ifft_modulation.h

it is a program about ofdm,and it is programed on dsk6455

/*    IFFT modulation   */
void DSP_ifft16x32(const short *w, int nsamp, int *x, int *y);

void IFFT_Modulation(short *buffer_QAM,short *signal,short *Lfm_Data,int *x,int buffer_QAM_len)
{
  unsigned int i,j;
  int A;
  int N_symbol;
  int Num=Fs*Ts;
  double K=B/Ts;
  int max;
  A=QAM_buffer_len%data_per_symbol;
  if(A==0)  N_symbol=floor((float)buffer_QAM_len/(float)data_per_symbol);
  else      N_symbol=floor((float)buffer_QAM_len/(float)data_per_symbol)+1;
  
  for(j=0;j<N_symbol;j++)
    {
      for(i=0;i<FFT_Size;i++)
       { 
	    x[2*i]=0;
	    x[2*i+1]=0;
	   }
     
      for(i=Carrier_Start;i<Carrier_Start+data_per_symbol;i++)
	   {
	    x[2*i]=1000;//buffer_QAM[2*(data_per_symbol*j+i-Carrier_Start)];
		x[2*i+1]=1000;//buffer_QAM[2*(data_per_symbol*j+i-Carrier_Start)+1];
	    }
	  for(i=0;i<data_per_symbol;i++)
       {
	     x[2*(FFT_Size-Carrier_Start-1-i)]=1000;//buffer_QAM[2*(data_per_symbol*j+i)];
	     x[2*(FFT_Size-Carrier_Start-1-i)+1]=-1000;//buffer_QAM[2*(data_per_symbol*j+i)+1];
	    }
	  DSP_ifft16x32(w,FFT_Size,x,y);
	  //DSP_fft16x32(w,FFT_Size,y,x);
	  for(i=0;i<CP_len;i++)
	   {
	     signal[(FFT_Size+CP_len)*j+i+3764]=y[2*(i+FFT_Size-CP_len)];
	   }
	  for(i=CP_len;i<FFT_Size+CP_len;i++)
	   {
	     signal[(FFT_Size+CP_len)*j+i+3764]=y[2*(i-CP_len)];
	   }
	}
  for(i=0;i<2000;i++)
   {
     signal[i]=0;
   }
  for(i=0;i<Num;i++)
    {   
      Lfm_Data[i]=(int)(cos(2*pi*i*F_start/Fs+pi*K*pow(i,2)/pow(Fs,2))*10000);
    }
  for(i=2000;i<2882;i++)
   {
     signal[i]=Lfm_Data[i-2000];
   }
  for(i=2882;i<3764;i++)
   {
     signal[i]=0;
   }
  for(i=34484;i<35484;i++)
   {
     signal[i]=0;
   }
  max=signal[3764];
  for(i=3764;i<34484;i++)
   {
     if(abs(signal[i])>max)
      {
	   max=abs(signal[i]);
       }
   }
  for(i=3764;i<34484;i++)
   {
     signal[i]=((double)signal[i]/max)*10000;
   }
  return;
}