WSJT-X/lib/fst4_decode.f90

854 lines
28 KiB
Fortran

module fst4_decode
type :: fst4_decoder
procedure(fst4_decode_callback), pointer :: callback
contains
procedure :: decode
end type fst4_decoder
abstract interface
subroutine fst4_decode_callback (this,nutc,sync,nsnr,dt,freq, &
decoded,nap,qual,ntrperiod,lwspr,fmid,w50)
import fst4_decoder
implicit none
class(fst4_decoder), intent(inout) :: this
integer, intent(in) :: nutc
real, intent(in) :: sync
integer, intent(in) :: nsnr
real, intent(in) :: dt
real, intent(in) :: freq
character(len=37), intent(in) :: decoded
integer, intent(in) :: nap
real, intent(in) :: qual
integer, intent(in) :: ntrperiod
logical, intent(in) :: lwspr
real, intent(in) :: fmid
real, intent(in) :: w50
end subroutine fst4_decode_callback
end interface
contains
subroutine decode(this,callback,iwave,nutc,nQSOProgress,nfa,nfb,nfqso, &
ndepth,ntrperiod,nexp_decode,ntol,emedelay,lapcqonly,mycall, &
hiscall,iwspr)
use timer_module, only: timer
use packjt77
use, intrinsic :: iso_c_binding
include 'fst4/fst4_params.f90'
parameter (MAXCAND=100)
class(fst4_decoder), intent(inout) :: this
procedure(fst4_decode_callback) :: callback
character*37 decodes(100)
character*37 msg,msgsent
character*77 c77
character*12 mycall,hiscall
character*12 mycall0,hiscall0
complex, allocatable :: c2(:)
complex, allocatable :: cframe(:)
complex, allocatable :: c_bigfft(:) !Complex waveform
real llr(240),llrs(240,4)
real candidates(200,5)
real bitmetrics(320,4)
real s4(0:3,NN)
real minsync
logical lapcqonly
integer itone(NN)
integer hmod
integer*1 apmask(240),cw(240)
integer*1 message101(101),message74(74),message77(77)
integer*1 rvec(77)
integer apbits(240)
integer nappasses(0:5) ! # of decoding passes for QSO states 0-5
integer naptypes(0:5,4) ! (nQSOProgress,decoding pass)
integer mcq(29),mrrr(19),m73(19),mrr73(19)
logical badsync,unpk77_success,single_decode
logical first,nohiscall,lwspr,ex
integer*2 iwave(30*60*12000)
data mcq/0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0/
data mrrr/0,1,1,1,1,1,1,0,1,0,0,1,0,0,1,0,0,0,1/
data m73/0,1,1,1,1,1,1,0,1,0,0,1,0,1,0,0,0,0,1/
data mrr73/0,1,1,1,1,1,1,0,0,1,1,1,0,1,0,1,0,0,1/
data rvec/0,1,0,0,1,0,1,0,0,1,0,1,1,1,1,0,1,0,0,0,1,0,0,1,1,0,1,1,0, &
1,0,0,1,0,1,1,0,0,0,0,1,0,0,0,1,0,1,0,0,1,1,1,1,0,0,1,0,1, &
0,1,0,1,0,1,1,0,1,1,1,1,1,0,0,0,1,0,1/
data first/.true./,hmod/1/
save first,apbits,nappasses,naptypes,mycall0,hiscall0
this%callback => callback
dxcall13=hiscall ! initialize for use in packjt77
mycall13=mycall
if(iwspr.ne.0.and.iwspr.ne.1) return
if(first) then
mcq=2*mod(mcq+rvec(1:29),2)-1
mrrr=2*mod(mrrr+rvec(59:77),2)-1
m73=2*mod(m73+rvec(59:77),2)-1
mrr73=2*mod(mrr73+rvec(59:77),2)-1
nappasses(0)=2
nappasses(1)=2
nappasses(2)=2
nappasses(3)=2
nappasses(4)=2
nappasses(5)=3
! iaptype
!------------------------
! 1 CQ ??? ??? (29 ap bits)
! 2 MyCall ??? ??? (29 ap bits)
! 3 MyCall DxCall ??? (58 ap bits)
! 4 MyCall DxCall RRR (77 ap bits)
! 5 MyCall DxCall 73 (77 ap bits)
! 6 MyCall DxCall RR73 (77 ap bits)
!********
naptypes(0,1:4)=(/1,2,0,0/) ! Tx6 selected (CQ)
naptypes(1,1:4)=(/2,3,0,0/) ! Tx1
naptypes(2,1:4)=(/2,3,0,0/) ! Tx2
naptypes(3,1:4)=(/3,6,0,0/) ! Tx3
naptypes(4,1:4)=(/3,6,0,0/) ! Tx4
naptypes(5,1:4)=(/3,1,2,0/) ! Tx5
mycall0=''
hiscall0=''
first=.false.
