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Add a new (174,74) LDPC code (regular, column weight 3) and supporting files.

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This commit is contained in:
Steven Franke 2020-04-13 10:23:02 -05:00
parent 74dc865c4c
commit 65fa6aed6c
7 changed files with 1127 additions and 0 deletions
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113
lib/fsk4hf/bpdecode174_74.f90 Normal file
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subroutine bpdecode174_74(llr,apmask,maxiterations,message50,cw,nharderror,iter)
!
! A log-domain belief propagation 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 message50(50)
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)
real llr(N)
real Tmn
include "ldpc_174_74_parity.f90"
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
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
if( ncheck .eq. 0 ) then ! we have a codeword - if crc is good, return it
decoded=cw(1:74)
call get_crc24(decoded,nbadcrc)
nharderror=count( (2*cw-1)*llr .lt. 0.0 )
if(nbadcrc.eq.0) then
message50=decoded(1:50)
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 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
nharderror=-1
return
end subroutine bpdecode174_74

47
lib/fsk4hf/encode174_74.f90 Normal file
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subroutine encode174_74(message,codeword)
use, intrinsic :: iso_c_binding
use iso_c_binding, only: c_loc,c_size_t
use crc
integer, parameter:: N=174, K=74, M=N-K
character*24 c24
integer*1 codeword(N)
integer*1 gen(M,K)
integer*1 message(K)
integer*1 pchecks(M)
integer*1, target :: i1MsgBytes(10)
integer*4 ncrc24
include "ldpc_174_74_generator.f90"
logical first
data first/.true./
save first,gen
if( first ) then ! fill the generator matrix
gen=0
do i=1,M
do j=1,19
read(g(i)(j:j),"(Z1)") istr
ibmax=4
if(j.eq.19) ibmax=2
do jj=1, ibmax
icol=(j-1)*4+jj
if( btest(istr,4-jj) ) gen(i,icol)=1
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
codeword(1:K)=message
codeword(K+1:N)=pchecks
return
end subroutine encode174_74

25
lib/fsk4hf/get_crc24.f90 Normal file
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subroutine get_crc24(mc,ncrc)
!
! 1. To calculate 24-bit CRC, mc(1:50) is the message and mc(51:74) are zero.
! 2. To check a received CRC, mc(1:74) is the received message plus CRC.
! ncrc will be zero if the received message/CRC are consistent.
!
character c24*24
integer*1 mc(74),r(25),p(25)
integer ncrc
! polynomial for 24-bit CRC 0x100065b
data p/1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,1,0,1,1,0,1,1/
! divide by polynomial
r=mc(1:25)
do i=0,49
r(25)=mc(i+25)
r=mod(r+r(1)*p,2)
r=cshift(r,1)
enddo
write(c24,'(24b1)') r(1:24)
read(c24,'(b24.24)') ncrc
end subroutine get_crc24

105
lib/fsk4hf/ldpc_174_74_generator.f90 Normal file
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! generator matrix for regular column weight 3 (174,74) LDPC code.
