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402
lib/fsk4hf/bpdecode174.f90 Normal file
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subroutine bpdecode174(llr,apmask,maxiterations,decoded,niterations)
!
! A log-domain belief propagation decoder for the (174,87) code.
!
integer, parameter:: N=174, K=87, 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, 30, 4, 5, 6, 7, 8, 9, 10, 11, 32, 12, 40, 13, 14, 15, 16,&
17, 18, 37, 45, 29, 19, 20, 21, 41, 22, 42, 31, 33, 34, 44, 35, 47, 51, 50, 43,&
36, 52, 63, 46, 25, 55, 27, 24, 23, 53, 39, 49, 59, 38, 48, 61, 60, 57, 28, 62,&
56, 58, 65, 66, 26, 70, 64, 69, 68, 67, 74, 71, 54, 76, 72, 75, 78, 77, 80, 79,&
73, 83, 84, 81, 82, 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,&
160,161,162,163,164,165,166,167,168,169,170,171,172,173/
data Mn/ &
1, 25, 69, &
2, 5, 73, &
3, 32, 68, &
4, 51, 61, &
6, 63, 70, &
7, 33, 79, &
8, 50, 86, &
9, 37, 43, &
10, 41, 65, &
11, 14, 64, &
12, 75, 77, &
13, 23, 81, &
15, 16, 82, &
17, 56, 66, &
18, 53, 60, &
19, 31, 52, &
20, 67, 84, &
21, 29, 72, &
22, 24, 44, &
26, 35, 76, &
27, 36, 38, &
28, 40, 42, &
30, 54, 55, &
34, 49, 87, &
39, 57, 58, &
45, 74, 83, &
46, 62, 80, &
47, 48, 85, &
59, 71, 78, &
1, 50, 53, &
2, 47, 84, &
3, 25, 79, &
4, 6, 14, &
5, 7, 80, &
8, 34, 55, &
9, 36, 69, &
10, 43, 83, &
11, 23, 74, &
12, 17, 44, &
13, 57, 76, &
15, 27, 56, &
16, 28, 29, &
18, 19, 59, &
20, 40, 63, &
21, 35, 52, &
22, 54, 64, &
24, 62, 78, &
26, 32, 77, &
30, 72, 85, &
31, 65, 87, &
33, 39, 51, &
37, 48, 75, &
38, 70, 71, &
41, 42, 68, &
45, 67, 86, &
46, 81, 82, &
49, 66, 73, &
58, 60, 66, &
61, 65, 85, &
1, 14, 21, &
2, 13, 59, &
3, 67, 82, &
4, 32, 73, &
5, 36, 54, &
6, 43, 46, &
7, 28, 75, &
8, 33, 71, &
9, 49, 76, &
10, 58, 64, &
11, 48, 68, &
12, 19, 45, &
15, 50, 61, &
16, 22, 26, &
17, 72, 80, &
18, 40, 55, &
20, 35, 51, &
23, 25, 34, &
24, 63, 87, &
27, 39, 74, &
29, 78, 83, &
30, 70, 77, &
31, 69, 84, &
22, 37, 86, &
38, 41, 81, &
42, 44, 57, &
47, 53, 62, &
52, 56, 79, &
60, 75, 81, &
1, 39, 77, &
2, 16, 41, &
3, 31, 54, &
4, 36, 78, &
5, 45, 65, &
6, 57, 85, &
7, 14, 49, &
8, 21, 46, &
9, 15, 72, &
10, 20, 62, &
11, 17, 71, &
12, 34, 47, &
13, 68, 86, &
18, 23, 43, &
19, 64, 73, &
24, 48, 79, &
25, 70, 83, &
26, 80, 87, &
27, 32, 40, &
28, 56, 69, &
29, 63, 66, &
30, 42, 50, &
33, 37, 82, &
35, 60, 74, &
38, 55, 84, &
44, 52, 61, &
51, 53, 72, &
58, 59, 67, &
47, 56, 76, &
1, 19, 37, &
2, 61, 75, &
3, 8, 66, &
