subroutine detectmsk144(cbig,n,pchk_file,lines,nmessages,nutc) use timer_module, only: timer parameter (NSPM=864, NPTS=3*NSPM, MAXSTEPS=1700, NFFT=NSPM, MAXCAND=20) character*22 msgreceived,allmessages(20) character*80 lines(100) character*512 pchk_file,gen_file complex cbig(n) complex cdat(NPTS) !Analytic signal complex cdat2(NPTS) complex c(NSPM) complex ctmp(NFFT) complex cb(42) !Complex waveform for sync word complex cbr(42) !Complex waveform for reversed sync word complex cfac,cca,ccb complex cc(NPTS) complex ccr(NPTS) complex cc1(NPTS) complex cc2(NPTS) complex ccr1(NPTS) complex ccr2(NPTS) complex bb(6) integer s8(8),s8r(8),hardbits(144) integer, dimension(1) :: iloc integer*1 decoded(80) integer indices(MAXSTEPS) integer ipeaks(10) logical ismask(NFFT) real cbi(42),cbq(42) real detmet(-2:MAXSTEPS+3) real detfer(MAXSTEPS) real hannwindow(NPTS) real rcw(12) real dd(NPTS) real ddr(NPTS) real ferrs(MAXCAND) real pp(12) !Half-sine pulse shape real snrs(MAXCAND) real times(MAXCAND) real tonespec(NFFT) real*8 dt, df, fs, pi, twopi real softbits(144) real*8 unscrambledsoftbits(128) real lratio(128) logical first data first/.true./ data s8/0,1,1,1,0,0,1,0/ data s8r/1,0,1,1,0,0,0,1/ save df,first,cb,fs,pi,twopi,dt,s8,rcw,pp,hannwindow,nmatchedfilter if(first) then nmatchedfilter=1 i=index(pchk_file,".pchk") gen_file=pchk_file(1:i-1)//".gen" call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0)) ! define half-sine pulse and raised-cosine edge window pi=4d0*datan(1d0) twopi=8d0*datan(1d0) fs=12000.0 dt=1.0/fs df=fs/NFFT do i=1,12 angle=(i-1)*pi/12.0 pp(i)=sin(angle) rcw(i)=(1-cos(angle))/2 enddo do i=1,NPTS hannwindow(i)=0.5*(1-cos(twopi*(i-1)/NPTS)) 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) 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) cbr=cmplx(cbi,cbq) first=.false. endif ! fill the detmet, detferr arrays nstep=(n-NPTS)/216 ! 72ms/4=18ms steps detmet=0 detmax=-999.99 detfer=-999.99 do istp=1,nstep ns=1+216*(istp-1) ne=ns+NSPM-1 if( ne .gt. n ) exit ctmp=cmplx(0.0,0.0) ctmp(1:NSPM)=cbig(ns:ne) ! Coarse carrier frequency sync - seek tones at 2000 Hz and 4000 Hz in ! squared signal spectrum. ! search range for coarse frequency error is +/- 100 Hz ctmp=ctmp**2 ctmp(1:12)=ctmp(1:12)*rcw ctmp(NSPM-11:NSPM)=ctmp(NSPM-11:NSPM)*rcw(12:1:-1) ! ctmp(1:NSPM)=ctmp(1:NSPM)*hannwindow call four2a(ctmp,NFFT,1,-1,1) tonespec=abs(ctmp)**2 i3800=3800/df+1 i4200=4200/df+1 ismask=.false. ismask(i3800:i4200)=.true. ! high tone search window iloc=maxloc(tonespec,ismask) ihpk=iloc(1) deltah=-real( (ctmp(ihpk-1)-ctmp(ihpk+1)) / (2*ctmp(ihpk)-ctmp(ihpk-1)-ctmp(ihpk+1)) ) ah=tonespec(ihpk) i1800=1800/df+1 i2200=2200/df+1 ismask=.false. ismask(i1800:i2200)=.true. ! window for low tone iloc=maxloc(tonespec,ismask) ilpk=iloc(1) deltal=-real( (ctmp(ilpk-1)-ctmp(ilpk+1)) / (2*ctmp(ilpk)-ctmp(ilpk-1)-ctmp(ilpk+1)) ) al=tonespec(ilpk) fdiff=(ihpk+deltah-ilpk-deltal)*df i2000=2000/df+1 i4000=4000/df+1 ferrh=(ihpk+deltah-i4000)*df/2.0 ferrl=(ilpk+deltal-i2000)*df/2.0 if( ah .ge. al ) then ferr=ferrh else ferr=ferrl endif detmet(istp)=max(ah,al) detfer(istp)=ferr