character*19 g(100)
data g/ &
"b190e319bd45882ed74", &
"b159282d395467cabe4", &
"f502387ec63db738358", &
"a6c7911729277b2a178", &
"05d812d04122ff2842c", &
"eb040701b66b26d12ec", &
"c617358e34398e73c6c", &
"37b62b499bbb84aeb0c", &
"60257b5d4e41594a250", &
"e8ac26253c0268ba33c", &
"0f243baf67353230318", &
"521d5eb1268bed86854", &
"53bab7dbe89962bba00", &
"417abaf10e0912604b8", &
"c0d371dbb301f49aae8", &
"e7014cf533a2cb9fd24", &
"948175882e16ecd8cc8", &
"87db37137999fb15504", &
"2557139852451e678c8", &
"aaaf0b6b1f70db8e5ac", &
"f5be069b0a41fd5bb28", &
"e7789f2237b2175d494", &
"94554737d22b00d5980", &
"525e935db67c1af214c", &
"9c57c640427a2c2e33c", &
"9a82e00fb570e371cac", &
"39ebbdd43570f690818", &
"a037514614e0d5cc2a4", &
"ff19fc0eee4376f6de0", &
"f8853aad262b1a14cf0", &
"f5687424fe7c5156ee0", &
"fba0aa4876b79e45d78", &
"dfdfb60046769dec900", &
"600b4517a14560fad64", &
"39c618d3f629809c064", &
"5c821087e8c365869f8", &
"a4f26e15e3ef8264c04", &
"ac230e4147016f5bf98", &
"e11a6981f5257957d84", &
"b9dd003c09cf2abc5b0", &
"326ff2588a1bfa6a310", &
"a84e8e04722185f23ac", &
"8a66abe81aff313f9a8", &
"f6047ea2cad01957e08", &
"f14b63fdff262eb74bc", &
"7588be7336de21f7680", &
"312d0e1d5d1c3666fec", &
"5ab69333712cdbf9c38", &
"3c8e8c949be183939f4", &
"ed3b36d068e55ef76d8", &
"8193b051800415c06e0", &
"bc8e88949be18393bd4", &
"a7db37037999fb15404", &
"c5ec69ecc57ed7800b8", &
"475b645148268e10afc", &
"1fe90fea7ae941c04a8", &
"513b196d2a6e43c9504", &
"ffc27ceba420d04f468", &
"972c2cc31e578dba968", &
"7fc874b734a8188a2f8", &
"3d0327a801275734cc4", &
"b1e77d50857f56b6a40", &
"f25389644e47dae2384", &
"4e7e815e6b3c20507a0", &
"27d63d2e80a23f057cc", &
"381388a8a6fad77ec50", &
"b785abf747ea18bc350", &
"40a2a8214e2bed48090", &
"0e891f175b06fed80d4", &
"dbd155acd9fbec5b4a4", &
"9d3476e615c702f8e60", &
"050ea06fbd1f532d164", &
"d03767bca8394f31628", &
"455d568ff3047e9d5ac", &
"6b343bcf7378e1283f4", &
"a0d371dbb311f49aae8", &
"36ea237c911eb2ac27c", &
"54a636ec612a744f368", &
"5cabf5c9d5a0d2d9ba4", &
"00d632bffc3dac0d548", &
"d86bf5593c70dcb91fc", &
"bada10bb78be8c219c0", &
"b98028f926fed2beab0", &
"c0347b3cc45c2888094", &
"0662d6a3c2974e0a910", &
"8036b9e83c9fdc2cda8", &
"e5db38aad196024c21c", &
"746c8af5783b5daedcc", &
"1dc47211c27e39ec5dc", &
"6b98898e40559a2e128", &
"52d9077dbfa44c6d75c", &
"9ca1e6bd4515559a054", &
"7b2dd815e5991f88d14", &
"bfde5ebc6e09940460c", &
"487f5ffeaf139c209f4", &
"08d6b3c9686cc0f6ff4", &
"e198f5466141f53ab84", &
"0a7c7af0ac612d14f40", &
"a4192113ec53f4d165c", &
"1423ae72e003614be88"/

288
lib/fsk4hf/ldpc_174_74_parity.f90 Normal file
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! parity check matrix for regular column weight 3 (174,74) LDPC code
data Mn/ &
28, 32, 98, &
1, 94, 95, &
70, 71, 94, &
