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