4, 60, 84, &
5, 34, 39, &
6, 26, 53, &
7, 32, 57, &
9, 52, 67, &
10, 12, 15, &
11, 51, 69, &
13, 14, 65, &
16, 31, 43, &
17, 20, 36, &
18, 80, 86, &
21, 48, 59, &
22, 40, 46, &
23, 33, 62, &
24, 30, 74, &
25, 42, 64, &
27, 49, 85, &
28, 38, 73, &
29, 44, 81, &
35, 68, 70, &
41, 63, 76, &
45, 49, 71, &
50, 58, 87, &
48, 54, 83, &
13, 55, 79, &
77, 78, 82, &
1, 2, 24, &
3, 6, 75, &
4, 56, 87, &
5, 44, 53, &
7, 50, 83, &
8, 10, 28, &
9, 55, 62, &
11, 29, 67, &
12, 33, 40, &
14, 16, 20, &
15, 35, 73, &
17, 31, 39, &
18, 36, 57, &
19, 46, 76, &
21, 42, 84, &
22, 34, 59, &
23, 26, 61, &
25, 60, 65, &
27, 64, 80, &
30, 37, 66, &
32, 45, 72, &
38, 51, 86, &
41, 77, 79, &
43, 56, 68, &
47, 74, 82, &
40, 52, 78, &
54, 61, 71, &
46, 58, 69/
data Nm/ &
1, 30, 60, 89, 118, 147, 0, &
2, 31, 61, 90, 119, 147, 0, &
3, 32, 62, 91, 120, 148, 0, &
4, 33, 63, 92, 121, 149, 0, &
2, 34, 64, 93, 122, 150, 0, &
5, 33, 65, 94, 123, 148, 0, &
6, 34, 66, 95, 124, 151, 0, &
7, 35, 67, 96, 120, 152, 0, &
8, 36, 68, 97, 125, 153, 0, &
9, 37, 69, 98, 126, 152, 0, &
10, 38, 70, 99, 127, 154, 0, &
11, 39, 71, 100, 126, 155, 0, &
12, 40, 61, 101, 128, 145, 0, &
10, 33, 60, 95, 128, 156, 0, &
13, 41, 72, 97, 126, 157, 0, &
13, 42, 73, 90, 129, 156, 0, &
14, 39, 74, 99, 130, 158, 0, &
15, 43, 75, 102, 131, 159, 0, &
16, 43, 71, 103, 118, 160, 0, &
17, 44, 76, 98, 130, 156, 0, &
18, 45, 60, 96, 132, 161, 0, &
19, 46, 73, 83, 133, 162, 0, &
12, 38, 77, 102, 134, 163, 0, &
19, 47, 78, 104, 135, 147, 0, &
1, 32, 77, 105, 136, 164, 0, &
20, 48, 73, 106, 123, 163, 0, &
21, 41, 79, 107, 137, 165, 0, &
22, 42, 66, 108, 138, 152, 0, &
18, 42, 80, 109, 139, 154, 0, &
23, 49, 81, 110, 135, 166, 0, &
16, 50, 82, 91, 129, 158, 0, &
3, 48, 63, 107, 124, 167, 0, &
6, 51, 67, 111, 134, 155, 0, &
24, 35, 77, 100, 122, 162, 0, &
20, 45, 76, 112, 140, 157, 0, &
21, 36, 64, 92, 130, 159, 0, &
8, 52, 83, 111, 118, 166, 0, &
21, 53, 84, 113, 138, 168, 0, &
25, 51, 79, 89, 122, 158, 0, &
22, 44, 75, 107, 133, 155, 172, &
9, 54, 84, 90, 141, 169, 0, &
22, 54, 85, 110, 136, 161, 0, &
8, 37, 65, 102, 129, 170, 0, &
19, 39, 85, 114, 139, 150, 0, &
26, 55, 71, 93, 142, 167, 0, &
27, 56, 65, 96, 133, 160, 174, &
28, 31, 86, 100, 117, 171, 0, &
28, 52, 70, 104, 132, 144, 0, &
24, 57, 68, 95, 137, 142, 0, &
7, 30, 72, 110, 143, 151, 0, &
4, 51, 76, 115, 127, 168, 0, &
16, 45, 87, 114, 125, 172, 0, &
15, 30, 86, 115, 123, 150, 0, &
23, 46, 64, 91, 144, 173, 0, &
23, 35, 75, 113, 145, 153, 0, &