3, 9, 39, &
4, 22, 84, &
5, 25, 85, &
6, 55, 100, &
7, 41, 67, &
8, 62, 77, &
10, 37, 40, &
11, 16, 36, &
12, 29, 47, &
14, 57, 91, &
15, 49, 59, &
17, 18, 52, &
19, 48, 58, &
20, 34, 72, &
21, 38, 87, &
23, 46, 79, &
24, 43, 83, &
26, 74, 78, &
27, 51, 98, &
30, 35, 42, &
31, 63, 88, &
25, 33, 82, &
44, 53, 96, &
50, 75, 90, &
46, 54, 71, &
56, 76, 81, &
60, 65, 69, &
61, 95, 97, &
64, 89, 99, &
66, 73, 76, &
68, 80, 92, &
74, 86, 87, &
52, 55, 93, &
1, 3, 21, &
2, 57, 64, &
4, 11, 82, &
5, 60, 81, &
6, 13, 66, &
7, 43, 59, &
8, 27, 85, &
9, 34, 94, &
10, 28, 88, &
12, 19, 53, &
14, 33, 65, &
15, 75, 84, &
16, 56, 68, &
17, 44, 90, &
18, 23, 73, &
20, 26, 83, &
22, 42, 91, &
24, 70, 79, &
29, 96, 97, &
30, 48, 77, &
31, 37, 67, &
32, 35, 78, &
36, 80, 89, &
38, 62, 93, &
39, 54, 72, &
40, 58, 61, &
41, 51, 86, &
9, 45, 63, &
46, 47, 92, &
49, 50, 80, &
69, 75, 98, &
14, 71, 99, &
21, 85, 100, &
1, 6, 50, &
2, 74, 98, &
3, 73, 92, &
4, 32, 79, &
5, 63, 96, &
1, 29, 79, &
2, 6, 84, &
3, 36, 78, &
4, 59, 69, &
5, 72, 80, &
2, 41, 44, &
7, 38, 90, &
8, 58, 99, &
9, 42, 49, &
10, 46, 74, &
11, 14, 73, &
12, 85, 88, &
13, 25, 93, &
5, 11, 61, &
15, 16, 94, &
8, 15, 32, &
17, 64, 76, &
18, 60, 71, &
19, 34, 57, &
20, 77, 96, &
21, 31, 82, &
22, 23, 48, &
16, 17, 22, &
24, 35, 86, &
13, 51, 64, &
26, 33, 39, &
4, 27, 47, &
28, 54, 56, &
1, 62, 76, &
30, 53, 100, &
21, 46, 57, &
32, 55, 61, &
33, 92, 95, &
19, 67, 68, &
14, 35, 75, &
3, 84, 99, &
37, 75, 92, &
7, 30, 63, &
23, 39, 50, &
27, 40, 44, &
41, 66, 91, &
9, 10, 69, &
12, 43, 52, &
6, 20, 88, &
43, 45, 89, &
24, 31, 60, &
47, 50, 70, &
26, 38, 45, &
25, 42, 98, &
40, 79, 87, &
51, 68, 83, &
52, 97, 98, &
48, 71, 78, &
28, 29, 80, &
53, 59, 73, &
49, 54, 95, &
34, 36, 90, &
55, 82, 89, &
4, 77, 90, &
49, 58, 81, &
18, 56, 77, &
62, 63, 65, &
60, 91, 100, &
2, 11, 62, &
15, 24, 93, &
37, 66, 83, &
65, 85, 86, &
5, 10, 48, &
1, 69, 89, &
67, 81, 87, &
13, 56, 75, &
70, 72, 97, &
8, 50, 57, &
6, 19, 33, &
7, 25, 99, &
74, 94, 96, &
14, 52, 87, &
16, 30, 40, &
20, 42, 79, &
17, 21, 72, &
9, 12, 41, &
18, 61, 67, &
3, 83, 97, &
26, 80, 91, &
23, 55, 65, &
27, 31, 95, &
28, 84, 86, &
29, 34, 93, &
46, 51, 63, &
35, 39, 76, &
13, 44, 78, &
32, 37, 38, &
22, 43, 92, &
45, 53, 54, &
58, 73, 74, &
47, 64, 100, &
59, 68, 85, &
66, 82, 96, &
36, 81, 88, &
2, 45, 70/
data Nm/ &
2, 37, 70, 75, 103, 143, &
38, 71, 76, 80, 138, 174, &
4, 37, 72, 77, 110, 157, &
5, 39, 73, 78, 101, 133, &
6, 40, 74, 79, 88, 142, &
7, 41, 70, 76, 118, 148, &
8, 42, 81, 112, 149, 0, &
9, 43, 82, 90, 147, 0, &
4, 44, 64, 83, 116, 155, &
10, 45, 84, 116, 142, 0, &
11, 39, 85, 88, 138, 0, &
12, 46, 86, 117, 155, 0, &
41, 87, 99, 145, 165, 0, &
13, 47, 68, 85, 109, 151, &
