filtering.h

This a framework to test new ideas in transmission technology. Actual development is a LDPC-coder in

#ifndef _FILTERING_H__
#define _FILTERING_H__


#include "midamble.h"

/**
 * @author Alessandro Nordio 03/04/2001
 *
 *  This function builds the matched filter. The matched filter (MF) 
 * is in general a complex vector. In order to simplify the matched 
 * filtering operation, this routine computes separately the real and 
 * imaginary parts of the MFs and store it into two different vectors
 *
 * @param m the pointer to the midamble used in this slot
 * @param est pointer to the channel estimation structure. 
 *  (Where this function reads the channel estimates and where
 *  it writes the real and imaginary parts of the matched filters)
 * @param midamble_index the indexe of the midamble shift used
 */
int matched_filter_build(midamble_t *m,
                         estimation_vars_t *est,
                         unsigned int midamble_index );


/**
 * @author Alessandro Nordio 04/04/2001
 *
 * This routine performs the matched filtering operation filtering 
 * the same input x with two filters h1 and h2 (main application: 
 * h1 and h2 are the real and imaginary parts of a complex matched filter)
 * 
 * It computes the output y1 and y2 as
 * y1[n] = \sum_{k=0}^{length-1} x[shift*n+k]*h1[k]   for n=0..n_y-1
 * y2[n] = \sum_{k=0}^{length-1} x[shift*n+k]*h2[k]   for n=0..n_y-1
 *
 * The elements x,h1,h2 and y are real and are represented on a 
 * short integer (16 bit). The elements of x, h1 and h2 are stored 
 * four by four in mmx_t structures so they are loaded 4 at a time 
 * into the MMX registers. The length of the vector h (the MF) is 
 * 'length' that we assume a multiple of 4. The routine computes 
 * n_y output.
 *
 * @param x the input vector in the format [x0,x1,x2,x3,x4,x5,x6,x7,...] 
 *   where xn is a real short integer (16 bit) with 
 *   12 bit dynamic  (-2048, +2047)
 * @param h1 the real filter coefficients in the same format as x.
 * @param h2 the real (imaginary?) filter coefficients in the same format as x.
 * @param length the length of h
 * @param downsample_factor the shift on x between one output and the other
 * @param n_y the number of output computed by the routine
 * @param y the output of the filters in the format 
 *  [y10,y20,y11,y21,.....y1n,y2n,....] where y1n is the n-th output of 
 *  the first filter and is on 16 bit
 * @param wrap_point a pointer to the end of the input array.  Used 
 *  to force the filter to wrap back to the beginning of the buffer.
 * @param wrap_period the length of the input buffer
 */
int matched_filtering( mmx_t *x, mmx_t *h1, mmx_t *h2, SYMBOL_COMPLEX *y, 
		       unsigned int length, unsigned int downsample_factor, 
		       unsigned int n_y );

#endif