diff.c

TI的DSP C55X的应用程序

/***********************************************************************************/
/*                      IS54 Baseband Simulation Software                          */
/*                                                                                 */
/*  File Description : IS54 DQPSK Differential Detector                            */
/*  File Name        : diff.c                                                      */
/*  Date             : 12/30/93                                                    */
/*                   : July, 20001 - Modified for TMS320C55x project               */
/*                                                                                 */
/*   This decoder produces two symbol bits for every input IS54 DQPSK              */
/*   modulation I,Q vector pair.                                                   */
/*                                                                                 */
/*   The decoding algorithm is based on looking at the sign of                     */
/*   the real and imaginary parts of the phase transitions from                    */
/*   an old I,Q vector to a new I,Q vector.                                        */
/*                                                                                 */
/*   Note that we take advantage of the fact that the 1st bit of                   */
/*   the symbol is dependent on the imaginary part of the phase transition         */
/*   only, while the 2nd bit is dependent only on the real part of                 */
/*   the phase transition.                                                         */
/*                                                                                 */
/*    Inputs  :                                                                    */
/*                irx : Pointer to floating point array of                         */
/*                      at least 163 I samples.                                    */
/*                                                                                 */
/*                qrx : Pointer to floating point array of                         */
/*                      at least 163 Q samples.                                    */
/*                                                                                 */
/*    Outputs :                                                                    */
/*               bits : Pointer to unsigned array where                            */
/*                      324 symbol bits are to be stored.                          */
/*                      Note that each element of the array                        */
/*                      will contain a single bit (i.e. 0                          */
/*                      or 1 only)                                                 */
/*                                                                                 */
/*    Return Value :                                                               */
/*              NONE                                                               */
/*                                                                                 */
/***********************************************************************************/ 

/* Include Files */

#include <intrindefs.h>

/* Defines */

#define OLD_I           (*irx)
#define OLD_Q           (*qrx)
#define NEW_I           (*(irx+1))
#define NEW_Q           (*(qrx+1))
#define SLOT_LENGTH     162

/* Function Prototypes */

void    diff( int*, int*, unsigned* );

/* External Functions */

/* Data */

/* Extrenal Data */

/* Code */

void    diff( int *irx, int *qrx, unsigned *bits )
{
    int i;
    long ltemp;
    
    for (i=0; i < SLOT_LENGTH; i++ )
    {     
   
    /* Determione 1st bit */
       /*   if( (OLD_I*NEW_Q - OLD_Q*NEW_I) >= 0)  *(bits++) = 0; */   
       /*   else                                   *(bits++) = 1; */
        ltemp = _lsmpy(OLD_I, NEW_Q);
        ltemp = _smas(ltemp, OLD_Q, NEW_I);    
        if (ltemp >= 0) *(bits++) = 0;
        else            *(bits++) = 1;
            
    /* Determine 2nd bit */
        /* if( (OLD_I*NEW_I + OLD_Q*NEW_Q) >= 0 ) *(bits++) = 0; */
        /* else                                   *(bits++) = 1; */
        ltemp = _lsmpy(OLD_I, NEW_I);
        ltemp = _smac(ltemp, OLD_Q, NEW_Q);
        if (ltemp >= 0) *(bits++) = 0;
        else            *(bits++) = 1;
        
    /* Update Pointers */
        irx++;
        qrx++;
    }
    return;
}