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new combined detector/demodulator/decoder routine for msk144
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6768 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Steven Franke
parent
f585500505
commit
d45dc65a87
373
lib/detectmsk144.f90
Normal file
373
lib/detectmsk144.f90
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@ -0,0 +1,373 @@
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subroutine detectmsk144(cbig,n,pchk_file,lines,nmessages,nutc)
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!nutc and t0 are for debug output
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use iso_c_binding, only: c_loc,c_size_t
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use packjt
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use hashing
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use timer_module, only: timer
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parameter (NSPM=864, NPTS=3*NSPM)
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character*22 msgreceived,allmessages(20)
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character*80 lines(100)
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character*512 pchk_file,gen_file
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complex cbig(n)
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complex cdat(NPTS) !Analytic signal
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complex cdat2(NPTS)
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complex c(NSPM)
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complex ctmp(6000)
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complex cb(42) !Complex waveform for sync word
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complex cfac,cca,ccb
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complex cc(NPTS)
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complex cc1(NPTS)
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complex cc2(NPTS)
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complex bb(6)
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integer s8(8),hardbits(144)
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integer*1, target:: i1Dec8BitBytes(10)
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integer, dimension(1) :: iloc
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integer*4 i4Dec6BitWords(12)
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integer*1 decoded(80)
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integer*1 i1hashdec
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integer indices(700)
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integer ipeaks(10)
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logical ismask(6000)
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real cbi(42),cbq(42)
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real detmet(700)
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real detfer(700)
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real tonespec(6000)
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real rcw(12)
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real dd(NPTS)
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real ferrs(20)
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real pp(12) !Half-sine pulse shape
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real snrs(20)
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real times(20)
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real*8 dt, df, fs, pi, twopi
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real softbits(144)
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real*8 unscrambledsoftbits(128)
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real lratio(128)
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real ttt(NPTS)
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logical first
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data first/.true./
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data s8/0,1,1,1,0,0,1,0/
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save df,first,cb,fs,nfft,pi,twopi,dt,s8,rcw,pp
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if(first) then
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allmessages=' '
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lines=' '
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i=index(pchk_file,".pchk")
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gen_file=pchk_file(1:i-1)//".gen"
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call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
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! define half-sine pulse and raised-cosine edge window
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pi=4d0*datan(1d0)
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twopi=8d0*datan(1d0)
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fs=12000.0
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dt=1.0/fs
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nfft=6000 !using a zero-padded fft to get 2 Hz bins
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df=fs/nfft
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do i=1,12
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angle=(i-1)*pi/12.0
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pp(i)=sin(angle)
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rcw(i)=(1-cos(angle))/2
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enddo
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! define the sync word waveform
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s8=2*s8-1
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cbq(1:6)=pp(7:12)*s8(1)
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cbq(7:18)=pp*s8(3)
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cbq(19:30)=pp*s8(5)
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cbq(31:42)=pp*s8(7)
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cbi(1:12)=pp*s8(2)
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cbi(13:24)=pp*s8(4)
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cbi(25:36)=pp*s8(6)
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cbi(37:42)=pp(1:6)*s8(8)
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cb=cmplx(cbi,cbq)
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ttt=(/ (i, i=1,NPTS) /)
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ttt=(ttt-NPTS/2)/(NPTS/2)
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first=.false.
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endif
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nstep=694 ! fill the detmet, detsnr, detferr arrays
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do istp=1,nstep
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ns=1+256*(istp-1)
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ne=ns+NPTS-1
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tt=(ns+ne)/2.0/12000.0
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cdat=cbig(ns:ne)
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! Coarse carrier frequency sync - seek tones at 2000 Hz and 4000 Hz in
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! squared signal spectrum.
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! search range for coarse frequency error is +/- 100 Hz
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ctmp=cmplx(0.0,0.0)
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ctmp(1:NPTS)=cdat**2
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ctmp(1:12)=ctmp(1:12)*rcw
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ctmp(NPTS-11:NPTS)=ctmp(NPTS-11:NPTS)*rcw(12:1:-1)
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call four2a(ctmp,nfft,1,-1,1)
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tonespec=abs(ctmp)**2
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ismask=.false.
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ismask(1901:2101)=.true. ! high tone search window
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iloc=maxloc(tonespec,ismask)
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ihpk=iloc(1)
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ah=tonespec(ihpk)
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ismask=.false.