14, 48, 89, 90, 139, 0, &
11, 49, 89, 97, 152, 0, &
15, 50, 91, 97, 154, 0, &
15, 51, 92, 135, 156, 0, &
16, 46, 93, 108, 148, 0, &
17, 52, 94, 118, 153, 0, &
18, 37, 69, 95, 105, 154, &
5, 53, 96, 97, 167, 0, &
19, 51, 96, 113, 159, 0, &
20, 54, 98, 120, 139, 0, &
6, 25, 87, 123, 149, 0, &
21, 52, 100, 122, 158, 0, &
22, 43, 101, 114, 160, 0, &
1, 45, 102, 128, 161, 0, &
12, 55, 75, 128, 162, 0, &
23, 56, 104, 112, 152, 0, &
24, 57, 95, 120, 160, 0, &
1, 58, 73, 90, 106, 166, &
25, 47, 100, 107, 148, 0, &
17, 44, 93, 131, 162, 0, &
23, 58, 98, 109, 164, 0, &
11, 59, 77, 131, 173, 0, &
10, 57, 111, 140, 166, 0, &
18, 60, 81, 122, 166, 0, &
4, 61, 100, 113, 164, 0, &
10, 62, 114, 124, 152, 0, &
8, 63, 80, 115, 155, 0, &
23, 53, 83, 123, 153, 0, &
20, 42, 117, 119, 167, 0, &
26, 50, 80, 114, 165, 0, &
64, 119, 122, 168, 174, 0, &
19, 28, 65, 84, 105, 163, &
12, 65, 101, 121, 170, 0, &
16, 56, 96, 127, 142, 0, &
14, 66, 83, 130, 134, 0, &
27, 66, 70, 113, 121, 147, &
22, 63, 99, 125, 163, 0, &
15, 36, 117, 126, 151, 0, &
26, 46, 104, 129, 168, 0, &
28, 61, 102, 130, 168, 0, &
7, 36, 106, 132, 159, 0, &
29, 49, 102, 135, 145, 0, &
13, 38, 93, 105, 147, 0, &
16, 62, 82, 134, 169, 0, &
14, 42, 78, 129, 171, 0, &
30, 40, 92, 120, 137, 0, &
31, 62, 88, 106, 156, 0, &
9, 60, 103, 136, 138, 0, &
24, 64, 74, 112, 136, 163, &
32, 38, 91, 99, 170, 0, &
30, 47, 136, 141, 159, 0, &
33, 41, 115, 140, 172, 0, &
8, 57, 108, 144, 156, 0, &
34, 49, 108, 125, 171, 0, &
30, 67, 78, 116, 143, 0, &
3, 54, 121, 146, 174, 0, &
3, 28, 68, 92, 127, 0, &
17, 61, 79, 146, 154, 0, &
33, 51, 72, 85, 129, 169, &
21, 35, 71, 84, 150, 169, &
27, 48, 67, 109, 111, 145, &
29, 33, 91, 103, 164, 0, &
9, 56, 94, 133, 135, 0, &
21, 58, 77, 127, 165, 0, &
19, 54, 73, 75, 124, 153, &
34, 59, 66, 79, 128, 158, &
29, 40, 134, 144, 173, 0, &
25, 39, 95, 132, 172, 0, &
20, 52, 125, 140, 157, 0, &
5, 48, 76, 110, 161, 0, &
6, 43, 69, 86, 141, 171, &
35, 63, 98, 141, 161, 0, &
18, 35, 124, 144, 151, 0, &
24, 45, 86, 118, 173, 0, &
32, 59, 119, 132, 143, 0, &
27, 50, 81, 131, 133, 0, &
13, 53, 115, 137, 158, 0, &
34, 65, 72, 107, 111, 167, &
36, 60, 87, 139, 162, 0, &
2, 3, 44, 89, 150, 0, &
2, 31, 107, 130, 160, 0, &
26, 55, 74, 94, 150, 172, &
31, 55, 126, 146, 157, 0, &
1, 22, 67, 71, 123, 126, &
32, 68, 82, 110, 149, 0, &
7, 69, 104, 137, 170, 0/
data nrw/ &
6,6,6,6,6,6,5,5,6,5,5,5,5,6,5,5,5,5,5,5, &
6,5,5,5,5,5,5,5,5,5,5,6,5,5,5,5,5,5,5,5, &
5,5,5,5,5,6,5,5,5,6,5,5,5,5,5,5,5,5,5,5, &
5,5,6,5,5,5,5,5,5,5,5,5,6,6,6,5,5,5,6,6, &
5,5,5,5,6,5,5,5,5,5,5,6,5,5,5,6,5,6,5,5/
ncw=3

144
lib/fsk4hf/ldpcsim174_74.f90 Normal file
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program ldpcsim174_74
! End-to-end test of the (174,74)/crc24 encoder and decoders.
