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For fst4sim, use Lorentzian fading spectrum when fspread is negative.
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@ -118,7 +118,8 @@ program fst4sim
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do ifile=1,nfiles
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c=c0
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if(fspread.ne.0.0 .or. delay.ne.0.0) call watterson(c,nwave,NZ,fs,delay,fspread)
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if(fspread.gt.0.0 .or. delay.ne.0.0) call watterson(c,nwave,NZ,fs,delay,fspread)
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if(fspread.lt.0.0) call lorentzian_fading(c,nwave,fs,-fspread)
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c=sig*c
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wave=real(c)
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if(snrdb.lt.90) then
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43
lib/fst4/lorentzian_fading.f90
Normal file
43
lib/fst4/lorentzian_fading.f90
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@ -0,0 +1,43 @@
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subroutine lorentzian_fading(c,npts,fs,fspread)
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!
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! npts is the total length of the simulated data vector
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!
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complex c(0:npts-1)
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complex cspread(0:npts-1)
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complex z
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twopi=8.0*atan(1.0)
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df=fs/npts
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nh=npts/2
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cspread(0)=1.0
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cspread(nh)=0.
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b=6.0
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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
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a=sqrt(1.111/(1.0+x*x)-0.1)
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phi1=twopi*rran()
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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
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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(npts-i)=z
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enddo
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call four2a(cspread,npts,1,1,1)
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s=sum(abs(cspread)**2)
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avep=s/npts
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fac=sqrt(1.0/avep)
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cspread=fac*cspread
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c=cspread*c
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return
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end subroutine lorentzian_fading
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