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This commit is contained in:
Steven Franke 2020-04-21 15:02:57 -05:00
parent 01d555c898
commit 8da98fee1e
1 changed files with 112 additions and 112 deletions
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224
lib/fsk4hf/decode174_74.f90
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@ -2,127 +2,127 @@ subroutine decode174_74(llr,Keff,ndeep,apmask,maxsuper,message74,cw,nharderror,i
!
! A hybrid bp/osd decoder for the (174,74) code.
!
integer, parameter:: N=174, K=74, M=N-K
integer*1 cw(N),apmask(N)
integer*1 decoded(K)
integer*1 message74(74)
integer nrw(M),ncw
integer Nm(6,M)
integer Mn(3,N) ! 3 checks per bit
integer synd(M)
real tov(3,N)
real toc(6,M)
real tanhtoc(6,M)
real zn(N),zsum(N)
real llr(N)
real Tmn
integer, parameter:: N=174, K=74, M=N-K
integer*1 cw(N),apmask(N)
integer*1 decoded(K)
integer*1 message74(74)
integer nrw(M),ncw
integer Nm(6,M)
integer Mn(3,N) ! 3 checks per bit
integer synd(M)
real tov(3,N)
real toc(6,M)
real tanhtoc(6,M)
real zn(N),zsum(N)
real llr(N)
real Tmn
include "ldpc_174_74_parity.f90"
include "ldpc_174_74_parity.f90"
decoded=0
toc=0
tov=0
tanhtoc=0
decoded=0
toc=0
tov=0
tanhtoc=0
! initialize messages to checks
do j=1,M
do i=1,nrw(j)
toc(i,j)=llr((Nm(i,j)))
enddo
enddo
ncnt=0
nclast=0
maxiterations=1
zsum=0.0
do isuper=1,maxsuper
do iter=0,maxiterations
! Update bit log likelihood ratios (tov=0 in iteration 0).
do i=1,N
if( apmask(i) .ne. 1 ) then
zn(i)=llr(i)+sum(tov(1:ncw,i))
else
zn(i)=llr(i)
endif
enddo
zsum=zsum+zn
! Check to see if we have a codeword (check before we do any iteration).
cw=0
where( zn .gt. 0. ) cw=1
ncheck=0
do i=1,M
synd(i)=sum(cw(Nm(1:nrw(i),i)))
if( mod(synd(i),2) .ne. 0 ) ncheck=ncheck+1
! if( mod(synd(i),2) .ne. 0 ) write(*,*) 'check ',i,' unsatisfied'
enddo
! write(*,*) 'number of unsatisfied parity checks ',ncheck
if( ncheck .eq. 0 ) then ! we have a codeword - if crc is good, return it
decoded=cw(1:K)
call get_crc24(decoded,74,nbadcrc)
nharderror=count( (2*cw-1)*llr .lt. 0.0 )
if(nbadcrc.eq.0) then
message74=decoded(1:74)
dmin=0.0
return
endif
endif
! if( iter.gt.0 ) then ! this code block implements an early stopping criterion
if( iter.gt.10000 ) then ! this code block implements an early stopping criterion
nd=ncheck-nclast
if( nd .lt. 0 ) then ! # of unsatisfied parity checks decreased
ncnt=0 ! reset counter
else
ncnt=ncnt+1
endif
! write(*,*) iter,ncheck,nd,ncnt
if( ncnt .ge. 5 .and. iter .ge. 10 .and. ncheck .gt. 15) then
nharderror=-1
return
endif
endif
nclast=ncheck
! Send messages from bits to check nodes
do j=1,M
do i=1,nrw(j)
ibj=Nm(i,j)
toc(i,j)=zn(ibj)
do kk=1,ncw ! subtract off what the bit had received from the check
if( Mn(kk,ibj) .eq. j ) then
toc(i,j)=toc(i,j)-tov(kk,ibj)
endif
do j=1,M
do i=1,nrw(j)
toc(i,j)=llr((Nm(i,j)))
enddo
enddo
enddo
enddo
ncnt=0
nclast=0
maxiterations=1
zsum=0.0
do isuper=1,maxsuper
do iter=0,maxiterations
! Update bit log likelihood ratios (tov=0 in iteration 0).
do i=1,N
if( apmask(i) .ne. 1 ) then
zn(i)=llr(i)+sum(tov(1:ncw,i))
else
zn(i)=llr(i)
endif
enddo
zsum=zsum+zn
! Check to see if we have a codeword (check before we do any iteration).
cw=0
where( zn .gt. 0. ) cw=1
ncheck=0
do i=1,M
synd(i)=sum(cw(Nm(1:nrw(i),i)))
if( mod(synd(i),2) .ne. 0 ) ncheck=ncheck+1
! if( mod(synd(i),2) .ne. 0 ) write(*,*) 'check ',i,' unsatisfied'
enddo
! write(*,*) 'number of unsatisfied parity checks ',ncheck
if( ncheck .eq. 0 ) then ! we have a codeword - if crc is good, return it
decoded=cw(1:K)
call get_crc24(decoded,74,nbadcrc)
nharderror=count( (2*cw-1)*llr .lt. 0.0 )
if(nbadcrc.eq.0) then
message74=decoded(1:74)
dmin=0.0
return
endif
endif
! if( iter.gt.0 ) then ! this code block implements an early stopping criterion
if( iter.gt.10000 ) then ! this code block implements an early stopping criterion
nd=ncheck-nclast
if( nd .lt. 0 ) then ! # of unsatisfied parity checks decreased
ncnt=0 ! reset counter
else
ncnt=ncnt+1
endif
! write(*,*) iter,ncheck,nd,ncnt
if( ncnt .ge. 5 .and. iter .ge. 10 .and. ncheck .gt. 15) then
nharderror=-1
return
endif
endif
nclast=ncheck
! Send messages from bits to check nodes
do j=1,M
do i=1,nrw(j)
ibj=Nm(i,j)
toc(i,j)=zn(ibj)
do kk=1,ncw ! subtract off what the bit had received from the check
if( Mn(kk,ibj) .eq. j ) then
toc(i,j)=toc(i,j)-tov(kk,ibj)
endif
enddo
enddo
enddo
! send messages from check nodes to variable nodes
do i=1,M
tanhtoc(1:6,i)=tanh(-toc(1:6,i)/2)
enddo
do i=1,M
tanhtoc(1:6,i)=tanh(-toc(1:6,i)/2)
enddo
do j=1,N
do i=1,ncw
ichk=Mn(i,j) ! Mn(:,j) are the checks that include bit j
Tmn=product(tanhtoc(1:nrw(ichk),ichk),mask=Nm(1:nrw(ichk),ichk).ne.j)
call platanh(-Tmn,y)
do j=1,N
do i=1,ncw
ichk=Mn(i,j) ! Mn(:,j) are the checks that include bit j
Tmn=product(tanhtoc(1:nrw(ichk),ichk),mask=Nm(1:nrw(ichk),ichk).ne.j)
call platanh(-Tmn,y)
! y=atanh(-Tmn)
tov(i,j)=2*y
enddo
enddo
tov(i,j)=2*y
enddo
enddo
enddo ! bp iterations
llr=zsum
call osd174_74(llr,Keff,apmask,ndeep,message74,cw,nharderror,dmin)
if(nharderror.gt.0) then
return
endif
enddo ! super iterations
enddo ! bp iterations
llr=zsum
call osd174_74(llr,Keff,apmask,ndeep,message74,cw,nharderror,dmin)
if(nharderror.gt.0) then
return
endif
enddo ! super iterations
nharderror=-1
nharderror=-1
return
return
end subroutine decode174_74