WSJT-X/lib/q65_sync.f90
2020-12-06 08:12:58 -05:00

230 lines
6.6 KiB
Fortran

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
parameter (PLOG_MIN=-240.0) !List decoding threshold
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 :: 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
nsmo=int(0.7*mode_q65*mode_q65)
if(nsmo.lt.1) nsmo=1
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))
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?
do i=1,nsmo
call smo121(s1(1:iz,j),iz)
enddo
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".
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-1)*df
xdt=jpk*dtstep
imsg_best=imsg
endif
enddo ! imsg
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
ibwa=1.8*log(baud*mode_q65) + 2
ibwb=min(10,ibwa+4)
do ibw=ibwa,ibwb
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)
if(irc.ge.0 .and. plog.ge.PLOG_MIN) 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')
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)
close(55)
go to 900
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