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Merge branch 'develop' of bitbucket.org:k1jt/wsjtx into develop

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This commit is contained in:
Joe Taylor 2020-04-21 15:52:23 -04:00
commit 088c27acf2
5 changed files with 144 additions and 13 deletions
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2
CMakeLists.txt
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@ -602,7 +602,7 @@ set (wsjt_FSRCS
lib/fsk4hf/osd204.f90
lib/fsk4hf/genwsprcpm.f90
lib/fsk4hf/encode204.f90
# lib/ft8/decode174_91.f90
lib/fsk4hf/decode174_74.f90
lib/fsk4hf/ldpcsim174_91.f90
lib/fsk4hf/ldpcsim174_74.f90
lib/fsk4hf/ldpcsim174_101.f90

128
lib/fsk4hf/decode174_74.f90 Normal file
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@ -0,0 +1,128 @@
subroutine decode174_74(llr,Keff,ndeep,apmask,maxsuper,message74,cw,nharderror,iter,ncheck,dmin,isuper)
!
! A hybrid bp/osd 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 message74(74)
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),zsum(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
maxiterations=1
zsum=0.0
do isuper=1,maxsuper
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
zsum=zsum+zn
! 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 - if crc is good, return it
decoded=cw(1:K)
call get_crc24(decoded,74,nbadcrc)
nharderror=count( (2*cw-1)*llr .lt. 0.0 )
if(nbadcrc.eq.0) then
message74=decoded(1:74)
dmin=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,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 ! bp iterations
llr=zsum
call osd174_74(llr,Keff,apmask,ndeep,message74,cw,nharderror,dmin)
if(nharderror.gt.0) then
return
endif
enddo ! super iterations
nharderror=-1
return
end subroutine decode174_74

7
lib/fsk4hf/ldpcsim174_74.f90
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@ -98,10 +98,6 @@ program ldpcsim174_74
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
@ -114,7 +110,8 @@ program ldpcsim174_74
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)
! call osd174_74(llr, Keff, apmask, ndeep, message, cw, nharderror, dmin)
call decode174_74(llr,Keff,ndeep,apmask,max_iterations,message,cw,nharderror,niterations,ncheck,dmin,isuper)
endif
if(nharderror.ge.0) then

2
lib/fsk4hf/osd174_74.f90
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@ -22,7 +22,7 @@ subroutine osd174_74(llr,k,apmask,ndeep,message74,cw,nhardmin,dmin)
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*1 message74(74)
integer indx(N)
real llr(N),rx(N),absrx(N)

18
lib/fsk4hf/wspr4d.f90
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@ -119,13 +119,13 @@ program wspr4d
enddo
if(smax .lt. 100.0 ) cycle
idecoded=0
do ijitter=0,4
do ijitter=0,2
if(idecoded.eq.1) exit
if(ijitter.eq.1) ioffset=20
if(ijitter.eq.2) ioffset=-20
if(ijitter.eq.3) ioffset=40
if(ijitter.eq.4) ioffset=-40
if(ijitter.eq.0) ioffset=0
if(ijitter.eq.1) ioffset=50
if(ijitter.eq.2) ioffset=-50
is0=isbest+ioffset
if(is0.lt.0) cycle
cframe=c2(is0:is0+103*416-1)
@ -168,7 +168,13 @@ program wspr4d
dmin=0.0
call bpdecode174_74(llr,apmask,max_iterations,message,cw,nhardbp,niterations)
Keff=64
if(nhardbp.lt.0) call osd174_74(llr,Keff,apmask,5,message,cw,nhardosd,dmin)
! if(nhardbp.lt.0) call osd174_74(llr,Keff,apmask,5,message,cw,nhardosd,dmin)
maxsuperits=2
ndeep=4
if(nhardbp.lt.0) then
call decode174_74(llr,Keff,ndeep,apmask,maxsuperits,message,cw,nhardosd,iter,ncheck,dmin,isuper)
endif
if(nhardbp.ge.0 .or. nhardosd.ge.0) then
write(c77,'(50i1)') message
c77(51:77)='000000000000000000000110000'