mirror of https://github.com/saitohirga/WSJT-X.git
163 lines
5.0 KiB
Fortran
163 lines
5.0 KiB
Fortran
program wspr5d
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! Simulate characteristics of a potential "WSPR-LF" mode using LDPC (300,60)
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! code, OQPSK modulation, and 5 minute T/R sequences.
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! Reception and Demodulation algorithm:
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! 1. Compute coarse spectrum; find fc1 = approx carrier freq
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! 2. Mix from fc1 to 0; LPF at +/- 0.75*R
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! 3. Square, FFT; find peaks near -R/2 and +R/2 to get fc2
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! 4. Mix from fc2 to 0
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! 5. Fit cb13 (central part of csync) to c -> lag, phase
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! 6. Fit complex ploynomial for channel equalization
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! 7. Get soft bits from equalized data
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include 'wsprlf_params.f90'
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! Q: Would it be better for central Sync array to use both I and Q channels?
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character arg*8,message*22,cbits*50
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complex csync(0:NZ-1) !Sync symbols only, from cbb
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complex c(0:NZ-1) !Complex waveform
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complex c1(0:NZ-1) !Complex waveform
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complex zz(NS+ND) !Complex symbol values (intermediate)
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complex z
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real rxdata(ND),llr(ND) !Soft symbols
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real pp(2*NSPS) !Shaped pulse for OQPSK
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real a(5) !For twkfreq1
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real aa(20),bb(20) !Fitted polyco's
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integer id(NS+ND) !NRZ values (+/-1) for Sync and Data
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integer ierror(NS+ND)
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integer isync(48) !Long sync vector
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integer ib13(13) !Barker 13 code
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integer*8 n8
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integer*1 idat(7)
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integer*1 decoded(KK),apmask(ND),cw(ND)
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data ib13/1,1,1,1,1,-1,-1,1,1,-1,1,-1,1/
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nargs=iargc()
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if(nargs.ne.1) then
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print*,'Usage: wspr5d maxn'
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! print*,'Example: wsprlfsim 0 0 0 5 10 -20'
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go to 999
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endif
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call getarg(1,arg)
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read(arg,*) maxn
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twopi=8.0*atan(1.0)
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fs=NSPS*12000.0/NSPS0 !Sample rate
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dt=1.0/fs !Sample interval (s)
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tt=NSPS*dt !Duration of "itone" symbols (s)
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ts=2*NSPS*dt !Duration of OQPSK symbols (s)
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baud=1.0/tt !Keying rate for "itone" symbols (baud)
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txt=NZ*dt !Transmission length (s)
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do i=1,N2 !Half-sine pulse shape
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pp(i)=sin(0.5*(i-1)*twopi/(2*NSPS))
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enddo
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n8=z'cbf089223a51'
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do i=1,48
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isync(i)=-1
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if(iand(n8,1).eq.1) isync(i)=1
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n8=n8/2
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enddo
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! Defind array id() for sync symbols
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id=0
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do j=1,48 !First group of 48
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id(2*j-1)=2*isync(j)
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enddo
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do j=1,13 !Barker 13 code
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id(j+96)=2*ib13(j)
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enddo
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do j=1,48 !Second group of 48
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id(2*j+109)=2*isync(j)
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enddo
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do ifile=1,9999
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read(10,end=999) c
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! do i=0,NZ-1
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! write(40,4001) i,c(i)
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!4001 format(i8,2f10.6)
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! enddo
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call getfc1w(c,fs,fc1) !First approx for freq
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call getfc2w(c,csync,fs,fc1,fc2,fc3) !Refined freq
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!NB: Measured performance is about equally good using fc2 or fc3 here:
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a(1)=-(fc1+fc2)
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a(2:5)=0.
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call twkfreq1(c,NZ,fs,a,c) !Mix c down by fc1+fc2
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!---------------------------------------------------------------- DT
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! Not presently used:
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amax=0.
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jpk=0
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iaa=0
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ibb=NZ-1
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do j=-20*NSPS,20*NSPS,NSPS/8
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ia=j
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ib=NZ-1+j
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if(ia.lt.0) then
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ia=0
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iaa=-j
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else
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iaa=0
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endif
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if(ib.gt.NZ-1) then
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ib=NZ-1
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ibb=NZ-1-j
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endif
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z=sum(c(ia:ib)*conjg(csync(iaa:ibb)))
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if(abs(z).gt.amax) then
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amax=abs(z)
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jpk=j
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endif
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enddo
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xdt=jpk/fs
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!-----------------------------------------------------------------
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nterms=maxn
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c1=c
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! do itry=1,1000
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do itry=1,20
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idf=itry/2
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if(mod(itry,2).eq.0) idf=-idf
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nhard0=0
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nhardsync0=0
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ifer=1
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a(1)=idf*0.00085
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a(2:5)=0.
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call twkfreq1(c1,NZ,fs,a,c) !Mix c1 into c
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call cpolyfitw(c,pp,id,maxn,aa,bb,zz,nhs)
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call msksoftsymw(zz,aa,bb,id,nterms,ierror,rxdata,nhard0,nhardsync0)
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if(nhardsync0.gt.35) cycle
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rxav=sum(rxdata)/ND
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rx2av=sum(rxdata*rxdata)/ND
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rxsig=sqrt(rx2av-rxav*rxav)
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rxdata=rxdata/rxsig
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ss=0.84
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llr=2.0*rxdata/(ss*ss)
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apmask=0
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max_iterations=40
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ifer=0
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call bpdecode300(llr,apmask,max_iterations,decoded,niterations,cw)
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nbadcrc=0
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if(niterations.ge.0) call chkcrc10(decoded,nbadcrc)
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if(niterations.lt.0 .or. nbadcrc.ne.0) ifer=1
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if(ifer.eq.0) exit
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enddo !Freq dither loop
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message=' '
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if(ifer.eq.0) then
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write(cbits,1100) decoded(1:50)
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1100 format(50i1)
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read(cbits,1102) idat
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1102 format(6b8,b2)
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idat(7)=ishft(idat(7),6)
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call wqdecode(idat,message,itype)
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endif
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write(*,1110) nsnr,xdt,fc1+fc2,message
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1110 format(i4,f7.2,f7.2,2x,a22)
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enddo
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999 end program wspr5d
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