detect_pre.c

This model is just testing an idea of MIMO, which IEEE802.11n will have. But I havo not seen the s

/*****************************************************************************/
/*   FIle Name : detect_pre.c                                                */
/*   Description : WLAN detection of preamble                                */
/*   author : miffie                                                         */
/*   Date   : aug/18/05                                                      */
/*   Copyright (c) 2005 miffie   All rights reserved.                        */
/*****************************************************************************/
///////////////////////////////////////////////////////////////////////////////

int detect_pre( struct complexset datain ) { // 
double  radius ;
double  maxr, minr ;
double  peak_radius ;
double  bottom_radius ;
double  accum_radius, accum_diff ;
struct	complex tmp1 , tmp2 ;
struct	complexset cset ;
short   octet_cnt ;
short   minimum_position ;
int     RADIUS_THRESHOLD = 0.25 ;
int	ii , jj ;
int     detection ;
double  drift_phase, drift_amount ;


 //Main 
  PRINTF("detect_pre size=%d \n", datain.size ) ;
  //detect short sequence
  ii=16 ;
  detection = datain.size +1 ;
  octet_cnt=0 ;
  drift_phase=0 ;
  drift_amount=0 ;
  while(ii< (datain.size-16) ) { //loop
    accum_radius=0 ;
    peak_radius=0 ;
    accum_diff=0 ;
    accum_radius=0 ;
    bottom_radius=1 ;
    minimum_position=1 ;
    cset = extract_complexset(datain , ii-16 , 24 ) ; //Short sequence
    for(jj=0;jj<8;jj++) { //each sample
      //calculate radius
      tmp1 = cordic( datain.data[ii+jj] ) ;
      tmp2 = cordic( datain.data[ii+jj-16] ) ;
      radius = tmp1.realp ;
      //calculate  difference from one of 16 cycles before
      accum_diff += fabs(tmp1.realp-tmp2.realp) ;
      accum_radius += radius ;
      if ( radius > peak_radius ) peak_radius= radius ;
      if ( radius < bottom_radius ) { //smallest
           bottom_radius= radius ;
           minimum_position = jj ;
      } //smallest
      //diff_phase = tmp1.image - tmp2.image ;
      //cset = phase_drift(cset , &drift_phase , &drift_amount ) ;
      //drift_amount =   detect_drift( cset , 16 ) ;


      //calculate phase
      // Aug/19/05 This idea did not work, 
      //if ADC phase shifted half cycle(50ns) against transmitter
      //phase = fabs(datain.data[ii+jj-1].realp-datain.data[ii+jj+1].image) +
      //        fabs(datain.data[ii+jj-1].image-datain.data[ii+jj+1].realp) +
      //        fabs(datain.data[ii+jj-2].realp-datain.data[ii+jj+2].image) +
      //        fabs(datain.data[ii+jj-2].image-datain.data[ii+jj+2].realp) +
      //        fabs(datain.data[ii+jj-3].realp-datain.data[ii+jj+3].image) +
      //        fabs(datain.data[ii+jj-3].image-datain.data[ii+jj+3].realp) ;
      //PRINTF(" phase (%d) =%6.3f\n", ii+jj , phase ) ;
      //if ( bottom_radius > phase ) {//smallest
      //    bottom_radius = phase ;
      //} //smallest
    } //each sample

    PRINTF("detect_pre(%d) accum_radius=%6.3f accum_diff=%6.3f octet_cnt=%d\n", ii, 
                           accum_radius, accum_diff , octet_cnt ) ;
    PRINTF("bottom_radius(%d)=%6.3f\n", minimum_position, bottom_radius ) ;

    //octet_cnt as count # of octets(8 samples) in short seq
    if (((accum_radius/4.0) > accum_diff) & //if accum_diff is small enough
        (accum_radius>RADIUS_THRESHOLD)) {  //if accum_radius is big enough
        octet_cnt++ ;
    } //detected
    else { //not detected
        if(octet_cnt>4)  { //start of longseq
          detection = ii+160-128-8 ;
          ii=datain.size ; //exit loop
        } //start of longseq
        octet_cnt=0 ;
    } //not detected
    
    //take peak_radius for AutoGainControl

    if (octet_cnt>2) {//short seq detected
      ii += 7+minimum_position ;
    }//short seq detected
    else { //
     ii += 8 ; 
    } //
  } //loop
  PRINTF("detection =%d\n" , detection ) ;
  return( detection ) ;
} //detect_pre