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More work on osd decoder.

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7671 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Steven Franke 2017-05-11 22:55:31 +00:00
parent b3775f015a
commit a2447fe344
3 changed files with 55 additions and 58 deletions
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25
lib/fsk4hf/ldpcsim168.f90
View File

@ -10,7 +10,7 @@ character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
integer*1, target:: i1Msg8BitBytes(11)
integer*1 msgbits(84)
integer*1 apmask(168)
integer*1 apmask(168), cw(168)
integer*2 checksum
integer*4 i4Msg6BitWords(13)
integer colorder(168)
@ -124,9 +124,8 @@ allocate ( rxdata(N), llr(N) )
write(*,'(21(8i1,1x))') codeword
write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
do idb = -10, 24
do idb = 6,-6,-1
db=idb/2.0-1.0
! sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
sigma=1/sqrt( 2*(10**(db/10.0)) )
ngood=0
nue=0
@ -180,14 +179,18 @@ do idb = -10, 24
! max_iterations is max number of belief propagation iterations
call bpdecode168(llr, apmask, max_iterations, decoded, niterations)
if( niterations .eq. -1 ) then
norder=3
call osd168(llr, norder, decoded, niterations, cw)
endif
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
call extractmessage168(decoded,msgreceived,ncrcflag,recent_calls,nrecent)
if( ncrcflag .ne. 1 ) then
nbadcrc=nbadcrc+1
endif
nueflag=0
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
@ -195,12 +198,16 @@ do idb = -10, 24
nerrmpc=nerrmpc+1
endif
enddo
write(37,*) niterations, ncrcflag, nueflag
nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1
if( ncrcflag .eq. 1 .and. nueflag .eq. 0 ) then
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else if( ncrcflag .eq. 1 .and. nueflag .eq. 1 ) then
nue=nue+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

2
lib/fsk4hf/ldpcsim300.f90
View File

@ -117,7 +117,7 @@ write(*,*) i1Msg8BitBytes(1:9)
write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
do idb = 20,-16,-1
!do idb = -14, -16, -1
!do idb = -16, -16, -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

86
lib/fsk4hf/osd300.f90
View File

@ -10,7 +10,7 @@ include "ldpc_300_60_params.f90"
integer*1 gen(K,N)
integer*1 genmrb(K,N)
integer*1 temp(K),m0(K),me(K)
integer*1 temp(K),m0(K),me(0:K)
integer indices(N)
integer*1 codeword(N),cw(N),hdec(N)
integer*1 decoded(K)
@ -48,37 +48,33 @@ 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.
! re-order the columns of the generator matrix in order of decreasing reliability.
do i=1,N
genmrb(1:K,N+1-i)=gen(1:K,indx(N+1-i))
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 as the systematic bits. if it happens that the K most reliable
! bits are not independent, then we will encounter a zero pivot, in that case
! we dip into the less reliable bits to find K independent MRBs.
! the "indices" array will track any column reordering that is done as part
! of the gaussian elimination.
do i=1,N
indices(i)=indx(i)
enddo
! received bits in positions 1:K in order of decreasing reliability (more or less).
! reliability will not be strictly decreasing because column re-ordering is needed
! to put the generator matrix in systematic form. the "indices" array tracks
! column permutations caused by reliability sorting and gaussian elimination.
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)
do icol=id,K+20 ! The 20 is ad hoc - beware
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)
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(M+id)
indices(M+id)=indices(icol)
itmp=indices(id)
indices(id)=indices(icol)
indices(icol)=itmp
endif
do ii=1,K
if( ii .ne. id .and. genmrb(ii,N-K+id) .eq. 1 ) then
if( ii .ne. id .and. genmrb(ii,id) .eq. 1 ) then
genmrb(ii,1:N)=mod(genmrb(ii,1:N)+genmrb(id,1:N),2)
endif
enddo
@ -87,17 +83,15 @@ do id=1,K ! diagonal element indices
enddo
enddo
! now, use the indices of the K MRB bits to find the hard-decisions
! for those bits. the resulting message is encoded to find the
! zero'th order codeword estimate (assuming no errors in the MRB).
m0=0
where (rx(indices(M+1:N)).ge.0.0) m0=1
! 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. Test all such codewords against the received word to decide which
! codeword is most likely to be correct.
hdec=hdec(indices)
m0=hdec(1:K)
! the MRB should have only a few errors. Try various error patterns,
! re-encode each errored version of the MRBs, re-order the resulting codeword
! and compare with the original received vector. Keep the best codeword.
nhardmin=N
corrmax=-1.0e32
j0=0
j1=0
j2=0
@ -106,45 +100,41 @@ if( norder.ge.4 ) j0=K
if( norder.ge.3 ) j1=K
if( norder.ge.2 ) j2=K
if( norder.ge.1 ) j3=K
! me(0) is a dummy position --- only me(1:K) are actually used. This is done
! to avoid "if" statements within the inner loop.
do i1=0,j0
do i2=i1,j1
do i3=i2,j2
do i4=i3,j3
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(1:K)=m0
me(i1)=1-me(i1)
me(i2)=1-me(i2)
me(i3)=1-me(i3)
me(i4)=1-me(i4)
! me is the MRB message + error pattern
! use the modified generator matrix to encode this message,
! producing a codeword that will be tested against the received vector
! 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)))
nsum=sum(iand(me(1:K),genmrb(1:K,i)))
codeword(i)=mod(nsum,2)
enddo
! undo the index permutations 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. 85 ) goto 200 ! tune for each code
endif
enddo
enddo
enddo
enddo
200 decoded=cw(M+1:N)
niterations=-1
if( nhardmin .le. 90 ) niterations=1 ! tune for each code
! re-order the codeword to place message bits at the end
cw(indices)=cw
decoded=cw(M+1:N)
niterations=1
return
end subroutine osd300