diff --git a/lib/ft4/ft4_decode.f90 b/lib/ft4/ft4_decode.f90
index 95f725829..f8515ac56 100644
--- a/lib/ft4/ft4_decode.f90
+++ b/lib/ft4/ft4_decode.f90
@@ -3,6 +3,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
use packjt77
include 'ft4_params.f90'
parameter (NSS=NSPS/NDOWN)
+
character message*37
character c77*77
character*61 line
@@ -13,7 +14,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
complex cd2(0:NMAX/NDOWN-1) !Complex waveform
complex cb(0:NMAX/NDOWN-1)
- complex cd(0:NN*NSS-1) !Complex waveform
+ complex cd(0:NN*NSS-1) !Complex waveform
complex ctwk(4*NSS),ctwk2(4*NSS)
complex csymb(NSS)
complex cs(0:3,NN)
@@ -26,6 +27,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
real s2(0:255)
real candidate(3,100)
real savg(NH1),sbase(NH1)
+
integer icos4(0:3)
integer*2 iwave(NMAX) !Generated full-length waveform
integer*1 message77(77),apmask(2*ND),cw(2*ND)
@@ -35,16 +37,17 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
logical unpk77_success
logical one(0:255,0:7) ! 256 4-symbol sequences, 8 bits
logical first
+
data icos4/0,1,3,2/
data graymap/0,1,3,2/
data first/.true./
- save one
+ save one,first
hhmmss=cdatetime0(8:13)
- fs=12000.0/NDOWN !Sample rate
- dt=1/fs !Sample interval after downsample (s)
- tt=NSPS*dt !Duration of "itone" symbols (s)
- txt=NZ*dt !Transmission length (s)
+ fs=12000.0/NDOWN !Sample rate after downsampling
+ dt=1/fs !Sample interval after downsample (s)
+ tt=NSPS*dt !Duration of "itone" symbols (s)
+ txt=NZ*dt !Transmission length (s) without ramp up/down
twopi=8.0*atan(1.0)
h=1.0
@@ -58,30 +61,29 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
first=.false.
endif
- data_dir="."
- fMHz=7.074
-
candidate=0.0
ncand=0
-
- fa=400.0
- fb=3000.0
syncmin=1.2
maxcand=100
-! call syncft4(iwave,nfa,nfb,syncmin,nfqso,maxcand,s,candidate,ncand,sbase)
- call getcandidates4(iwave,fa,fb,syncmin,nfqso,100,savg,candidate,ncand,sbase)
+! These are temporary. Correct values should be passed in as arguments.
+ data_dir="."
+ fMHz=7.074
+ fa=400.0
+ fb=3000.0
+
+ call getcandidates4(iwave,fa,fb,syncmin,nfqso,maxcand,savg,candidate, &
+ ncand,sbase)
+
ndecodes=0
do icand=1,ncand
f0=candidate(1,icand)
xsnr=10*log10(candidate(3,icand))-18.0
- if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle
- call ft4_downsample(iwave,f0,cd2) ! downsample from 512 Sa/Symbol to 32 Sa/Symbol
+ if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle !### TBD? ###
+ call ft4_downsample(iwave,f0,cd2) !Downsample to 32 Samples/Symbol
sum2=sum(cd2*conjg(cd2))/(20.0*76)
if(sum2.gt.0.0) cd2=cd2/sqrt(sum2)
-
-! 750 samples/second here
-
+! Sample rate is now 12000/16 = 750 samples/second
do isync=1,2
if(isync.eq.1) then
idfmin=-50
@@ -107,7 +109,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
ctwk=1.
