jkch.c

TI的DSP C55X的应用程序

/***********************************************************************************/
/*                      IS54 Baseband Simulation Software                          */
/*                                                                                 */
/*  File Description : Jakes' Fader                                                */
/*  File Name        : jkch.c                                                      */
/*  Date             : 1/4/94                                                      */
/*                   : July, 20001 - Modified for TMS320C55x project               */
/*                                                                                 */
/*    This is a subroutine implementation of a Jakes' fader.  The method and       */
/*    design equations are found on p. 70 of Microwave Mobile Communications       */
/*    by William C. Jakes, Wiley 1974.  Essentially the code is as straight-       */
/*    forward as I could make it, but I put in some flexibility as far as          */
/*    sample rate and the number of points generated. (This subroutine takes       */
/*    the oversampling rate into account by assuming that each symbol is           */
/*    41.17 uS long).                                                              */
/*                                                                                 */
/*    Inputs to this routine consist of vehicle speed, carrier frequency,          */
/*    number of I,Q input pairs to be corrupted, oversampling rate, and pointers   */
/*    to arrays of input I,Q vector pairs.                                         */
/*                                                                                 */
/*    This routine will produce fading vectors corresponding to the suppied        */
/*    inputs, and these vectors will be used to corrupt the I,Q input data         */
/*    in place. (i.e. the input I,Q arrays will be OVERWRITTEN with corrupted      */
/*    data).                                                                       */
/*                                                                                 */
/*    NOTE : THIS MODEL FAILS WHEN VEHICLE SPEED IS ZERO.                          */
/*                                                                                 */
/*  INPUTS                                                                         */
/*    mph         : Simulated vehicle speed in miles per hour                      */
/*    fc          : Simulated carrier frequency in MHz                             */
/*    num_terms   : The number of I,Q pairs to corrupt with multipath fading       */
/*    ovsamp      : Oversampling rate:  the number of samples per symbol           */
/*    I           : Input (uncorrupted) I (in-phase) sample                        */
/*    Q           : Input (uncorrupted) Q (quadrature) sample                      */
/*                                                                                 */
/*  OUTPUTS                                                                        */
/*    I           : Output I (in-phase) sample corrupted with vector of cosine     */
/*                  (in-phase) fading data                                         */
/*    Q           : Output Q (quadrature) sample corrupted with vector of sine     */
/*                  (quadrature) fading data                                       */
/*                                                                                 */
/***********************************************************************************/

/* Includes */

#include <intrindefs.h>

/* Defines */  

#define N0                      8
#define N                       34
#define USER_PI                 ((float)3.1415926)  

/* Function Prototypes */

void    jkch( int, int*, int*, float);
float   jkch_init( float, float, int);
extern int cosine(int);
extern int rand_num(void);

/* External Function Prototypes */

/* Data */

int      jkch_fn1[N0+1],jkch_fn2[N0+1];
float    cosval[N0+1]={1.000000,0.982973,0.932472,0.850217,
                      0.739009,0.602635,0.445738,0.273663,0.092268};

#if 0
// Orginal array
float   jkch_gs[N0+1]={1.000000,1.847759,1.414214,0.765367,
                       0.000000,-0.765367,-1.414213,-1.847759,-2.000000}, 
        jkch_gc[N0+1]={1.000000,0.765367,1.414214,1.847759,
                       2.000000,1.847759,1.414214,0.765367,0.000000};

//      Normalized array using: norm=0.3430, /* norm=1/sqrt(8.5) */
float   jkch_gs[N0+1]={0.343000,0.633781,0.485075,0.262521,
                       0.000000,-0.262521,-0.485075,-0.633781,-0.686000}, 
        jkch_gc[N0+1]={0.343000,0.262521,0.485075,0.633781,
                       0.686000,0.633781,0.485075,0.262521,0.000000};
#endif
//		Q15 format array                       
int     jkch_gsi[N0+1]={0x2BE7,0x511F,0x3E16,0x219A,0x0000,-0x219A,-0x3E16,-0x511F,-0x57CE}, 
        jkch_gci[N0+1]={0x2BE7,0x219A,0x3E16,0x511F,0x57CE,0x511F,0x3E16,0x219A,0x0000};                       

/* External Data */

/* Code */

float    jkch_init(float mph, float fc, int ovsamp)
{
    float   fm, cap_t, temp1, temp2;
    int     i;

    fm = ((float)0.001490515247)*mph*fc;

    for (i = 0 ; i <= N0 ; i++)
    {
        temp1 = (int)(fm*cosval[i]);      // Integer   
        temp2 = fm*cosval[i];
        temp2 -= temp1;                   // fraction   
        
        // Note:, the following arrys are in different format:
		// jkch_fn1[i] is an integer array in deciaml format
		// jkch_fn2[i] is a fractional array in Q15 format      
        jkch_fn1[i] = (int)temp1; 
        jkch_fn2[i] = (int)(temp2*32767.0);
    }

    cap_t = (float)1.0 / ((float)ovsamp * (float)24300.0);    

    return(cap_t);
}

#define  SCALE 2	/* (divide by 4) */
void    jkch(int num_terms, int *I, int *Q, float cap_t)
{
    float   t;
    int     i,j,xc,xs,angle,itemp,itemp2;
    long    lxc,lxs,ltemp,ltemp2;
    
    t = (float)rand_num()/32767.0;  
          
    for (i = 0 ; i < num_terms ; i++)
    {                    
        t += cap_t;
        lxc = 0;
        lxs = 0;
        itemp2 = (int)(t*32767.0);

        for (j = 0 ; j <= N0 ; j++)
        {                   
            ltemp = _lsmpy(itemp2, jkch_fn1[j]);  /* ltemp = jkch_fn1[j]*t; */
            ltemp2 = _lsmpy(itemp2, jkch_fn2[j]); /* ltemp2 = jkch_fn2[j]*t; */
            ltemp2 = _lsadd(ltemp, (ltemp2>>16)); /* ltemp = ltemp - (int)ltemp; */ 
			angle = ((unsigned int)(ltemp2)>>1);  /* angle = ltemp */
            itemp = (cosine(angle)>>SCALE);       /* itemp = cos(angle)*SCALE */
            lxc = _smac(lxc, itemp, jkch_gci[j]); /* xc += itemp * jkch_gc[j]; */
            lxs = _smac(lxs, itemp, jkch_gsi[j]); /* xs += itemp * jkch_gs[j]; */
        }                           

		xc = (lxc>>16);
		xs = (lxs>>16);		
		
        ltemp  = _lsmpy(*I, xc );
        ltemp  = _smas(ltemp, *Q, xs );
        ltemp2 = _lsmpy(*Q, xc );
        ltemp2 = _smac(ltemp2, *I, xs );    	/* temp  =((*I) * xc)-((*Q)*xs); */
        *(I++) = ltemp>>16;                     /* *(Q++)=((*Q) * xc)+((*I)*xs); */
        *(Q++) = ltemp2>>16;                    /* *(I++)=temp; */
    }      
    
    return;
}