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ismask(901:1101)=.true. ! window for low tone
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iloc=maxloc(tonespec,ismask)
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ilpk=iloc(1)
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al=tonespec(ilpk)
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fdiff=(ihpk-ilpk)*df
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ferrh=(ihpk-2001)*df/2.0
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ferrl=(ilpk-1001)*df/2.0
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if( abs(fdiff-2000) .le. 16.0 ) then
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if( ah .ge. al ) then
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ferr=ferrh
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else
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ferr=ferrl
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endif
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else
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ferr=-999.99
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endif
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detmet(istp)=ah+al
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detfer(istp)=ferr
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enddo ! end of detection-metric, snr, and frequency error estimation loop
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call indexx(detmet,nstep,indices) !find median of detection metric vector
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xmed=detmet(indices(nstep/2))
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detmet=detmet/xmed ! noise floor of detection metric is 1.0
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ndet=0
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do ip=1,20 ! use something like the "clean" algorithm to find candidates
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iloc=maxloc(detmet)
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il=iloc(1)
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if( (detmet(il) .lt. 2.0) .or. (abs(detfer(il)) .gt. 100.0) ) cycle
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ndet=ndet+1
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times(ndet)=((il-1)*256+NPTS/2)*dt
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ferrs(ndet)=detfer(il)
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snrs(ndet)=10.0*log10(detmet(il))/2-5.0 !/2 because detmet is a 4th order moment
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detmet(il-3:il+3)=0.0
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enddo
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nmessages=0
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do ip=1,ndet
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imid=times(ip)*fs
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t0=times(ip)
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cdat=cbig(imid-NPTS/2+1:imid+NPTS/2)
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ferr=ferrs(ip)
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nsnr=snrs(ip)
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! remove coarse freq error - should now be within a few Hz
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call tweak1(cdat,NPTS,-(1500+ferr),cdat)
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! attempt frame synchronization
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! correlate with sync word waveforms
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cc=0
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cc1=0
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cc2=0
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do i=1,NPTS-(56*6+41)
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cc1(i)=sum(cdat(i:i+41)*conjg(cb))
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cc2(i)=sum(cdat(i+56*6:i+56*6+41)*conjg(cb))
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enddo
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cc=cc1+cc2
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dd=abs(cc1)*abs(cc2)
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! Find 5 largest peaks
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do ipk=1,5
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iloc=maxloc(abs(cc))
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ic1=iloc(1)
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iloc=maxloc(dd)
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ic2=iloc(1)
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ipeaks(ipk)=ic2
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dd(max(1,ic2-7):min(NPTS-56*6-41,ic2+7))=0.0
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enddo
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do ipk=1,5
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! we want ic to be the index of the first sample of the frame
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ic0=ipeaks(ipk)
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! fine adjustment of sync index
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! bb lag used to place the sampling index at the center of the eye
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do i=1,6
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if( ic0+11+NSPM .le. NPTS ) then
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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 )
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else
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bb(i) = sum( ( cdat(ic0+i-1+6:NPTS:6) * conjg( cdat(ic0+i-1:NPTS-6:6) ) )*2 )
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endif
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enddo
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iloc=maxloc(abs(bb))
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ibb=iloc(1)
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bba=abs(bb(ibb))
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if( ibb .le. 3 ) ibb=ibb-1
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if( ibb .gt. 3 ) ibb=ibb-7
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do id=1,3 ! slicer dither
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if( id .eq. 1 ) is=0
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if( id .eq. 2 ) is=-1
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if( id .eq. 3 ) is=1
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! Adjust frame index to place peak of bb at desired lag
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ic=ic0+ibb+is
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if( ic .lt. 1 ) ic=ic+864
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! Estimate fine frequency error.
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! Should a larger separation be used when frames are averaged?
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cca=sum(cdat(ic:ic+41)*conjg(cb))
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if( ic+56*6+41 .le. NPTS ) then
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ccb=sum(cdat(ic+56*6:ic+56*6+41)*conjg(cb))
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cfac=ccb*conjg(cca)
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ferr2=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt)
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else
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ccb=sum(cdat(ic-88*6:ic-88*6+41)*conjg(cb))
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cfac=cca*conjg(ccb)
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ferr2=atan2(imag(cfac),real(cfac))/(twopi*88*6*dt)
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endif
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! Final estimate of the carrier frequency - returned to the calling program
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fest=1500+ferr+ferr2
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! Remove fine frequency error
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call tweak1(cdat,NPTS,-ferr2,cdat2)
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! place the beginning of frame at index NSPM+1
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cdat2=cshift(cdat2,ic-(NSPM+1))
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do iav=1,7 ! try each of 7 averaging patterns, hope that one works
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if( iav .eq. 1 ) then
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c(1:NSPM)=cdat2(NSPM+1:2*NSPM) !avg 1 frame to the right of ic
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elseif( iav .eq. 2 ) then
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c=cdat2(NSPM-431:NSPM+432) !1 frame centered on ic
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c=cshift(c,-432)
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elseif( iav .eq. 3 ) then !1 frame to the left of ic
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c=cdat2(1:NSPM)
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elseif( iav .eq. 4 ) then
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c=cdat2(NSPM+432:NSPM+432+863) !1 frame beginning 36ms to the right of ic
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c=cshift(c,432)
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elseif( iav .eq. 5 ) then
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c=cdat2(1:NSPM)+cdat2(NSPM+1:2*NSPM)
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elseif( iav .eq. 6 ) then
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c=cdat2(NSPM+1:2*NSPM)+cdat2(2*NSPM+1:NPTS)
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elseif( iav .eq. 7 ) then
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c=cdat2(1:NSPM)+cdat2(NSPM+1:2*NSPM)+cdat2(2*NSPM+1:NPTS)
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endif
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! Estimate final frequency error and carrier phase.
