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subroutine ft2_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
use crc
use packjt77
include 'ft2_params.f90'
character message*37,c77*77
character*61 line
character*37 decodes(100)
character*120 data_dir
character*17 cdatetime0,cdatetime
character*6 mycall,hiscall,hhmmss
complex c2(0:NMAX/16-1) !Complex waveform
complex cb(0:NMAX/16-1)
complex cd(0:144*10-1) !Complex waveform
complex c1(0:9),c0(0:9)
complex ccor(0:1,144)
complex csum,cterm,cc0,cc1,csync1
real*8 fMHz
real a(5)
real rxdata(128),llr(128) !Soft symbols
real llr2(128)
real sbits(144),sbits1(144),sbits3(144)
real ps(0:8191),psbest(0:8191)
real candidate(3,100)
real savg(NH1)
integer*2 iwave(NMAX) !Generated full-length waveform
integer*1 message77(77),apmask(128),cw(128)
integer*1 hbits(144),hbits1(144),hbits3(144)
integer*1 s16(16)
logical unpk77_success
data s16/0,0,0,0,1,1,1,1,1,1,1,1,0,0,0,0/
hhmmss=cdatetime0(8:13)
fs=12000.0/NDOWN !Sample rate
dt=1/fs !Sample interval after downsample (s)
tt=NSPS*dt !Duration of "itone" symbols (s)
baud=1.0/tt !Keying rate for "itone" symbols (baud)
txt=NZ*dt !Transmission length (s)
twopi=8.0*atan(1.0)
h=0.8 !h=0.8 seems to be optimum for AWGN sensitivity (not for fading)
dphi=twopi/2*baud*h*dt*16 ! dt*16 is samp interval after downsample
dphi0=-1*dphi
dphi1=+1*dphi
phi0=0.0
phi1=0.0
do i=0,9
c1(i)=cmplx(cos(phi1),sin(phi1))
c0(i)=cmplx(cos(phi0),sin(phi0))
phi1=mod(phi1+dphi1,twopi)
phi0=mod(phi0+dphi0,twopi)
enddo
the=twopi*h/2.0
cc1=cmplx(cos(the),-sin(the))
cc0=cmplx(cos(the),sin(the))
data_dir="."
fMHz=7.074
ncoh=1
candidate=0.0
ncand=0
fa=375.0
fb=3000.0
syncmin=0.2
maxcand=100
nfqso=-1
call getcandidates2a(iwave,fa,fb,maxcand,savg,candidate,ncand)
ndecodes=0
do icand=1,ncand
f0=candidate(1,icand)
if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle
call ft2_downsample(iwave,f0,c2) ! downsample from 160s/Symbol to 10s/Symbol
! 750 samples/second here
ibest=-1
sybest=-99.
dfbest=-1.
!### do if=-15,+15
do if=-30,30
df=if
a=0.
a(1)=-df
call twkfreq1(c2,NMAX/16,fs,a,cb)
do is=0,374 !DT search range is 0 - 0.5 s
csync1=0.
cterm=1
do ib=1,16
i1=(ib-1)*10+is
i2=i1+136*10
if(s16(ib).eq.1) then
csync1=csync1+sum(cb(i1:i1+9)*conjg(c1(0:9)))*cterm
cterm=cterm*cc1
else
csync1=csync1+sum(cb(i1:i1+9)*conjg(c0(0:9)))*cterm
cterm=cterm*cc0
endif
enddo
if(abs(csync1).gt.sybest) then
ibest=is
sybest=abs(csync1)
dfbest=df
endif
enddo
enddo
a=0.
a(1)=-dfbest
call twkfreq1(c2,NMAX/16,fs,a,cb)
ib=ibest
cd=cb(ib:ib+144*10-1)
s2=sum(real(cd*conjg(cd)))/(10*144)
cd=cd/sqrt(s2)
do nseq=1,5
if( nseq.eq.1 ) then ! noncoherent single-symbol detection
sbits1=0.0
do ibit=1,144
ib=(ibit-1)*10
ccor(1,ibit)=sum(cd(ib:ib+9)*conjg(c1(0:9)))
ccor(0,ibit)=sum(cd(ib:ib+9)*conjg(c0(0:9)))
sbits1(ibit)=abs(ccor(1,ibit))-abs(ccor(0,ibit))
hbits1(ibit)=0
if(sbits1(ibit).gt.0) hbits1(ibit)=1
enddo
sbits=sbits1
hbits=hbits1
sbits3=sbits1
hbits3=hbits1
elseif( nseq.ge.2 ) then
nbit=2*nseq-1
numseq=2**(nbit)
ps=0
do ibit=nbit/2+1,144-nbit/2
ps=0.0
pmax=0.0
do iseq=0,numseq-1
csum=0.0
cterm=1.0
k=1
do i=nbit-1,0,-1
ibb=iand(iseq/(2**i),1)
csum=csum+ccor(ibb,ibit-(nbit/2+1)+k)*cterm
if(ibb.eq.0) cterm=cterm*cc0
if(ibb.eq.1) cterm=cterm*cc1
k=k+1
enddo
ps(iseq)=abs(csum)
if( ps(iseq) .gt. pmax ) then
pmax=ps(iseq)
ibflag=1
endif
enddo
if( ibflag .eq. 1 ) then
psbest=ps
ibflag=0
endif
call getbitmetric(2**(nbit/2),psbest,numseq,sbits3(ibit))
