WSJT-X/lib/q65_sync.f90

subroutine q65_sync(nutc,iwave,nmax,mode_q65,codewords,ncw,nsps,nfqso,ntol,    &
     xdt,f0,snr1,dat4,snr2,id1)

! Detect and align with the Q65 sync vector, returning time and frequency
! offsets and SNR estimate.

! Input:  iwave(0:nmax-1)        Raw data
!         mode_q65               Tone spacing 1 2 4 8 16 (A-E)
!         nsps                   Samples per symbol at 12000 Sa/s
!         nfqso                  Target frequency (Hz)
!         ntol                   Search range around nfqso (Hz)
! Output: xdt                    Time offset from nominal (s)
!         f0                     Frequency of sync tone
!         snr1                   Relative SNR of sync signal

  use packjt77
  parameter (NSTEP=8)                    !Step size nsps/NSTEP
  parameter (LN=2176*63)           !LN=LL*NN; LL=64*(mode_q65+2), NN=63
  integer*2 iwave(0:nmax-1)              !Raw data
  integer isync(22)                      !Indices of sync symbols
  integer itone(85)
  integer codewords(63,64)
  integer dat4(13)
  integer ijpk(2)
  logical unpk77_success
  character*77 c77,decoded*37
  real, allocatable :: s1(:,:)           !Symbol spectra, 1/8-symbol steps
  real, allocatable :: s3(:,:)           !Data-symbol energies s3(LL,63)
  real, allocatable :: ccf(:,:)          !CCF(freq,lag)
  
  ! real, allocatable :: ccfcw(:)        ! Method 2
  ! real, allocatable :: ccfpk(:)        ! Method 2
  ! integer cwpk(1)                      ! Method 2
  ! integer, allocatable :: cwtone(:,:)  ! Method 2
  
  real, allocatable :: ccf1(:)           !CCF(freq) at best lag
  real s3prob(0:63,63)                   !Symbol-value probabilities
  real sync(85)                          !sync vector
  complex, allocatable :: c0(:)          !Complex spectrum of symbol
  data isync/1,9,12,13,15,22,23,26,27,33,35,38,46,50,55,60,62,66,69,74,76,85/
  data sync(1)/99.0/
  save sync

  id1=0
  dat4=0
  LL=64*(2+mode_q65)
  nfft=nsps
  df=12000.0/nfft                        !Freq resolution = baud
  istep=nsps/NSTEP
  iz=5000.0/df                           !Uppermost frequency bin, at 5000 Hz
  txt=85.0*nsps/12000.0
  jz=(txt+1.0)*12000.0/istep             !Number of quarter-symbol steps
  if(nsps.ge.6912) jz=(txt+2.0)*12000.0/istep   !For TR 60 s and higher
  ia=ntol/df

  allocate(s1(iz,jz))
  allocate(s3(-64:LL-65,63))
  allocate(c0(0:nfft-1))
  allocate(ccf(-ia:ia,-53:214))
  allocate(ccf1(-ia:ia))
  
  ! allocate(ccfcw(1:ncw))               ! Method 2
  ! allocate(ccfpk(1:ncw))               ! Method 2
  ! allocate(cwtone(ncw,85))             ! Method 2

  if(sync(1).eq.99.0) then               !Generate the sync vector
     sync=-22.0/63.0                     !Sync tone OFF  
     do k=1,22
        sync(isync(k))=1.0               !Sync tone ON
     enddo
  endif

  fac=1/32767.0
  do j=1,jz                              !Compute symbol spectra at step size
     ia=(j-1)*istep
     ib=ia+nsps-1
     k=-1
     do i=ia,ib,2          !Load iwave data into complex array c0, for r2c FFT
        xx=iwave(i)
        yy=iwave(i+1)
        k=k+1
        c0(k)=fac*cmplx(xx,yy)
     enddo
     c0(k+1:)=0.
     call four2a(c0,nfft,1,-1,0)              !r2c FFT
     do i=1,iz
        s1(i,j)=real(c0(i))**2 + aimag(c0(i))**2
     enddo
! For large Doppler spreads, should we smooth the spectra here?
!    call smo121(s1(1:iz,j),iz)
  enddo

  i0=nint(nfqso/df)                           !Target QSO frequency
  call pctile(s1(i0-64:i0-65+LL,1:jz),LL*jz,40,base)
  s1=s1/base

