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48 lines
1.2 KiB
Fortran
48 lines
1.2 KiB
Fortran
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subroutine fspread_lorentz(cdat,fspread)
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parameter (NZ=3*12000)
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complex cdat(0:NZ-1)
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complex cspread(0:NZ-1)
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complex z
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twopi=8.0*atan(1.0)
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nfft=NZ
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nh=nfft/2
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df=12000.0/nfft
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cspread(0)=1.0
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cspread(nh)=0.
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b=6.0 !Use truncated Lorenzian shape for fspread
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do i=1,nh
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f=i*df
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x=b*f/fspread
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z=0.
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a=0.
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if(x.lt.3.0) then !Cutoff beyond x=3
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a=sqrt(1.111/(1.0+x*x)-0.1) !Lorentzian amplitude
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phi1=twopi*rran() !Random phase
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z=a*cmplx(cos(phi1),sin(phi1))
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endif
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cspread(i)=z
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z=0.
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if(x.lt.3.0) then !Same thing for negative freqs
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phi2=twopi*rran()
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z=a*cmplx(cos(phi2),sin(phi2))
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endif
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cspread(nfft-i)=z
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enddo
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call four2a(cspread,nfft,1,1,1) !Transform to time domain
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sum=0.
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do i=0,nfft-1
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p=real(cspread(i))**2 + aimag(cspread(i))**2
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sum=sum+p
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enddo
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avep=sum/nfft
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fac=sqrt(1.0/avep)
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cspread=fac*cspread !Normalize to constant avg power
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cdat=cspread*cdat !Apply Rayleigh fading
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return
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end subroutine fspread_lorentz
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