use crc
use packjt
parameter(N=174, K=74, M=N-K)
character*8 arg
character*50 cmsg
character*24 c24
integer*1 msgbits(74)
integer*1 apmask(174)
integer*1 cw(174)
integer*1 codeword(N),message(50)
integer ncrc24
integer nerrtot(174),nerrdec(174),nmpcbad(74)
real rxdata(N),llr(N)
real dllr(174),llrd(174)
data cmsg/'11111111000000001111111100000000111111110000000011'/
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.5) then
print*,'Usage: ldpcsim niter ndeep #trials s K'
print*,'e.g. ldpcsim174_74 20 5 1000 0.85 64'
print*,'s : if negative, then value is ignored and sigma is calculated from SNR.'
print*,'niter: is the number of BP iterations.'
print*,'ndeep: -1 is BP only, ndeep>=0 is OSD order'
print*,'K :is the number of message+CRC bits and must be in the range [50,74]'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) ndeep
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
call getarg(5,arg)
read(arg,*) Keff
rate=real(Keff)/real(N)
write(*,*) "code rate: ",rate
write(*,*) "niter : ",max_iterations
write(*,*) "ndeep : ",ndeep
write(*,*) "s : ",s
write(*,*) "K : ",Keff
msgbits=0
read(cmsg,'(50i1)') msgbits(1:50)
write(*,*) 'message'
write(*,'(74i1)') msgbits
call get_crc24(msgbits,ncrc24)
write(c24,'(b24.24)') ncrc24
read(c24,'(24i1)') msgbits(51:74)
call encode174_74(msgbits,codeword)
call init_random_seed()
call sgran()
write(*,*) 'codeword'
write(*,'(50i1,1x,24i1,1x,100i1)') codeword
write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma symbol error rate"
do idb = 8,-3,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) ) ! to make db represent Eb/No
! sigma=1/sqrt( 2*(10**(db/10.0)) ) ! db represents Es/No
ngood=0
nue=0
nberr=0
do itrial=1, ntrials
! Create a realization of a noisy received word
do i=1,N
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
enddo
nerr=0
do i=1,N
if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
enddo
if(nerr.ge.1) nerrtot(nerr)=nerrtot(nerr)+1
nberr=nberr+nerr
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)
apmask=0
! max_iterations is max number of belief propagation iterations
call bpdecode174_74(llr,apmask,max_iterations,message,cw,nharderror,niterations)
dmin=0.0
if( (nharderror .lt. 0) .and. (ndeep .ge. 0) ) then
call osd174_74(llr, Keff, apmask, ndeep, message, cw, nharderror, dmin)
endif
if(nharderror.ge.0) then
n2err=0
do i=1,N
if( cw(i)*(2*codeword(i)-1.0) .lt. 0 ) n2err=n2err+1
enddo
if(n2err.eq.0) then
ngood=ngood+1
else
nue=nue+1
endif
endif
enddo
! snr2500=db+10*log10(200.0/116.0/2500.0)
esn0=db+10*log10(rate)
pberr=real(nberr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,esn0,ngood,nue,ss,pberr
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,120
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=1,68
write(25,'(i4,2x,i10)') i,nmpcbad(i)
enddo
close(25)
end program ldpcsim174_74

405
lib/fsk4hf/osd174_74.f90 Normal file
View File

@ -0,0 +1,405 @@
subroutine osd174_74(llr,k,apmask,ndeep,message74,cw,nhardmin,dmin)
!
