108 lines
2.7 KiB
Fortran
108 lines
2.7 KiB
Fortran
subroutine msk144decodeframe(c,softbits,msgreceived,nsuccess,recent_calls,nrecent)
|
|
! use timer_module, only: timer
|
|
|
|
parameter (NSPM=864)
|
|
character*22 msgreceived
|
|
character*12 recent_calls(nrecent)
|
|
complex cb(42)
|
|
complex cfac,cca,ccb
|
|
complex c(NSPM)
|
|
integer*1 decoded(80)
|
|
integer s8(8),hardbits(144)
|
|
real*8 dt, fs, pi, twopi
|
|
real cbi(42),cbq(42)
|
|
real pp(12)
|
|
real softbits(144)
|
|
real llr(128)
|
|
logical first
|
|
data first/.true./
|
|
data s8/0,1,1,1,0,0,1,0/
|
|
save first,cb,fs,pi,twopi,dt,s8,pp
|
|
|
|
if(first) then
|
|
! define half-sine pulse and raised-cosine edge window
|
|
pi=4d0*datan(1d0)
|
|
twopi=8d0*datan(1d0)
|
|
fs=12000.0
|
|
dt=1.0/fs
|
|
|
|
do i=1,12
|
|
angle=(i-1)*pi/12.0
|
|
pp(i)=sin(angle)
|
|
enddo
|
|
|
|
! define the sync word waveforms
|
|
s8=2*s8-1
|
|
cbq(1:6)=pp(7:12)*s8(1)
|
|
cbq(7:18)=pp*s8(3)
|
|
cbq(19:30)=pp*s8(5)
|
|
cbq(31:42)=pp*s8(7)
|
|
cbi(1:12)=pp*s8(2)
|
|
cbi(13:24)=pp*s8(4)
|
|
cbi(25:36)=pp*s8(6)
|
|
cbi(37:42)=pp(1:6)*s8(8)
|
|
cb=cmplx(cbi,cbq)
|
|
first=.false.
|
|
endif
|
|
|
|
nsuccess=0
|
|
msgreceived=' '
|
|
|
|
! Estimate carrier phase.
|
|
cca=sum(c(1:1+41)*conjg(cb))
|
|
ccb=sum(c(1+56*6:1+56*6+41)*conjg(cb))
|
|
cfac=ccb*conjg(cca)
|
|
phase0=atan2(imag(cca+ccb),real(cca+ccb))
|
|
|
|
! Remove phase error - want constellation rotated so that sample points lie on I/Q axes
|
|
cfac=cmplx(cos(phase0),sin(phase0))
|
|
c=c*conjg(cfac)
|
|
|
|
! matched filter -
|
|
softbits(1)=sum(imag(c(1:6))*pp(7:12))+sum(imag(c(864-5:864))*pp(1:6))
|
|
softbits(2)=sum(real(c(1:12))*pp)
|
|
do i=2,72
|
|
softbits(2*i-1)=sum(imag(c(1+(i-1)*12-6:1+(i-1)*12+5))*pp)
|
|
softbits(2*i)=sum(real(c(7+(i-1)*12-6:7+(i-1)*12+5))*pp)
|
|
enddo
|
|
|
|
! sync word hard error weight is used as a discriminator for
|
|
! frames that have reasonable probability of decoding
|
|
hardbits=0
|
|
do i=1,144
|
|
if( softbits(i) .ge. 0.0 ) then
|
|
hardbits(i)=1
|
|
endif
|
|
enddo
|
|
nbadsync1=(8-sum( (2*hardbits(1:8)-1)*s8 ) )/2
|
|
nbadsync2=(8-sum( (2*hardbits(1+56:8+56)-1)*s8 ) )/2
|
|
nbadsync=nbadsync1+nbadsync2
|
|
if( nbadsync .gt. 4 ) then
|
|
return
|
|
endif
|
|
|
|
! normalize the softsymbols before submitting to decoder
|
|
sav=sum(softbits)/144
|
|
s2av=sum(softbits*softbits)/144
|
|
ssig=sqrt(s2av-sav*sav)
|
|
softbits=softbits/ssig
|
|
|
|
sigma=0.75
|
|
llr(1:48)=softbits(9:9+47)
|
|
llr(49:128)=softbits(65:65+80-1)
|
|
llr=2.0*llr/(sigma*sigma)
|
|
|
|
max_iterations=10
|
|
! call timer('bpdec144 ',0)
|
|
call bpdecode144(llr,max_iterations,decoded,niterations)
|
|
! call timer('bpdec144 ',1)
|
|
if( niterations .ge. 0.0 ) then
|
|
call extractmessage144(decoded,msgreceived,nhashflag,recent_calls,nrecent)
|
|
if( nhashflag .gt. 0 ) then !Hash codes match, so print it
|
|
nsuccess=1
|
|
endif
|
|
endif
|
|
|
|
return
|
|
end subroutine msk144decodeframe
|