endif
l1=index(mycall,char(0))
if(l1.ne.0) mycall(l1:)=" "
l1=index(hiscall,char(0))
if(l1.ne.0) hiscall(l1:)=" "
if(mycall.ne.mycall0 .or. hiscall.ne.hiscall0) then
apbits=0
apbits(1)=99
apbits(30)=99
if(len(trim(mycall)) .lt. 3) go to 10
nohiscall=.false.
hiscall0=hiscall
if(len(trim(hiscall0)).lt.3) then
hiscall0=mycall ! use mycall for dummy hiscall - mycall won't be hashed.
nohiscall=.true.
endif
msg=trim(mycall)//' '//trim(hiscall0)//' RR73'
i3=-1
n3=-1
call pack77(msg,i3,n3,c77)
call unpack77(c77,1,msgsent,unpk77_success)
if(i3.ne.1 .or. (msg.ne.msgsent) .or. .not.unpk77_success) go to 10
read(c77,'(77i1)') message77
message77=mod(message77+rvec,2)
apbits(1:77)=2*message77-1
if(nohiscall) apbits(30)=99
10 continue
mycall0=mycall
hiscall0=hiscall
endif
!************************************
if(nfqso+nqsoprogress.eq.-999) return
Keff=91
nmax=15*12000
if(ntrperiod.eq.15) then
nsps=720
nmax=15*12000
ndown=18 !nss=40,80,160,400
nfft1=int(nmax/ndown)*ndown
else if(ntrperiod.eq.30) then
nsps=1680
nmax=30*12000
ndown=42 !nss=40,80,168,336
nfft1=359856 !nfft2=8568=2^3*3^2*7*17
else if(ntrperiod.eq.60) then
nsps=3888
nmax=60*12000
ndown=108
nfft1=7500*96 ! nfft2=7500=2^2*3*5^4
else if(ntrperiod.eq.120) then
nsps=8200
nmax=120*12000
ndown=205 !nss=40,82,164,328
nfft1=7200*200 ! nfft2=7200=2^5*3^2*5^2
else if(ntrperiod.eq.300) then
nsps=21504
nmax=300*12000
ndown=512 !nss=42,84,168,336
nfft1=7020*512 ! nfft2=7020=2^2*3^3*5*13
else if(ntrperiod.eq.900) then
nsps=66560
nmax=900*12000
ndown=1664 !nss=40,80,160,320
nfft1=6480*1664 ! nfft2=6480=2^4*3^4*5
else if(ntrperiod.eq.1800) then
nsps=134400
nmax=1800*12000
ndown=3360 !nss=40,80,160,320
nfft1=6426*3360 ! nfft2=6426=2*3^3*7*17
end if
nss=nsps/ndown
fs=12000.0 !Sample rate
fs2=fs/ndown
nspsec=nint(fs2)
dt=1.0/fs !Sample interval (s)
dt2=1.0/fs2
tt=nsps*dt !Duration of "itone" symbols (s)
baud=1.0/tt
sigbw=4.0*baud
nfft2=nfft1/ndown !make sure that nfft1 is exactly nfft2*ndown
nfft1=nfft2*ndown
nh1=nfft1/2
allocate( c_bigfft(0:nfft1/2) )
allocate( c2(0:nfft2-1) )
allocate( cframe(0:160*nss-1) )
jittermax=2
if(ndepth.eq.3) then
nblock=4
jittermax=2
elseif(ndepth.eq.2) then
nblock=3
jittermax=0
elseif(ndepth.eq.1) then
nblock=1
jittermax=0
endif
ndropmax=1
npct=nexp_decode/256
call blanker(iwave,nfft1,ndropmax,npct,c_bigfft)
! The big fft is done once and is used for calculating the smoothed spectrum
! and also for downconverting/downsampling each candidate.
