Improvements to a7 decoding for FT8.

This commit is contained in:
Joe Taylor 2021-10-29 15:28:42 -04:00
parent 48b1ad1e46
commit f13e318204
2 changed files with 225 additions and 9 deletions

209
lib/ft8_a7.f90 Normal file
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@ -0,0 +1,209 @@
module ft8_a7
parameter(MAXDEC=100)
! For the following three arrays
! First index i=decode number in this sequence
! Second index j=0 or 1 for even or odd sequence
! Third index k=0 or 1 for previous or current tally for this j
real dt0(MAXDEC,0:1,0:1) !dt0(i,j,k)
real f0(MAXDEC,0:1,0:1) !f0(i,j,k)
character*37 msg0(MAXDEC,0:1,0:1) !msg0(i,j,k)
integer jseq !even=0, odd=1
integer ndec(0:1,0:1) !ndec(j,k)
data ndec/4*0/,jseq/0/
contains
subroutine ft8_a7_save(nutc,dt,f,msg)
use packjt77
character*37 msg,msg1
character*13 w(19)
character*4 g4
integer nw(19)
logical isgrid4
! Statement function:
isgrid4(g4)=(len_trim(g4).eq.4 .and. &
ichar(g4(1:1)).ge.ichar('A') .and. ichar(g4(1:1)).le.ichar('R') .and. &
ichar(g4(2:2)).ge.ichar('A') .and. ichar(g4(2:2)).le.ichar('R') .and. &
ichar(g4(3:3)).ge.ichar('0') .and. ichar(g4(3:3)).le.ichar('9') .and. &
ichar(g4(4:4)).ge.ichar('0') .and. ichar(g4(4:4)).le.ichar('9'))
j=mod(nutc/5,2) !j is 0 or 1 for odd/even sequence
jseq=j
! Add this decode to current table for this sequence
ndec(j,1)=ndec(j,1)+1 !Number of decodes in this sequence
i=ndec(j,1) !i is pointer to new table entry
if(i.ge.MAXDEC-1) return !Prevent table overflow
if(index(msg,'<...>').ge.1) return !Don't save an unknown hashcall
dt0(i,j,1)=dt !Save dt in table
f0(i,j,1)=f !Save f in table
f0(i+1,j,1)=-99.0 !Flag after last entry in current table
call split77(msg,nwords,nw,w) !Parse msg into words
msg0(i,j,1)=trim(w(1))//' '//trim(w(2))
if(w(1)(1:3).eq.'CQ ' .and. nw(2).le.2) then
msg0(i,j,1)='CQ '//trim(w(2))//' '//trim(w(3))
endif
msg1=msg0(i,j,1) !Message without grid
nn=len(trim(msg1)) !Message length without grid
if(isgrid4(w(nwords))) msg0(i,j,1)=trim(msg0(i,j,1))//' '//trim(w(nwords))
! If a transmission at this frequency with this message fragment
! was decoded in the previous sequence, flag it as "DO NOT USE" because
! we have already decoded that station's next transmission.
call split77(msg1,nwords,nw,w) !Parse msg into words
do i=1,ndec(j,0)
if(f0(i,j,0).le.-98.0) cycle
i2=index(msg0(i,j,0),' '//trim(w(2)))
if(abs(f-f0(i,j,0)).lt.2.0 .and. i2.ge.3) then
f0(i,j,0)=-98.0 !Remove from list of to-be-tried a7 decodes
endif
enddo
return
end subroutine ft8_a7_save
subroutine ft8_dec7(cd,xdt0,f0,msg0,xdt,xsnr,msgbest,snr7,snr7b)
! Get a7 (q3-style) decodes for FT8.
use packjt77
parameter(NN=79,NSPS=32)
parameter(NWAVE=NN*NSPS) !2528
parameter(NZ=3200,NLAGS=NZ-NWAVE)
parameter(MAXMSG=206)
character*12 call_1,call_2
character*13 w(19)
character*4 grid4
character*37 msg0,msg,msgbest,msgsent
character c77*77
complex cwave(0:NWAVE-1)
complex cd(0:NZ-1)
complex z
real xjunk(NWAVE)
real ccf(0:NLAGS-1)
real ccfmsg(MAXMSG)
integer itone(NN)
integer nw(19)
integer*1 msgbits(77)
logical std_1,std_2
if(xdt0.eq.-999.0) return !Silence compiler warning
snr7=0.
ccfmsg=0.
call split77(msg0,nwords,nw,w) !Parse msg0 into words
call_1=w(1)(1:12)
call_2=w(2)(1:12)
grid4=w(3)(1:4)
if(call_1(1:3).eq.'CQ_') call_1(3:3)=' '
call stdcall(call_1,std_1)
if(call_1(1:3).eq.'CQ ') std_1=.true.
call stdcall(call_2,std_2)
fs=200.0 !Sample rate (Hz)
bt=2.0
ccfbest=0.
lagbest=-1
imsgbest=1
do imsg=1,MAXMSG
msg=trim(call_1)//' '//trim(call_2)
i=imsg
if(call_1(1:3).eq.'CQ ' .and. i.ne.5) msg='CQ0XYZ '//trim(call_2)
if(.not.std_1) then
if(i.eq.1 .or. i.ge.6) msg='<'//trim(call_1)//'> '//trim(call_2)
if(i.ge.2 .and. i.le.4) msg=trim(call_1)//' <'//trim(call_2)//'>'
else if(.not.std_2) then
if(i.le.4 .or. i.eq.6) msg='<'//trim(call_1)//'> '//trim(call_2)
if(i.ge.7) msg=trim(call_1)//' <'//trim(call_2)//'>'
endif
j0=len(trim(msg))+2
if(i.eq.2) msg(j0:j0+2)='RRR'
if(i.eq.3) msg(j0:j0+3)='RR73'
if(i.eq.4) msg(j0:j0+1)='73'
if(i.eq.5) then
if(std_2) then
msg='CQ '//trim(call_2)
if(call_1(3:3).eq.'_') msg=trim(call_1)//' '//trim(call_2)
if(grid4.ne.'RR73') msg=trim(msg)//' '//grid4
endif
if(.not.std_2) msg='CQ '//trim(call_2)
endif
if(i.eq.6 .and. std_2) msg(j0:j0+3)=grid4
if(i.ge.7) then
isnr = -50 + (i-7)/2
if(iand(i,1).eq.1) then
write(msg(j0:j0+2),'(i3.2)') isnr
if(msg(j0:j0).eq.' ') msg(j0:j0)='+'
else
write(msg(j0:j0+3),'("R",i3.2)') isnr
if(msg(j0+1:j0+1).eq.' ') msg(j0+1:j0+1)='+'
endif
endif
! Source-encode, then get itone()
i3=-1
n3=-1
call pack77(msg,i3,n3,c77)
call genft8(msg,i3,n3,msgsent,msgbits,itone)
! Generate complex cwave
f00=0.0
call gen_ft8wave(itone,NN,NSPS,bt,fs,f00,cwave,xjunk,1,NWAVE)
lagmax=-1
ccfmax=0.
nsum=32*2
lag0=200.0*(xdt0+0.5)
lag1=max(0,lag0-20)
lag2=min(nlags-1,lag0+20)
do lag=lag1,lag2
z=0.
s=0.
do i=0,NWAVE-1
z=z + cd(i+lag)*conjg(cwave(i))
if(mod(i,nsum).eq.nsum-1 .or. i.eq.NWAVE-1) then
s=s + abs(z)
z=0.
endif
enddo
ccf(lag)=s
if(ccf(lag).gt.ccfmax) then
ccfmax=ccf(lag)
lagmax=lag
endif
enddo ! lag
ccfmsg(imsg)=ccfmax
if(ccfmax.gt.ccfbest) then
ccfbest=ccfmax
lagbest=lagmax
msgbest=msg
imsgbest=imsg
endif
enddo ! imsg
call pctile(ccfmsg,MAXMSG,50,base)
call pctile(ccfmsg,MAXMSG,84,sigma)
sigma=sigma-base
if(sigma.eq.0.0) sigma=1.0
ccfmsg=(ccfmsg-base)/sigma
xdt=lagbest/200.0 - 0.5
snr7=maxval(ccfmsg)
ccfmsg(imsgbest)=0.
snr7b=snr7/maxval(ccfmsg)
if(index(msgbest,'CQ0XYZ').ge.1) snr7=0.
xsnr=-99.0
if(snr7.gt.4.0) xsnr=db(snr7)-24.0
return
end subroutine ft8_dec7
end module ft8_a7