! Apply fast AGC
  s1max=20.0                                  !Empirical choice
  do j=1,jz                                   !### Maybe wrong way? ###
     smax=maxval(s1(i0-64:i0-65+LL,j))
     if(smax.gt.s1max) s1(i0-64:i0-65+LL,j)=s1(i0-64:i0-65+LL,j)*s1max/smax
  enddo

  dtstep=nsps/(NSTEP*12000.0)                 !Step size in seconds
  ia=ntol/df
  lag1=-1.0/dtstep
  lag2=1.0/dtstep + 0.9999
  j0=0.5/dtstep
  if(nsps.ge.7200) then
     j0=1.0/dtstep              !Nominal index for start of signal
     lag2=4.0/dtstep + 0.9999   !Include EME delays
  endif

  if(ncw.lt.1) go to 100
  
!######################################################################
! Try list decoding via "Deep Likelihood".

! Joe's method
  ipk=0
  jpk=0
  ccf_best=0.
  imsg_best=-1
  do imsg=1,ncw
     i=1
     k=0
     do j=1,85
        if(j.eq.isync(i)) then
           i=i+1
           itone(j)=-1
        else
           k=k+1
           itone(j)=codewords(k,imsg)
        endif
     enddo
! Compute 2D ccf using all 85 symbols in the list message
     ccf=0.
     do lag=lag1,lag2
        do k=1,85
           j=j0 + NSTEP*(k-1) + 1 + lag
           if(j.ge.1 .and. j.le.jz) then
              do i=-ia,ia
                 ii=i0+mode_q65*itone(k)+i
                 ccf(i,lag)=ccf(i,lag) + s1(ii,j)
              enddo
           endif
        enddo
     enddo
     ccfmax=maxval(ccf)
     if(ccfmax.gt.ccf_best) then
        ccf_best=ccfmax
        ijpk=maxloc(ccf)
        ipk=ijpk(1)-ia-1
        jpk=ijpk(2)-53-1     
        f0=nfqso + ipk*df
        xdt=jpk*dtstep
        imsg_best=imsg
     endif
  enddo  ! imsg

! Nico's Method 2
! Computes the ccf in a different order so that
! we can see what the ccfs of the list looked like
! on ccfmax

! Compute codeword tones
! cwtone = 0
! do imsg=1,ncw
!     i=1
!     k=0
!     do j=1,85
!        if(j.eq.isync(i)) then
!           i=i+1
!           cwtone(imsg,j)=-1
!        else
!           k=k+1
!           cwtone(imsg,j)=codewords(k,imsg)
!        endif
!     enddo
! enddo

! ipk=0
! jpk=0
! ccf_best=0.
! imsg_best=-1
! ccf=0.
! do lag=lag1,lag2
!    do i=-ia,ia
!		ccfcw = 0.
!        do k=1,85
!            j=j0 + NSTEP*(k-1) + 1 + lag
!            if(j.ge.1 .and. j.le.jz) then
!				do imsg=1,ncw
!				    ! if we would like to check only non systematic symbols
!					! uncomment the following if
!					!if (k.gt.18 .or. cwtone(imsg,k).eq.-1) then
!						ii=i0+mode_q65*cwtone(imsg,k)+i
!						ccfcw(imsg)=ccfcw(imsg) + s1(ii,j)
!					!endif
!			    enddo
!			endif
!		enddo
!		ccfmax=maxval(ccfcw)
!		ccf(i,lag) = ccfmax
!       if(ccfmax.gt.ccf_best) then
!		    ccfpk = ccfcw
!			cwpk = maxloc(ccfpk)
!			imsg_best = cwpk(1)
!			ccf_best = ccfmax
!		endif
!	enddo
! enddo
! ccfmax=maxval(ccf)
! ccf_best=ccfmax
! ijpk=maxloc(ccf)
! ipk=ijpk(1)-ia-1
! jpk=ijpk(2)-53-1     
! f0=nfqso + ipk*df
! xdt=jpk*dtstep
  
