WSJT-X/lib/fst240/ldpcsim240_74.f90

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Fortran
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program ldpcsim240_74
! End-to-end test of the (240,74)/crc24 encoder and decoders.
use packjt77
parameter(N=240, K=74, M=N-K)
character*8 arg
character*37 msg0,msg
character*77 c77
character*24 c24
integer*1 msgbits(74)
integer*1 apmask(240)
integer*1 cw(240)
integer*1 codeword(N),message74(74)
integer ncrc24
real rxdata(N),llr(N)
logical first,unpk77_success
data first/.true./
nargs=iargc()
if(nargs.ne.5 .and. nargs.ne.6) then
print*,'Usage: ldpcsim niter ndeep #trials s K [msg]'
print*,'e.g. ldpcsim240_74 20 5 1000 0.85 64 "K9AN K1JT FN20"'
print*,'s : if negative, then value is ignored and sigma is calculated from SNR.'
print*,'niter: is the number of BP iterations.'
print*,'ndeep: -1 is BP only, ndeep>=0 is OSD order'
print*,'K :is the number of message+CRC bits and must be in the range [50,74]'
print*,'WSPR-format message is optional'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) norder
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
call getarg(5,arg)
read(arg,*) Keff
msg0='K9AN K1JT FN20 '
if(nargs.eq.6) call getarg(6,msg0)
call pack77(msg0,i3,n3,c77)
rate=real(Keff)/real(N)
write(*,*) "code rate: ",rate
write(*,*) "niter : ",max_iterations
write(*,*) "norder : ",norder
write(*,*) "s : ",s
write(*,*) "K : ",Keff
msgbits=0
read(c77,'(50i1)') msgbits(1:50)
write(*,*) 'message'
write(*,'(50i1)') msgbits(1:50)
call get_crc24(msgbits,74,ncrc24)
write(c24,'(b24.24)') ncrc24
read(c24,'(24i1)') msgbits(51:74)
write(*,'(24i1)') msgbits(51:74)
write(*,*) 'message with crc24'
write(*,'(74i1)') msgbits(1:74)
call encode240_74(msgbits,codeword)
call init_random_seed()
call sgran()
write(*,*) 'codeword'
write(*,'(77i1,1x,24i1,1x,73i1)') codeword
write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma symbol error rate"
do idb = 8,-3,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) ) ! to make db represent Eb/No
! sigma=1/sqrt( 2*(10**(db/10.0)) ) ! db represents Es/No
ngood=0
nue=0
nberr=0
do itrial=1, ntrials
! Create a realization of a noisy received word
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
nberr=nberr+nerr
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)
apmask=0
dmin=0.0
maxosd=0
call decode240_74(llr, Keff, maxosd, norder, apmask, message74, cw, ntype, nharderror, dmin)
if(nharderror.ge.0) then
n2err=0
do i=1,N
if( cw(i).ne.codeword(i) ) n2err=n2err+1
enddo
if(n2err.eq.0) then
ngood=ngood+1
else
nue=nue+1
endif
endif
enddo
! snr2500=db+10*log10(200.0/116.0/2500.0)
esn0=db+10*log10(rate)
pberr=real(nberr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,e10.3)") db,esn0,ngood,nue,pberr
enddo
end program ldpcsim240_74