subroutine msk40decodeframe(c,mycall,hiscall,xsnr,msgreceived,nsuccess) ! use timer_module, only: timer parameter (NSPM=240) character*4 rpt(0:15) character*6 mycall,hiscall,mycall0,hiscall0 character*22 hashmsg,msgreceived complex cb(42) complex cfac,cca complex c(NSPM) integer*1 cw(32) integer*1 decoded(16) integer s8r(8),hardbits(40) integer nhashes(0:15) real*8 dt, fs, pi, twopi real cbi(42),cbq(42) real pp(12) real softbits(40) real llr(32) logical first data first/.true./ data s8r/1,0,1,1,0,0,0,1/ data mycall0/'dummy'/,hiscall0/'dummy'/ data rpt/"-03 ","+00 ","+03 ","+06 ","+10 ","+13 ","+16 ", & "R-03","R+00","R+03","R+06","R+10","R+13","R+16", & "RRR ","73 "/ save first,cb,fs,nhashes,pi,twopi,dt,s8r,pp,rpt,mycall0,hiscall0 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 s8r=2*s8r-1 cbq(1:6)=pp(7:12)*s8r(1) cbq(7:18)=pp*s8r(3) cbq(19:30)=pp*s8r(5) cbq(31:42)=pp*s8r(7) cbi(1:12)=pp*s8r(2) cbi(13:24)=pp*s8r(4) cbi(25:36)=pp*s8r(6) cbi(37:42)=pp(1:6)*s8r(8) cb=cmplx(cbi,cbq) first=.false. endif if(mycall.ne.mycall0 .or. hiscall.ne.hiscall0) then do i=0,15 hashmsg=trim(mycall)//' '//trim(hiscall)//' '//rpt(i) call fmtmsg(hashmsg,iz) call hash(hashmsg,22,ihash) nhashes(i)=iand(ihash,4095) enddo mycall0=mycall hiscall0=hiscall endif nsuccess=0 msgreceived=' ' ! Estimate carrier phase. cca=sum(c(1:1+41)*conjg(cb)) phase0=atan2(imag(cca),real(cca)) ! 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(NSPM-5:NSPM))*pp(1:6)) softbits(2)=sum(real(c(1:12))*pp) do i=2,20 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=1,40 if( softbits(i) .ge. 0.0 ) then hardbits(i)=1 endif enddo nbadsync1=(8-sum( (2*hardbits(1:8)-1)*s8r ) )/2 nbadsync=nbadsync1 if( nbadsync .gt. 3 ) then return endif ! normalize the softsymbols before submitting to decoder sav=sum(softbits)/40 s2av=sum(softbits*softbits)/40 ssig=sqrt(s2av-sav*sav) softbits=softbits/ssig sigma=0.75 if(xsnr.lt.0.0) sigma=0.75-0.0875*xsnr llr(1:32)=softbits(9:40) llr=2.0*llr/(sigma*sigma) max_iterations=5 call bpdecode40(llr,max_iterations,decoded,niterations) if( niterations .ge. 0.0 ) then call encode_msk40(decoded,cw) nhammd=0 cord=0.0 do i=1,32 if( cw(i) .ne. hardbits(i+8) ) then nhammd=nhammd+1 cord=cord+abs(softbits(i+8)) endif enddo imsg=0 do i=1,16 imsg=ishft(imsg,1)+iand(1,decoded(17-i)) enddo nrxrpt=iand(imsg,15) nrxhash=(imsg-nrxrpt)/16 !write(*,*) 'decodeframe ',nhammd,cord,nrxhash,nrxrpt,nhashes(nrxrpt) if(nhammd.le.5 .and. cord .lt. 1.7 .and. nrxhash.eq.nhashes(nrxrpt)) then nsuccess=1 write(msgreceived,'(a1,a,1x,a,a1,1x,a4)') "<",trim(mycall), & trim(hiscall),">",rpt(nrxrpt) return endif endif return end subroutine msk40decodeframe