mirror of https://github.com/saitohirga/WSJT-X.git
278 lines
7.7 KiB
Fortran
278 lines
7.7 KiB
Fortran
subroutine ft2_decode(nutc,nfqso,iwave)
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use crc
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use packjt77
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include 'ft2_params.f90'
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character message*37,c77*77
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character*37 decodes(100)
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character*120 data_dir
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complex c2(0:NMAX/16-1) !Complex waveform
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complex cb(0:NMAX/16-1)
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complex cd(0:144*10-1) !Complex waveform
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complex c1(0:9),c0(0:9)
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complex ccor(0:1,144)
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complex csum,cterm,cc0,cc1,csync1
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real*8 fMHz
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real a(5)
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real rxdata(128),llr(128) !Soft symbols
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real llr2(128)
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real sbits(144),sbits1(144),sbits3(144)
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real ps(0:8191),psbest(0:8191)
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real candidate(3,100)
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real savg(NH1)
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integer*2 iwave(NMAX) !Generated full-length waveform
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integer*1 message77(77),apmask(128),cw(128)
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integer*1 hbits(144),hbits1(144),hbits3(144)
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integer*1 s16(16)
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logical unpk77_success
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data s16/0,0,0,0,1,1,1,1,1,1,1,1,0,0,0,0/
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fs=12000.0/NDOWN !Sample rate
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dt=1/fs !Sample interval after downsample (s)
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tt=NSPS*dt !Duration of "itone" symbols (s)
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baud=1.0/tt !Keying rate for "itone" symbols (baud)
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txt=NZ*dt !Transmission length (s)
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twopi=8.0*atan(1.0)
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h=0.8 !h=0.8 seems to be optimum for AWGN sensitivity (not for fading)
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dphi=twopi/2*baud*h*dt*16 ! dt*16 is samp interval after downsample
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dphi0=-1*dphi
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dphi1=+1*dphi
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phi0=0.0
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phi1=0.0
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do i=0,9
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c1(i)=cmplx(cos(phi1),sin(phi1))
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c0(i)=cmplx(cos(phi0),sin(phi0))
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phi1=mod(phi1+dphi1,twopi)
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phi0=mod(phi0+dphi0,twopi)
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enddo
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the=twopi*h/2.0
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cc1=cmplx(cos(the),-sin(the))
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cc0=cmplx(cos(the),sin(the))
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data_dir="."
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fMHz=7.074
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ncoh=1
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candidate=0.0
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ncand=0
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fa=375.0
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fb=3000.0
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syncmin=0.2
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maxcand=100
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nfqso=-1
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call getcandidates2(iwave,fa,fb,maxcand,savg,candidate,ncand)
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ndecodes=0
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do icand=1,ncand
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f0=candidate(1,icand)
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! print*,'A',ncand,f0
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xsnr=1.0
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if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle
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call ft2_downsample(iwave,f0,c2) ! downsample from 160s/Symbol to 10s/Symbol
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! 750 samples/second here
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ibest=-1
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sybest=-99.
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dfbest=-1.
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!### do if=-15,+15
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do if=-30,30
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df=if
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a=0.
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a(1)=-df
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call twkfreq1(c2,NMAX/16,fs,a,cb)
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do is=0,374
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csync1=0.
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cterm=1
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do ib=1,16
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i1=(ib-1)*10+is
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i2=i1+136*10
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if(s16(ib).eq.1) then
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csync1=csync1+sum(cb(i1:i1+9)*conjg(c1(0:9)))*cterm
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cterm=cterm*cc1
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else
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csync1=csync1+sum(cb(i1:i1+9)*conjg(c0(0:9)))*cterm
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cterm=cterm*cc0
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endif
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enddo
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! write(60,3001) if,is,abs(csync1)
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!3001 format(2i6,f10.3)
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if(abs(csync1).gt.sybest) then
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ibest=is
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sybest=abs(csync1)
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dfbest=df
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endif
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enddo
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enddo
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!dfbest=0.0
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!ibest=187
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a=0.
