WSJT-X/lib/sync4.f90
Joe Taylor 4bcc4f35a1 Much improved detection of sync in JT4 decoder.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6686 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2016-05-19 19:19:47 +00:00

180 lines
4.9 KiB
Fortran

subroutine sync4(dat,jz,ntol,NFreeze,MouseDF,mode,mode4,minwidth, &
dtx,dfx,snrx,snrsync,ccfblue,ccfred1,flip,width,ps0)
! Synchronizes JT4 data, finding the best-fit DT and DF.
parameter (NFFTMAX=2520) !Max length of FFTs
parameter (NHMAX=NFFTMAX/2) !Max length of power spectra
parameter (NSMAX=525) !Max number of half-symbol steps
integer ntol !Range of DF search
real dat(jz)
real psavg(NHMAX) !Average spectrum of whole record
real ps0(450) !Avg spectrum for plotting
real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols
real ccfblue(-5:540) !CCF with pseudorandom sequence
real ccfred(-450:450) !Peak of ccfblue, as function of freq
real red(-450:450) !Peak of ccfblue, as function of freq
real ccfred1(-224:224) !Peak of ccfblue, as function of freq
real tmp(1260)
integer ipk1(1)
integer nch(7)
logical savered
equivalence (ipk1,ipk1a)
data nch/1,2,4,9,18,36,72/
save
! write(*,3001) 'A',ntol,nfreeze,mousedf,mode,mode4,minwidth
!3001 format(a1,6i6)
! Do FFTs of twice symbol length, stepped by half symbols. Note that
! we have already downsampled the data by factor of 2.
nsym=207
nfft=2520
nh=nfft/2
nq=nfft/4
nsteps=jz/nq - 1
df=0.5*11025.0/nfft
psavg(1:nh)=0.
if(mode.eq.-999) width=0. !Silence compiler warning
do j=1,nsteps !Compute spectrum for each step, get average
k=(j-1)*nq + 1
call ps4(dat(k),nfft,s2(1,j))
psavg(1:nh)=psavg(1:nh) + s2(1:nh,j)
enddo
nsmo=min(10*mode4,150)
call flat1b(psavg,nsmo,s2,nh,nsteps,NHMAX,NSMAX) !Flatten spectra
if(mode4.ge.9) call smo(psavg,nh,tmp,mode4/4)
i0=132
do i=1,450
ps0(i)=5.0*(psavg(i0+2*i) + psavg(i0+2*i+1) - 2.0)
enddo
! Set freq and lag ranges
famin=200.0 + 3*mode4*df
fbmax=2700.0 - 3*mode4*df
fa=famin
fb=fbmax
if(NFreeze.eq.1) then
fa=max(famin,1270.46+MouseDF-ntol)
fb=min(fbmax,1270.46+MouseDF+ntol)
else
fa=max(famin,1270.46+MouseDF-600)
fb=min(fbmax,1270.46+MouseDF+600)
endif
ia=fa/df - 3*mode4 !Index of lowest tone, bottom of range
ib=fb/df - 3*mode4 !Index of lowest tone, top of range
i0=nint(1270.46/df)
irange=450
if(ia-i0.lt.-irange) ia=i0-irange
if(ib-i0.gt.irange) ib=i0+irange
lag1=-5
lag2=59
syncbest=-1.e30
ccfred=0.
jmax=-1000
jmin=1000
do ich=minwidth,7 !Find best width
kz=nch(ich)/2
savered=.false.
do i=ia+kz,ib-kz !Find best frequency channel for CCF
call xcor4(s2,i,nsteps,nsym,lag1,lag2,ich,mode4,ccfblue,ccf0, &
lagpk0,flip)
j=i-i0 + 3*mode4
if(j.ge.-372 .and. j.le.372) then
ccfred(j)=ccf0
jmax=max(j,jmax)
jmin=min(j,jmin)
endif
! Find rms of the CCF, without main peak
call slope(ccfblue(lag1),lag2-lag1+1,lagpk0-lag1+1.0)
sync=abs(ccfblue(lagpk0))
! Find best sync value
if(sync.gt.syncbest) then
ipk=i
lagpk=lagpk0
ichpk=ich
syncbest=sync
savered=.true.
endif
enddo
if(savered) red=ccfred
enddo
ccfred=red
! width=df*nch(ichpk)
dfx=(ipk-i0 + 3*mode4)*df
! Peak up in time, at best whole-channel frequency
call xcor4(s2,ipk,nsteps,nsym,lag1,lag2,ichpk,mode4,ccfblue,ccfmax, &
lagpk,flip)
xlag=lagpk
if(lagpk.gt.lag1 .and. lagpk.lt.lag2) then
call peakup(ccfblue(lagpk-1),ccfmax,ccfblue(lagpk+1),dx2)
xlag=lagpk+dx2
endif
! Find rms of the CCF, without the main peak
call slope(ccfblue(lag1),lag2-lag1+1,xlag-lag1+1.0)
sq=0.
nsq=0
do lag=lag1,lag2
if(abs(lag-xlag).gt.2.0) then
sq=sq+ccfblue(lag)**2
nsq=nsq+1
endif
enddo
rms=sqrt(sq/nsq)
snrsync=max(0.0,db(abs(ccfblue(lagpk)/rms - 1.0)) - 4.5)
snrx=-26.
if(mode4.eq.2) snrx=-25.
if(mode4.eq.4) snrx=-24.
if(mode4.eq.9) snrx=-23.
if(mode4.eq.18) snrx=-22.
if(mode4.eq.36) snrx=-21.
if(mode4.eq.72) snrx=-20.
snrx=snrx + snrsync
dt=2.0/11025.0
istart=xlag*nq
dtx=istart*dt
ccfred1=0.
jmin=max(jmin,-224)
jmax=min(jmax,224)
do i=jmin,jmax
ccfred1(i)=ccfred(i)
enddo
ipk1=maxloc(ccfred1) - 225
ns=0
s=0.
iw=min(mode4,(ib-ia)/4)
do i=jmin,jmax
if(abs(i-ipk1a).gt.iw) then
s=s+ccfred1(i)
ns=ns+1
endif
enddo
base=s/ns
ccfred1=ccfred1-base
ccf10=0.5*maxval(ccfred1)
do i=ipk1a,jmin,-1
if(ccfred1(i).le.ccf10) exit
enddo
i1=i
do i=ipk1a,jmax
if(ccfred1(i).le.ccf10) exit
enddo
width=(i-i1)*df
return
end subroutine sync4
include 'flat1b.f90'