WSJT-X/lib/fsk4hf/mskhfsim.f90
Joe Taylor 3124648fbc Add/update some experimental routines.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7636 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2017-04-19 16:06:42 +00:00

348 lines
12 KiB
Fortran

program msksim
! Simulate characteristics of a potential "MSK10" mode using LDPC (168,84)
! code, OQPDK modulation, and 30 s T/R sequences.
! Reception and Demodulation algorithm:
! 1. Compute coarse spectrum; find fc1 = approx carrier freq
! 2. Mix from fc1 to 0; LPF at +/- 0.75*R
! 3. Square, FFT; find peaks near -R/2 and +R/2 to get fc2
! 4. Mix from fc2 to 0
! 5. Fit cb13 (central part of csync) to c -> lag, phase
! 6. Fit complex ploynomial for channel equalization
! 7. Get soft bits from equalized data
parameter (KK=84) !Information bits (72 + CRC12)
parameter (ND=168) !Data symbols: LDPC (168,84), r=1/2
parameter (NS=65) !Sync symbols (2 x 26 + Barker 13)
parameter (NR=3) !Ramp up/down
parameter (NN=NR+NS+ND) !Total symbols (236)
parameter (NSPS=16) !Samples per MSK symbol (16)
parameter (N2=2*NSPS) !Samples per OQPSK symbol (32)
parameter (N13=13*N2) !Samples in central sync vector (416)
parameter (NZ=NSPS*NN) !Samples in baseband waveform (3760)
parameter (NFFT1=4*NSPS,NH1=NFFT1/2)
character*8 arg
complex cbb(0:NZ-1) !Complex baseband waveform
complex csync(0:NZ-1) !Sync symbols only, from cbb
complex cb13(0:N13-1) !Barker 13 waveform
complex c(0:NZ-1) !Complex waveform
complex cs(0:NZ-1) !For computing spectrum
complex c2(0:NFFT1-1) !Short spectra
complex zz(NS+ND) !Complex symbol values (intermediate)
complex z,z0
real s(-NH1+1:NH1) !Coarse spectrum
real xnoise(0:NZ-1) !Generated random noise
real ynoise(0:NZ-1) !Generated random noise
real x(NS),yi(NS),yq(NS) !For complex polyfit
real rxdata(ND),llr(ND) !Soft symbols
real pp(2*NSPS) !Shaped pulse for OQPSK
real a(5) !For twkfreq1
real aa(20),bb(20) !Fitted polyco's
integer id(NS+ND) !NRZ values (+/-1) for Sync and Data
integer icw(NN)
integer*1 msgbits(KK),decoded(KK),apmask(ND),cw(ND)
! integer*1 codeword(ND)
data msgbits/0,0,1,0,0,1,1,1,1,0,0,1,0,0,0,0,0,0,0,0,1,0,0,0,1,1,0,0,0,1, &
1,1,1,0,1,1,1,1,1,1,1,0,0,1,0,0,1,1,0,1,0,1,1,1,0,1,1,0,1,1, &
1,1,0,1,0,1,1,0,0,0,0,0,1,0,0,0,0,0,1,0,1,0,1,0/
nargs=iargc()
if(nargs.ne.6) then
print*,'Usage: msksim f0(Hz) delay(ms) fspread(Hz) maxn iters snr(dB)'
print*,'Example: msksim 20 0 0 5 10 -20'
print*,'Set snr=0 to cycle through a range'
go to 999
endif
call getarg(1,arg)
read(arg,*) f0 !Generated carrier frequency
call getarg(2,arg)
read(arg,*) delay !Delta_t (ms) for Watterson model
call getarg(3,arg)
read(arg,*) fspread !Fspread (Hz) for Watterson model
call getarg(4,arg)
read(arg,*) maxn !Max nterms for polyfit
call getarg(5,arg)
read(arg,*) iters !Iterations at each SNR
call getarg(6,arg)
read(arg,*) snrdb !Specified SNR_2500
twopi=8.0*atan(1.0)
fs=12000.0/72.0 !Sample rate = 166.6666667 Hz
dt=1.0/fs !Sample interval (s)
tt=NSPS*dt !Duration of "itone" symbols (s)
ts=2*NSPS*dt !Duration of OQPSK symbols (s)
baud=1.0/tt !Keying rate for "itone" symbols (baud)
txt=NZ*dt !Transmission length (s)
bandwidth_ratio=2500.0/(fs/2.0)
write(*,1000) f0,delay,fspread,maxn,iters,baud,1.5*baud,txt
1000 format('f0:',f5.1,' Delay:',f4.1,' fSpread:',f5.2,' maxn:',i3, &
' Iters:',i6/'Baud:',f7.3,' BW:',f5.1,' TxT:',f5.1,f5.2/)
write(*,1004)
1004 format(/' SNR err ber fer fsigma'/37('-'))
do i=1,N2 !Half-sine pulse shape
pp(i)=sin(0.5*(i-1)*twopi/(2*NSPS))
enddo
call genmskhf(msgbits,id,icw,cbb,csync) !Generate baseband waveform and csync
cb13=csync(1680:2095) !Copy the Barker 13 waveform
a=0.