14, 41, 87, 108, 117, 149, 170, &
25, 40, 85, 94, 124, 159, 0, &
25, 58, 69, 116, 143, 174, 0, &
29, 43, 61, 116, 132, 162, 0, &
15, 58, 88, 112, 121, 164, 0, &
4, 59, 72, 114, 119, 163, 173, &
27, 47, 86, 98, 134, 153, 0, &
5, 44, 78, 109, 141, 0, 0, &
10, 46, 69, 103, 136, 165, 0, &
9, 50, 59, 93, 128, 164, 0, &
14, 57, 58, 109, 120, 166, 0, &
17, 55, 62, 116, 125, 154, 0, &
3, 54, 70, 101, 140, 170, 0, &
1, 36, 82, 108, 127, 174, 0, &
5, 53, 81, 105, 140, 0, 0, &
29, 53, 67, 99, 142, 173, 0, &
18, 49, 74, 97, 115, 167, 0, &
2, 57, 63, 103, 138, 157, 0, &
26, 38, 79, 112, 135, 171, 0, &
11, 52, 66, 88, 119, 148, 0, &
20, 40, 68, 117, 141, 160, 0, &
11, 48, 81, 89, 146, 169, 0, &
29, 47, 80, 92, 146, 172, 0, &
6, 32, 87, 104, 145, 169, 0, &
27, 34, 74, 106, 131, 165, 0, &
12, 56, 84, 88, 139, 0, 0, &
13, 56, 62, 111, 146, 171, 0, &
26, 37, 80, 105, 144, 151, 0, &
17, 31, 82, 113, 121, 161, 0, &
28, 49, 59, 94, 137, 0, 0, &
7, 55, 83, 101, 131, 168, 0, &
24, 50, 78, 106, 143, 149, 0/
data nrw/ &
6,6,6,6,6,6,6,6,6,6, &
6,6,6,6,6,6,6,6,6,6, &
6,6,6,6,6,6,6,6,6,6, &
6,6,6,6,6,6,6,6,6,7, &
6,6,6,6,6,7,6,6,6,6, &
6,6,6,6,6,7,6,6,6,6, &
7,6,5,6,6,6,6,6,6,5, &
6,6,6,6,6,6,6,6,6,6, &
5,6,6,6,5,6,6/
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)
nerr=0
do i=1,N
if( (2*cw(i)-1)*llr(i) .lt. 0.0 ) nerr=nerr+1
enddo
niterations=nerr
return
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
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 bpdecode174

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lib/fsk4hf/encode174.f90 Normal file
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subroutine encode174(message,codeword)
! Encode an 101-bit message and return a 174-bit codeword.
! The generator matrix has dimensions (73,101).
! The code is a (174,101) regular ldpc code with column weight 3.
! The code was generated using the PEG algorithm.
! After creating the codeword, the columns are re-ordered according to
! "colorder" to make the codeword compatible with the parity-check matrix
!
include "ldpc_174_87_params.f90"
integer*1 codeword(N)
integer*1 gen(M,K)
integer*1 itmp(N)
integer*1 message(K)
integer*1 pchecks(M)
logical first
data first/.true./
save first,gen
if( first ) then ! fill the generator matrix
gen=0
do i=1,M
do j=1,11
read(g(i)( (j-1)*2+1:(j-1)*2+2 ),"(Z2)") istr
do jj=1, 8
icol=(j-1)*8+jj
if( icol .le. 87 ) then
if( btest(istr,8-jj) ) gen(i,icol)=1
endif
enddo
enddo
enddo
first=.false.
