242 lines
7.6 KiB
Plaintext
242 lines
7.6 KiB
Plaintext
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program dbpsksim
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parameter (ND=121) !Data symbols: LDPC (120,60), r=1/2
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parameter (NN=ND) !Total symbols (121)
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parameter (NSPS=28800) !Samples per symbol at 12000 sps
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parameter (NZ=NSPS*NN) !Samples in waveform (3484800)
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parameter (NFFT1=65536,NH1=NFFT1/2)
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parameter (NFFT2=128,NH2=NFFT2/2)
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character*8 arg
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complex c(0:NZ-1) !Complex waveform
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complex c2(0:NFFT1-1) !Short spectra
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complex cr(0:NZ-1)
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complex ct(0:NZ-1)
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complex cz(0:NFFT2-1)
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complex z0,z,zp
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real s(-NH1+1:NH1)
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real s2(-NH2+1:NH2)
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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 rxdata(120),llr(120)
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integer id(NN) !Encoded NRZ data (values +/-1)
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integer id1(NN) !Recovered data (1st pass)
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integer id2(NN) !Recovered data (2nd pass)
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! integer icw(NN)
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integer*1 msgbits(60),decoded(60),codeword(120),apmask(120),cw(120)
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data msgbits/0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,&
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0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,1,0,0,1,0,1,1,0,1,0/
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nnn=0
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nargs=iargc()
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if(nargs.ne.6) then
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print*,'Usage: dbpsksim f0(Hz) delay(ms) fspread(Hz) ndiff iters snr(dB)'
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print*,'Example: dbpsksim 1500 0 0 10 -35'
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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 !Low tone frequency
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call getarg(2,arg)
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read(arg,*) delay
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call getarg(3,arg)
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read(arg,*) fspread
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call getarg(4,arg)
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read(arg,*) ndiff
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call getarg(5,arg)
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read(arg,*) iters
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call getarg(6,arg)
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read(arg,*) snrdb
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twopi=8.d0*atan(1.d0)
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fs=12000.d0
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dt=1.0/fs
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ts=NSPS*dt
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baud=1.d0/ts
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txt=NZ*dt
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bandwidth_ratio=2500.0/6000.0
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write(*,1000) baud,5*baud,txt,delay,fspread,ndiff
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1000 format('Baud:',f6.3,' BW:',f4.1,' TxT:',f6.1,' Delay:',f5.2, &
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' fSpread:',f5.2,' ndiff:',i2/)
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write(*,1004)
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1004 format(' SNR err ber fer fsigma'/35('-'))
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call encode120(msgbits,codeword) !Encode the test message
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isna=-28
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isnb=-40
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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
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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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nhardc=0
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nfe1=0
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nfe2=0
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sqf=0.
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do iter=1,iters
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nnn=nnn+1
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id(1)=1 !First bit is always 1
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id(2:NN)=2*codeword-1
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call genbpsk(id,f0,ndiff,0,c) !Generate the 4-FSK waveform
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if(delay.ne.0.0 .or. fspread.ne.0.0) call watterson(c,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 noise to signal
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endif
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! First attempt at finding carrier frequency fc: 64k FFTs ==> avg power spectra
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nspec=NZ/NFFT1
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df1=12000.0/NFFT1
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s=0.
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do k=1,nspec
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ia=(k-1)*NSPS
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ib=ia+NSPS-1
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c2(0:NSPS-1)=c(ia:ib)
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c2(NSPS:)=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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s=1.e-6*s
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smax=0.