hbits3(ibit)=0
if(sbits3(ibit).gt.0) hbits3(ibit)=1
enddo
sbits=sbits3
hbits=hbits3
endif
nsync_qual=count(hbits(1:16).eq.s16)
if(nsync_qual.lt.10) exit
rxdata=sbits(17:144)
rxav=sum(rxdata(1:128))/128.0
rx2av=sum(rxdata(1:128)*rxdata(1:128))/128.0
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
sigma=0.80
llr(1:128)=2*rxdata/(sigma*sigma)
apmask=0
max_iterations=40
do ibias=0,0
llr2=llr
if(ibias.eq.1) llr2=llr+0.4
if(ibias.eq.2) llr2=llr-0.4
call bpdecode128_90(llr2,apmask,max_iterations,message77,cw,nharderror,niterations)
if(nharderror.ge.0) exit
enddo
nhardmin=-1
if(sum(message77).eq.0) cycle
if( nharderror.ge.0 ) then
write(c77,'(77i1)') message77(1:77)
call unpack77(c77,nrx,message,unpk77_success)
idupe=0
do i=1,ndecodes
if(decodes(i).eq.message) idupe=1
enddo
if(idupe.eq.1) exit
ndecodes=ndecodes+1
decodes(ndecodes)=message
xsnr=db(sybest*sybest) - 115.0 !### Rough estimate of S/N ###
nsnr=nint(xsnr)
freq=f0+dfbest
write(line,1000) hhmmss,nsnr,ibest/750.0,nint(freq),message
1000 format(a6,i4,f5.2,i5,' + ',1x,a37)
open(24,file='all_ft2.txt',status='unknown',position='append')
write(24,1002) cdatetime0,nsnr,ibest/750.0,nint(freq),message, &
nseq,nharderror,nhardmin
if(hhmmss.eq.' ') write(*,1002) cdatetime0,nsnr, &
ibest/750.0,nint(freq),message,nseq,nharderror,nhardmin
1002 format(a17,i4,f6.2,i5,' Rx ',a37,3i5)
close(24)
!### Temporary: assume most recent decoded message conveys "hiscall".
i0=index(message,' ')
if(i0.ge.3 .and. i0.le.7) then
hiscall=message(i0+1:i0+6)
i1=index(hiscall,' ')
if(i1.gt.0) hiscall=hiscall(1:i1)
endif
nrx=-1
if(index(message,'CQ ').eq.1) nrx=1
if((index(message,trim(mycall)//' ').eq.1) .and. &
(index(message,' '//trim(hiscall)//' ').ge.4)) then
if(index(message,' 559 ').gt.8) nrx=2
if(index(message,' R 559 ').gt.8) nrx=3
if(index(message,' RR73 ').gt.8) nrx=4
endif
!###
exit
endif
enddo ! nseq
enddo !candidate list
return
end subroutine ft2_decode
subroutine getbitmetric(ib,ps,ns,xmet)
real ps(0:ns-1)
xm1=0
xm0=0
do i=0,ns-1
if( iand(i/ib,1) .eq. 1 .and. ps(i) .gt. xm1 ) xm1=ps(i)
if( iand(i/ib,1) .eq. 0 .and. ps(i) .gt. xm0 ) xm0=ps(i)
enddo
xmet=xm1-xm0
return
end subroutine getbitmetric
subroutine downsample2(ci,f0,co)
parameter(NI=144*160,NH=NI/2,NO=NI/16) ! downsample from 200 samples per symbol to 10
complex ci(0:NI-1),ct(0:NI-1)
complex co(0:NO-1)
fs=12000.0
df=fs/NI
ct=ci
call four2a(ct,NI,1,-1,1) !c2c FFT to freq domain
i0=nint(f0/df)
ct=cshift(ct,i0)
co=0.0
co(0)=ct(0)
b=8.0
do i=1,NO/2
arg=(i*df/b)**2
filt=exp(-arg)
co(i)=ct(i)*filt
co(NO-i)=ct(NI-i)*filt
enddo
co=co/NO
call four2a(co,NO,1,1,1) !c2c FFT back to time domain
return
end subroutine downsample2
subroutine ft2_downsample(iwave,f0,c)
! Input: i*2 data in iwave() at sample rate 12000 Hz
! Output: Complex data in c(), sampled at 1200 Hz
include 'ft2_params.f90'
parameter (NFFT2=NMAX/16)
integer*2 iwave(NMAX)
complex c(0:NMAX/16-1)
complex c1(0:NFFT2-1)
complex cx(0:NMAX/2)
real x(NMAX)
equivalence (x,cx)
BW=4.0*75
df=12000.0/NMAX
x=iwave
call four2a(x,NMAX,1,-1,0) !r2c FFT to freq domain
ibw=nint(BW/df)
i0=nint(f0/df)
c1=0.
c1(0)=cx(i0)
do i=1,NFFT2/2
arg=(i-1)*df/bw
win=exp(-arg*arg)
c1(i)=cx(i0+i)*win
c1(NFFT2-i)=cx(i0-i)*win
enddo
c1=c1/NFFT2
call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
c=c1(0:NMAX/16-1)
return
end subroutine ft2_downsample
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