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Compensate for LPF filter step response at beginning and end of transmission.

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@5629 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Steven Franke 2015-06-24 02:08:59 +00:00
parent b27710cf83
commit eabab6027f
1 changed files with 16 additions and 4 deletions
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20
lib/wsprd/wsprd_exp.c
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@ -391,6 +391,7 @@ void subtract_signal2(double *id, double *qd, long np,
double dt=1.0/375.0, df=375.0/256.0;
double pi=4.*atan(1.0), twopidt, phi=0, dphi, cs;
int i, j, k, ii, nsym=162, nspersym=256, nfilt=256; //nfilt must be even number.
int nsig=nsym*nspersym;
double refi[45000],refq[45000];
double ci[45000],cq[45000],cfi[45000],cfq[45000];
@ -445,7 +446,8 @@ void subtract_signal2(double *id, double *qd, long np,
}
//quick and dirty filter - may want to do better
double w[nfilt], norm=0;
double w[nfilt], norm=0, partialsum[nfilt];
memset(partialsum,0,sizeof(double)*nfilt);
for (i=0; i<nfilt; i++) {
w[i]=sin(pi*(float)i/(float)(nfilt-1));
norm=norm+w[i];
@ -453,6 +455,9 @@ void subtract_signal2(double *id, double *qd, long np,
for (i=0; i<nfilt; i++) {
w[i]=w[i]/norm;
}
for (i=1; i<nfilt; i++) {
partialsum[i]=partialsum[i-1]+w[i];
}
// LPF
for (i=nfilt/2; i<45000-nfilt/2; i++) {
@ -467,12 +472,19 @@ void subtract_signal2(double *id, double *qd, long np,
// (ci+j*cq)(refi+j*refq)=(ci*refi-cq*refq)+j(ci*refq)+cq*refi)
// beginning of first symbol in reference signal is at i=nfilt
// beginning of first symbol in received data is at shift0.
for (i=0; i<41472; i++) {
for (i=0; i<nsig; i++) {
if( i<nfilt/2 ) { // take care of the end effect (LPF step response) here
norm=partialsum[nfilt/2+i];
} else if( i>(nsig-1-nfilt/2) ) {
norm=partialsum[nfilt/2+nsig-1-i];
} else {
norm=1.0;
}
k=shift0+i;
j=i+nfilt;
if( (k>0) & (k<np) ) {
id[k]=id[k] - (cfi[j]*refi[i]-cfq[j]*refq[i]);
qd[k]=qd[k] - (cfi[j]*refq[i]+cfq[j]*refi[i]);
id[k]=id[k] - (cfi[j]*refi[i]-cfq[j]*refq[i])/norm;
qd[k]=qd[k] - (cfi[j]*refq[i]+cfq[j]*refi[i])/norm;
}
}
return;