enddo ! end of detection-metric and frequency error estimation loop call indexx(detmet(1:nstep),nstep,indices) !find median of detection metric vector ! xmed=detmet(indices(nstep/2)) xmed=detmet(indices(nstep/4)) detmet=detmet/xmed ! noise floor of detection metric is 1.0 ndet=0 do ip=1,MAXCAND ! use something like the "clean" algorithm to find candidates iloc=maxloc(detmet(1:nstep)) il=iloc(1) if( (detmet(il) .lt. 3.5) ) exit if( abs(detfer(il)) .le. 100.0 ) then ndet=ndet+1 times(ndet)=((il-1)*216+NSPM/2)*dt ferrs(ndet)=detfer(il) snrs(ndet)=12.0*log10(detmet(il))/2-9.0 endif ! detmet(max(1,il-3):min(nstep,il+3))=0.0 detmet(il)=0.0 enddo ! do ip=1,ndet ! write(*,*) ip,times(ip),snrs(ip),ferrs(ip) ! enddo nmessages=0 allmessages=char(0) lines=char(0) do ip=1,1 !run through the candidates and try to sync/demod/decode imid=times(ip)*fs if( imid .lt. NPTS/2 ) imid=NPTS/2 if( imid .gt. n-NPTS/2 ) imid=n-NPTS/2 t0=times(ip) cdat=cbig(imid-NPTS/2+1:imid+NPTS/2) ferr=ferrs(ip) nsnr=snrs(ip) ! remove coarse freq error - should now be within a few Hz call tweak1(cdat,NPTS,-(1500+ferr),cdat) ! attempt frame synchronization ! correlate with sync word waveforms cc=0 ccr=0 cc1=0 cc2=0 ccr1=0 ccr2=0 do i=1,NPTS-(56*6+41) cc1(i)=sum(cdat(i:i+41)*conjg(cb)) cc2(i)=sum(cdat(i+56*6:i+56*6+41)*conjg(cb)) enddo cc=cc1+cc2 dd=abs(cc1)*abs(cc2) do i=1,NPTS-(32*6+41) ccr1(i)=sum(cdat(i:i+41)*conjg(cbr)) ccr2(i)=sum(cdat(i+32*6:i+32*6+41)*conjg(cbr)) enddo ccr=ccr1+ccr2 ddr=abs(ccr1)*abs(ccr2) cmax=maxval(abs(cc)) crmax=maxval(abs(ccr)) ishort=0 if( crmax .gt. cmax ) ishort=1 ! Find 6 largest peaks do ipk=1,6 iloc=maxloc(abs(cc)) ic1=iloc(1) iloc=maxloc(dd) ic2=iloc(1) ! ipeaks(ipk)=ic2 ! dd(max(1,ic2-7):min(NPTS-56*6-41,ic2+7))=0.0 ipeaks(ipk)=ic1 cc(max(1,ic1-7):min(NPTS-56*6-41,ic1+7))=0.0 !write(*,*) ipk,ic1 enddo do ipk=1,6 ! we want ic to be the index of the first sample of the frame ic0=ipeaks(ipk) ! fine adjustment of sync index do i=1,6 if( ic0+11+NSPM .le. NPTS ) then bb(i) = sum( ( cdat(ic0+i-1+6:ic0+i-1+6+NSPM:6) * conjg( cdat(ic0+i-1:ic0+i-1+NSPM:6) ) )**2 ) else bb(i) = sum( ( cdat(ic0+i-1+6:NPTS:6) * conjg( cdat(ic0+i-1:NPTS-6:6) ) )**2 ) endif enddo iloc=maxloc(abs(bb)) ibb=iloc(1) bba=abs(bb(ibb)) bbp=atan2(-imag(bb(ibb)),-real(bb(ibb)))/(2*twopi*6*dt) if( ibb .le. 3 ) ibb=ibb-1 if( ibb .gt. 3 ) ibb=ibb-7 do id=1,3 ! slicer dither. bb is very good - may be able to remove this. if( id .eq. 1 ) is=0 if( id .eq. 2 ) is=-1 if( id .eq. 3 ) is=1 ! Adjust frame index to place peak of bb at desired lag ic=ic0+ibb+is if( ic .lt. 1 ) ic=ic+864 ! Estimate fine frequency error. ! Should a larger separation be used when frames are averaged? cca=sum(cdat(ic:ic+41)*conjg(cb)) if( ic+56*6+41 .le. NPTS ) then ccb=sum(cdat(ic+56*6:ic+56*6+41)*conjg(cb)) cfac=ccb*conjg(cca) ferr2=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt) else ccb=sum(cdat(ic-88*6:ic-88*6+41)*conjg(cb)) cfac=cca*conjg(ccb) ferr2=atan2(imag(cfac),real(cfac))/(twopi*88*6*dt) endif ! Final estimate of the carrier frequency - returned to the calling program fest=1500+ferr+ferr2 