Please stick to the list. On 09/01/2014 05:35 PM, adream wrote: > Thanks for your reply > May be I should make my question more specifically, > > den = -32 * M_PI * alpha * alpha * xindx/spb; > > I can't understand well why there is "-32"
That I don't know. Of course, it's just a gain change, so it won't affect the spectral shape. Perhaps Tom can weigh in here. M > > thank you > > > 2014-09-01 23:18 GMT+08:00 Martin Braun <martin.br...@ettus.com > <mailto:martin.br...@ettus.com>>: > > On 09/01/2014 05:01 PM, adream wrote: > > Hi, > > I get the source code of root_raised_cosine function in > gr_firdes.cc, > > but I can't understand why it writes in that way, is there any > paper can > > give me more details about the principle of root_raised_cosine > > Any standard textbook on digital communications will explain this. You > might want to look out for keywords such as pulse shaping and Nyquist > criterion. Have a look at the wiki page for recommended reading. > > M > > > Thank you > > > > this is the source code of root_raised_cosine > > vector<float> gr_firdes::root_raised_cosine (double gain, > > double sampling_freq, > > double symbol_rate, > > double alpha, > > int ntaps) > > { > > ntaps |= 1; // ensure that ntaps is odd > > > > double spb = sampling_freq/symbol_rate; // samples per bit/symbol > > vector<float> taps(ntaps); > > double scale = 0; > > for(int i=0;i<ntaps;i++) > > { > > double x1,x2,x3,num,den; > > double xindx = i - ntaps/2; > > x1 = M_PI * xindx/spb; > > x2 = 4 * alpha * xindx / spb; > > x3 = x2*x2 - 1; > > if( fabs(x3) >= 0.000001 ) // Avoid Rounding errors... > > { > > if( i != ntaps/2 ) > > num = cos((1+alpha)*x1) + > sin((1-alpha)*x1)/(4*alpha*xindx/spb); > > else > > num = cos((1+alpha)*x1) + (1-alpha) * M_PI / (4*alpha); > > den = x3 * M_PI; > > } > > else > > { > > if(alpha==1) > > { > > taps[i] = -1; > > continue; > > } > > x3 = (1-alpha)*x1; > > x2 = (1+alpha)*x1; > > num = (sin(x2)*(1+alpha)*M_PI > > - cos(x3)*((1-alpha)*M_PI*spb)/(4*alpha*xindx) > > + sin(x3)*spb*spb/(4*alpha*xindx*xindx)); > > den = -32 * M_PI * alpha * alpha * xindx/spb; > > } > > taps[i] = 4 * alpha * num / den; > > scale += taps[i]; > > } > > > > for(int i=0;i<ntaps;i++) > > taps[i] = taps[i] * gain / scale; > > > > return taps; > > } > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
