WSJT-X/lib/syncmsk144.f90
Steven Franke 374282920c First working decoder for experimental jtmsk 72ms ldpc-coded messages.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6711 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2016-05-28 20:53:35 +00:00

256 lines
6.8 KiB
Fortran

subroutine syncmsk144(cdat,npts,jpk,ipk,idf,rmax,snr,metric,msgreceived,fest)
! Attempt synchronization, and if successful decode using Viterbi algorithm.
use iso_c_binding, only: c_loc,c_size_t
use packjt
use hashing
use timer_module, only: timer
parameter (NSPM=864,NSAVE=2000)
character*22 msgreceived
character*85 pchk_file,gen_file
complex cdat(npts) !Analytic signal
complex c(NSPM)
complex ctmp(6000)
complex cb(42) !Complex waveform for sync word
complex csum,cfac,cca,ccb
complex cc(npts)
complex cc1(npts)
complex cc2(npts)
complex cc3(npts)
integer s8(8),hardbits(144),hardword(128),unscrambledhardbits(128)
integer*1, target:: i1Dec8BitBytes(10)
integer, dimension(1) :: iloc
integer*4 i4Msg6BitWords(12) !72-bit message as 6-bit words
integer*4 i4Dec6BitWords(12)
integer*1 decoded(80)
integer*1, allocatable :: message(:)
integer*1 i1hashdec
logical ismask(6000)
real cbi(42),cbq(42)
real tonespec(6000)
real rcw(12)
real dd(npts)
real pp(12) !Half-sine pulse shape
real*8 dt, df, fs, 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/
save first,cb,cd,pi,twopi,dt,f0,f1
if(first) then
print*,"Initializing ldpc."
pchk_file="peg-128-80-reg3.pchk"
gen_file="peg-128-80-reg3.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)
dt=1.0/12000.0
do i=1,12
angle=(i-1)*pi/12.0
pp(i)=sin(angle)
rcw(i)=(1-cos(angle))/2
enddo
! define the sync word waveform
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)
! print*,"cb"
! do i=1,42
! print*,i,cbi(i),cbq(i)
! enddo
first=.false.
endif
! Coarse carrier frequency sync
! look for tones near 2k and 4k in the analytic signal spectrum
! search range for coarse frequency error is +/- 100 Hz
fs=12000.0
nfft=6000 !using a zero-padded fft to get 2 Hz bins
df=fs/nfft
ctmp=cmplx(0.0,0.0)
ctmp(1:npts)=cdat**2
ctmp(1:12)=ctmp(1:12)*rcw
ctmp(npts-11:npts)=ctmp(npts-11:npts)*rcw(12:1:-1)
call four2a(ctmp,nfft,1,-1,1)
tonespec=abs(ctmp)**2
ismask=.false.
ismask(1901:2101)=.true. ! high tone search window
iloc=maxloc(tonespec,ismask)
ihpk=iloc(1)
ah=tonespec(ihpk)
ismask=.false.
