WSJT-X/libm65/ccf65.f90
Joe Taylor 5b977444d1 Fix decoding of shorthand messages after changing nfast.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/map65@2582 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2012-09-13 20:16:07 +00:00

125 lines
3.8 KiB
Fortran

subroutine ccf65(ss,nhsym,nfast,ssmax,sync1,ipol1,jpz,dt1,flipk, &
syncshort,snr2,ipol2,dt2)
parameter (NFFT=512,NH=NFFT/2)
real ss(4,322) !Input: half-symbol powers, 4 pol'ns
real s(NFFT) !CCF = ss*pr
complex cs(0:NH) !Complex FT of s
real s2(NFFT) !CCF = ss*pr2
complex cs2(0:NH) !Complex FT of s2
real pr(NFFT) !JT65 pseudo-random sync pattern
complex cpr(0:NH) !Complex FT of pr
real pr2(NFFT) !JT65 shorthand pattern
complex cpr2(0:NH) !Complex FT of pr2
real tmp1(322)
real tmp2(322)
real ccf(-11:54,4)
logical first
integer npr(126)
data first/.true./,nfast0/-99/
equivalence (s,cs),(pr,cpr),(s2,cs2),(pr2,cpr2)
save
! The JT65 pseudo-random sync pattern:
data npr/ &
1,0,0,1,1,0,0,0,1,1,1,1,1,1,0,1,0,1,0,0, &
0,1,0,1,1,0,0,1,0,0,0,1,1,1,0,0,1,1,1,1, &
0,1,1,0,1,1,1,1,0,0,0,1,1,0,1,0,1,0,1,1, &
0,0,1,1,0,1,0,1,0,1,0,0,1,0,0,0,0,0,0,1, &
1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,1,1,0,1, &
0,1,0,1,0,0,1,1,0,0,1,0,0,1,0,0,0,0,1,1, &
1,1,1,1,1,1/
if(first .or. nfast.ne.nfast0) then
! Initialize pr, pr2; compute cpr, cpr2.
fac=1.0/NFFT
do i=1,NFFT
pr(i)=0.
pr2(i)=0.
k=2*mod((i-1)/8,2)-1
if(nfast.eq.2) k=2*mod((i-1)/16,2)-1
if(i.le.NH) pr2(i)=fac*k
enddo
do i=1,126
j=2*i
pr(j)=fac*(2*npr(i)-1)
! Not sure why, but it works significantly better without the following line:
! pr(j-1)=pr(j)
enddo
call four2a(pr,NFFT,1,-1,0)
call four2a(pr2,NFFT,1,-1,0)
first=.false.
nfast0=nfast
endif
! Look for JT65 sync pattern and shorthand square-wave pattern.
ccfbest=0.
ccfbest2=0.
ipol1=1
ipol2=1
do ip=1,jpz !Do jpz polarizations
do i=1,nhsym-1
! s(i)=ss(ip,i)+ss(ip,i+1)
s(i)=min(ssmax,ss(ip,i)+ss(ip,i+1))
enddo
call pctile(s,tmp1,nhsym-1,50,base)
s(1:nhsym-1)=s(1:nhsym-1)-base
s(nhsym:NFFT)=0.
call four2a(s,NFFT,1,-1,0) !Real-to-complex FFT
do i=0,NH
cs2(i)=cs(i)*conjg(cpr2(i)) !Mult by complex FFT of pr2
cs(i)=cs(i)*conjg(cpr(i)) !Mult by complex FFT of pr
enddo
call four2a(cs,NFFT,1,1,-1) !Complex-to-real inv-FFT
call four2a(cs2,NFFT,1,1,-1) !Complex-to-real inv-FFT
do lag=-11,54 !Check for best JT65 sync
j=lag
if(j.lt.1) j=j+NFFT
ccf(lag,ip)=s(j)
if(abs(ccf(lag,ip)).gt.ccfbest) then
ccfbest=abs(ccf(lag,ip))
lagpk=lag
ipol1=ip
flipk=1.0
if(ccf(lag,ip).lt.0.0) flipk=-1.0
endif
enddo
do lag=-11,54 !Check for best shorthand
ccf2=s2(lag+28)
if(ccf2.gt.ccfbest2) then
ccfbest2=ccf2
lagpk2=lag
ipol2=ip
endif
enddo
enddo
! Find rms level on baseline of "ccfblue", for normalization.
sum=0.
do lag=-11,54
if(abs(lag-lagpk).gt.1) sum=sum + ccf(lag,ipol1)
enddo
base=sum/50.0
sq=0.
do lag=-11,54
if(abs(lag-lagpk).gt.1) sq=sq + (ccf(lag,ipol1)-base)**2
enddo
rms=sqrt(sq/49.0)
sync1=ccfbest/rms - 4.0
dt1=lagpk*(2048.0/11025.0)/nfast - 2.5
! Find base level for normalizing snr2.
do i=1,nhsym
tmp1(i)=ss(ipol2,i)
enddo
call pctile(tmp1,tmp2,nhsym,40,base)
snr2=0.398107*ccfbest2/base !### empirical
syncshort=0.5*ccfbest2/rms - 4.0 !### better normalizer than rms?
dt2=(2.5 + lagpk2*(2048.0/11025.0))/nfast
return
end subroutine ccf65