call four2a(c_bigfft,nfft1,1,-1,0) !r2c
nhicoh=1
nsyncoh=8
fa=nfa
fb=nfb
single_decode=iand(nexp_decode,32).ne.0
if(single_decode) then
fa=max(100,nint(nfqso+1.5*baud-ntol))
fb=min(4800,nint(nfqso+1.5*baud+ntol))
endif
minsync=1.20
if(ntrperiod.eq.15) minsync=1.15
! Get first approximation of candidate frequencies
call get_candidates_fst4(c_bigfft,nfft1,nsps,hmod,fs,fa,fb,nfa,nfb, &
minsync,ncand,candidates)
ndecodes=0
decodes=' '
isbest=0
fc2=0.
do icand=1,ncand
fc0=candidates(icand,1)
detmet=candidates(icand,2)
! Downconvert and downsample a slice of the spectrum centered on the
! rough estimate of the candidates frequency.
! Output array c2 is complex baseband sampled at 12000/ndown Sa/sec.
! The size of the downsampled c2 array is nfft2=nfft1/ndown
call timer('dwnsmpl ',0)
call fst4_downsample(c_bigfft,nfft1,ndown,fc0,sigbw,c2)
call timer('dwnsmpl ',1)
call timer('sync240 ',0)
call fst4_sync_search(c2,nfft2,hmod,fs2,nss,ntrperiod,nsyncoh,emedelay,sbest,fcbest,isbest)
call timer('sync240 ',1)
fc_synced = fc0 + fcbest
dt_synced = (isbest-fs2)*dt2 !nominal dt is 1 second so frame starts at sample fs2
candidates(icand,3)=fc_synced
candidates(icand,4)=isbest
enddo
! remove duplicate candidates
do icand=1,ncand
fc=candidates(icand,3)
isbest=nint(candidates(icand,4))
do ic2=1,ncand
fc2=candidates(ic2,3)
isbest2=nint(candidates(ic2,4))
if(ic2.ne.icand .and. fc2.gt.0.0) then
if(abs(fc2-fc).lt.0.10*baud) then ! same frequency
if(abs(isbest2-isbest).le.2) then
candidates(ic2,3)=-1
endif
endif
endif
enddo
enddo
ic=0
do icand=1,ncand
if(candidates(icand,3).gt.0) then
ic=ic+1
candidates(ic,:)=candidates(icand,:)
endif
enddo
ncand=ic
xsnr=0.