endif
do i=1,M
nsum=0
do j=1,K
nsum=nsum+message(j)*gen(i,j)
enddo
pchecks(i)=mod(nsum,2)
enddo
itmp(1:M)=pchecks
itmp(M+1:N)=message(1:K)
codeword(colorder+1)=itmp(1:N)
return
end subroutine encode174

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lib/fsk4hf/ldpc_174_87_params.f90 Normal file
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integer, parameter:: N=174, K=87, M=N-K
character*22 g(87)
integer colorder(N)
data g/ & !parity generator matrix for (174,87) code
"23bba830e23b6b6f509828", &
"1f8e55da218c5df3309050", &
"ca7b3217cd92bd59a5ae20", &
"56f78313537d0f43829648", &
"29c29dba9c545e267762f8", &
"6be396b5e2e819e3733408", &
"293548a138858328af4210", &
"cb6c6afcdc28bb3f7c6e80", &
"3f2a86f5c5bd225c961150", &
"849dd2d63673481860f628", &
"56cdaec6e7ae14b43feee8", &
"04ef5cfa3766ba778f45a0", &
"c525ae4bd4f627320a3970", &
"fe37802941d66dde02b998", &
"41fd9520b2e4abeb2f9898", &
"40907b01280f03c0323940", &
"7fb36c24085a34d8c1dbc0", &
"40fc3e44bb7d2bb2756e40", &
"d38ab0a1d2e52a8ec3bc70", &
"3d0f929ef3949bd84d4730", &
"45d3814f504064f80549a8", &
"f14dbf263825d0bd04b058", &
"f08a91fb2e1f78290619a8", &
"7a8dec79a51e8ac5388020", &
"ca4186dd44c3121565cf58", &
"db714f8f64e8ac7af1a768", &
"8d0274de71e7c1a8055eb0", &
"51f81573dd4049b082de10", &
"d037db825175d851f3af00", &
"d8f937f31822e57c562370", &
"1bf1490607c54032660ed8", &
"1616d78018d0b4745ca0f0", &
"a9fa8e50bcb032c85e3300", &
"83f640f1a48a8ebc0443e8", &
"eca9afa0f6b01d92305ed8", &
"3776af54ccfbae916afde0", &
"6abb212d9739dfc02580f0", &
"05209a0abb530b9e7e34b0", &
"612f63acc025b6ab476f78", &
"0af7723161ec223080be80", &
"a8fc906976c35669e79ce0", &
"45b7ab6242b77474d9f118", &
"b274db8abd3c6f396ea350", &
"9059dfa2bb20ef7ef73ad0", &
"3d188ea477f6fa41317a48", &
"8d9071b7e7a6a2eed69658", &
"a377253773ea678367c3f0", &
"ecbd7c73b9cd34c3720c88", &
"b6537f417e61d1a7085330", &
"6c280d2a0523d9c4bc5940", &
"d36d662a69ae24b74dcbd8", &
"d747bfc5fd65ef70fbd9b8", &
"a9fa2eefa6f8796a355770", &
"cc9da55fe046d0cb3a7708", &
"f6ad4824b87c80ebfce460", &
"cc6de59755420925f90ed0", &
"164cc861bdd803c547f2a8", &
"c0fc3ec4fb7d2bb2756640", &
"0dbd816fba1543f721dc70", &
"a0c0033a52ab6299802fd0", &
"bf4f56e073271f6ab4bf80", &
"57da6d13cb96a7689b2790", &
"81cfc6f18c35b1e1f17110", &
"481a2a0df8a23583f82d68", &
"1ac4672b549cd6dba79bc8", &
"c87af9a5d5206abca532a8", &
"97d4169cb33e7435718d90", &
"a6573f3dc8b16c9d19f740", &
"2c4142bf42b01e71076ac8", &
"081c29a10d468ccdbcecb0", &
"5b0f7742bca86b80126098", &
"012dee2198eba82b19a1d8", &
"f1627701a2d692fd9449e0", &
"35ad3fb0faeb5f1b0c30d8", &
"b1ca4ea2e3d173bad43798", &
"37d8e0af9258b9e8c5f9b0", &
"cd921fdf59e882683763f0", &
"6114e08483043fd3f38a88", &
"2e547dd7a05f6597aac510", &
"95e45ecd0135aca9d6e6a8", &
"b33ec97be83ce413f9acc8", &
"c8b5dffc335095dcdcaf28", &
"3dd01a59d86310743ec750", &
"14cd0f642fc0c5fe3a65c8", &
"3a0a1dfd7eee29c2e827e0", &
"8abdb889efbe39a510a118", &
"3f231f212055371cf3e2a0"/
data colorder/ &
0, 1, 2, 3, 30, 4, 5, 6, 7, 8, 9, 10, 11, 32, 12, 40, 13, 14, 15, 16,&
17, 18, 37, 45, 29, 19, 20, 21, 41, 22, 42, 31, 33, 34, 44, 35, 47, 51, 50, 43,&
36, 52, 63, 46, 25, 55, 27, 24, 23, 53, 39, 49, 59, 38, 48, 61, 60, 57, 28, 62,&
56, 58, 65, 66, 26, 70, 64, 69, 68, 67, 74, 71, 54, 76, 72, 75, 78, 77, 80, 79,&
73, 83, 84, 81, 82, 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,&
160,161,162,163,164,165,166,167,168,169,170,171,172,173/

241
lib/fsk4hf/ldpcsim174.f90 Normal file
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program ldpcsim174
! End to end test of the (174,75)/crc12 encoder and decoder.
