More work on osd decoder.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7671 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

lib/fsk4hf/ldpcsim168.f90

@@ -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

lib/fsk4hf/ldpcsim300.f90

@@ -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

lib/fsk4hf/osd300.f90

@@ -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