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Improved estimates of Doppler spread. Comment the code in write_ref().

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This commit is contained in:
Joe Taylor 2020-07-16 11:47:07 -04:00
parent f61cb1dcbd
commit 7bd797c0e9
1 changed files with 88 additions and 77 deletions

165
lib/fst240_decode.f90
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@ -811,88 +811,99 @@ contains
end subroutine get_candidates_fst240
subroutine write_ref(itone,iwave,nsps,nmax,ndown,hmod,i0,fc,fmid,w50)
complex cwave(nmax)
complex, allocatable :: c(:)
real,allocatable :: ss(:)
integer itone(160)
integer*2 iwave(nmax)
integer hmod
data ncall/0/
save ncall
ncall=ncall+1
allocate(c(0:nmax-1))
wave=0
fsample=12000.0
nsym=160
! On "plotspec" special request, compute Doppler spread for a decoded signal
call gen_fst240wave(itone,nsym,nsps,nmax,fsample,hmod,fc, &
1,cwave,wave)
cwave=cshift(cwave,-i0*ndown)
! do i=1,nmax
! write(51,1000) i,iwave(i),cwave(i)
!1000 format(2i10,f12.6)
! enddo
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
fac=1.0/32768
c=fac*float(iwave)*conjg(cwave)
call four2a(c,nmax,1,-1,1) !Forward c2c FFT
ncall=ncall+1
nfft=2*nmax
allocate(cwave(0:nmax-1))
allocate(g(0:nfft-1))
wave=0
fsample=12000.0
nsym=160
call gen_fst240wave(itone,nsym,nsps,nmax,fsample,hmod,fc,1,cwave,wave)
cwave=cshift(cwave,-i0*ndown)
fac=1.0/32768
g(0:nmax-1)=fac*float(iwave)*conjg(cwave)
g(nmax:)=0.
call four2a(g,nfft,1,-1,1) !Forward c2c FFT
df=12000.0/nmax
ia=1.0/df
smax=0.
do i=-ia,ia
j=i
if(j.lt.0) j=i+nmax
s=real(c(j))**2 + aimag(c(j))**2
smax=max(s,smax)
enddo
ia=10.1/df
allocate(ss(-ia:ia))
sum1=0.
sum2=0.
ns=0
do i=-ia,ia
j=i
if(j.lt.0) j=i+nmax
ss(i)=(real(c(j))**2 + aimag(c(j))**2)/smax
f=i*df
if(f.ge.-4.0 .and. f.le.-2.0) then
sum1=sum1 + ss(i)
ns=ns+1
else if(f.ge.2.0 .and. f.le.4.0) then
sum2=sum2 + ss(i)
endif
enddo
avg=min(sum1/ns,sum2/ns)
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.
ns=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
ns=ns+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/ns,sum2/ns) !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
y=0.99*ss(i) + ncall-1
write(52,1010) f,y
1010 format(f12.6,f12.6)
enddo
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)
sum2=0.0
i1=-999
i2=-999
i3=-999
do i=-ia,ia
sum2=sum2 + ss(i)-avg
if(sum2.ge.0.25*sum1 .and. i1.eq.-999) i1=i
if(sum2.ge.0.50*sum1 .and. i2.eq.-999) i2=i
if(sum2.ge.0.75*sum1) then
i3=i
exit
endif
enddo
fmid=i2*df
w50=(i3-i1+1)*df
return
end subroutine write_ref
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
f=i*df
y=0.99*ss(i+nint(xi2)) + ncall-1
write(52,1010) f,y
1010 format(f12.6,f12.6)
enddo
return
end subroutine write_ref
end module fst240_decode