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a(1)=-dfbest
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call twkfreq1(c2,NMAX/16,fs,a,cb)
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ib=ibest
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cd=cb(ib:ib+144*10-1)
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s2=sum(real(cd*conjg(cd)))/(10*144)
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cd=cd/sqrt(s2)
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do nseq=1,5
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if( nseq.eq.1 ) then ! noncoherent single-symbol detection
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sbits1=0.0
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do ibit=1,144
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ib=(ibit-1)*10
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ccor(1,ibit)=sum(cd(ib:ib+9)*conjg(c1(0:9)))
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ccor(0,ibit)=sum(cd(ib:ib+9)*conjg(c0(0:9)))
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sbits1(ibit)=abs(ccor(1,ibit))-abs(ccor(0,ibit))
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hbits1(ibit)=0
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if(sbits1(ibit).gt.0) hbits1(ibit)=1
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enddo
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sbits=sbits1
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hbits=hbits1
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sbits3=sbits1
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hbits3=hbits1
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elseif( nseq.ge.2 ) then
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nbit=2*nseq-1
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numseq=2**(nbit)
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ps=0
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do ibit=nbit/2+1,144-nbit/2
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ps=0.0
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pmax=0.0
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do iseq=0,numseq-1
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csum=0.0
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cterm=1.0
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k=1
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do i=nbit-1,0,-1
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ibb=iand(iseq/(2**i),1)
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csum=csum+ccor(ibb,ibit-(nbit/2+1)+k)*cterm
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if(ibb.eq.0) cterm=cterm*cc0
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if(ibb.eq.1) cterm=cterm*cc1
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k=k+1
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enddo
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ps(iseq)=abs(csum)
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if( ps(iseq) .gt. pmax ) then
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pmax=ps(iseq)
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ibflag=1
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endif
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enddo
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if( ibflag .eq. 1 ) then
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psbest=ps
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ibflag=0
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endif
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call getbitmetric(2**(nbit/2),psbest,numseq,sbits3(ibit))
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hbits3(ibit)=0
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if(sbits3(ibit).gt.0) hbits3(ibit)=1
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enddo
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sbits=sbits3
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hbits=hbits3
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endif
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nsync_qual=count(hbits(1:16).eq.s16)
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if(nsync_qual.lt.10) exit
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rxdata=sbits(17:144)
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rxav=sum(rxdata(1:128))/128.0
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rx2av=sum(rxdata(1:128)*rxdata(1:128))/128.0
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rxsig=sqrt(rx2av-rxav*rxav)
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rxdata=rxdata/rxsig
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sigma=0.80
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llr(1:128)=2*rxdata/(sigma*sigma)
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apmask=0
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max_iterations=40
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do ibias=0,0
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llr2=llr
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if(ibias.eq.1) llr2=llr+0.4
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if(ibias.eq.2) llr2=llr-0.4
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call bpdecode128_90(llr2,apmask,max_iterations,message77,cw,nharderror,niterations)
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if(nharderror.ge.0) exit
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enddo
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nhardmin=-1
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if(sum(message77).eq.0) cycle
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if( nharderror.ge.0 ) then
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write(c77,'(77i1)') message77(1:77)
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call unpack77(c77,message,unpk77_success)
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idupe=0
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do i=1,ndecodes
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if(decodes(i).eq.message) idupe=1
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enddo
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if(idupe.eq.1) goto 888
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ndecodes=ndecodes+1
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decodes(ndecodes)=message
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nsnr=nint(xsnr)
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freq=f0+dfbest
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write(*,1212) nutc,nsnr,ibest/750.0,nint(freq),message, &
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nseq,nharderror,nhardmin
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1212 format(i4.4,i4,f6.2,i6,2x,a37,3i5)
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goto 888
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endif
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enddo ! nseq
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888 continue
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enddo !candidate list
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end subroutine ft2_decode
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subroutine getbitmetric(ib,ps,ns,xmet)
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real ps(0:ns-1)
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xm1=0
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xm0=0
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do i=0,ns-1
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if( iand(i/ib,1) .eq. 1 .and. ps(i) .gt. xm1 ) xm1=ps(i)
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if( iand(i/ib,1) .eq. 0 .and. ps(i) .gt. xm0 ) xm0=ps(i)
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enddo
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xmet=xm1-xm0
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return
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end subroutine getbitmetric
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subroutine downsample2(ci,f0,co)
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parameter(NI=144*160,NH=NI/2,NO=NI/16) ! downsample from 200 samples per symbol to 10
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complex ci(0:NI-1),ct(0:NI-1)
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complex co(0:NO-1)
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fs=12000.0
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df=fs/NI
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ct=ci
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call four2a(ct,NI,1,-1,1) !c2c FFT to freq domain
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i0=nint(f0/df)
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ct=cshift(ct,i0)
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co=0.0
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co(0)=ct(0)
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b=8.0
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do i=1,NO/2
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arg=(i*df/b)**2
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filt=exp(-arg)
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co(i)=ct(i)*filt
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co(NO-i)=ct(NI-i)*filt
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enddo
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co=co/NO
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call four2a(co,NO,1,1,1) !c2c FFT back to time domain
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return
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end subroutine downsample2
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subroutine ft2_downsample(iwave,f0,c)
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! Input: i*2 data in iwave() at sample rate 12000 Hz
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! Output: Complex data in c(), sampled at 1200 Hz
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include 'ft2_params.f90'
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parameter (NFFT2=NMAX/16)
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integer*2 iwave(NMAX)
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complex c(0:NMAX/16-1)
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complex c1(0:NFFT2-1)
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complex cx(0:NMAX/2)
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real x(NMAX)
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equivalence (x,cx)
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BW=4.0*75
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df=12000.0/NMAX
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x=iwave
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call four2a(x,NMAX,1,-1,0) !r2c FFT to freq domain
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ibw=nint(BW/df)
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i0=nint(f0/df)
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c1=0.
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c1(0)=cx(i0)
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do i=1,NFFT2/2
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arg=(i-1)*df/bw
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win=exp(-arg*arg)
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c1(i)=cx(i0+i)*win
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c1(NFFT2-i)=cx(i0-i)*win
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enddo
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c1=c1/NFFT2
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call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
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c=c1(0:NMAX/16-1)
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return
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end subroutine ft2_downsample
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