!write(*,*) 'ncand ',ncand
do icand=1,ncand
sync=candidates(icand,2)
fc_synced=candidates(icand,3)
isbest=nint(candidates(icand,4))
xdt=(isbest-nspsec)/fs2
if(ntrperiod.eq.15) xdt=(isbest-real(nspsec)/2.0)/fs2
call timer('dwnsmpl ',0)
call fst4_downsample(c_bigfft,nfft1,ndown,fc_synced,sigbw,c2)
call timer('dwnsmpl ',1)
do ijitter=0,jittermax
if(ijitter.eq.0) ioffset=0
if(ijitter.eq.1) ioffset=1
if(ijitter.eq.2) ioffset=-1
is0=isbest+ioffset
if(is0.lt.0) cycle
cframe=c2(is0:is0+160*nss-1)
bitmetrics=0
call timer('bitmetrc',0)
call get_fst4_bitmetrics(cframe,nss,nblock,nhicoh,bitmetrics, &
s4,nsync_qual,badsync)
call timer('bitmetrc',1)
if(badsync) cycle
do il=1,4
llrs( 1: 60,il)=bitmetrics( 17: 76, il)
llrs( 61:120,il)=bitmetrics( 93:152, il)
llrs(121:180,il)=bitmetrics(169:228, il)
llrs(181:240,il)=bitmetrics(245:304, il)
enddo
apmag=maxval(abs(llrs(:,1)))*1.1
ntmax=nblock+nappasses(nQSOProgress)
if(lapcqonly) ntmax=nblock+1
if(ndepth.eq.1) ntmax=nblock
apmask=0
if(iwspr.eq.1) then ! 50-bit msgs, no ap decoding
nblock=4
ntmax=nblock
endif
do itry=1,ntmax
if(itry.eq.1) llr=llrs(:,1)
if(itry.eq.2.and.itry.le.nblock) llr=llrs(:,2)
if(itry.eq.3.and.itry.le.nblock) llr=llrs(:,3)
if(itry.eq.4.and.itry.le.nblock) llr=llrs(:,4)
if(itry.le.nblock) then
apmask=0
iaptype=0
endif
if(itry.gt.nblock) then ! do ap passes
llr=llrs(:,nblock) ! Use largest blocksize as the basis for AP passes
iaptype=naptypes(nQSOProgress,itry-nblock)
if(lapcqonly) iaptype=1
if(iaptype.ge.2 .and. apbits(1).gt.1) cycle ! No, or nonstandard, mycall
if(iaptype.ge.3 .and. apbits(30).gt.1) cycle ! No, or nonstandard, dxcall
if(iaptype.eq.1) then ! CQ
apmask=0
apmask(1:29)=1
llr(1:29)=apmag*mcq(1:29)
endif
if(iaptype.eq.2) then ! MyCall ??? ???
apmask=0
apmask(1:29)=1
llr(1:29)=apmag*apbits(1:29)
endif
if(iaptype.eq.3) then ! MyCall DxCall ???
apmask=0
apmask(1:58)=1
llr(1:58)=apmag*apbits(1:58)
endif
if(iaptype.eq.4 .or. iaptype.eq.5 .or. iaptype .eq.6) then
apmask=0
apmask(1:77)=1
llr(1:58)=apmag*apbits(1:58)
if(iaptype.eq.4) llr(59:77)=apmag*mrrr(1:19)
if(iaptype.eq.5) llr(59:77)=apmag*m73(1:19)
if(iaptype.eq.6) llr(59:77)=apmag*mrr73(1:19)
endif
endif
dmin=0.0
nharderrors=-1
unpk77_success=.false.
if(iwspr.eq.0) then
maxosd=2
Keff=91
norder=3
call timer('d240_101',0)
call decode240_101(llr,Keff,maxosd,norder,apmask,message101, &
cw,ntype,nharderrors,dmin)
call timer('d240_101',1)
elseif(iwspr.eq.1) then
maxosd=2
call timer('d240_74 ',0)
Keff=64
norder=4
call decode240_74(llr,Keff,maxosd,norder,apmask,message74,cw, &
ntype,nharderrors,dmin)
call timer('d240_74 ',1)
endif
if(nharderrors .ge.0) then
if(count(cw.eq.1).eq.0) then
nharderrors=-nharderrors
cycle
endif
if(iwspr.eq.0) then
write(c77,'(77i1)') mod(message101(1:77)+rvec,2)
call unpack77(c77,1,msg,unpk77_success)
else
write(c77,'(50i1)') message74(1:50)
c77(51:77)='000000000000000000000110000'
call unpack77(c77,1,msg,unpk77_success)
endif
if(unpk77_success) then
idupe=0
do i=1,ndecodes
if(decodes(i).eq.msg) idupe=1
enddo
if(idupe.eq.1) goto 2002
ndecodes=ndecodes+1
decodes(ndecodes)=msg
if(iwspr.eq.0) then
call get_fst4_tones_from_bits(message101,itone,0)
else
call get_fst4_tones_from_bits(message74,itone,1)
endif
inquire(file='plotspec',exist=ex)
fmid=-999.0
call timer('dopsprd ',0)
if(ex) then
call dopspread(itone,iwave,nsps,nmax,ndown,hmod, &
isbest,fc_synced,fmid,w50)
endif
call timer('dopsprd ',1)
xsig=0
do i=1,NN
xsig=xsig+s4(itone(i),i)
enddo
base=candidates(icand,5)
arg=600.0*(xsig/base)-1.0
if(arg.gt.0.0) then
xsnr=10*log10(arg)-35.5-12.5*log10(nsps/8200.0)
if(ntrperiod.eq. 15) xsnr=xsnr+2
if(ntrperiod.eq. 30) xsnr=xsnr+1
if(ntrperiod.eq. 900) xsnr=xsnr+1
if(ntrperiod.eq.1800) xsnr=xsnr+2
else
xsnr=-99.9
endif
else
cycle
endif
nsnr=nint(xsnr)
qual=0.
