diffenc.c

TI的DSP C55X的应用程序

/***********************************************************************************/
/*                      IS54 Baseband Simulation Software                          */
/*                                                                                 */
/*  File Description : IS54 DQPSK Differential Encoder                             */
/*  File Name        : diffenc.c                                                   */
/*  Date             : 12/30/93                                                    */
/*                   : July, 20001 - Modified for TMS320C55x project               */
/*                                                                                 */
/*   Differential Encoder for IS-54 DQPSK                                          */
/*                                                                                 */
/*   This encoder receives two bits from the data stream, and encodes them         */
/*   into DQPSK modulation.  It outputs I and Q for each input symbol pair.        */
/*                                                                                 */
/*   The input symbols and their bit relationship and phase changes                */
/*   are listed below:                                                             */
/*                                                                                 */
/*   input data           phase changes                                            */
/*                                                                                 */
/*   00                    pi/4, pi/4                                              */
/*   01                   -pi/4, pi/4                                              */
/*   10                   -pi/4,-pi/4                                              */
/*   11                    pi/4,-pi/4                                              */
/*                                                                                 */
/*   Inputs :                                                                      */
/*            packed : Pointer to array containing 384 symbol                      */
/*                     bits to be encoded. Note that each element                  */
/*                     of the array consists of a single bit (i.e.                 */
/*                     a 0 or 1 only)                                              */
/*                                                                                 */
/*    Outputs :                                                                    */
/*            out_I   : Pointer to floating point array where                      */
/*                      192 modulation vector I-components shall                   */
/*                      be stored.                                                 */
/*                                                                                 */
/*            out_Q   : Pointer to floating point array where                      */
/*                      192 modulation vector Q-components shall                   */
/*                      be stored.                                                 */
/*                                                                                 */
/*    Return Value :                                                               */
/*            NONE                                                                 */
/*                                                                                 */
/***********************************************************************************/

/* Include Files */

#include <intrindefs.h>

/* Defines */

#define Z   0x5a82		/* Q15 format of 0.70710678 */

/* Function Prototypes */

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

/* External Function Prototypes */

/* Data */

/* External Data */

/* Code */

void diffenc( unsigned *packed, int *out_I, int *out_Q )
{
    long   ltemp;
    int    i, phase_i, phase_r, i_old, q_old;

    *(out_I) = 0x7fff;
    *(out_Q) = 0;
    for (i = 192 ; i > 0 ; i--)
    {   
        i_old = *(out_I++);
        q_old = *(out_Q++);
        phase_i = Z;
        phase_r = Z;                   /* assume both bits are zero     */
        if( *(packed++) != 0 )  
            phase_i = -Z;              /* 1st bit determines imag phase */
        if( *(packed++) != 0 )
            phase_r = -Z;              /* 2nd bit determines real phase */
        ltemp = _lsmpy(i_old, phase_r);
        ltemp = _smas(ltemp, q_old, phase_i);
        *(out_I) = (ltemp>>16);        /* *(out_I) = i_old*phase_r - q_old*phase_i; */
        ltemp = _lsmpy(i_old, phase_i);
        ltemp = _smac(ltemp, q_old, phase_r);       
        *(out_Q) = (ltemp>>16);        /* *(out_Q) = i_old*phase_i + q_old*phase_r; */
    }
    return;
}