mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-03-23 12:38:53 -04:00
Test program to simulate MSK modulation and coherent reception.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6478 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
parent
2994a924e5
commit
b88affa2ee
112
lib/mskber.f90
Normal file
112
lib/mskber.f90
Normal file
@ -0,0 +1,112 @@
|
||||
program mskber
|
||||
|
||||
! Generate an MSK waveform, pass it through an AWGN channel, apply coherent
|
||||
! MSK receiver, and count number of errors at each Eb/No.
|
||||
|
||||
parameter (NSYM=100000) !Number of symbols to test
|
||||
parameter (NSPS=6) !Samples per symbol
|
||||
real ct(-NSPS:NSPS*NSYM-1) !cos(pi*t/2T)
|
||||
real st(-NSPS:NSPS*NSYM-1) !sin(pi*t/2T)
|
||||
real r(NSYM) !Random numbers to determine test bits
|
||||
real ai(0:NSPS*(NSYM+1)-1) !Rectangular pulses for even symbols
|
||||
real aq(0:NSPS*(NSYM+1)-1) !Rectangular pulses for odd symbols
|
||||
|
||||
real xe(0:NSPS*(NSYM+3)-1) !Temp array for received even symbols
|
||||
real xo(0:NSPS*(NSYM+3)-1) !Temp array for received odd symbols
|
||||
real xsym(0:NSYM-1) !Soft Rx symbols
|
||||
|
||||
complex xt(0:NSPS*(NSYM+1)-1) !Complex baseband Tx waveform
|
||||
complex nt(0:NSPS*(NSYM+1)-1) !Generated AWGN channel noise
|
||||
complex yt(0:NSPS*(NSYM+1)-1) !Received signal, yt = xt + fac*nt
|
||||
|
||||
integer sym0(0:NSYM-1) !Generated test bits
|
||||
integer sym(0:NSYM-1) !Hard-copy received bits
|
||||
|
||||
pi=4.0*atan(1.0)
|
||||
iz=NSPS*(NSYM+1)
|
||||
|
||||
do i=-NSPS,NSPS*NSYM-1 !Define ct, st arrays
|
||||
t=i*pi/(2.0*NSPS)
|
||||
ct(i)=cos(t)
|
||||
st(i)=sin(t)
|
||||
enddo
|
||||
fac=1.0/sqrt(float(NSPS))
|
||||
|
||||
do iEbNo=0,10 !Loop over a range of Eb/No
|
||||
sym0=0
|
||||
call random_number(r)
|
||||
where(r.gt.0.5) sym0=1 !Generate random data bits
|
||||
call mskmod(sym0,NSYM,NSPS,ct,st,xt) !Generate Tx waveform at baseband
|
||||
! NB: In WSJT-X, will mix xt upward from 0 to 1500 Hz.
|
||||
|
||||
do i=0,iz-1 !Generate Gaussian noise
|
||||
xx=0.707*gran()
|
||||
yy=0.707*gran()
|
||||
nt(i)=cmplx(xx,yy)
|
||||
enddo
|
||||
fac_noise=10.0**(-iEbNo/20.0)
|
||||
yt=xt + fac_noise*nt !Rx signal, with noise
|
||||
|
||||
call mskdemod(yt,NSYM,NSPS,ct,st,xsym) !MSK demodulator
|
||||
|
||||
sym=0
|
||||
where(xsym.gt.0.0) sym=1
|
||||
|
||||
! Count the hard errors
|
||||
nerr=count(sym(0:NSYM-1).ne.sym0(0:NSYM-1))
|
||||
thber=0.5*erfc(10.0**(iEbNo/20.0))
|
||||
write(*,1000) iEbNo,thber,float(nerr)/NSYM
|
||||
1000 format(i3,2f10.6)
|
||||
enddo
|
||||
|
||||
end program mskber
|
||||
|
||||
subroutine mskmod(sym,nsym,nsps,ct,st,xt)
|
||||
|
||||
! Generate MSK Tx waveform at baseband.
|
||||
|
||||
integer sym(0:nsym-1) !Hard-copy received bits
|
||||
complex xt(0:nsps*(nsym+1)-1) !Complex baseband Tx waveform
|
||||
real ct(-nsps:nsps*nsym-1) !cos(pi*t/2T)
|
||||
real st(-nsps:nsps*nsym-1) !sin(pi*t/2T)
|
||||
real ai(0:nsps*(nsym+1)-1) !Rectangular pulses for even symbols
|
||||
real aq(0:nsps*(nsym+1)-1) !Rectangular pulses for odd symbols
|
||||
|
||||
fac=1.0/sqrt(float(nsps))
|
||||
do j=0,nsym-1,2
|
||||
ia=j*nsps
|
||||
ib=ia+2*nsps-1
|
||||
ai(ia:ib)=2*sym(j)-1 !Even bits as rectangular pulses
|
||||
aq(ia+nsps:ib+nsps)=2*sym(j+1)-1 !Odd bits as rectangular pulses
|
||||
enddo
|
||||
ai(ib+1:)=0 !Pad ai with zeros at end
|
||||
aq(0:nsps-1)=0 !Pad aq with zeros at start
|
||||
xt=fac*cmplx(ai*ct,aq*st) !Baseband Tx waveform
|
||||
|
||||
return
|
||||
end subroutine mskmod
|
||||
|
||||
subroutine mskdemod(yt,nsym,nsps,ct,st,xsym)
|
||||
|
||||
! MSK demodulator
|
||||
! Rx phase must be known and stable; symbol sync must be established.
|
||||
|
||||
complex yt(0:nsps*(nsym+1)-1) !Received signal
|
||||
real ct(-nsps:nsps*nsym-1) !cos(pi*t/2T)
|
||||
real st(-nsps:nsps*nsym-1) !sin(pi*t/2T)
|
||||
real xe(0:nsps*(nsym+3)-1) !Temp array for received even symbols
|
||||
real xo(0:nsps*(nsym+3)-1) !Temp array for received odd symbols
|
||||
real xsym(0:nsym-1) !Soft Rx symbols
|
||||
|
||||
iz=nsps*nsym
|
||||
xe(0:iz-1)=real(yt)*ct
|
||||
xo(0:iz-1)=aimag(yt)*st
|
||||
do j=0,nsym-1,2
|
||||
ia=j*nsps
|
||||
ib=ia+2*nsps-1
|
||||
xsym(j)=sum(xe(ia:ib)) !Integrate over 2 successive symbols
|
||||
xsym(j+1)=sum(xo(ia+6:ib+6))
|
||||
enddo
|
||||
|
||||
return
|
||||
end subroutine mskdemod
|
Loading…
Reference in New Issue
Block a user