subroutine msk144decodeframe(c,softbits,msgreceived,nsuccess) ! use timer_module, only: timer use packjt77 parameter (NSPM=864) character*37 msgreceived character*77 c77 complex cb(42) complex cfac,cca,ccb complex c(NSPM) integer*1 decoded77(77),apmask(128),cw(128) 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,unpk77_success 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=0.60 llr(1:48)=softbits(9:9+47) llr(49:128)=softbits(65:65+80-1) llr=2.0*llr/(sigma*sigma) max_iterations=10 apmask=0 dmin=0.0 call bpdecode128_90(llr,apmask,max_iterations,decoded77,cw,nharderror,niterations) if( nharderror .ge. 0 .and. nharderror .lt. 18 ) then nsuccess=1 write(c77,'(77i1)') decoded77 read(c77(72:77),'(2b3)') n3,i3 if( (i3.eq.0.and.(n3.eq.1 .or. n3.eq.3 .or. n3.eq.4 .or. n3.gt.5)) .or. i3.eq.3 .or. i3.gt.4 ) then nsuccess=0 else call unpack77(c77,1,msgreceived,unpk77_success) if(.not.unpk77_success) nsuccess=0 endif endif return end subroutine msk144decodeframe