! An ordered-statistics decoder for the (174,74) code.
! Message payload is 50 bits. Any or all of a 24-bit CRC can be
! used for detecting incorrect codewords. The remaining CRC bits are
! cascaded with the LDPC code for the purpose of improving the
! distance spectrum of the code.
!
! If p1 (0.le.p1.le.24) is the number of CRC24 bits that are
! to be used for bad codeword detection, then the argument k should
! be set to 50+p1.
!
! Valid values for k are in the range [50,74].
!
character*24 c24
integer, parameter:: N=174
integer*1 apmask(N),apmaskr(N)
integer*1, allocatable, save :: gen(:,:)
integer*1, allocatable :: genmrb(:,:),g2(:,:)
integer*1, allocatable :: temp(:),m0(:),me(:),mi(:),misub(:),e2sub(:),e2(:),ui(:)
integer*1, allocatable :: r2pat(:)
integer indices(N),nxor(N)
integer*1 cw(N),ce(N),c0(N),hdec(N)
integer*1, allocatable :: decoded(:)
integer*1 message50(50),message74(74)
integer indx(N)
real llr(N),rx(N),absrx(N)
!include "ldpc_174_74_generator.f90"
logical first,reset
data first/.true./
save first
allocate( genmrb(k,N), g2(N,k) )
allocate( temp(k), m0(k), me(k), mi(k), misub(k), e2sub(N-k), e2(N-k), ui(N-k) )
allocate( r2pat(N-k), decoded(k) )
if( first ) then ! fill the generator matrix
!
! Create generator matrix for partial CRC cascaded with LDPC code.
!
! Let p2=74-k and p1+p2=24.
!
! The last p2 bits of the CRC24 are cascaded with the LDPC code.
!
! The first p1=k-50 CRC24 bits will be used for error detection.
!
allocate( gen(k,N) )
gen=0
do i=1,k
message74=0
message74(i)=1
if(i.le.50) then
call get_crc24(message74,ncrc24)
write(c24,'(b24.24)') ncrc24
read(c24,'(24i1)') message74(51:74)
message74(51:k)=0
endif
call encode174_74(message74,cw)
gen(i,:)=cw
enddo
first=.false.
endif
rx=llr
apmaskr=apmask
! Hard decisions on 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 decreasing reliability.
do i=1,N
genmrb(1:k,i)=gen(1:k,indx(N+1-i))
indices(i)=indx(N+1-i)
enddo
! Do gaussian elimination to create a generator matrix with the most reliable
! received bits in positions 1:k in order of decreasing reliability (more or less).
do id=1,k ! diagonal element indices
do icol=id,k+20 ! The 20 is ad hoc - beware
iflag=0
if( genmrb(id,icol) .eq. 1 ) then
iflag=1
if( icol .ne. id ) then ! reorder column
temp(1:k)=genmrb(1:k,id)
genmrb(1:k,id)=genmrb(1:k,icol)
genmrb(1:k,icol)=temp(1:k)
itmp=indices(id)
indices(id)=indices(icol)
indices(icol)=itmp
endif
do ii=1,k
if( ii .ne. id .and. genmrb(ii,id) .eq. 1 ) then
genmrb(ii,1:N)=ieor(genmrb(ii,1:N),genmrb(id,1:N))
endif
enddo
exit
endif
enddo
enddo
g2=transpose(genmrb)
! The hard decisions for the k MRB bits define the order 0 message, m0.
! Encode m0 using the modified generator matrix to find the "order 0" codeword.