a(1)=f0
call twkfreq1(cbb,NZ,fs,a,cbb) !Mix to specified frequency
isna=-10
isnb=-30
if(snrdb.ne.0.0) then
isna=nint(snrdb)
isnb=isna
endif
do isnr=isna,isnb,-1 !Loop over SNR range
snrdb=isnr
sig=sqrt(bandwidth_ratio) * 10.0**(0.05*snrdb)
if(snrdb.gt.90.0) sig=1.0
nhard=0
nhardsync=0
nfe=0
sqf=0.
do iter=1,iters !Loop over requested iterations
nhard0=0
nhardsync0=0
c=cbb
if(delay.ne.0.0 .or. fspread.ne.0.0) call watterson(c,fs,delay,fspread)
c=sig*c !Scale to requested SNR
if(snrdb.lt.90) then
do i=0,NZ-1 !Generate gaussian noise
xnoise(i)=gran()
ynoise(i)=gran()
enddo
c=c + cmplx(xnoise,ynoise) !Add AWGN noise
endif
!----------------------------------------------------------------- fc1
! First attempt at finding carrier frequency, fc1: low-resolution power spectra
nspec=NZ/NFFT1
df1=fs/NFFT1
s=0.
do k=1,nspec
ia=(k-1)*N2
ib=ia+N2-1
c2(0:N2-1)=c(ia:ib)
c2(N2:)=0.
call four2a(c2,NFFT1,1,-1,1)
do i=0,NFFT1-1
j=i
if(j.gt.NH1) j=j-NFFT1
s(j)=s(j) + real(c2(i))**2 + aimag(c2(i))**2
enddo
enddo
! call smo121(s,NFFT1)
smax=0.
ipk=0
fc1=0.
ia=nint(40.0/df1)
do i=-ia,ia
f=i*df1
if(s(i).gt.smax) then
smax=s(i)
ipk=i
fc1=f
endif
! write(51,3001) f,s(i),db(s(i))
! 3001 format(f10.3,e12.3,f10.3)
enddo
! The following is for testing SNR calibration:
! sp3n=(s(ipk-1)+s(ipk)+s(ipk+1)) !Sig + 3*noise
! base=(sum(s)-sp3n)/(NFFT1-3.0) !Noise per bin
! psig=sp3n-3*base !Sig only
! pnoise=(2500.0/df1)*base !Noise in 2500 Hz
! xsnrdb=db(psig/pnoise)
a(1)=-fc1
a(2:5)=0.
call twkfreq1(c,NZ,fs,a,cs) !Mix down by fc1
!----------------------------------------------------------------- fc2
! Filter, square, then FFT to get refined carrier frequency fc2.
call four2a(cs,NZ,1,-1,1) !To freq domain
df=fs/NZ
ia=nint(0.75*baud/df)
cs(ia:NZ-1-ia)=0. !Save only freqs around fc1
call four2a(cs,NZ,1,1,1) !Back to time domain
cs=cs/NZ
cs=cs*cs !Square the data
call four2a(cs,NZ,1,-1,1) !Compute squared spectrum
! Find two peaks separated by baud
pmax=0.
fc2=0.
ic=nint(baud/df)
ja=nint(0.5*baud/df)
do j=-ja,ja
f2=j*df
ia=nint((f2-0.5*baud)/df)
if(ia.lt.0) ia=ia+NZ
ib=nint((f2+0.5*baud)/df)
p=real(cs(ia))**2 + aimag(cs(ia))**2 + &
real(cs(ib))**2 + aimag(cs(ib))**2
if(p.gt.pmax) then
pmax=p
fc2=0.5*f2
endif
! write(52,1200) f2,p,db(p)
!1200 format(f10.3,2f15.3)
enddo
sqf=sqf + (fc1+fc2-f0)**2
a(1)=-(fc1+fc2)
a(2:5)=0.
call twkfreq1(c,NZ,fs,a,c) !Mix c down by fc1+fc2
! z=sum(c(1680:2095)*cb13)/208.0 !Get phase from Barker 13 vector
! z0=z/abs(z)
! c=c*conjg(z0)
!---------------------------------------------------------------- DT
amax=0.
