-1)
complex cd(0:NN*NSS-1) !Complex waveform
complex ctwk(4*NSS),ctwk2(4*NSS)
complex csymb(NSS)
complex cs(0:3,NN)
real s4(0:3,NN)
real bmeta(2*NN),bmetb(2*NN),bmetc(2*NN)
real s(NH1,NHSYM)
real a(5)
real llr(2*ND),llr2(2*ND),llra(2*ND),llrb(2*ND),llrc(2*ND)
real s2(0:255)
real candidate(3,100)
real savg(NH1),sbase(NH1)
integer icos4(0:3)
integer*2 iwave(NMAX) !Generated full-length waveform
integer*1 message77(77),apmask(2*ND),cw(2*ND)
integer*1 hbits(2*NN)
integer graymap(0:3)
integer ip(1)
logical unpk77_success
logical one(0:255,0:7) ! 256 4-symbol sequences, 8 bits
logical first
data icos4/0,1,3,2/
data graymap/0,1,3,2/
data first/.true./
save one,first
hhmmss=cdatetime0(8:13)
fs=12000.0/NDOWN !Sample rate after downsampling
dt=1/fs !Sample interval after downsample (s)
tt=NSPS*dt !Duration of "itone" symbols (s)
txt=NZ*dt !Transmission length (s) without ramp up/down
twopi=8.0*atan(1.0)
h=1.0
if(first) then
one=.false.
do i=0,255
do j=0,7
if(iand(i,2**j).ne.0) one(i,j)=.true.
enddo
enddo
first=.false.
endif
candidate=0.0
ncand=0
syncmin=1.2
maxcand=100
! These are temporary. Correct values should be passed in as arguments.
data_dir="."
fMHz=7.074
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fa=400.0
fb=3000.0
call getcandidates4(iwave,fa,fb,syncmin,nfqso,maxcand,savg,candidate, &
ncand,sbase)
ndecodes=0
do icand=1,ncand
f0=candidate(1,icand)
xsnr=10*log10(candidate(3,icand))-18.0
if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle
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call ft4_downsample(iwave,f0,cd2) ! downsample from 512 Sa/Symbol to 32 Sa/Symbol
sum2=sum(cd2*conjg(cd2))/(real(NMAX)/real(NDOWN))
if(sum2.gt.0.0) cd2=cd2/sqrt(sum2)
! Sample rate is now 12000/16 = 750 samples/second
do isync=1,2
if(isync.eq.1) then
idfmin=-50
idfmax=50
idfstp=3
ibmin=0
ibmax=374
ibstp=4
else
idfmin=idfbest-5
idfmax=idfbest+5
idfstp=1
ibmin=max(0,ibest-5)
ibmax=min(ibest+5,NMAX/NDOWN-1)
ibstp=1
endif
ibest=-1
smax=-99.
idfbest=0
do idf=idfmin,idfmax,idfstp
a=0.
a(1)=real(idf)
ctwk=1.
call twkfreq1(ctwk,4*NSS,fs,a,ctwk2)
do istart=ibmin,ibmax,ibstp
call sync4d(cd2,istart,ctwk2,1,sync) !Find sync power
if(sync.gt.smax) then
smax=sync
ibest=istart
idfbest=idf
endif
enddo
enddo
enddo
f0=f0+real(idfbest)
call ft4_downsample(iwave,f0,cb) !Final downsample with corrected f0
sum2=sum(abs(cb)**2)/(real(NSS)*NN)
if(sum2.gt.0.0) cb=cb/sqrt(sum2)
cd=cb(ibest:ibest+NN*NSS-1)
do k=1,NN
i1=(k-1)*NSS
csymb=cd(i1:i1+NSS-1)
call four2a(csymb,NSS,1,-1,1)
cs(0:3,k)=csymb(1:4)
s4(0:3,k)=abs(csymb(1:4))
enddo
! Sync quality check
is1=0
is2=0
is3=0
is4=0
do k=1,4
ip=maxloc(s4(:,k))
if(icos4(k-1).eq.(ip(1)-1)) is1=is1+1
ip=maxloc(s4(:,k+33))
if(icos4(k-1).eq.(ip(1)-1)) is2=is2+1
ip=maxloc(s4(:,k+66))
if(icos4(k-1).eq.(ip(1)-1)) is3=is3+1
ip=maxloc(s4(:,k+99))
if(icos4(k-1).eq.(ip(1)-1)) is4=is4+1
enddo
nsync=is1+is2+is3+is4 !Number of hard sync errors, 0-16
if(smax .lt. 0.9 .or. nsync .lt. 9) cycle
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do nseq=1,3 !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
nt=2**(2*nsym)
do ks=1,NN-nsym+1,nsym !87+16=103 symbols.
amax=-1.0
do i=0,nt-1
i1=i/64
i2=iand(i,63)/16
i3=iand(i,15)/4
i4=iand(i,3)
if(nsym.eq.1) then
s2(i)=abs(cs(graymap(i4),ks))
elseif(nsym.eq.2) then
s2(i)=abs(cs(graymap(i3),ks)+cs(graymap(i4),ks+1))
elseif(nsym.eq.4) then
s2(i)=abs(cs(graymap(i1),ks ) + &
cs(graymap(i2),ks+1) + &
cs(graymap(i3),ks+2) + &
cs(graymap(i4),ks+3) &
)
else
print*,"Error - nsym must be 1, 2, or 4."