use crc
use packjt
parameter(NRECENT=10)
character*12 recent_calls(NRECENT)
character*22 msg,msgsent,msgreceived
character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
integer*1, target:: i1Msg8BitBytes(11)
integer*1 msgbits(87)
integer*1 apmask(174), cw(174)
integer*2 checksum
integer*4 i4Msg6BitWords(13)
integer colorder(174)
integer nerrtot(174),nerrdec(174),nmpcbad(87)
logical checksumok,fsk,bpsk
real*8, allocatable :: rxdata(:)
real, allocatable :: llr(:)
data colorder/ &
0, 1, 2, 3, 30, 4, 5, 6, 7, 8, 9, 10, 11, 32, 12, 40, 13, 14, 15, 16,&
17, 18, 37, 45, 29, 19, 20, 21, 41, 22, 42, 31, 33, 34, 44, 35, 47, 51, 50, 43,&
36, 52, 63, 46, 25, 55, 27, 24, 23, 53, 39, 49, 59, 38, 48, 61, 60, 57, 28, 62,&
56, 58, 65, 66, 26, 70, 64, 69, 68, 67, 74, 71, 54, 76, 72, 75, 78, 77, 80, 79,&
73, 83, 84, 81, 82, 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,&
160,161,162,163,164,165,166,167,168,169,170,171,172,173/
do i=1,NRECENT
recent_calls(i)=' '
enddo
nerrtot=0
nerrdec=0
nmpcbad=0 ! Used to collect the number of errors in the message+crc part of the codeword
nargs=iargc()
if(nargs.ne.4) then
print*,'Usage: ldpcsim niter norder #trials s '
print*,'eg: ldpcsim 10 2 1000 0.84'
print*,'belief propagation iterations: niter, ordered-statistics order: norder'
print*,'If s is negative, then value is ignored and sigma is calculated from SNR.'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) norder
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
fsk=.false.
bpsk=.true.
! don't count crc bits as data bits
N=174
K=87
! scale Eb/No for a (174,87) code
rate=real(87)/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( rxdata(N), llr(N) )
! msg="K1JT K9AN EN50"
msg="G4WJS K9AN EN50"
call packmsg(msg,i4Msg6BitWords,itype) !Pack into 12 6-bit bytes
call unpackmsg(i4Msg6BitWords,msgsent) !Unpack to get msgsent
write(*,*) "message sent ",msgsent
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
i1Msg8BitBytes(10:11)=0
checksum = crc12 (c_loc (i1Msg8BitBytes), 11)
! For reference, the next 3 lines show how to check the CRC
i1Msg8BitBytes(10)=checksum/256
i1Msg8BitBytes(11)=iand (checksum,255)
checksumok = crc12_check(c_loc (i1Msg8BitBytes), 11)
if( checksumok ) write(*,*) 'Good checksum'
! K=87, For now:
! msgbits(1:72) JT message bits
! msgbits(73:75) 3 free message bits (set to 0)
! msgbits(76:87) CRC12
mbit=0
do i=1, 9
i1=i1Msg8BitBytes(i)
do ibit=1,8
mbit=mbit+1
msgbits(mbit)=iand(1,ishft(i1,ibit-8))
enddo
enddo
msgbits(73:75)=0 ! the three extra message bits go here
i1=i1Msg8BitBytes(10) ! First 4 bits of crc12 are LSB of this byte
do ibit=1,4
msgbits(75+ibit)=iand(1,ishft(i1,ibit-4))
enddo
i1=i1Msg8BitBytes(11) ! Now shift in last 8 bits of the CRC
do ibit=1,8
msgbits(79+ibit)=iand(1,ishft(i1,ibit-8))
enddo
write(*,*) 'message'
write(*,'(11(8i1,1x))') msgbits
