mirror of https://github.com/saitohirga/WSJT-X.git
147 lines
4.6 KiB
Fortran
147 lines
4.6 KiB
Fortran
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 (MAXSYM=1000*1000)
|
|
parameter (NSPS=5) !Samples per symbol
|
|
real ct(-NSPS:NSPS*MAXSYM-1) !cos(pi*t/2T)
|
|
real st(-NSPS:NSPS*MAXSYM-1) !sin(pi*t/2T)
|
|
real r(0:MAXSYM-1) !Random numbers to set test bits
|
|
real xsym(0:MAXSYM-1) !Soft Rx symbols
|
|
|
|
complex xt(-NSPS:NSPS*MAXSYM-1) !Complex baseband Tx waveform
|
|
complex nt(-NSPS:NSPS*MAXSYM-1) !Generated AWGN channel noise
|
|
complex yt(-NSPS:NSPS*MAXSYM-1) !Received signal, yt = xt + fac*nt
|
|
complex cwave(-NSPS:NSPS*MAXSYM-1) !Audio waveform, Tx real part
|
|
complex z
|
|
|
|
integer sym0(0:MAXSYM-1) !Generated test bits
|
|
integer sym(0:MAXSYM-1) !Hard-copy received bits
|
|
integer sym1(0:7)
|
|
|
|
character*12 arg
|
|
data sym1/1,1,0,0,0,1,1,1/
|
|
|
|
nargs=iargc()
|
|
if(nargs.ne.2) then
|
|
print*,'Usage: mskber nsym EbNo'
|
|
go to 999
|
|
endif
|
|
call getarg(1,arg)
|
|
read(arg,*) nsym
|
|
call getarg(2,arg)
|
|
read(arg,*) EbNo
|
|
|
|
pi=4.0*atan(1.0)
|
|
|
|
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(0:nsym-1).gt.0.5) sym0(0:nsym-1)=1 !Generate random data bits
|
|
if(nsym.eq.8) sym0(0:nsym-1)=sym1
|
|
call mskmod(sym0,nsym,NSPS,ct,st,xt,cwave) !Generate Tx waveform
|
|
|
|
do i=-NSPS,NSPS*nsym-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)
|
|
if(EbNo.ne.0.0) fac_noise=10.0**(-EbNo/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
|
|
|
|
if(nsym.le.160 .and. EbNo.ne.0.0) then
|
|
write(*,1012) sym0(0:nsym-1)
|
|
if(nsym.gt.50) write(*,1012)
|
|
write(*,1012) sym(0:nsym-1)
|
|
1012 format(50i1)
|
|
do i=-nsps,nsps*nsym-1
|
|
phi=i*2.0*pi*1500/12000.0
|
|
z=cwave(i)*cmplx(cos(phi),sin(phi)) !Mix back to baseband
|
|
write(51,1014) float(i)/nsps,xt(i),abs(xt(i)),cwave(i),z
|
|
1014 format(8f8.4)
|
|
enddo
|
|
endif
|
|
|
|
! Count the hard errors
|
|
nerr=count(sym(0:nsym-1).ne.sym0(0:nsym-1))
|
|
thber=0.5*erfc(10.0**(iEbNo/20.0))
|
|
xEbNo=iEbNo
|
|
if(EbNo.ne.0.0) xEbNo=EbNo
|
|
write(*,1000) xEbNo,thber,float(nerr)/nsym
|
|
1000 format(f6.1,2f10.6)
|
|
if(EbNo.ne.0.0) exit
|
|
enddo
|
|
|
|
999 end program mskber
|
|
|
|
subroutine mskmod(sym,nsym,nsps,ct,st,xt,cwave)
|
|
|
|
! Generate MSK Tx waveform at baseband.
|
|
|
|
integer sym(0:nsym-1) !Hard-copy received bits
|
|
complex xt(-nsps:nsps*nsym-1) !Complex baseband Tx waveform
|
|
complex cwave(-nsps:nsps*nsym-1) !Audio waveform, fc=1500 Hz.
|
|
real ct(-nsps:nsps*nsym-1) !cos(pi*t/2T)
|
|
real st(-nsps:nsps*nsym-1) !sin(pi*t/2T)
|
|
real ai(-nsps:nsps*nsym-1) !Rectangular pulses for even symbols
|
|
real aq(-nsps:nsps*nsym-1) !Rectangular pulses for odd symbols
|
|
|
|
ai=0.
|
|
aq=0.
|
|
fac=1.0/sqrt(float(nsps))
|
|
do j=0,nsym-1,2
|
|
ia=(j-1)*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
|
|
xt=fac*cmplx(ai*ct,aq*st) !Baseband Tx waveform
|
|
|
|
twopi=8.0*atan(1.0)
|
|
do i=-nsps,nsps*nsym-1
|
|
phi=i*twopi*1500/12000.0
|
|
cwave(i)=xt(i)*cmplx(cos(phi),-sin(phi))
|
|
enddo
|
|
|
|
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(-nsps:nsps*nsym-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(-nsps:nsps*nsym-1) !Temp array for received even symbols
|
|
real xo(-nsps:nsps*nsym-1) !Temp array for received odd symbols
|
|
real xsym(0:nsym-1) !Soft Rx symbols
|
|
|
|
iz=nsps*(nsym+1)
|
|
xe(-nsps:nsps*nsym-1)=real(yt)*ct !Apply matched filters
|
|
xo(-nsps:nsps*nsym-1)=aimag(yt)*st
|
|
do j=0,nsym-1,2
|
|
ia=(j-1)*nsps
|
|
ib=ia+2*nsps-1
|
|
xsym(j)=sum(xe(ia:ib)) !Integrate over 2 symbol lengths
|
|
xsym(j+1)=sum(xo(ia+nsps:ib+nsps))
|
|
enddo
|
|
|
|
return
|
|
end subroutine mskdemod
|