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Move CRC13 creation into encode128_90.f90 and CRC checking into bpdecode128_90.f90.

This commit is contained in:
Steve Franke 2018-06-16 16:42:02 -05:00
parent e16e78790a
commit 2cdb164446
6 changed files with 153 additions and 172 deletions
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2
CMakeLists.txt
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@ -425,7 +425,7 @@ set (wsjt_FSRCS
lib/extract.f90
lib/extract4.f90
lib/extractmessage144.f90
lib/extractmessage128_90.f90
lib/extractmessage77.f90
lib/fsk4hf/extractmessage168.f90
lib/ft8/extractmessage174.f90
lib/ft8/extractmessage174_91.f90

199
lib/bpdecode128_90.f90
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@ -1,113 +1,116 @@
subroutine bpdecode128_90(llr,apmask,maxiterations,decoded,cw,nharderror,iter)
subroutine bpdecode128_90(llr,apmask,maxiterations,message77,cw,nharderror,iter)
!
! A log-domain belief propagation decoder for the (128,90) code.
!
integer, parameter:: N=128, K=90, M=N-K
integer*1 codeword(N),cw(N),apmask(N)
integer*1 decoded(K)
integer Nm(12,M)
integer Mn(4,N)
integer synd(M)
real tov(4,N)
real toc(12,M)
real tanhtoc(12,M)
real zn(N)
real llr(N)
real Tmn
integer nrw(M),ncw(N)
use iso_c_binding, only: c_loc,c_size_t
use crc
integer, parameter:: N=128, K=90, M=N-K
integer*1 cw(N),apmask(N)
integer*1 decoded(K)
integer*1 message77(77)
integer Nm(12,M)
integer Mn(4,N)
integer nrw(M),ncw(N)
integer synd(M)
real tov(4,N)
real toc(12,M)
real tanhtoc(12,M)
real zn(N)
real llr(N)
real Tmn
include "ldpc_128_90_b_reordered_parity.f90"
include "ldpc_128_90_b_reordered_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
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),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
codeword=cw
decoded=codeword(1:K)
nerr=0
do i=1,N
if( (2*cw(i)-1)*llr(i) .lt. 0.0 ) nerr=nerr+1
enddo
nharderror=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
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=1,4 ! 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
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),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
decoded=cw(1:K)
call chkcrc13a(decoded,nbadcrc)
if(nbadcrc.eq.0) then
message77=decoded(1:77)
nharderror=count( (2*cw-1)*llr .lt. 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=1,4 ! 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
enddo
! send messages from check nodes to variable nodes
do i=1,M
tanhtoc(1:12,i)=tanh(-toc(1:12,i)/2)
enddo
do j=1,N
do i=1,ncw(j)
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
do i=1,M
tanhtoc(1:12,i)=tanh(-toc(1:12,i)/2)
enddo
enddo
enddo
nharderror=-1
return
do j=1,N
do i=1,ncw(j)
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 bpdecode128_90

19
lib/encode128_90.f90
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@ -1,15 +1,19 @@
subroutine encode128_90(message,codeword)
subroutine encode128_90(message77,codeword)
! Encode an 90-bit message and return a 128-bit codeword.
! The generator matrix has dimensions (38,90).
! The code is a (128,90) regular ldpc code with column weight 3.
!
use, intrinsic :: iso_c_binding
use iso_c_binding, only: c_loc,c_size_t
use crc
integer, parameter:: N=128, K=90, M=N-K
character*90 tmpchar
integer*1 codeword(N)
integer*1 gen(M,K)
integer*1 message(K)
integer*1 message77(77),message(K)
integer*1 pchecks(M)
integer*1, target :: i1MsgBytes(12)
include "ldpc_128_90_b_generator.f90"
logical first
data first/.true./
@ -31,6 +35,15 @@ if( first ) then ! fill the generator matrix
first=.false.
endif
! Add 13 bit CRC to form 90-bit message+CRC13
write(tmpchar,'(77i1)') message77
tmpchar(78:80)='000'
i1MsgBytes=0
read(tmpchar,'(10b8)') i1MsgBytes(1:10)
ncrc13 = crc13 (c_loc (i1MsgBytes), 12)
write(tmpchar(78:90),'(b13)') ncrc13
read(tmpchar,'(90i1)') message
do i=1,M
nsum=0
do j=1,K

35
lib/extractmessage128_90.f90
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@ -1,35 +0,0 @@
subroutine extractmessage128_90(decoded,msgreceived,ncrcflag)
use iso_c_binding, only: c_loc,c_size_t
use crc
use packjt
character*22 msgreceived
character*90 cbits
integer*1 decoded(90)
integer*1, target:: i1Dec8BitBytes(12)
integer*2 icrc13
integer*4 i4Dec6BitWords(12)
! Write decoded bits into cbits: 77-bit message plus 13-bit CRC
write(cbits,1000) decoded
1000 format(90i1)
read(cbits,1001) i1Dec8BitBytes
1001 format(12b8)
read(cbits,1002) ncrc13 !Received CRC12
1002 format(77x,b13)
i1Dec8BitBytes(10)=iand(i1Dec8BitBytes(10),128+64+32+16+8)
i1Dec8BitBytes(11:12)=0
icrc13=crc13(c_loc(i1Dec8BitBytes),12) !CRC13 computed from 77 msg bits
if(ncrc13.eq.icrc13) then !### Kludge ### ???
! CRC13 checks out --- unpack 72-bit message
read(cbits,'(12b6)') i4Dec6BitWords
call unpackmsg(i4Dec6BitWords,msgreceived,.false.,' ')
ncrcflag=1
else
msgreceived=' '
ncrcflag=-1
endif
return
end subroutine extractmessage128_90