! Flip various combinations of bits in m0 and re-encode to generate a list of
! codewords. Return the member of the list that has the smallest Euclidean
! distance to the received word.
hdec=hdec(indices) ! hard decisions from received symbols
m0=hdec(1:k) ! zero'th order message
absrx=absrx(indices)
rx=rx(indices)
apmaskr=apmaskr(indices)
call mrbencode74(m0,c0,g2,N,k)
nxor=ieor(c0,hdec)
nhardmin=sum(nxor)
dmin=sum(nxor*absrx)
cw=c0
ntotal=0
nrejected=0
npre1=0
npre2=0
if(ndeep.eq.0) goto 998 ! norder=0
if(ndeep.gt.6) ndeep=6
if( ndeep.eq. 1) then
nord=1
npre1=0
npre2=0
nt=40
ntheta=12
elseif(ndeep.eq.2) then
nord=1
npre1=1
npre2=0
nt=40
ntheta=12
elseif(ndeep.eq.3) then
nord=1
npre1=1
npre2=1
nt=40
ntheta=12
ntau=14
elseif(ndeep.eq.4) then
nord=2
npre1=1
npre2=1
nt=40
ntheta=12
ntau=19
elseif(ndeep.eq.5) then
nord=3
npre1=1
npre2=1
nt=40
ntheta=12
ntau=19
elseif(ndeep.eq.6) then
nord=4
npre1=1
npre2=1
nt=40
ntheta=12
ntau=19
endif
do iorder=1,nord
misub(1:k-iorder)=0
misub(k-iorder+1:k)=1
iflag=k-iorder+1
do while(iflag .ge.0)
if(iorder.eq.nord .and. npre1.eq.0) then
iend=iflag
else
iend=1
endif
d1=0.
do n1=iflag,iend,-1
mi=misub
mi(n1)=1
if(any(iand(apmaskr(1:k),mi).eq.1)) cycle
ntotal=ntotal+1
me=ieor(m0,mi)
if(n1.eq.iflag) then
call mrbencode74(me,ce,g2,N,k)
e2sub=ieor(ce(k+1:N),hdec(k+1:N))
e2=e2sub
nd1kpt=sum(e2sub(1:nt))+1
d1=sum(ieor(me(1:k),hdec(1:k))*absrx(1:k))
else
e2=ieor(e2sub,g2(k+1:N,n1))
nd1kpt=sum(e2(1:nt))+2
endif
if(nd1kpt .le. ntheta) then
call mrbencode74(me,ce,g2,N,k)
nxor=ieor(ce,hdec)
if(n1.eq.iflag) then
dd=d1+sum(e2sub*absrx(k+1:N))
else
dd=d1+ieor(ce(n1),hdec(n1))*absrx(n1)+sum(e2*absrx(k+1:N))
endif
if( dd .lt. dmin ) then
dmin=dd
cw=ce
nhardmin=sum(nxor)
nd1kptbest=nd1kpt
endif
else
nrejected=nrejected+1
endif
enddo
! Get the next test error pattern, iflag will go negative
! when the last pattern with weight iorder has been generated.
call nextpat74(misub,k,iorder,iflag)
enddo
enddo
if(npre2.eq.1) then
reset=.true.
ntotal=0
do i1=k,1,-1
do i2=i1-1,1,-1
ntotal=ntotal+1
mi(1:ntau)=ieor(g2(k+1:k+ntau,i1),g2(k+1:k+ntau,i2))
call boxit74(reset,mi(1:ntau),ntau,ntotal,i1,i2)
enddo
enddo
ncount2=0
ntotal2=0
reset=.true.