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@ -237,17 +237,24 @@ contains
do i=1,ndec(jseq,0)
if(f0(i,jseq,0).eq.-99.0) exit
if(f0(i,jseq,0).eq.-98.0) cycle
if(index(msg0(i,jseq,0),'<').ge.1) cycle !### Temporary ###
call ft8_downsample(dd,newdat,f0(i,jseq,0),cd0)
call ft8_dec7(cd0,dt0(i,jseq,0),f0(i,jseq,0),msg0(i,jseq,0), &
xdt,xsnr,msg37)
if(xsnr.gt.-99.0) then
if(associated(this%callback)) then
nsnr=nint(xsnr)
f1=f0(i,jseq,0)
iaptype=7
qual=1.0
call this%callback(sync,nsnr,xdt,f1,msg37,iaptype,qual)
endif
xdt,xsnr,msg37,snr7,snr7b)
ddt=xdt-dt0(i,jseq,0)
write(41,3041) nutc,snr7,snr7b,xdt,ddt,nint(f0(i,jseq,0)),trim(msg37)
3041 format(i6.6,3f7.2,2f6.2,i5,2x,a)
if(snr7.lt.6.0 .or. snr7b.lt.1.8) cycle
write(42,3041) nutc,snr7,snr7b,xdt,ddt,nint(f0(i,jseq,0)),trim(msg37)
flush(41)
flush(42)
if(xsnr.gt.-99.0 .and. associated(this%callback)) then
nsnr=xsnr
f1=f0(i,jseq,0)
iaptype=7
qual=1.0
call this%callback(sync,nsnr,xdt,f1,msg37,iaptype,qual)
! Call subtract here?
endif
newdat=.false.
enddo