mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-10-31 15:47:10 -04:00
76ca91c363
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7048 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
149 lines
3.1 KiB
Fortran
149 lines
3.1 KiB
Fortran
subroutine bpdecode40(llr,maxiterations,decoded,niterations)
|
|
!
|
|
! A log-domain belief propagation decoder for the msk40 code.
|
|
! The code is a regular (32,16) code with column weight 3, row weights 5,6,7.
|
|
! k9an August, 2016
|
|
!
|
|
integer, parameter:: N=32, K=16, M=N-K
|
|
integer*1 codeword(N),cw(N)
|
|
integer*1 colorder(N)
|
|
integer*1 decoded(K)
|
|
integer Nm(7,M) ! 5,6 or 7 bits per check
|
|
integer Mn(3,N) ! 3 checks per bit
|
|
integer synd(M)
|
|
real tov(3,N)
|
|
real toc(7,M)
|
|
real tanhtoc(7,M)
|
|
real zn(N)
|
|
real llr(N)
|
|
real Tmn
|
|
integer nrw(M)
|
|
|
|
data colorder/ &
|
|
4, 1, 2, 3, 0, 8, 6, 10, &
|
|
13, 28, 20, 23, 17, 15, 27, 25, &
|
|
16, 12, 18, 19, 7, 21, 22, 11, &
|
|
24, 5, 26, 14, 9, 29, 30, 31/
|
|
|
|
data Mn/ &
|
|
1, 6, 13, &
|
|
2, 3, 14, &
|
|
4, 8, 15, &
|
|
5, 11, 12, &
|
|
7, 10, 16, &
|
|
6, 9, 15, &
|
|
1, 11, 16, &
|
|
2, 4, 5, &
|
|
3, 7, 9, &
|
|
8, 10, 12, &
|
|
8, 13, 14, &
|
|
1, 4, 12, &
|
|
2, 6, 10, &
|
|
3, 11, 15, &
|
|
5, 9, 14, &
|
|
7, 13, 15, &
|
|
12, 14, 16, &
|
|
1, 2, 8, &
|
|
3, 5, 6, &
|
|
4, 9, 11, &
|
|
1, 7, 14, &
|
|
5, 10, 13, &
|
|
3, 4, 16, &
|
|
2, 15, 16, &
|
|
6, 7, 12, &
|
|
7, 8, 11, &
|
|
1, 9, 10, &
|
|
2, 11, 13, &
|
|
3, 12, 13, &
|
|
4, 6, 14, &
|
|
1, 5, 15, &
|
|
8, 9, 16/
|
|
|
|
data Nm/ &
|
|
1, 7, 12, 18, 21, 27, 31, &
|
|
2, 8, 13, 18, 24, 28, 0, &
|
|
2, 9, 14, 19, 23, 29, 0, &
|
|
3, 8, 12, 20, 23, 30, 0, &
|
|
4, 8, 15, 19, 22, 31, 0, &
|
|
1, 6, 13, 19, 25, 30, 0, &
|
|
5, 9, 16, 21, 25, 26, 0, &
|
|
3, 10, 11, 18, 26, 32, 0, &
|
|
6, 9, 15, 20, 27, 32, 0,&
|
|
5, 10, 13, 22, 27, 0, 0, &
|
|
4, 7, 14, 20, 26, 28, 0, &
|
|
4, 10, 12, 17, 25, 29, 0, &
|
|
1, 11, 16, 22, 28, 29, 0, &
|
|
2, 11, 15, 17, 21, 30, 0, &
|
|
3, 6, 14, 16, 24, 31, 0, &
|
|
5, 7, 17, 23, 24, 32, 0/
|
|
|
|
data nrw/7,6,6,6,6,6,6,6,6,5,6,6,6,6,6,6/
|
|
|
|
ncw=3
|
|
|
|
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
|
|
|
|
do iter=0,maxiterations
|
|
|
|
! Update bit log likelihood ratios (tov=0 in iteration 0).
|
|
do i=1,N
|
|
zn(i)=llr(i)+sum(tov(1:ncw,i))
|
|
enddo
|
|
|
|
! 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
|
|
enddo
|
|
|
|
if( ncheck .eq. 0 ) then ! we have a codeword - reorder the columns and return it
|
|
niterations=iter
|
|
codeword=cw(colorder+1)
|
|
decoded=codeword(M+1:N)
|
|
return
|
|
endif
|
|
|
|
! 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(1:7,i)=tanh(-toc(1:7,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)
|
|
tov(i,j)=2*y
|
|
enddo
|
|
enddo
|
|
|
|
enddo
|
|
niterations=-1
|
|
return
|
|
end subroutine bpdecode40
|