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63 lines
1.5 KiB
Fortran
63 lines
1.5 KiB
Fortran
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subroutine dopspread(c,fspread)
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parameter (NFFT=268800,NH=NFFT/2)
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complex c(0:NFFT-1)
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complex cspread(0:NFFT-1)
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df=12000.0/nfft
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twopi=8*atan(1.0)
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cspread(0)=1.0
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cspread(NH)=0.
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b=6.0 !Lorenzian 3/28 onward
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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
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call random_number(r1)
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phi1=twopi*r1
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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.50.0) then
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call random_number(r2)
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phi2=twopi*r2
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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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izh=fspread/df
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do i=-izh,izh
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f=i*df
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j=i
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if(j.lt.0) j=j+nfft
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s=real(cspread(j))**2 + aimag(cspread(j))**2
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! write(23,3000) f,s,cspread(j)
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!3000 format(f10.3,3f12.6)
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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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c=cspread*c !Apply Rayleigh fading to c()
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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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! write(24,3010) i,p,cspread(i)
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!3010 format(i8,3f12.6)
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enddo
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return
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end subroutine dopspread
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