WSJT-X/lib/ft8/ldpcsim174_91.f90

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Fortran
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program ldpcsim174_91
! End to end test of the (174,91)/crc14 encoder and decoder.
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use packjt77
integer, parameter:: N=174, K=91, M=N-K
character*37 msg,msgsent,msgreceived
character*77 c77
character*8 arg
character*6 grid
character*96 tmpchar
integer*1, allocatable :: codeword(:), decoded(:), message(:)
integer*1 msgbits(77)
integer*1 message77(77),message91(91)
integer*1 apmask(N), cw(N)
integer nerrtot(0:N),nerrdec(0:N)
logical unpk77_success
real*8, allocatable :: rxdata(:)
real, allocatable :: llr(:)
nerrtot=0
nerrdec=0
nargs=iargc()
if(nargs.ne.6) then
print*,'Usage: ldpcsim niter ndepth #trials s Keff nbposd'
print*,'eg: ldpcsim 10 2 1000 0.84 91 1'
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print*,'niter: max BP iterations'
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print*,'ndepth: OSD order'
print*,'s: noise sigma; if negative value is ignored and sigma is calculated from SNR.'
print*,'nbposd=0, no coupling. nbposd>0, maxsuper=nbposd; nbposd<0, no OSD'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) ndepth
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
call getarg(5,arg)
read(arg,*) Keff
call getarg(6,arg)
read(arg,*) nbposd
! scale Eb/No for a (174,91) code
rate=real(K)/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( rxdata(N), llr(N) )
msg="K9ABC K1ABC FN20"
i3=0
n3=1
call pack77(msg,i3,n3,c77) !Pack into 12 6-bit bytes
call unpack77(c77,1,msgsent,unpk77_success) !Unpack to get msgsent
write(*,*) "message sent ",msgsent
read(c77,'(77i1)') msgbits(1:77)
write(*,*) 'message'
write(*,'(a71,1x,a3,1x,a3)') c77(1:71),c77(72:74),c77(75:77)
call init_random_seed()
call encode174_91(msgbits,codeword)
write(*,*) 'crc14'
write(*,'(14i1)') codeword(78:91)
write(*,*) 'codeword'
write(*,'(22(8i1,1x))') codeword
write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma psymerr"
do idb = 10,-4,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
ngood=0
nue=0
nsumerr=0
do itrial=1, ntrials
! Create a realization of a noisy received word
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do i=1,N
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
enddo
nerr=0
do i=1,N
if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
enddo
if(nerr.ge.1) nerrtot(nerr)=nerrtot(nerr)+1
rxav=sum(rxdata)/N
rx2av=sum(rxdata*rxdata)/N
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
if( s .lt. 0 ) then
ss=sigma
else
ss=s
endif
llr=2.0*rxdata/(ss*ss)
nap=0 ! number of AP bits
llr(1:nap)=5*(2.0*msgbits(1:nap)-1.0)
apmask=0
apmask(1:nap)=1
call decode174_91(llr,Keff,nbposd,ndepth,apmask,message91,cw,ntype,nharderrors,dmin)
! If the decoder finds a valid codeword, nharderrors will be .ge. 0.
if( nharderrors.ge.0 ) then
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nhw=count(cw.ne.codeword)
if(nhw.eq.0) then ! this is a good decode
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else
nue=nue+1
endif
endif
nsumerr=nsumerr+nerr
enddo
esn0=db+10.0*log10(rate)
pberr=real(nsumerr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,esn0,ngood,nue,ss,pberr
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,174
write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
enddo
close(23)
end program ldpcsim174_91