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ipk=0
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ia=(1400.0)/df1
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ib=(1600.0)/df1
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do i=ia,ib
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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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fc=f
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endif
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enddo
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a=(s(ipk+1)-s(ipk-1))/2.0
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b=(s(ipk+1)+s(ipk-1)-2.0*s(ipk))/2.0
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dx=-a/(2.0*b)
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fc=fc + df1*dx !Estimated carrier frequency
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sqf=sqf + (fc-f0)**2
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! The following is for testing SNR calibration:
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! sp5n=(s(ipk-2)+s(ipk-1)+s(ipk)+s(ipk+1)+s(ipk+2)) !Sig + 5*noise
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! base=(sum(s)-sp5n)/(NFFT1-5.0) !Noise per bin
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! psig=sp5n-5*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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call genbpsk(id,fc,ndiff,1,cr) !Generate reference carrier
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c=c*conjg(cr) !Mix signal to baseband
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z0=1.0
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do j=1,NN !Demodulate
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ia=(j-1)*NSPS
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ib=ia+NSPS-1
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z=sum(c(ia:ib))
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cz(j-1)=z
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zp=z*conjg(z0)
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p=1.e-4*real(zp)
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id1(j)=-1
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if(p.ge.0.0) id1(j)=1
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if(j.ge.2) rxdata(j-1)=p
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z0=z
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enddo
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rxav=sum(rxdata)/120
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rx2av=sum(rxdata*rxdata)/120
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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=10
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call bpdecode120(llr,apmask,max_iterations,decoded,niterations,cw)
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! Count frame errors
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if(niterations.lt.0 .or. count(msgbits.ne.decoded).gt.0) nfe1=nfe1+1
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! Find carrier frequency from squared cz array.
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cz(121:)=0.
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cz=cz*cz
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call four2a(cz,NFFT2,1,-1,1)
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s2max=0.
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do i=0,NFFT2-1
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j=i
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if(i.gt.NH2) j=j-NFFT2
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s2(j)=real(cz(i))**2 + aimag(cz(i))**2
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if(s2(j).gt.s2max) then
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s2max=s2(j)
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jpk=j
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endif
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! write(16,1200) j*baud/NFFT2,1.e-12*s2(j)
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!1200 format(2f12.3)
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enddo
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a=(s2(jpk+1)-s2(jpk-1))/2.0
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b=(s2(jpk+1)+s2(jpk-1)-2.0*s2(jpk))/2.0
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dx=-a/(2.0*b)
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fc2=0.5*(jpk+dx)*baud/NFFT2
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call genbpsk(id,fc2,ndiff,1,cr) !Generate new ref carrier at fc2
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c=c*conjg(cr)
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z0=1.0
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do j=1,NN !Demodulate
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ia=(j-1)*NSPS
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ib=ia+NSPS-1
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z=sum(c(ia:ib))
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if(j.eq.1) z0=z
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zp=z*conjg(z0)
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p=1.e-4*real(zp)
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id2(j)=-1
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if(p.ge.0.0) id2(j)=1
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if(j.ge.2) rxdata(j-1)=p
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ierr=0
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if(id2(j).ne.id(j)) ierr=1
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id3=-1
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if(real(z).ge.0.0) id3=1
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if(j.ge.2 .and. id3.ne.id(j)) nhardc=nhardc+1
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if(j.ge.2 .and. ndiff.eq.0) rxdata(j-1)=real(z)
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z0=z
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enddo
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nhard=nhard + count(id2.ne.id) !Count hard errors
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rxav=sum(rxdata)/120
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rx2av=sum(rxdata*rxdata)/120
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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) !Soft symbols
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apmask=0
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max_iterations=10
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decoded=0
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call bpdecode120(llr,apmask,max_iterations,decoded,niterations,cw)
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! if(niterations.lt.0) then
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! llr=-llr
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! call bpdecode120(llr,apmask,max_iterations,decoded,niterations,cw)
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! if(niterations.ge.0) nhard=NN*iters-nhard
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! endif
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if(niterations.ge.0) call chkcrc10(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) nfe2=nfe2+1
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enddo
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if(ndiff.eq.0) nhard=nhardc
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fsigma=sqrt(sqf/iters)
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ber=float(nhard)/(NN*iters)
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fer=float(nfe2)/iters
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write(*,1050) snrdb,nhard,ber,fer,fsigma
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write(14,1050) snrdb,nhard,ber,fer,fsigma
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1050 format(f6.1,i5,f8.4,f7.3,f8.2)
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enddo
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999 end program dbpsksim
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