  ia=i0+ipk-64
  ib=ia+LL-1
  j=j0+jpk-7
  n=0
  do k=1,85
     j=j+8
     if(sync(k).gt.0.0) then
        cycle
     endif
     n=n+1
     if(j.ge.1 .and. j.le.jz) s3(-64:LL-65,n)=s1(ia:ib,j)
  enddo

  nsubmode=0
  if(mode_q65.eq.2) nsubmode=1
  if(mode_q65.eq.4) nsubmode=2
  if(mode_q65.eq.8) nsubmode=3
  if(mode_q65.eq.16) nsubmode=4
  nFadingModel=1
  baud=12000.0/nsps
  isreport = 0;
  do ibw=2,4
     b90=1.72**ibw
     call q65_intrinsics_ff(s3,nsubmode,b90/baud,nFadingModel,s3prob)
     call q65_dec_fullaplist(s3,s3prob,codewords,ncw,esnodb,dat4,plog,irc)
!    Joe's threshold	 
!     if(irc.ge.0 .and. plog.ge.-255.0) then
!    Nico's threshold
	 if (irc.ge.0) then
	   ! if it is an RRR type or a CQ Mycall grid
	   ! we accept the fullaplist threshold
	   ! other cases in the list are reports which
	   ! are more frequent in the list and then 
	   ! must be filtered with a higher threshold
	   if((irc.le.3.0 .or. irc.eq.56.0) .or. plog.ge.-250.0) then
        snr2=esnodb - db(2500.0/baud)
        id1=1
        write(c77,1000) dat4(1:12),dat4(13)/2
1000    format(12b6.6,b5.5)
        call unpack77(c77,0,decoded,unpk77_success) !Unpack to get msgsent
        open(55,file='fort.55',status='unknown',position='append')
		
! Joe's dump		
!        write(55,3055) nutc,ibw,xdt,f0,85.0*base,ccfmax,snr2,plog,   &
!             irc,trim(decoded)
!3055    format(i6,i3,6f8.2,i5,2x,a)

! Nico's dump for Method 2
!       This are the ccfs of the codeword in the list at the
!       ccf peak
!       write(55,3083) ccfpk
!3083	format(10f6.1)
!       Show also the imsg_best in order to compare it with
!       irc. (Interestingly they are always equal!)
!       write(55,3055) nutc,ibw,xdt,f0,85.0*base,ccfmax,snr2,plog,   &
!             irc,(imsg_best-1),trim(decoded)
!3055    format(i6,i3,6f8.2,2i5,2x,a)
        close(55)
        go to 900
	   endif
     endif
  enddo

!######################################################################
! Establish xdt, f0, and snr1 using sync symbols (and perhaps some AP symbols)
100 ccf=0.
  irc=-2
  dat4=0
  ia=ntol/df
  do lag=lag1,lag2
     do k=1,85
        n=NSTEP*(k-1) + 1
        j=n+lag+j0
        if(j.ge.1 .and. j.le.jz) then
           ccf(-ia:ia,lag)=ccf(-ia:ia,lag) + sync(k)*s1(i0-ia:i0+ia,j)
        endif
     enddo
  enddo
  ijpk=maxloc(ccf)
  ipk=ijpk(1)-ia-1
  jpk=ijpk(2)-53-1
  f0=nfqso + ipk*df
  xdt=jpk*dtstep
  sq=0.
  nsq=0
  do j=lag1,lag2
     if(abs(j-jpk).gt.6) then
        sq=sq + ccf(ipk,j)**2
        nsq=nsq+1
     endif
  enddo
  rms=sqrt(sq/nsq)
  smax=ccf(ipk,jpk)
  snr1=smax/rms
  
900 return
end subroutine q65_sync