mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-01 08:07:10 -04:00
5b78deddb3
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6645 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
195 lines
4.9 KiB
Fortran
195 lines
4.9 KiB
Fortran
program ldpcsim
|
|
|
|
! simulate with packed 72-bit messages and 8-bit hash - so only makes
|
|
! sense to use this with codes having K=80.
|
|
|
|
use, intrinsic :: iso_c_binding
|
|
use hashing
|
|
use packjt
|
|
|
|
character*22 msg,msgsent,msgreceived
|
|
integer*4 i4Msg6BitWords(12),i4Dec6BitWords(12)
|
|
integer*1, target:: i1Msg8BitBytes(10) ! 72 bit msg + 8 bit hash
|
|
integer*1, target:: i1Dec8BitBytes(10) ! 72 bit msg + 8 bit hash
|
|
integer*1 i1hashdec
|
|
character*80 prefix
|
|
character*85 pchk_file,gen_file
|
|
character*8 arg
|
|
integer*1, allocatable :: codeword(:), decoded(:), message(:)
|
|
real*8, allocatable :: lratio(:), rxdata(:)
|
|
integer*1 i1hash(4),i1
|
|
equivalence (ihash,i1hash)
|
|
|
|
nargs=iargc()
|
|
if(nargs.ne.7) then
|
|
print*,'Usage: ldpcsim <pchk file prefix > N K niter ndither #trials s '
|
|
print*,'eg: ldpcsim "/pathto/128-80-peg-reg3" 128 80 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)
|
|
! don't count hash bits as data bits
|
|
rate=72.0/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="123"
|
|
call fmtmsg(msg,iz)
|
|
call packmsg(msg,i4Msg6BitWords,itype)
|
|
call unpackmsg(i4Msg6BitWords,msgsent)
|
|
write(*,*) "Message: ",msgsent
|
|
|
|
! Convert from 12 6-bit words to 10 8-bit words
|
|
i4=0
|
|
ik=0
|
|
im=0
|
|
do i=1,12
|
|
nn=i4Msg6BitWords(i)
|
|
do j=1, 6
|
|
ik=ik+1
|
|
i4=i4+i4+iand(1,ishft(nn,j-6))
|
|
i4=iand(i4,255)
|
|
if(ik.eq.8) then
|
|
im=im+1
|
|
! if(i4.gt.127) i4=i4-256
|
|
i1Msg8BitBytes(im)=i4
|
|
ik=0
|
|
endif
|
|
enddo
|
|
enddo
|
|
ihash=nhash(c_loc(i1Msg8BitBytes),int(9,c_size_t),146)
|
|
ihash=2*iand(ihash,255)
|
|
i1Msg8BitBytes(10)=i1hash(1)
|
|
|
|
mbit=0
|
|
do i=1, 10
|
|
i1=i1Msg8BitBytes(i)
|
|
do ibit=1,8
|
|
mbit=mbit+1
|
|
message(mbit)=iand(1,ishft(i1,ibit-8))
|
|
enddo
|
|
enddo
|
|
|
|
call ldpc_encode(message,codeword)
|
|
|
|
write(*,*) "Eb/N0 ngood nundetected nbadhash"
|
|
do idb = 0, 11
|
|
db=idb/2.0-0.5
|
|
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
|
|
|
|
ngood=0
|
|
nue=0
|
|
nbadhash=0
|
|
|
|
do itrial=1, ntrials
|
|
|
|
! Create a realization of a noisy received word
|
|
do i=1,N
|
|
rxdata(i) = 2.0*(codeword(i)-0.5) + sigma*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
|
|
do i=1,N
|
|
if( s .le. 0 ) then
|
|
ss=sigma
|
|
else
|
|
ss=s
|
|
endif
|
|
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
|
|
|
|
! The decoder found a codeword. Compare received hash (byte 10) with computed hash.
|
|
! 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
|
|
if( i1hashdec .ne. i1Dec8BitBytes(10) ) 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
|
|
|
|
! don't bother to unpack while testing
|
|
if( .false. ) then
|
|
! 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)
|
|
print*,"Received ",msgreceived
|
|
endif
|
|
|
|
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
|