WSJT-X/lib/fsk4hf/bpdecode168.f90

381 lines
7.7 KiB
Fortran
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subroutine bpdecode168(llr,apmask,maxiterations,decoded,niterations)
!
! A log-domain belief propagation decoder for the (168,84) code.
!
integer, parameter:: N=168, K=84, M=N-K
integer*1 codeword(N),cw(N),apmask(N)
integer 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/0,1,2,3,28,4,5,6,7,8,9,10,11,34,12,32,13,14,15,16,17, &
18,36,29,42,31,20,21,41,40,30,38,22,19,47,37,46,35,44,33,49,24, &
43,51,25,26,27,50,52,57,69,54,55,45,59,58,56,61,60,53,48,23,62, &
63,64,67,66,65,68,39,70,71,72,74,73,75,76,77,80,81,78,82,79,83, &
84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104, &
105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125, &
126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146, &
147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167/
data Mn/ &
1,24,67, &
2,5,71, &
3,31,66, &
4,50,58, &
6,60,65, &
7,32,76, &
8,49,83, &
9,36,41, &
10,40,63, &
11,14,62, &
12,72,75, &
13,23,78, &
15,16,80, &
17,54,64, &
18,51,59, &
19,30,48, &
20,68,81, &
21,29,70, &
22,25,43, &
26,34,73, &
27,35,37, &
28,39,44, &
33,53,55, &
38,52,84, &
42,56,57, &
45,74,82, &
46,69,79, &
47,61,77, &
1,4,5, &
2,48,52, &
3,47,82, &
6,26,76, &
7,9,16, &
8,10,78, &
11,36,56, &
12,38,65, &
13,43,81, &
14,33,68, &
15,18,44, &
17,59,77, &
19,27,69, &
20,21,58, &
22,45,79, &
23,34,54, &
24,28,40, &
25,80,84, &
29,37,51, &
30,42,83, &
31,63,72, &
32,50,66, &
35,67,73, &
39,55,74, &
41,61,71, &
46,60,62, &
49,70,74, &
53,64,75, &
25,57,67, &
1,46,64, &
2,51,63, &
3,14,80, &
4,15,78, &
5,27,74, &
6,13,70, &
7,19,20, &
8,38,77, &
9,75,83, &
10,36,69, &
11,22,29, &
12,58,82, &
16,35,60, &
17,32,43, &
18,42,45, &
21,53,84, &
23,39,48, &
24,52,68, &
26,33,61, &
28,56,76, &
30,65,66, &
31,34,49, &
37,47,81, &
16,40,54, &
41,44,65, &
50,73,79, &
55,59,60, &
54,57,71, &
23,62,72, &
1,36,47, &
2,32,70, &
3,28,69, &
4,7,33, &
5,20,26, &
6,14,63, &
8,22,68, &
9,13,67, &
10,55,71, &
11,15,19, &
12,51,56, &
17,27,52, &
18,34,46, &
21,41,42, &
24,50,80, &
25,39,75, &
29,54,76, &
30,40,84, &
31,35,58, &
37,79,83, &
38,43,73, &
44,72,81, &
7,45,62, &
47,48,49, &
53,57,78, &
20,59,66, &
28,61,64, &
11,75,77, &
33,54,82, &
1,14,44, &
2,62,73, &
3,9,26, &
4,37,84, &
5,56,80, &
6,45,71, &
8,67,72, &
10,76,81, &
12,32,78, &
13,59,82, &
15,17,79, &
16,42,69, &
18,61,70, &
19,31,64, &
21,39,63, &
22,30,58, &
23,27,66, &
24,41,49, &
25,36,60, &
29,65,67, &
34,36,53, &
35,48,76, &
15,38,55, &
40,43,74, &
46,52,57, &
50,63,77, &
51,68,69, &
2,44,83, &
1,30,55, &
3,29,78, &
4,34,65, &
5,31,38, &
6,52,58, &
7,25,51, &
8,16,66, &
9,46,74, &
10,70,75, &
11,32,84, &
12,48,79, &
13,50,64, &
14,37,57, &
17,42,72, &
18,43,48, &
19,24,60, &
20,54,83, &
21,47,62, &
22,28,59, &
23,61,80, &
8,26,39, &
27,44,53, &
33,49,56, &
35,68,71, &
12,26,40/
data Nm/ &
1,29,58,87,116,144,0,&