fsig=fc_synced - 1.5*baud
if(ex) then
write(21,3021) nutc,icand,itry,nsyncoh,iaptype, &
ijitter,ntype,nsync_qual,nharderrors,dmin, &
sync,xsnr,xdt,fsig,w50,trim(msg)
3021 format(i6.6,6i3,2i4,f6.1,f7.2,f6.1,f6.2,f7.1,f7.3,1x,a)
flush(21)
endif
call this%callback(nutc,smax1,nsnr,xdt,fsig,msg, &
iaptype,qual,ntrperiod,lwspr,fmid,w50)
goto 2002
endif
enddo ! metrics
enddo ! istart jitter
2002 enddo !candidate list
return
end subroutine decode
subroutine sync_fst4(cd0,i0,f0,hmod,ncoh,np,nss,ntr,fs,sync)
! Compute sync power for a complex, downsampled FST4 signal.
use timer_module, only: timer
include 'fst4/fst4_params.f90'
complex cd0(0:np-1)
complex csync1,csync2,csynct1,csynct2
complex ctwk(3200)
complex z1,z2,z3,z4,z5
integer hmod,isyncword1(0:7),isyncword2(0:7)
real f0save
common/sync240com/csync1(3200),csync2(3200),csynct1(3200),csynct2(3200)
data isyncword1/0,1,3,2,1,0,2,3/
data isyncword2/2,3,1,0,3,2,0,1/
data f0save/-99.9/,nss0/-1/,ntr0/-1/
save twopi,dt,fac,f0save,nss0,ntr0
p(z1)=(real(z1*fac)**2 + aimag(z1*fac)**2)**0.5 !Compute power
nz=8*nss
call timer('sync240a',0)
if(nss.ne.nss0 .or. ntr.ne.ntr0) then
twopi=8.0*atan(1.0)
dt=1/fs
k=1
phi1=0.0
phi2=0.0
do i=0,7
dphi1=twopi*hmod*(isyncword1(i)-1.5)/real(nss)
dphi2=twopi*hmod*(isyncword2(i)-1.5)/real(nss)
do j=1,nss
csync1(k)=cmplx(cos(phi1),sin(phi1))
csync2(k)=cmplx(cos(phi2),sin(phi2))
phi1=mod(phi1+dphi1,twopi)
phi2=mod(phi2+dphi2,twopi)
k=k+1
enddo
enddo
fac=1.0/(8.0*nss)
nss0=nss
ntr0=ntr
f0save=-1.e30
endif
if(f0.ne.f0save) then
dphi=twopi*f0*dt
phi=0.0
do i=1,nz
ctwk(i)=cmplx(cos(phi),sin(phi))
phi=mod(phi+dphi,twopi)
enddo
csynct1(1:nz)=ctwk(1:nz)*csync1(1:nz)