call encode174(msgbits,codeword)
call init_random_seed()
call sgran()
write(*,*) 'codeword'
write(*,'(22(8i1,1x))') codeword
write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
do idb = 14,-6,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*(10**(db/10.0)) )
ngood=0
nue=0
nbadcrc=0
nberr=0
do itrial=1, ntrials
! Create a realization of a noisy received word
do i=1,N
if( bpsk ) then
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
elseif( fsk ) then
if( codeword(i) .eq. 1 ) then
r1=(1.0 + sigma*gran())**2 + (sigma*gran())**2
r2=(sigma*gran())**2 + (sigma*gran())**2
elseif( codeword(i) .eq. 0 ) then
r2=(1.0 + sigma*gran())**2 + (sigma*gran())**2
r1=(sigma*gran())**2 + (sigma*gran())**2
endif
rxdata(i)=0.35*(sqrt(r1)-sqrt(r2))
! rxdata(i)=0.35*(exp(r1)-exp(r2))
! rxdata(i)=0.12*(log(r1)-log(r2))
endif
enddo
nerr=0
do i=1,N
if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
enddo
nerrtot(nerr)=nerrtot(nerr)+1
nberr=nberr+nerr
! 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 .lt. 0 ) then
ss=sigma
else
ss=s
endif
llr=2.0*rxdata/(ss*ss)
nap=0 ! number of AP bits
llr(colorder(174-87+1:174-87+nap)+1)=5*(2.0*msgbits(1:nap)-1.0)
apmask=0
apmask(colorder(174-87+1:174-87+nap)+1)=1
! max_iterations is max number of belief propagation iterations
call bpdecode174(llr, apmask, max_iterations, decoded, niterations)
ni1=niterations
if( norder .ge. 0 .and. niterations .lt. 0 ) call osd174(llr, norder, decoded, niterations, cw)
ni2=niterations
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
call extractmessage174(decoded,msgreceived,ncrcflag,recent_calls,nrecent)
if( ncrcflag .ne. 1 ) then
nbadcrc=nbadcrc+1
endif
nueflag=0
nerrmpc=0
do i=1,K ! find number of errors in message+crc part of codeword
if( msgbits(i) .ne. decoded(i) ) then
nueflag=1
nerrmpc=nerrmpc+1
endif
enddo
nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1
if( ncrcflag .eq. 1 ) then
if( nueflag .eq. 0 ) then
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else if( nueflag .eq. 1 ) then
nue=nue+1;
endif
endif
endif
enddo
snr2500=db+10*log10(6.08/2500.0)
pberr=real(nberr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,snr2500,ngood,nue,nbadcrc,ss,pberr
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,174
write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
enddo
close(23)
open(unit=25,file='nmpcbad.dat',status='unknown')
do i=1,87
write(25,'(i4,2x,i10)') i,nmpcbad(i)
enddo
close(25)
end program ldpcsim174

151
lib/fsk4hf/osd174.f90 Normal file
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@ -0,0 +1,151 @@
subroutine osd174(llr,norder,decoded,niterations,cw)
!
! An ordered-statistics decoder based on ideas from:
! "Soft-decision decoding of linear block codes based on ordered statistics,"
! by Marc P. C. Fossorier and Shu Lin,
! IEEE Trans Inf Theory, Vol 41, No 5, Sep 1995
!
