WSJT-X/lib/fsk4hf/genbpsk.f90

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subroutine genbpsk(id,f00,ndiff,nref,c)
parameter (ND=121) !Data symbols: LDPC (120,60), r=1/2
parameter (NN=ND) !Total symbols (121)
parameter (NSPS=28800) !Samples per symbol at 12000 sps
parameter (NZ=NSPS*NN) !Samples in waveform (3456000)
complex c(0:NZ-1) !Complex waveform
real*8 twopi,dt,fs,baud,f0,dphi,phi
integer id(NN) !Encoded NRZ data (values +/-1)
integer ie(NN) !Differentially encoded data
f0=f00
twopi=8.d0*atan(1.d0)
fs=12000.d0
dt=1.0/fs
baud=1.d0/(NSPS*dt)
if(ndiff.ne.0) then
ie(1)=1 !First bit is always 1
do i=2,NN !Differentially encode
ie(i)=id(i)*ie(i-1)
enddo
endif
! Generate the BPSK waveform
phi=0.d0
k=-1
do j=1,NN
dphi=twopi*f0*dt
x=id(j)
if(ndiff.ne.0) x=ie(j) !Differential
if(nref.ne.0) x=1.0 !Generate reference carrier
do i=1,NSPS
k=k+1
phi=phi+dphi
if(phi.gt.twopi) phi=phi-twopi
xphi=phi
c(k)=x*cmplx(cos(xphi),sin(xphi))
enddo
enddo
return
end subroutine genbpsk