18
lib/extractmessage77.f90 Normal file
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@ -0,0 +1,18 @@
subroutine extractmessage77(decoded77,msgreceived)
use packjt
character*22 msgreceived
character*77 cbits
integer*1 decoded77(77)
integer*1, target:: i1Dec8BitBytes(12)
integer*4 i4Dec6BitWords(12)
write(cbits,'(77i1)') decoded77
!**** Temporary: For now, just handle i5bit=0.
read(cbits,'(12b6)') i4Dec6BitWords
read(cbits,'(72x,i5.5)') i5bit
if( i5bit .eq. 0 ) then
call unpackmsg(i4Dec6BitWords,msgreceived,.false.,' ')
endif
return
end subroutine extractmessage77

52
lib/ldpcsim128_90.f90
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@ -1,23 +1,19 @@
program ldpcsim
use, intrinsic :: iso_c_binding
use iso_c_binding, only: c_loc,c_size_t
use crc
use packjt
integer, parameter:: NRECENT=10, N=128, K=90, M=N-K
character*12 recent_calls(NRECENT)
character*22 msg,msgsent,msgreceived
character*96 tmpchar
character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
integer*1, target:: i1Msg8BitBytes(12)
integer*1 codeword(N), message77(77)
integer*1 apmask(N),cw(N)
integer*1 msgbits(90)
integer*1 msgbits(77)
integer*2 ncrc13
integer*4 i4Msg6BitWords(13)
integer nerrtot(0:N),nerrdec(0:N),nmpcbad(0:K),nbadwt(0:N)
real*8, allocatable :: lratio(:), rxdata(:), rxavgd(:)
real, allocatable :: yy(:), llr(:)
real*8 rxdata(N), rxavgd(N)
real llr(N)
do i=1,NRECENT
recent_calls(i)=' '
@ -45,12 +41,8 @@ read(arg,*) s
rate=real(K)/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," navg= ",navg," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( lratio(N), rxdata(N), rxavgd(N), yy(N), llr(N) )
!msg="K9AN K1JT EN50"
msg="G4WJS K1JT FN20"
call packmsg(msg,i4Msg6BitWords,itype,.false.) !Pack into 12 6-bit bytes
@ -60,21 +52,17 @@ msg="G4WJS K1JT FN20"
tmpchar=' '
write(tmpchar,'(12b6.6)') i4Msg6BitWords(1:12)
tmpchar(73:77)="00000" !i5bit
read(tmpchar,'(10b8)') i1Msg8BitBytes(1:10)
i1Msg8BitBytes(10:12)=0
ncrc13 = crc13 (c_loc (i1Msg8BitBytes), 12)
write(tmpchar(78:90),'(b13)') ncrc13
read(tmpchar,'(90i1)') msgbits(1:90)
read(tmpchar,'(77i1)') msgbits(1:77)
write(*,*) 'msgbits'
write(*,'(28i1,1x,28i1,1x,16i1,1x,5i1,1x,13i1)') msgbits
! msgbits is the 77-bit message, codeword is 128 bits
call encode128_90(msgbits,codeword)
call init_random_seed()
write(*,*) "Eb/N0 SNR2500 ngood nundetected nbadcrc sigma psymerr"
write(*,*) "Eb/N0 SNR2500 ngood nundetected sigma psymerr"
do idb = 14,-6,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
@ -113,27 +101,20 @@ do idb = 14,-6,-1
endif
llr=2.0*rxdata/(ss*ss)
lratio=exp(llr)
yy=rxdata
apmask=0
! max_iterations is max number of belief propagation iterations
call bpdecode128_90(llr, apmask, max_iterations, decoded, cw, nharderrors, niterations)
call bpdecode128_90(llr, apmask, max_iterations, message77, cw, nharderrors, niterations)
! If the decoder finds a valid codeword, nharderrors will be .ge. 0.
if( nharderrors .ge. 0 ) then
call extractmessage128_90(decoded,msgreceived,ncrcflag)
nhw=count(cw.ne.codeword)
if(ncrcflag.eq.1) then
if(nhw.eq.0) then ! this is a good decode
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else ! this is an undetected error
nue=nue+1
endif
else
nbadcrc=nbadcrc+1
nbadwt(nhw)=nbadwt(nhw)+1 ! store the weight of the error vector
call extractmessage77(message77,msgreceived)
nhw=count(message77.ne.codeword(1:77))
if(nhw.eq.0) then ! this is a good decode
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else ! this is an undetected error
nue=nue+1
endif
endif
nsumerr=nsumerr+nerr
@ -141,7 +122,7 @@ do idb = 14,-6,-1
snr2500=db-2.5
pberr=real(nsumerr)/real(ntrials*N)
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,7x,f5.2,3x,e10.3)") db,snr2500,ngood,nue,nbadcrc,ss,pberr
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,7x,f5.2,3x,e10.3)") db,snr2500,ngood,nue,ss,pberr
enddo
@ -150,6 +131,7 @@ do i=0,N
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='badcrc_hamming_weight.dat',status='unknown')
do i=0,N
write(25,'(i4,2x,i10)') i,nbadwt(i)