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cca=sum(c(1:1+41)*conjg(cb))
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ccb=sum(c(1+56*6:1+56*6+41)*conjg(cb))
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cfac=ccb*conjg(cca)
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ffin=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt)
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phase0=atan2(imag(cca+ccb),real(cca+ccb))
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! Remove phase error - want constellation such that sample points lie on re,im axes
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cfac=cmplx(cos(phase0),sin(phase0))
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c=c*conjg(cfac)
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! sample to get softsamples
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! do i=1,72
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! softbits(2*i-1)=imag(c(1+(i-1)*12))
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! softbits(2*i)=real(c(7+(i-1)*12))
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! enddo
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! matched filter - might be possible to improve this
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softbits(1)=sum(imag(c(1:6))*pp(7:12))+sum(imag(c(864-5:864))*pp(1:6))
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softbits(2)=sum(real(c(1:12))*pp)
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do i=2,72
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softbits(2*i-1)=sum(imag(c(1+(i-1)*12-6:1+(i-1)*12+5))*pp)
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softbits(2*i)=sum(real(c(7+(i-1)*12-6:7+(i-1)*12+5))*pp)
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enddo
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hardbits=0
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do i=1,144
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if( softbits(i) .ge. 0.0 ) then
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hardbits(i)=1
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endif
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enddo
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nbadsync1=(8-sum( (2*hardbits(1:8)-1)*s8 ) )/2
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nbadsync2=(8-sum( (2*hardbits(1+56:8+56)-1)*s8 ) )/2
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nbadsync=nbadsync1+nbadsync2
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if( nbadsync .gt. 4 ) cycle
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! normalize the softsymbols before submitting to decoder
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sav=sum(softbits)/144
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s2av=sum(softbits*softbits)/144
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ssig=sqrt(s2av-sav*sav)
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softbits=softbits/ssig
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sigma=0.65
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lratio(1:48)=softbits(9:9+47)
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lratio(49:128)=softbits(65:65+80-1)
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lratio=exp(2.0*lratio/(sigma*sigma))
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unscrambledsoftbits(1:127:2)=lratio(1:64)
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unscrambledsoftbits(2:128:2)=lratio(65:128)
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max_iterations=20
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max_dither=50
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call ldpc_decode(unscrambledsoftbits, decoded, &
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max_iterations, niterations, max_dither, ndither)
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if( niterations .ge. 0.0 ) then
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goto 778
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endif
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enddo ! frame averaging loop
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enddo ! sample-time dither loop
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enddo ! peak loop - could be made more efficient
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msgreceived=' '
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phase0=-98
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i1hashdec=0
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goto 999
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778 continue
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! The decoder found a codeword - compare decoded hash with calculated
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! Collapse 80 decoded bits to 10 bytes. Bytes 1-9 are the message, byte 10 is the hash
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do ibyte=1,10
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itmp=0
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do ibit=1,8
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itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*8+ibit))
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enddo
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i1Dec8BitBytes(ibyte)=itmp
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enddo
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! Calculate the hash using the first 9 bytes.
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ihashdec=nhash(c_loc(i1Dec8BitBytes),int(9,c_size_t),146)
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ihashdec=2*iand(ihashdec,255)
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! Compare calculated hash with received byte 10 - if they agree, keep the message.
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i1hashdec=ihashdec
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if( i1hashdec .eq. i1Dec8BitBytes(10) ) then
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! Good hash --- unpack 72-bit message
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do ibyte=1,12
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itmp=0
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do ibit=1,6
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itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*6+ibit))
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enddo
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i4Dec6BitWords(ibyte)=itmp
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enddo
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call unpackmsg(i4Dec6BitWords,msgreceived)
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else
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msgreceived=' '
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phase0=-99
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endif
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if( msgreceived .ne. ' ' ) then
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ndupe=0
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do im=1,nmessages
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if( allmessages(im) .eq. msgreceived ) ndupe=1
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enddo
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if( ndupe .eq. 0 ) then
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nmessages=nmessages+1
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allmessages(nmessages)=msgreceived
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write(lines(nmessages),1020) nutc,nsnr,t0,nint(fest),msgreceived,char(0)
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1020 format(i6.6,i4,f5.1,i5,' & ',a22,a1)
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endif
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endif
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999 continue
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! write(78,1001) nutc,t0,iav,ipk,is,fest,ffin,nbadsync1,nbadsync2, &
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! phase0,niterations,ndither,i1hashdec,i1Dec8BitBytes(10),msgreceived
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!1001 format(i6,f8.2,i4,i4,i4,f8.2,f8.2,i4,i4,f8.2,i4,i4,i4,i4,2x,a22)
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enddo
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return
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end subroutine detectmsk144
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