rrcfilter.cpp

QPSK调制Modem的C实现及文档说明

/******************************************************************************
 * RRcFilter -- simulates a root raised cosine filter(64 taps, RECT. window)  *
 * Functions -- conv()                                                        *
 *   Returns -- the corresponding output                                      *
 ******************************************************************************/

/* Impulse response of a root raised cosine filter */
const NumTabs = 64;
const double h[NumTabs]= {  -0.2446, -0.1844,  0.0000,  0.2108,
                             0.3199,  0.2433,  0.0000, -0.2841,
                            -0.4362, -0.3360,  0.0000,  0.4037,
                             0.6301,  0.4942,  0.0000, -0.6190,
                            -0.9901, -0.7983,  0.0000,  1.0692,
                             1.7822,  1.5079,  0.0000, -2.2912,
                            -4.1584, -3.9206,  0.0000,  8.4012,
                            20.7919, 35.2850, 48.9898, 58.8084,
                            58.8084, 48.9898, 35.2850, 20.7919,
                             8.4012,  0.0000, -3.9206, -4.1584,
                            -2.2912,  0.0000,  1.5079,  1.7822,
                             1.0692,  0.0000, -0.7983, -0.9901,
                            -0.6190,  0.0000,  0.4942,  0.6301,
                             0.4037,  0.0000, -0.3360, -0.4362,
                             -0.2841,  0.0000,  0.2433, 0.3199,
                             0.2108,  0.0000, -0.1844, -0.2446
                           };   /* 64 taps;  T=1/2400 */

class RRcFilter
{
 private:
  double ProcessingBuffer[NumTabs];
  void LeftShift(double x);

 public:
  RRcFilter()
  { for (int i=0; i<NumTabs; ++i) ProcessingBuffer[i]=0; }
  double conv(double x);
};

void RRcFilter::LeftShift(double x)
 { for (int i=0; i<(NumTabs-1); ++i) ProcessingBuffer[i]=ProcessingBuffer[i+1];
   ProcessingBuffer[NumTabs-1]=x;
 }


double RRcFilter::conv(double x)
 { double temp=0;
   LeftShift(x);                 /* left shift one sample */
   for (int i=0; i<NumTabs; ++i) temp=temp+h[i]*ProcessingBuffer[NumTabs-1-i];
   return temp;
 }