WSJT-X/lib/ldpcsim.f90

138 lines
3.3 KiB
Fortran
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program ldpcsim
use, intrinsic :: iso_c_binding
use hashing
use packjt
character*22 msg,msgsent,msgreceived
character*80 prefix
character*85 pchk_file,gen_file
character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
real*8, allocatable :: lratio(:), rxdata(:)
integer ihash
nargs=iargc()
if(nargs.ne.7) then
print*,'Usage: ldpcsim <pchk file prefix > N K niter ndither #trials s '
print*,'eg: ldpcsim "/pathto/peg-32-16-reg3" 32 16 10 1 1000 0.75'
return
endif
call getarg(1,prefix)
call getarg(2,arg)
read(arg,*) N
call getarg(3,arg)
read(arg,*) K
call getarg(4,arg)
read(arg,*) max_iterations
call getarg(5,arg)
read(arg,*) max_dither
call getarg(6,arg)
read(arg,*) ntrials
call getarg(7,arg)
read(arg,*) s
pchk_file=trim(prefix)//".pchk"
gen_file=trim(prefix)//".gen"
rate=real(K)/real(N)
write(*,*) "rate: ",rate
! don't count hash bits as data bits
!rate=5.0/real(N)
write(*,*) "pchk file: ",pchk_file
write(*,*) "niter= ",max_iterations," ndither= ",max_dither," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( lratio(N), rxdata(N) )
call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
msg="K9AN K1JT RRR"
irpt=62
call hash(msg,22,ihash)
ihash=iand(ihash,1023) !10-bit hash
ig=64*ihash + irpt !6-bit report
write(*,*) irpt,ihash,ig
do i=1,16
message(i)=iand(1,ishft(ig,1-i))
enddo
call ldpc_encode(message,codeword)
call init_random_seed()
write(*,*) "Eb/N0 ngood nundetected nbadhash"
do idb = -6, 14
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
ngood=0
nue=0
nbadhash=0
do itrial=1, ntrials
call sgran()
! Create a realization of a noisy received word
do i=1,N
rxdata(i) = 2.0*(codeword(i)-0.5) + sigma*gran()
!write(*,*) i,gran()
enddo
! Correct signal normalization is important for this decoder.
rxav=sum(rxdata)/N
rx2av=sum(rxdata*rxdata)/N
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
! To match the metric to the channel, s should be set to the noise standard deviation.
! For now, set s to the value that optimizes decode probability near threshold.
! The s parameter can be tuned to trade a few tenth's dB of threshold for an order of
! magnitude in UER
if( s .le. 0 ) then
ss=sigma
else
ss=s
endif
do i=1,N
lratio(i)=exp(2.0*rxdata(i)/(ss*ss))
enddo
! max_iterations is max number of belief propagation iterations
call ldpc_decode(lratio, decoded, max_iterations, niterations, max_dither, ndither)
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
nueflag=0
nhashflag=0
imsg=0
do i=1,16
imsg=ishft(imsg,1)+iand(1,decoded(17-i))
enddo
nrxrpt=iand(imsg,63)
nrxhash=(imsg-nrxrpt)/64
if( nrxhash .ne. ihash ) then
nbadhash=nbadhash+1
nhashflag=1
endif
! Check the message plus hash against what was sent.
do i=1,K
if( message(i) .ne. decoded(i) ) then
nueflag=1
endif
enddo
if( nhashflag .eq. 0 .and. nueflag .eq. 0 ) then
ngood=ngood+1
else if( nhashflag .eq. 0 .and. nueflag .eq. 1 ) then
nue=nue+1;
endif
endif
enddo
write(*,"(f4.1,1x,i8,1x,i8,1x,i8)") db,ngood,nue,nbadhash
enddo
end program ldpcsim