csynct2(1:nz)=ctwk(1:nz)*csync2(1:nz)
f0save=f0
nss0=nss
endif
call timer('sync240a',1)
i1=i0 !Costas arrays
i2=i0+38*nss
i3=i0+76*nss
i4=i0+114*nss
i5=i0+152*nss
s1=0.0
s2=0.0
s3=0.0
s4=0.0
s5=0.0
if(ncoh.gt.0) then
nsec=8/ncoh
do i=1,nsec
is=(i-1)*ncoh*nss
z1=0
if(i1+is.ge.1) then
z1=sum(cd0(i1+is:i1+is+ncoh*nss-1)*conjg(csynct1(is+1:is+ncoh*nss)))
endif
z2=sum(cd0(i2+is:i2+is+ncoh*nss-1)*conjg(csynct2(is+1:is+ncoh*nss)))
z3=sum(cd0(i3+is:i3+is+ncoh*nss-1)*conjg(csynct1(is+1:is+ncoh*nss)))
z4=sum(cd0(i4+is:i4+is+ncoh*nss-1)*conjg(csynct2(is+1:is+ncoh*nss)))
z5=0
if(i5+is+ncoh*nss-1.le.np) then
z5=sum(cd0(i5+is:i5+is+ncoh*nss-1)*conjg(csynct1(is+1:is+ncoh*nss)))
endif
s1=s1+abs(z1)/nz
s2=s2+abs(z2)/nz
s3=s3+abs(z3)/nz
s4=s4+abs(z4)/nz
s5=s5+abs(z5)/nz
enddo
else
nsub=-ncoh
nps=nss/nsub
do i=1,8
do isub=1,nsub
is=(i-1)*nss+(isub-1)*nps
z1=0.0
if(i1+is.ge.1) then
z1=sum(cd0(i1+is:i1+is+nps-1)*conjg(csynct1(is+1:is+nps)))
endif
z2=sum(cd0(i2+is:i2+is+nps-1)*conjg(csynct2(is+1:is+nps)))
z3=sum(cd0(i3+is:i3+is+nps-1)*conjg(csynct1(is+1:is+nps)))
z4=sum(cd0(i4+is:i4+is+nps-1)*conjg(csynct2(is+1:is+nps)))
z5=0.0
if(i5+is+ncoh*nss-1.le.np) then
z5=sum(cd0(i5+is:i5+is+nps-1)*conjg(csynct1(is+1:is+nps)))
endif
s1=s1+abs(z1)/(8*nss)
s2=s2+abs(z2)/(8*nss)
s3=s3+abs(z3)/(8*nss)
s4=s4+abs(z4)/(8*nss)
s5=s5+abs(z5)/(8*nss)
enddo
enddo
endif
sync = s1+s2+s3+s4+s5
return
end subroutine sync_fst4
subroutine fst4_downsample(c_bigfft,nfft1,ndown,f0,sigbw,c1)
! Output: Complex data in c(), sampled at 12000/ndown Hz
complex c_bigfft(0:nfft1/2)
complex c1(0:nfft1/ndown-1)
df=12000.0/nfft1
i0=nint(f0/df)
ih=nint( ( f0 + 1.3*sigbw/2.0 )/df)
nbw=ih-i0+1
c1=0.