2,30,59,88,117,143,0,&
3,31,60,89,118,145,0,&
4,29,61,90,119,146,0,&
2,29,62,91,120,147,0,&
5,32,63,92,121,148,0,&
6,33,64,90,109,149,0,&
7,34,65,93,122,150,164,&
8,33,66,94,118,151,0,&
9,34,67,95,123,152,0,&
10,35,68,96,114,153,0,&
11,36,69,97,124,154,168,&
12,37,63,94,125,155,0,&
10,38,60,92,116,156,0,&
13,39,61,96,126,138,0,&
13,33,70,81,127,150,0,&
14,40,71,98,126,157,0,&
15,39,72,99,128,158,0,&
16,41,64,96,129,159,0,&
17,42,64,91,112,160,0,&
18,42,73,100,130,161,0,&
19,43,68,93,131,162,0,&
12,44,74,86,132,163,0,&
1,45,75,101,133,159,0,&
19,46,57,102,134,149,0,&
20,32,76,91,118,164,168,&
21,41,62,98,132,165,0,&
22,45,77,89,113,162,0,&
18,47,68,103,135,145,0,&
16,48,78,104,131,144,0,&
3,49,79,105,129,147,0,&
6,50,71,88,124,153,0,&
23,38,76,90,115,166,0,&
20,44,79,99,136,146,0,&
21,51,70,105,137,167,0,&
8,35,67,87,134,136,0,&
21,47,80,106,119,156,0,&
24,36,65,107,138,147,0,&
22,52,74,102,130,164,0,&
9,45,81,104,139,168,0,&
8,53,82,100,133,0,0,&
25,48,72,100,127,157,0,&
19,37,71,107,139,158,0,&
22,39,82,108,116,143,165,&
26,43,72,109,121,0,0,&
27,54,58,99,140,151,0,&
28,31,80,87,110,161,0,&
16,30,74,110,137,154,158,&
7,55,79,110,133,166,0,&
4,50,83,101,141,155,0,&
15,47,59,97,142,149,0,&
24,30,75,98,140,148,0,&
23,56,73,111,136,165,0,&
14,44,81,85,103,115,160,&
23,52,84,95,138,144,0,&
25,35,77,97,120,166,0,&
25,57,85,111,140,156,0,&
4,42,69,105,131,148,0,&
15,40,84,112,125,162,0,&
5,54,70,84,134,159,0,&
28,53,76,113,128,163,0,&
10,54,86,109,117,161,0,&
9,49,59,92,130,141,0,&
14,56,58,113,129,155,0,&
5,36,78,82,135,146,0,&
3,50,78,112,132,150,0,&
1,51,57,94,122,135,0,&
17,38,75,93,142,167,0,&
27,41,67,89,127,142,0,&
18,55,63,88,128,152,0,&
2,53,85,95,121,167,0,&
11,49,86,108,122,157,0,&
20,51,83,107,117,0,0,&
26,52,55,62,139,151,0,&
11,56,66,102,114,152,0,&
6,32,77,103,123,137,0,&
28,40,65,114,141,0,0,&
12,34,61,111,124,145,0,&
27,43,83,106,126,154,0,&
13,46,60,101,120,163,0,&
17,37,80,108,123,0,0,&
26,31,69,115,125,0,0,&
7,48,66,106,143,160,0,&
24,46,73,104,119,153,0/
data nrw/ &
6,6,6,6,6,6,6,7,6,6,6,7,6,6,6,6,6,6,6,6,6, &
6,6,6,6,7,6,6,6,6,6,6,6,6,6,6,6,6,6,6,5,6, &
6,7,5,6,6,7,6,6,6,6,6,7,6,6,6,6,6,6,6,6,6, &
6,6,6,6,6,6,6,6,6,5,6,6,6,5,6,6,6,5,5,6,6/
ncw=3
toc=0
tov=0
tanhtoc=0
!write(*,*) llr
! initialize messages to checks
do j=1,M
do i=1,nrw(j)
toc(i,j)=llr((Nm(i,j)))
enddo
enddo
ncnt=0
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
! 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 - reorder the columns and return it
niterations=iter
codeword=cw(colorder+1)
decoded=codeword(M+1:N)
return
endif
if( iter.gt.0 ) 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. 3 .and. iter .ge. 5 .and. ncheck .gt. 10) then
niterations=-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(1:7,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)
! y=atanh(-Tmn)
tov(i,j)=2*y
enddo
enddo
enddo
niterations=-1
return
end subroutine bpdecode168