WSJT-X/lib/fsk4hf/genmskhf.f90

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subroutine genmskhf(msgbits,id,icw,cbb,csync)
!Encode an MSK-HF message, produce baseband waveform and sync vector.
parameter (KK=84) !Information bits (72 + CRC12)
parameter (ND=168) !Data symbols: LDPC (168,84), r=1/2
parameter (NS=65) !Sync symbols (2 x 26 + Barker 13)
parameter (NR=3) !Ramp up/down
parameter (NN=NR+NS+ND) !Total symbols (236)
parameter (NSPS=16) !Samples per MSK symbol (16)
parameter (N2=2*NSPS) !Samples per OQPSK symbol (32)
parameter (NZ=NSPS*NN) !Samples in baseband waveform (3760)
complex cbb(0:NZ-1)
complex csync(0:NZ-1)
real x(0:NZ-1)
real y(0:NZ-1)
real pp(N2)
logical first
integer*1 msgbits(KK),codeword(ND)
integer icw(ND)
integer id(NS+ND)
integer isync(26) !Long sync vector
integer ib13(13) !Barker 13 code
data ib13/1,1,1,1,1,-1,-1,1,1,-1,1,-1,1/
data first/.true./
save first,isync,twopi,pp
if(first) then
n=z'2c1aeb1'
do i=1,26
isync(i)=-1
if(iand(n,1).eq.1) isync(i)=1
n=n/2
enddo
twopi=8.0*atan(1.0)
do i=1,N2 !Half-sine shaped pulse
pp(i)=sin(0.5*(i-1)*twopi/N2)
enddo
first=.false.
endif
call encode168(msgbits,codeword) !Encode the test message
icw=2*codeword - 1
! Message structure: R1 26*(S1+D1) S13 26*(D1+S1) R1
! Generate QPSK without any offset; then shift the y array to get OQPSK.
! Do the I channel first: results in array x
n=0
k=0
ia=0
ib=NSPS-1
x(ia:ib)=0. !Ramp up (half-symbol; shape TBD)
do j=1,26 !Insert group of 26*(S1+D1)
ia=ib+1
ib=ia+N2-1
n=n+1
id(n)=2*isync(j)
x(ia:ib)=isync(j)*pp !Insert Sync bit
ia=ib+1
ib=ia+N2-1
k=k+1
n=n+1
id(n)=icw(k)
x(ia:ib)=id(n)*pp !Insert data bit
enddo
do j=1,13 !Insert Barker 13 code
ia=ib+1
ib=ia+N2-1
n=n+1
id(n)=2*ib13(j)
x(ia:ib)=ib13(j)*pp
enddo
do j=1,26 !Insert group of 26*(S1+D1)
ia=ib+1
ib=ia+N2-1
k=k+1
n=n+1
id(n)=icw(k)
x(ia:ib)=id(n)*pp !Insert data bit
ia=ib+1
ib=ia+N2-1
n=n+1
id(n)=2*isync(j)
x(ia:ib)=isync(j)*pp !Insert Sync bit
enddo
ia=ib+1
ib=ia+NSPS-1
x(ia:ib)=0. !Ramp down (half-symbol; shape TBD)
! Now do the Q channel: results in array y
ia=0
ib=NSPS-1
y(ia:ib)=0. !Ramp up (half-symbol; shape TBD)
do j=1,116
ia=ib+1
ib=ia+N2-1
k=k+1
n=n+1
id(n)=icw(k)
y(ia:ib)=id(n)*pp
enddo
ia=ib+1
ib=ia+NSPS-1
y(ia:ib)=0. !Ramp down (half-symbol; shape TBD)
y=cshift(y,-NSPS) !Shift Q array to get OQPSK
cbb=cmplx(x,y) !Complex baseband waveform
ib=NSPS-1
ib2=NSPS-1+64*N2
do j=1,26 !Zero all data symbols in x
ia=ib+1+N2
ib=ia+N2-1
x(ia:ib)=0.
ia2=ib2+1+N2
ib2=ia2+N2-1
x(ia2:ib2)=0.
enddo
csync=x
return
end subroutine genmskhf