include "ldpc_174_87_params.f90"
integer*1 gen(K,N)
integer*1 genmrb(K,N)
integer*1 temp(K),m0(K),me(K)
integer indices(N)
integer*1 codeword(N),cw(N),hdec(N)
integer*1 decoded(K)
integer indx(N)
real llr(N),rx(N),absrx(N)
logical first
data first/.true./
save first,gen
if( first ) then ! fill the generator matrix
gen=0
do i=1,M
do j=1,21
read(g(i)(j:j),"(Z1)") istr
do jj=1, 4
irow=(j-1)*4+jj
if( irow .le. K ) then
if( btest(istr,4-jj) ) gen(irow,i)=1
endif
enddo
enddo
enddo
do irow=1,K
gen(irow,M+irow)=1
enddo
first=.false.
endif
! re-order received vector to place systematic msg bits at the end
rx=llr(colorder+1)
! hard decode the received word
hdec=0
where(rx .ge. 0) hdec=1
! use magnitude of received symbols as a measure of reliability.
absrx=abs(rx)
call indexx(absrx,N,indx)
! re-order the columns of the generator matrix in order of increasing reliability.
do i=1,N
genmrb(1:K,N+1-i)=gen(1:K,indx(N+1-i))
enddo
! do gaussian elimination to create a generator matrix with the most reliable
! received bits as the systematic bits. if it happens that the K most reliable
! bits are not independent, then we dip into the bits just below the K best bits
! to find K independent most reliable bits. the "indices" array tracks column
! permutations caused by reliability sorting and gaussian elimination.
do i=1,N
indices(i)=indx(i)
enddo
do id=1,K ! diagonal element indices
do ic=id,K+20 ! The 20 is ad hoc - beware
icol=N-K+ic
if( icol .gt. N ) icol=M+1-(icol-N)
iflag=0
if( genmrb(id,icol) .eq. 1 ) then
iflag=1
if( icol-M .ne. id ) then ! reorder column
temp(1:K)=genmrb(1:K,M+id)
genmrb(1:K,M+id)=genmrb(1:K,icol)
genmrb(1:K,icol)=temp(1:K)
itmp=indices(M+id)
indices(M+id)=indices(icol)
indices(icol)=itmp
endif
do ii=1,K
if( ii .ne. id .and. genmrb(ii,N-K+id) .eq. 1 ) then
genmrb(ii,1:N)=mod(genmrb(ii,1:N)+genmrb(id,1:N),2)
endif
enddo
exit
endif
enddo
enddo
! use the hard decisions for the K MRB bits to define the order 0
! message, m0. Encode m0 using the modified generator matrix to
! find the order 0 codeword. Flip all combinations of N bits in m0
! and re-encode to find the list of order N codewords. Test all such
! codewords against the received word to decide which codeword is
! most likely to be correct.
m0=0
where (rx(indices(M+1:N)).ge.0.0) m0=1
nhardmin=N
corrmax=-1.0e32
j0=0
j1=0
j2=0
j3=0
if( norder.ge.4 ) j0=K
if( norder.ge.3 ) j1=K
if( norder.ge.2 ) j2=K
if( norder.ge.1 ) j3=K
nt=0
do i1=0,j0
do i2=i1,j1
do i3=i2,j2
do i4=i3,j3
nt=nt+1
me=m0
if( i1 .ne. 0 ) me(i1)=1-me(i1)
if( i2 .ne. 0 ) me(i2)=1-me(i2)
if( i3 .ne. 0 ) me(i3)=1-me(i3)
if( i4 .ne. 0 ) me(i4)=1-me(i4)
! me is the m0 + error pattern. encode this message using genmrb to
! produce a codeword. test the codeword against the received vector
! and save it if it's the best that we've seen so far.
do i=1,N
nsum=sum(iand(me,genmrb(1:K,i)))
codeword(i)=mod(nsum,2)
enddo
! undo the bit re-ordering to put the "real" message bits at the end
codeword(indices)=codeword
nhard=count(codeword .ne. hdec)
! corr=sum(codeword*rx) ! to save time use nhard to pick best codeword
if( nhard .lt. nhardmin ) then
! if( corr .gt. corrmax ) then
cw=codeword
nhardmin=nhard
! corrmax=corr
i1min=i1
i2min=i2
i3min=i3
i4min=i4
if( nhardmin .le. 5 ) goto 200 ! early exit - tune for each code
endif
enddo
enddo
enddo
enddo
200 decoded=cw(M+1:N)
niterations=nhardmin
return
end subroutine osd174