From 8149fe24bee4ee89201dc62e4b1719ca674ac804 Mon Sep 17 00:00:00 2001
From: Steven Franke <s.j.franke@icloud.com>
Date: Sat, 28 Apr 2018 22:18:19 +0000
Subject: [PATCH] More work on block detection for dpsk.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8644 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
---
lib/fsk4hf/wsprdpskd.f90 | 92 ++++++++++++++++++++++++++++++++++------
1 file changed, 78 insertions(+), 14 deletions(-)
diff --git a/lib/fsk4hf/wsprdpskd.f90 b/lib/fsk4hf/wsprdpskd.f90
index 1790f218c..15e5665ec 100644
--- a/lib/fsk4hf/wsprdpskd.f90
+++ b/lib/fsk4hf/wsprdpskd.f90
@@ -38,6 +38,7 @@ program wsprdpskd
integer*1,target :: idat(9)
integer*1 decoded(68),apmask(204),cw(204)
integer*1 hbits(232),hbits1(232),hbits3(232)
+ integer*1 b(14),bbest(14)
data ipreamble/1,1,1,1,0,0,0,0,0,0,0,0,1,1,1,1/
data iuniqueword0/z'30C9E8AD'/
@@ -64,12 +65,7 @@ program wsprdpskd
isync2(113:116)=0
isync2(117:216)=isync(101:200)
-! data sync tone
-! 0 0 0
-! 0 1 1
-! 1 0 2
-! 1 1 3
- dphi=twopi*baud*(h/2.0)*dt*20 ! dt*10 is samp interval after downsample
+ dphi=twopi*baud*(h/2.0)*dt*20 ! dt*20 is samp interval after downsample
do j=0,1
if(j.eq.0) then
dphi0=-3*dphi
@@ -150,24 +146,76 @@ program wsprdpskd
fb=10.0
fs=12000.0/30.0
npts=120*12000.0/30.0
- nsync=16
- call getcandidate2(c2,npts,fs,fa,fb,ncand,candidates) !First approx for freq
+! call getcandidate2(c2,npts,fs,fa,fb,ncand,candidates) !First approx for freq
+ ncand=1
+ candidates(1,1)=0.0
+ candidates(1,2)=-28
ndecodes=0
do icand=1,ncand
fc0=candidates(icand,1)
xsnr=candidates(icand,2)
- fc0=0.0
call dsdpsk(c2,fc0,cd)
i0=40
do i=0,231
- cs(i)=cd(i0+10*i)
- enddo
+ cs(i)=cd(i0+10*i)/5e4
+ enddo
+! 2-bit differential detection
do i=1,231
- sbits(i)=-real(cs(i)*conjg(cs(i-1)))/5e4
+ sbits(i)=-real(cs(i)*conjg(cs(i-1)))
enddo
- rxdata(1:100)=sbits(1:100)
- rxdata(101:200)=sbits(132:231);
+! detect a differentially encoded block of symbols using the
+! Divsalar and Simon approach, except that we estimate only
+! the central symbol of the block and then step the block forward
+! by one symbol.
+!
+ sbits3=sbits
+goto 100
+ nbit=13 ! number of decoded bits to be derived from nbit+1 symbols
+ numseq=2**nbit
+ il=(nbit+1)/2
+ ih=231-nbit/2
+ do isym=il,ih
+ rmax=-1e32
+ b=0
+ do iseq=0,numseq-1
+ do i=1,nbit
+ b(i)=merge(1,0,iand(iseq,2**(nbit-i))>0)
+ enddo
+ b(1:nbit)=2*b(1:nbit)-1
+ i1=isym-(nbit+1)/2
+ csum=cs(i1)
+ do i=1,nbit
+ bb=1
+ do m=1,i
+ bb=bb*b(m)
+ enddo
+ csum=csum+bb*cs(i1+i)
+ enddo
+ ps(iseq)=abs(csum)**2
+ if(ps(iseq).gt.rmax) then
+ bbest=b
+ rmax=ps(iseq)
+ endif
+ enddo
+ if(isym.eq.il) then
+ do i=1,isym-1
+ call getmetric(2**(nbit-i),ps,numseq,xmet)
+ sbits3(i)=-xmet
+ enddo
+ endif
+ call getmetric(2**((nbit-1)/2),ps,numseq,xmet)
+ sbits3(isym)=-xmet
+ if(isym.eq.ih) then
+ do i=ih+1,231
+ call getmetric(2**(231-i),ps,numseq,xmet)
+ sbits3(i)=-xmet
+ enddo
+ endif
+ enddo
+100 continue
+ rxdata(1:100)=sbits3(1:100)
+ rxdata(101:200)=sbits3(132:231);
rxav=sum(rxdata(1:200))/200.0
rx2av=sum(rxdata(1:200)*rxdata(1:200))/200.0
rxsig=sqrt(rx2av-rxav*rxav)
@@ -227,6 +275,22 @@ program wsprdpskd
999 end program wsprdpskd
+subroutine getmetric(ib,ps,ns,xmet)
+ real ps(0:ns-1)
+ xm1=-1e32
+ xm0=-1e32
+ do i=0,ns-1
+ if( iand(i/ib,1) .eq. 1 .and. ps(i) .gt. xm1 ) then
+ xm1=ps(i)
+ endif
+ if( iand(i/ib,1) .eq. 0 .and. ps(i) .gt. xm0 ) then
+ xm0=ps(i)
+ endif
+ enddo
+ xmet=xm1-xm0
+ return
+end subroutine getmetric
+
subroutine dsdpsk(ci,f0,co)
parameter(NI=240*200,NH=NI/2,NO=NI/20) ! downsample from 200 samples per symbol to 10
complex ci(0:NI-1),ct(0:NI-1)