dft_dsp.c

详细的OFDM设计过程

// dft_DSP.c
// compute the fft and remove the complex mirror.


#include "receiver.h"
#include <math.h>
#include <stdio.h>
#include <C:/ti/c6700/dsplib/include/dspf_sp_cfftr2_dit.h>
#include "bit_rev.h"
//#pragma DATA_ALIGN(input, 8); // this has to be done in the main function
#pragma DATA_ALIGN(w,8);


//define the twiddle coefficients used to compute dft
float w[2 * 128] =
{
     1.000000,  0.000000,  0.000000,  1.000000,  0.707107,  0.707107, -0.707107,  0.707107,
     0.923880,  0.382683, -0.382683,  0.923880,  0.382683,  0.923880, -0.923880,  0.382683,
     0.980785,  0.195090, -0.195090,  0.980785,  0.555570,  0.831470, -0.831470,  0.555570,
     0.831470,  0.555570, -0.555570,  0.831470,  0.195090,  0.980785, -0.980785,  0.195090,
     0.995185,  0.098017, -0.098017,  0.995185,  0.634393,  0.773010, -0.773010,  0.634393,
     0.881921,  0.471397, -0.471397,  0.881921,  0.290285,  0.956940, -0.956940,  0.290285,
     0.956940,  0.290285, -0.290285,  0.956940,  0.471397,  0.881921, -0.881921,  0.471397,
     0.773010,  0.634393, -0.634393,  0.773010,  0.098017,  0.995185, -0.995185,  0.098017,
     0.998795,  0.049068, -0.049068,  0.998795,  0.671559,  0.740951, -0.740951,  0.671559,
     0.903989,  0.427555, -0.427555,  0.903989,  0.336890,  0.941544, -0.941544,  0.336890,
     0.970031,  0.242980, -0.242980,  0.970031,  0.514103,  0.857729, -0.857729,  0.514103,
     0.803208,  0.595699, -0.595699,  0.803208,  0.146730,  0.989177, -0.989177,  0.146730,
     0.989177,  0.146730, -0.146730,  0.989177,  0.595699,  0.803208, -0.803208,  0.595699,
     0.857729,  0.514103, -0.514103,  0.857729,  0.242980,  0.970031, -0.970031,  0.242980,
     0.941544,  0.336890, -0.336890,  0.941544,  0.427555,  0.903989, -0.903989,  0.427555,
     0.740951,  0.671559, -0.671559,  0.740951,  0.049068,  0.998795, -0.998795,  0.049068,
     0.999699,  0.024541, -0.024541,  0.999699,  0.689541,  0.724247, -0.724247,  0.689541,
     0.914210,  0.405241, -0.405241,  0.914210,  0.359895,  0.932993, -0.932993,  0.359895,
     0.975702,  0.219101, -0.219101,  0.975702,  0.534998,  0.844854, -0.844854,  0.534998,
     0.817585,  0.575808, -0.575808,  0.817585,  0.170962,  0.985278, -0.985278,  0.170962,
     0.992480,  0.122411, -0.122411,  0.992480,  0.615232,  0.788346, -0.788346,  0.615232,
     0.870087,  0.492898, -0.492898,  0.870087,  0.266713,  0.963776, -0.963776,  0.266713,
     0.949528,  0.313682, -0.313682,  0.949528,  0.449611,  0.893224, -0.893224,  0.449611,
     0.757209,  0.653173, -0.653173,  0.757209,  0.073565,  0.997290, -0.997290,  0.073565,
     0.997290,  0.073565, -0.073565,  0.997290,  0.653173,  0.757209, -0.757209,  0.653173,
     0.893224,  0.449611, -0.449611,  0.893224,  0.313682,  0.949528, -0.949528,  0.313682,
     0.963776,  0.266713, -0.266713,  0.963776,  0.492898,  0.870087, -0.870087,  0.492898,
     0.788346,  0.615232, -0.615232,  0.788346,  0.122411,  0.992480, -0.992480,  0.122411,
     0.985278,  0.170962, -0.170962,  0.985278,  0.575808,  0.817585, -0.817585,  0.575808,
     0.844854,  0.534998, -0.534998,  0.844854,  0.219101,  0.975702, -0.975702,  0.219101,
     0.932993,  0.359895, -0.359895,  0.932993,  0.405241,  0.914210, -0.914210,  0.405241,
     0.724247,  0.689541, -0.689541,  0.724247,  0.024541,  0.999699, -0.999699,  0.024541
};



// input in normal order, output in bit reversed
// order, coefficient table in bit-reversed
// order
#define FFT_SIZE 256
void dft_DSP(float *in, float *out) {

	// we compute only once this value
	
	float inv_size_fft=_rcpsp(16);		//sqrtf(FFT_SIZE));
	
	int i;
	
	// compute the fft
	
	DSPF_sp_cfftr2_dit(in, w, FFT_SIZE);
	
	// re reverse the output
	bit_rev(in, 2*FFT_SIZE>>1);
	
	// remove the complex mirror and scale
	
	for (i=0;i<NR_OF_CHANNELS*2;i++) 
	{
		out[i]=in[i+2+6]*inv_size_fft;
	}

}