endif
enddo
ipt=1+(ks-1)*2
if(nsym.eq.1) ibmax=1
if(nsym.eq.2) ibmax=3
if(nsym.eq.4) ibmax=7
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
if(nsym.eq.1) then
bmeta(ipt+ib)=bm
elseif(nsym.eq.2) then
bmetb(ipt+ib)=bm
elseif(nsym.eq.4) then
bmetc(ipt+ib)=bm
endif
enddo
enddo
enddo
call normalizebmet(bmeta,2*NN)
call normalizebmet(bmetb,2*NN)
call normalizebmet(bmetc,2*NN)
hbits=0
where(bmeta.ge.0) hbits=1
ns1=count(hbits( 1: 8).eq.(/0,0,0,1,1,0,1,1/))
ns2=count(hbits( 67: 74).eq.(/0,0,0,1,1,0,1,1/))
ns3=count(hbits(133:140).eq.(/0,0,0,1,1,0,1,1/))
ns4=count(hbits(199:206).eq.(/0,0,0,1,1,0,1,1/))
nsync_qual=ns1+ns2+ns3+ns4
if(nsync_qual.lt. 20) cycle
scalefac=2.83
llra( 1: 58)=bmeta( 9: 66)
llra( 59:116)=bmeta( 75:132)
llra(117:174)=bmeta(141:198)
llra=scalefac*llra
llrb( 1: 58)=bmetb( 9: 66)
llrb( 59:116)=bmetb( 75:132)
llrb(117:174)=bmetb(141:198)
llrb=scalefac*llrb
llrc( 1: 58)=bmetc( 9: 66)
llrc( 59:116)=bmetc( 75:132)
llrc(117:174)=bmetc(141:198)
llrc=scalefac*llrc
do isd=1,3
if(isd.eq.1) llr=llra
if(isd.eq.2) llr=llrb
if(isd.eq.3) llr=llrc
apmask=0
max_iterations=40
do ibias=0,0
llr2=llr
if(ibias.eq.1) llr2=llr+0.4
if(ibias.eq.2) llr2=llr-0.4
call bpdecode174_91(llr2,apmask,max_iterations,message77, &
cw,nharderror,niterations)
if(nharderror.ge.0) exit
enddo
if(sum(message77).eq.0) cycle
if( nharderror.ge.0 ) then
write(c77,'(77i1)') message77(1:77)
call unpack77(c77,1,message,unpk77_success)
idupe=0
do i=1,ndecodes
if(decodes(i).eq.message) idupe=1
enddo
if(idupe.eq.1) exit
ndecodes=ndecodes+1
decodes(ndecodes)=message
nsnr=nint(xsnr)
freq=f0
write(line,1000) hhmmss,nsnr,ibest/750.0,nint(freq),message
1000 format(a6,i4,f5.2,i5,' + ',1x,a37)
open(24,file='all_ft4.txt',status='unknown',position='append')
write(24,1002) cdatetime0,nsnr,ibest/750.0,nint(freq),message, &
nharderror,nsync_qual,isd,niterations
if(hhmmss.eq.' ') write(*,1002) cdatetime0,nsnr, &
ibest/750.0,nint(freq),message,nharderror,nsync_qual,isd, &
niterations
1002 format(a17,i4,f6.2,i5,' Rx ',a37,4i5)
close(24)
!### Temporary: assume most recent decoded message conveys "hiscall". ###
i0=index(message,' ')
if(i0.ge.3 .and. i0.le.7) then
hiscall=message(i0+1:i0+6)
i1=index(hiscall,' ')
if(i1.gt.0) hiscall=hiscall(1:i1)
endif
nrx=-1
if(index(message,'CQ ').eq.1) nrx=1
if((index(message,trim(mycall)//' ').eq.1) .and. &
(index(message,' '//trim(hiscall)//' ').ge.4)) then
if(index(message,' 559 ').gt.8) nrx=2
if(index(message,' R 559 ').gt.8) nrx=3
if(index(message,' RR73 ').gt.8) nrx=4
endif
!###
exit
endif
enddo !Sequence estimation
enddo !Candidate list
return
end subroutine ft4_decode
subroutine ft4_downsample(iwave,f0,c)
! Input: i*2 data in iwave() at sample rate 12000 Hz
! Output: Complex data in c(), sampled at 1200 Hz
include 'ft4_params.f90'
parameter (NFFT2=NMAX/16)
integer*2 iwave(NMAX)
complex c(0:NMAX/NDOWN-1)
complex c1(0:NFFT2-1)
complex cx(0:NMAX/2)
real x(NMAX), window(0:NFFT2-1)
equivalence (x,cx)
logical first
data first/.true./
save first,window
df=12000.0/NMAX
baud=12000.0/NSPS
if(first) then
bw_transition = 0.5*baud
bw_flat = 4*baud
iwt = bw_transition / df
iwf = bw_flat / df
pi=4.0*atan(1.0)
window(0:iwt-1) = 0.5*(1+cos(pi*(/(i,i=iwt-1,0,-1)/)/iwt))
window(iwt:iwt+iwf-1)=1.0
window(iwt+iwf:2*iwt+iwf-1) = 0.5*(1+cos(pi*(/(i,i=0,iwt)/)/iwt))
window(2*iwt+iwf:)=0.0
iws = baud / df
window=cshift(window,iws)
first=.false.
endif
x=iwave
call four2a(x,NMAX,1,-1,0) !r2c FFT to freq domain
i0=nint(f0/df)
c1=0.
c1(0)=cx(i0)
do i=1,NFFT2/2
if(i0+i.le.NMAX/2) c1(i)=cx(i0+i)
if(i0-i.ge.0) c1(NFFT2-i)=cx(i0-i)
enddo
c1=c1*window/NFFT2
call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
c=c1(0:NMAX/NDOWN-1)
return
end subroutine ft4_downsample