do idf=0,10 ! frequency jitter if( idf .eq. 0 ) then deltaf=0.0 elseif( mod(idf,2) .eq. 0 ) then deltaf=idf/2.0 else deltaf=-(idf+1)/2.0 endif ! Remove fine frequency error call tweak1(cdat,NPTS,-(ferr2+deltaf),cdat2) ! place the beginning of frame at index NSPM+1 cdat2=cshift(cdat2,ic-(NSPM+1)) do iav=1,8 ! Hopefully we can eliminate some of these after looking at more examples if( iav .eq. 1 ) then c=cdat2(NSPM+1:2*NSPM) elseif( iav .eq. 2 ) then c=cdat2(NSPM-431:NSPM+432) c=cshift(c,-432) elseif( iav .eq. 3 ) then c=cdat2(2*NSPM-431:2*NSPM+432) c=cshift(c,-432) elseif( iav .eq. 4 ) then c=cdat2(1:NSPM) elseif( iav .eq. 5 ) then c=cdat2(2*NSPM+1:NPTS) elseif( iav .eq. 6 ) then c=cdat2(1:NSPM)+cdat2(NSPM+1:2*NSPM) elseif( iav .eq. 7 ) then c=cdat2(NSPM+1:2*NSPM)+cdat2(2*NSPM+1:NPTS) elseif( iav .eq. 8 ) then c=cdat2(1:NSPM)+cdat2(NSPM+1:2*NSPM)+cdat2(2*NSPM+1:NPTS) endif ! Estimate final frequency error and 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) ffin=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt) 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) if( nmatchedfilter .eq. 0 ) then ! sample to get softsamples do i=1,72 softbits(2*i-1)=imag(c(1+(i-1)*12)) softbits(2*i)=real(c(7+(i-1)*12)) enddo else ! matched filter - ! how much mismatch does the RX/TX/analytic filter cause?, how rig (pair) dependent is this loss? 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 endif ! sync word hard error weight is a good 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 ) cycle ! 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 lratio(1:48)=softbits(9:9+47) lratio(49:128)=softbits(65:65+80-1) lratio=exp(2.0*lratio/(sigma*sigma)) unscrambledsoftbits(1:127:2)=lratio(1:64) unscrambledsoftbits(2:128:2)=lratio(65:128) max_iterations=10 max_dither=1 call ldpc_decode(unscrambledsoftbits, decoded, & max_iterations, niterations, max_dither, ndither) if( niterations .ge. 0.0 ) then call extractmessage144(decoded,msgreceived,nhashflag) if( nhashflag .gt. 0 ) then ! CRCs match, so print it ndupe=0 do im=1,nmessages if( allmessages(im) .eq. msgreceived ) ndupe=1 enddo if( ndupe .eq. 0 ) then nmessages=nmessages+1 allmessages(nmessages)=msgreceived write(lines(nmessages),1020) nutc,nsnr,t0,nint(fest),msgreceived 1020 format(i6.6,i4,f5.1,i5,' & ',a22) endif goto 999 else msgreceived=' ' ndither=-99 ! -99 is bad hash flag write(78,1001) nutc,t0,nsnr,ic,ipk,is,idf,iav,deltaf,fest,ferr,ferr2,ffin,bba,bbp,nbadsync1,nbadsync2, & phase0,niterations,ndither,msgreceived endif endif enddo ! frame averaging loop enddo ! frequency dithering loop enddo ! sample-time dither loop enddo ! peak loop - could be made more efficient by working harder to find good peaks msgreceived=' ' ndither=-98 999 continue if( nmessages .ge. 1 ) then write(78,1001) nutc,t0,nsnr,ic,ipk,is,idf,iav,deltaf,fest,ferr,ferr2,ffin,bba,bbp,nbadsync1,nbadsync2, & phase0,niterations,ndither,msgreceived call flush(78) 1001 format(i6.6,f8.2,i5,i5,i5,i5,i5,i5,f8.2,f8.2,f8.2,f8.2,f8.2,f10.2,f8.2,i5,i5,f8.2,i5,i5,2x,a22) exit endif enddo return end subroutine detectmsk144