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