jpk=0
do j=-20*NSPS,20*NSPS !Get jpk
z=sum(c(1680+j:2095+j)*cb13)/208.0
if(abs(z).gt.amax) then
amax=abs(z)
jpk=j
endif
! write(53,1220) j,j*dt,z
!1220 format(i6,3f10.4)
enddo
xdt=jpk/fs
!------------------------------------------------------------------ cpolyfit
ib=NSPS-1
ib2=N2-1
n=0
do j=1,117 !First-pass demodulation
ia=ib+1
ib=ia+N2-1
zz(j)=sum(pp*c(ia:ib))/NSPS
if(abs(id(j)).eq.2) then !Save all sync symbols
n=n+1
x(n)=float(ia+ib)/NZ - 1.0
yi(n)=real(zz(j))*0.5*id(j)
yq(n)=aimag(zz(j))*0.5*id(j)
! write(54,1225) n,x(n),yi(n),yq(n)
!1225 format(i5,3f12.4)
endif
if(j.le.116) then
zz(j+117)=sum(pp*c(ia+NSPS:ib+NSPS))/NSPS
endif
enddo
aa=0.
bb=0.
nterms=0
if(maxn.gt.0) then
! Fit sync info with a complex polynomial
npts=n
mode=0
chisqa0=1.e30
chisqb0=1.e30
do nterms=1,maxn
call polyfit4(x,yi,yi,npts,nterms,mode,aa,chisqa)
call polyfit4(x,yq,yq,npts,nterms,mode,bb,chisqb)
if(chisqa/chisqa0.ge.0.98 .and. chisqb/chisqb0.ge.0.98) exit
chisqa0=chisqa
chisqb0=chisqb
enddo
endif
!-------------------------------------------------------------- Soft Symbols
n=0
do j=1,117
xx=j*2.0/117.0 - 1.0
yii=1.
yqq=0.
if(nterms.gt.0) then
yii=aa(1)
yqq=bb(1)
do i=2,nterms
yii=yii + aa(i)*xx**(i-1)
yqq=yqq + bb(i)*xx**(i-1)
enddo
endif
z0=cmplx(yii,yqq)
z=zz(j)*conjg(z0)
if(abs(id(j)).eq.2) then
if(real(z)*id(j).lt.0) then
nhardsync=nhardsync+1
nhardsync0=nhardsync0+1
endif
! write(55,2002) j,id(j)/2,xx,z*id(j)/2 !Sync bit
!2002 format(2i5,3f10.3)
else
p=real(z) !Data bit
n=n+1
rxdata(n)=p
ierr=0
if(id(j)*p.lt.0) ierr=1
nhard0=nhard0+ierr
nhard=nhard+ierr
! write(56,2003) j,id(j),n,ierr,nhard,xx,p*id(j),z
!2003 format(5i6,4f10.3)
endif
enddo
do j=118,233
xx=(j-116.5)*2.0/117.0 - 1.0
yii=1.
yqq=0.
if(nterms.gt.0) then
yii=aa(1)
yqq=bb(1)
do i=2,nterms
yii=yii + aa(i)*xx**(i-1)
yqq=yqq + bb(i)*xx**(i-1)
enddo
endif
z0=cmplx(yii,yqq)
z=zz(j)*conjg(z0)
p=aimag(z)
n=n+1
rxdata(n)=p
ierr=0
if(id(j)*p.lt.0) ierr=1
nhard=nhard+ierr
enddo
rxav=sum(rxdata)/ND
rx2av=sum(rxdata*rxdata)/ND
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
ss=0.84
llr=2.0*rxdata/(ss*ss)
apmask=0
max_iterations=40
call bpdecode168(llr,apmask,max_iterations,decoded,niterations,cw)
nbadcrc=0
ifer=0
if(niterations.ge.0) call chkcrc12(decoded,nbadcrc)
if(niterations.lt.0 .or. count(msgbits.ne.decoded).gt.0 .or. &
nbadcrc.ne.0) ifer=1
nfe=nfe+ifer
write(58,1045) snrdb,nhard0,nhardsync0,niterations,nbadcrc,ifer, &
nterms,fc1+fc2-f0,xdt
if(ifer.eq.1) write(59,1045) snrdb,nhard0,nhardsync0,niterations, &
nbadcrc,ifer,nterms,fc1+fc2-f0,xdt
1045 format(f6.1,6i5,2f8.3)
enddo
fsigma=sqrt(sqf/iters)
ber=float(nhard)/((NS+ND)*iters)
fer=float(nfe)/iters
write(*,1050) snrdb,nhard,ber,fer,fsigma
write(60,1050) snrdb,nhard,ber,fer,fsigma
1050 format(f6.1,i7,f8.4,f7.3,f8.2)
enddo
999 end program msksim