! Now run through again and do the second pre-processing rule
misub(1:k-nord)=0
misub(k-nord+1:k)=1
iflag=k-nord+1
do while(iflag .ge.0)
me=ieor(m0,misub)
call mrbencode74(me,ce,g2,N,k)
e2sub=ieor(ce(k+1:N),hdec(k+1:N))
do i2=0,ntau
ntotal2=ntotal2+1
ui=0
if(i2.gt.0) ui(i2)=1
r2pat=ieor(e2sub,ui)
778 continue
call fetchit74(reset,r2pat(1:ntau),ntau,in1,in2)
if(in1.gt.0.and.in2.gt.0) then
ncount2=ncount2+1
mi=misub
mi(in1)=1
mi(in2)=1
if(sum(mi).lt.nord+npre1+npre2.or.any(iand(apmaskr(1:k),mi).eq.1)) cycle
me=ieor(m0,mi)
call mrbencode74(me,ce,g2,N,k)
nxor=ieor(ce,hdec)
dd=sum(nxor*absrx)
if( dd .lt. dmin ) then
dmin=dd
cw=ce
nhardmin=sum(nxor)
endif
goto 778
endif
enddo
call nextpat74(misub,k,nord,iflag)
enddo
endif
998 continue
! Re-order the codeword to [message bits][parity bits] format.
cw(indices)=cw
hdec(indices)=hdec
message74=cw(1:74)
call get_crc24(message74,nbadcrc)
if(nbadcrc.ne.0) nhardmin=-nhardmin
return
end subroutine osd174_74
subroutine mrbencode74(me,codeword,g2,N,K)
integer*1 me(K),codeword(N),g2(N,K)
! fast encoding for low-weight test patterns
codeword=0
do i=1,K
if( me(i) .eq. 1 ) then
codeword=ieor(codeword,g2(1:N,i))
endif
enddo
return
end subroutine mrbencode74
subroutine nextpat74(mi,k,iorder,iflag)
integer*1 mi(k),ms(k)
! generate the next test error pattern
ind=-1
do i=1,k-1
if( mi(i).eq.0 .and. mi(i+1).eq.1) ind=i
enddo
if( ind .lt. 0 ) then ! no more patterns of this order
iflag=ind
return
endif
ms=0
ms(1:ind-1)=mi(1:ind-1)
ms(ind)=1
ms(ind+1)=0
if( ind+1 .lt. k ) then
nz=iorder-sum(ms)
ms(k-nz+1:k)=1
endif
mi=ms
do i=1,k ! iflag will point to the lowest-index 1 in mi
if(mi(i).eq.1) then
iflag=i
exit
endif
enddo
return
end subroutine nextpat74
subroutine boxit74(reset,e2,ntau,npindex,i1,i2)
integer*1 e2(1:ntau)
integer indexes(5000,2),fp(0:525000),np(5000)
logical reset
common/boxes/indexes,fp,np
if(reset) then
patterns=-1
fp=-1
np=-1
sc=-1
indexes=-1
reset=.false.
endif
indexes(npindex,1)=i1
indexes(npindex,2)=i2
ipat=0
do i=1,ntau
if(e2(i).eq.1) then
ipat=ipat+ishft(1,ntau-i)
endif
enddo
ip=fp(ipat) ! see what's currently stored in fp(ipat)
if(ip.eq.-1) then
fp(ipat)=npindex
else
do while (np(ip).ne.-1)
ip=np(ip)
enddo
np(ip)=npindex
endif
return
end subroutine boxit74
subroutine fetchit74(reset,e2,ntau,i1,i2)
integer indexes(5000,2),fp(0:525000),np(5000)
integer lastpat
integer*1 e2(ntau)
logical reset
common/boxes/indexes,fp,np
save lastpat,inext
if(reset) then
lastpat=-1
reset=.false.
endif
ipat=0
do i=1,ntau
if(e2(i).eq.1) then
ipat=ipat+ishft(1,ntau-i)
endif
enddo
index=fp(ipat)
if(lastpat.ne.ipat .and. index.gt.0) then ! return first set of indices
i1=indexes(index,1)
i2=indexes(index,2)
inext=np(index)
elseif(lastpat.eq.ipat .and. inext.gt.0) then
i1=indexes(inext,1)
i2=indexes(inext,2)
inext=np(inext)
else
i1=-1
i2=-1
inext=-1
endif
lastpat=ipat
return
end subroutine fetchit74