ismask(901:1101)=.true. ! window for low tone
iloc=maxloc(tonespec,ismask)
ilpk=iloc(1)
al=tonespec(ilpk)
if( ah .ge. al ) then
ferr=(ihpk-2001)*df/2.0
tot=sum(tonespec(1901:2101))
q1=200*ah/(tot-tonespec(ihpk))
else
ferr=(ilpk-1001)*df/2.0
tot=sum(tonespec(901:1101))
q1=200*al/(tot-tonespec(ilpk))
endif
fdiff=(ihpk-ilpk)*df
write(*,*) "Coarse frequency error: ",ferr
write(*,*) "Tone / avg : ",q1
write(*,*) "Tone separation : ",fdiff
! remove coarse freq error - should now be within a few Hz
call tweak1(cdat,npts,-(1500+ferr),cdat)
! correlate with sync word waveform
cc=0
cc1=0
cc2=0
cc3=0
do i=1,npts-448-41
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)
iloc=maxloc(abs(cc))
ic1=iloc(1)
iloc=maxloc(dd)
ic2=iloc(1)
write(*,*) "Syncs: ic1,ic2 ",ic1,ic2
ic=ic2
! open(unit=78,file="blah.txt")
! do i=1,npts-448-41
! write(78,*) i,abs(cc1(i)),abs(cc2(i)),abs(cc(i)),dd(i),abs(cc3(i))
! enddo
! close(78)
cca=sum(cdat(ic:ic+41)*conjg(cb))
ccb=sum(cdat(ic+56*6:ic+56*6+41)*conjg(cb))
phase0=atan2(imag(cca+ccb),real(cca+ccb))
cfac=ccb*conjg(cca)
ferr2=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt)
write(*,*) "Fine frequency error: ",ferr2
write(*,*) "Coarse Carrier phase : ",phase0
fest=1500+ferr+ferr2
write(*,*) "Estimated f0 : ",fest
! Remove fine frequency error
call tweak1(cdat,npts,-ferr2,cdat)
! Estimate final carrier phase
cca=sum(cdat(ic:ic+41)*conjg(cb))
ccb=sum(cdat(ic+56*6:ic+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))
write(*,*) "Final freq error: ",ffin
cfac=cmplx(cos(phase0),sin(phase0))
cdat=cdat*conjg(cfac)
open(unit=79,file="cdat.txt")
write(*,*) "npts = ",npts
do i=1,864
ii=ic+i-1
if( ii .gt. npts ) then
ii=ii-864
endif
c(i)=cdat(ii)
write(79,*) i,real(c(i)),imag(c(i))
enddo
close(79)
do i=1,72
softbits(2*i-1)=imag(c(1+(i-1)*12))
softbits(2*i)=real(c(7+(i-1)*12))
enddo
hardbits=0
do i=1,144
if( softbits(i) .ge. 0.0 ) then
hardbits(i)=1
endif
enddo
! write(*,*) hardbits(1:8)
! write(*,*) hardbits(57:57+7)
hardword(1:48)=hardbits(9:9+47)
hardword(49:128)=hardbits(65:65+80-1)
unscrambledhardbits(1:127:2)=hardword(1:64)
unscrambledhardbits(2:128:2)=hardword(65:128)
sav=sum(softbits)/144
s2av=sum(softbits*softbits)/144
ssig=sqrt(s2av-sav*sav)
softbits=softbits/ssig
sigma=0.65
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=20
max_dither=100
call ldpc_decode(unscrambledsoftbits, decoded, max_iterations, niterations, max_dither, ndither)
write(*,*) 'Decoder used ',niterations,' and ',ndither,' dither trials.'
if( niterations .lt. 0 ) then
msgreceived=' '
return
endif
! The decoder found a codeword - compare decoded hash with calculated
! Collapse 80 decoded bits to 10 bytes. Bytes 1-9 are the message, byte 10 is the hash
do ibyte=1,10
itmp=0
do ibit=1,8
itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*8+ibit))
enddo
i1Dec8BitBytes(ibyte)=itmp
enddo
! Calculate the hash using the first 9 bytes.
ihashdec=nhash(c_loc(i1Dec8BitBytes),int(9,c_size_t),146)
ihashdec=2*iand(ihashdec,255)
! Compare calculated hash with received byte 10 - if they agree, keep the message.
i1hashdec=ihashdec
write(*,*) "Hashes",i1hashdec,i1Dec8BitBytes(10)
if( i1hashdec .eq. i1Dec8BitBytes(10) ) then
! Good hash --- unpack 72-bit message
do ibyte=1,12
itmp=0
do ibit=1,6
itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*6+ibit))
enddo
i4Dec6BitWords(ibyte)=itmp
enddo
call unpackmsg(i4Dec6BitWords,msgreceived)
endif
return
end subroutine syncmsk144