call twkfreq1(ctwk,4*NSS,fs,a,ctwk2)
do istart=ibmin,ibmax,ibstp
- call sync4d(cd2,istart,ctwk2,1,sync)
+ call sync4d(cd2,istart,ctwk2,1,sync) !Find sync power
if(sync.gt.smax) then
smax=sync
ibest=istart
@@ -118,7 +120,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
enddo
f0=f0+real(idfbest)
- call ft4_downsample(iwave,f0,cb) ! downsample from 320s/Symbol to 20s/Symbol
+ call ft4_downsample(iwave,f0,cb) !Final downsample with corrected f0
sum2=sum(abs(cb)**2)/(real(NSS)*NN)
if(sum2.gt.0.0) cb=cb/sqrt(sum2)
cd=cb(ibest:ibest+NN*NSS-1)
@@ -130,7 +132,7 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
s4(0:3,k)=abs(csymb(1:4))
enddo
-! sync quality check
+! Sync quality check
is1=0
is2=0
is3=0
@@ -145,10 +147,9 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
ip=maxloc(s4(:,k+99))
if(icos4(k-1).eq.(ip(1)-1)) is4=is4+1
enddo
-! hard sync sum - max is 16
- nsync=is1+is2+is3+is4
+ nsync=is1+is2+is3+is4 !Number of hard sync errors, 0-16
- do nseq=1,3
+ do nseq=1,3 !Try coherent sequences of 1, 2, and 4 symbols
if(nseq.eq.1) nsym=1
if(nseq.eq.2) nsym=2
if(nseq.eq.3) nsym=4
@@ -233,7 +234,8 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
llr2=llr
if(ibias.eq.1) llr2=llr+0.4
if(ibias.eq.2) llr2=llr-0.4
- call bpdecode174_91(llr2,apmask,max_iterations,message77,cw,nharderror,niterations)
+ call bpdecode174_91(llr2,apmask,max_iterations,message77, &
+ cw,nharderror,niterations)
if(nharderror.ge.0) exit
enddo
if(sum(message77).eq.0) cycle
@@ -256,11 +258,12 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
write(24,1002) cdatetime0,nsnr,ibest/750.0,nint(freq),message, &
nharderror,nsync_qual,isd,niterations
if(hhmmss.eq.' ') write(*,1002) cdatetime0,nsnr, &
- ibest/750.0,nint(freq),message,nharderror,nsync_qual,isd,niterations
+ ibest/750.0,nint(freq),message,nharderror,nsync_qual,isd, &
+ niterations
1002 format(a17,i4,f6.2,i5,' Rx ',a37,4i5)
close(24)
-!### Temporary: assume most recent decoded message conveys "hiscall".
+!### Temporary: assume most recent decoded message conveys "hiscall". ###
i0=index(message,' ')
if(i0.ge.3 .and. i0.le.7) then
hiscall=message(i0+1:i0+6)
@@ -279,8 +282,8 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
exit
endif
- enddo ! sequence estimation
- enddo !candidate list
+ enddo !Sequence estimation
+ enddo !Candidate list
return
end subroutine ft4_decode
@@ -317,6 +320,7 @@ subroutine ft4_downsample(iwave,f0,c)
c1=c1/NFFT2
call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
c=c1(0:NMAX/NDOWN-1)
+
return
end subroutine ft4_downsample
diff --git a/lib/ft4/ft4_params.f90 b/lib/ft4/ft4_params.f90
index 5acd63e59..4a14e7c95 100644
--- a/lib/ft4/ft4_params.f90
+++ b/lib/ft4/ft4_params.f90
@@ -1,12 +1,14 @@
! FT4
-! LDPC (174,91) code
+! LDPC(174,91) code, four 4x4 Costas arrays for Sync
parameter (KK=91) !Information bits (77 + CRC14)
parameter (ND=87) !Data symbols
parameter (NS=16) !Sync symbols
-parameter (NN=NS+ND) !Total channel symbols (103)
+parameter (NN=NS+ND) !Sync and data symbols (103)
+parameter (NN2=NS+ND+2) !Total channel symbols (105)
parameter (NSPS=512) !Samples per symbol at 12000 S/s
-parameter (NZ=NSPS*NN) !Samples in full 4.395 s message frame (52736)
+parameter (NZ=NSPS*NN) !Sync and Data samples (52736)
+parameter (NZ2=NSPS*NN2) !Total samples in shaped waveform (53760)
parameter (NMAX=5.0*12000) !Samples in iwave (60,000)
parameter (NFFT1=2048, NH1=NFFT1/2) !Length of FFTs for symbol spectra
parameter (NSTEP=NSPS/4) !Coarse time-sync step size