c1(0)=c_bigfft(i0)
nfft2=nfft1/ndown
do i=1,nbw
if(i0+i.le.nfft1/2) c1(i)=c_bigfft(i0+i)
if(i0-i.ge.0) c1(nfft2-i)=c_bigfft(i0-i)
enddo
c1=c1/nfft2
call four2a(c1,nfft2,1,1,1) !c2c FFT back to time domain
return
end subroutine fst4_downsample
subroutine get_candidates_fst4(c_bigfft,nfft1,nsps,hmod,fs,fa,fb,nfa,nfb, &
minsync,ncand,candidates)
complex c_bigfft(0:nfft1/2) !Full length FFT of raw data
integer hmod !Modulation index (submode)
integer im(1) !For maxloc
real candidates(200,5) !Candidate list
real, allocatable :: s(:) !Low resolution power spectrum
real, allocatable :: s2(:) !CCF of s() with 4 tones
real, allocatable :: sbase(:) !noise baseline estimate
real xdb(-3:3) !Model 4-tone CCF peaks
real minsync
data xdb/0.25,0.50,0.75,1.0,0.75,0.50,0.25/
nh1=nfft1/2
df1=fs/nfft1
baud=fs/nsps !Keying rate
df2=baud/2.0
nd=df2/df1 !s() sums this many bins of big FFT
ndh=nd/2
ia=nint(max(100.0,fa)/df2) !Low frequency search limit
ib=nint(min(4800.0,fb)/df2) !High frequency limit
ina=nint(max(100.0,real(nfa))/df2) !Low freq limit for noise baseline fit
inb=nint(min(4800.0,real(nfb))/df2) !High freq limit for noise fit
if(ia.lt.ina) ia=ina
if(ib.gt.inb) ib=inb
nnw=nint(48000.*nsps*2./fs)
allocate (s(nnw))
s=0. !Compute low-resolution power spectrum
do i=ina,inb ! noise analysis window includes signal analysis window
j0=nint(i*df2/df1)
do j=j0-ndh,j0+ndh
s(i)=s(i) + real(c_bigfft(j))**2 + aimag(c_bigfft(j))**2
enddo
enddo
ina=max(ina,1+3*hmod) !Don't run off the ends
inb=min(inb,nnw-3*hmod)
allocate (s2(nnw))
allocate (sbase(nnw))
s2=0.
do i=ina,inb !Compute CCF of s() and 4 tones
s2(i)=s(i-hmod*3) + s(i-hmod) +s(i+hmod) +s(i+hmod*3)
enddo
npct=30
call fst4_baseline(s2,nnw,ina+hmod*3,inb-hmod*3,npct,sbase)
if(any(sbase(ina:inb).le.0.0)) return
s2(ina:inb)=s2(ina:inb)/sbase(ina:inb) !Normalize wrt noise level
ncand=0
candidates=0
if(ia.lt.3) ia=3
if(ib.gt.nnw-2) ib=nnw-2
! Find candidates, using the CLEAN algorithm to remove a model of each one
! from s2() after it has been found.
pval=99.99
do while(ncand.lt.200)
im=maxloc(s2(ia:ib))
iploc=ia+im(1)-1 !Index of CCF peak
pval=s2(iploc) !Peak value
if(pval.lt.minsync) exit
do i=-3,+3 !Remove 0.9 of a model CCF at
k=iploc+2*hmod*i !this frequency from s2()
if(k.ge.ia .and. k.le.ib) then
s2(k)=max(0.,s2(k)-0.9*pval*xdb(i))
endif
enddo
ncand=ncand+1
candidates(ncand,1)=df2*iploc !Candidate frequency
candidates(ncand,2)=pval !Rough estimate of SNR
candidates(ncand,5)=sbase(iploc)
enddo
return
end subroutine get_candidates_fst4
subroutine fst4_sync_search(c2,nfft2,hmod,fs2,nss,ntrperiod,nsyncoh,emedelay,sbest,fcbest,isbest)
complex c2(0:nfft2-1)
integer hmod
nspsec=int(fs2)
baud=fs2/real(nss)
fc1=0.0
if(emedelay.lt.0.1) then ! search offsets from 0 s to 2 s
is0=1.5*nspsec
ishw=1.5*nspsec
else ! search plus or minus 1.5 s centered on emedelay
is0=nint((emedelay+1.0)*nspsec)
ishw=1.5*nspsec
endif
