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