sbest=-1.e30
do if=-12,12
fc=fc1 + 0.1*baud*if
do istart=max(1,is0-ishw),is0+ishw,4*hmod
call sync_fst4(c2,istart,fc,hmod,nsyncoh,nfft2,nss, &
ntrperiod,fs2,sync)
if(sync.gt.sbest) then
fcbest=fc
isbest=istart
sbest=sync
endif
enddo
enddo
fc1=fcbest
is0=isbest
ishw=4*hmod
isst=1*hmod
sbest=0.0
do if=-7,7
fc=fc1 + 0.02*baud*if
do istart=max(1,is0-ishw),is0+ishw,isst
call sync_fst4(c2,istart,fc,hmod,nsyncoh,nfft2,nss, &
ntrperiod,fs2,sync)
if(sync.gt.sbest) then
fcbest=fc
isbest=istart
sbest=sync
endif
enddo
enddo
end subroutine fst4_sync_search
subroutine dopspread(itone,iwave,nsps,nmax,ndown,hmod,i0,fc,fmid,w50)
! On "plotspec" special request, compute Doppler spread for a decoded signal
include 'fst4/fst4_params.f90'
complex, allocatable :: cwave(:) !Reconstructed complex signal
complex, allocatable :: g(:) !Channel gain, g(t) in QEX paper
real,allocatable :: ss(:) !Computed power spectrum of g(t)
integer itone(160) !Tones for this message
integer*2 iwave(nmax) !Raw Rx data
integer hmod !Modulation index
data ncall/0/
save ncall
ncall=ncall+1
nfft=2*nmax
nwave=max(nmax,(NN+2)*nsps)
allocate(cwave(0:nwave-1))
allocate(g(0:nfft-1))
wave=0
fsample=12000.0
call gen_fst4wave(itone,NN,nsps,nwave,fsample,hmod,fc,1,cwave,wave)
cwave=cshift(cwave,-i0*ndown)
fac=1.0/32768
g(0:nmax-1)=fac*float(iwave)*conjg(cwave(:nmax-1))
g(nmax:)=0.
call four2a(g,nfft,1,-1,1) !Forward c2c FFT
df=12000.0/nfft
ia=1.0/df
smax=0.
do i=-ia,ia !Find smax in +/- 1 Hz around 0.
j=i
if(j.lt.0) j=i+nfft
s=real(g(j))**2 + aimag(g(j))**2
smax=max(s,smax)
enddo
ia=10.1/df
allocate(ss(-ia:ia)) !Allocate space for +/- 10 Hz
sum1=0.
sum2=0.
nns=0
do i=-ia,ia
j=i
if(j.lt.0) j=i+nfft
ss(i)=(real(g(j))**2 + aimag(g(j))**2)/smax
f=i*df
if(f.ge.-4.0 .and. f.le.-2.0) then
sum1=sum1 + ss(i) !Power between -2 and -4 Hz
nns=nns+1
else if(f.ge.2.0 .and. f.le.4.0) then
sum2=sum2 + ss(i) !Power between +2 and +4 Hz
endif
enddo
avg=min(sum1/nns,sum2/nns) !Compute avg from smaller sum
sum1=0.
do i=-ia,ia
f=i*df
if(abs(f).le.1.0) sum1=sum1 + ss(i)-avg !Power in abs(f) < 1 Hz
enddo
ia=nint(1.0/df) + 1
sum2=0.0
xi1=-999
xi2=-999
xi3=-999
sum2z=0.
do i=-ia,ia !Find freq range that has 50% of signal power
sum2=sum2 + ss(i)-avg
if(sum2.ge.0.25*sum1 .and. xi1.eq.-999.0) then
xi1=i - 1 + (sum2-0.25*sum1)/(sum2-sum2z)
endif
if(sum2.ge.0.50*sum1 .and. xi2.eq.-999.0) then
xi2=i - 1 + (sum2-0.50*sum1)/(sum2-sum2z)
endif
if(sum2.ge.0.75*sum1) then
xi3=i - 1 + (sum2-0.75*sum1)/(sum2-sum2z)
exit
endif
sum2z=sum2
enddo
xdiff=sqrt(1.0+(xi3-xi1)**2) !Keep small values from fluctuating too widely
w50=xdiff*df !Compute Doppler spread
fmid=xi2*df !Frequency midpoint of signal powere
do i=-ia,ia !Save the spectrum for plotting
y=ncall-1
j=i+nint(xi2)
if(abs(j*df).lt.10.0) y=0.99*ss(i+nint(xi2)) + ncall-1
write(52,1010) i*df,y
1010 format(f12.6,f12.6)
enddo
return
end subroutine dopspread
end module fst4_decode