C语言实现QPSK调制与解调实用代码

/*
 * Copyright (c) 2007 - 2015 Joseph Gaeddert
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

//
// modem_common.c : common utilities specific to precision
//

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "liquid.internal.h"

#define DEBUG_DEMODULATE_SOFT 0

// modem structure used for both modulation and demodulation 
//
// The modem structure implements a variety of common modulation schemes,
// including (differential) phase-shift keying, and (quadrature) amplitude
// modulation.
//
// While the same modem structure may be used for both modulation and
// demodulation for most schemes, it is important to use separate objects
// for differential-mode modems (e.g. LIQUID_MODEM_DPSK) as the internal state
// will change after each symbol.  It is usually good practice to keep
// separate instances of modulators and demodulators.
struct MODEM(_s)
{
    // common data
    modulation_scheme scheme;   // modulation scheme
    unsigned int m;             // bits per symbol (modulation depth)
    unsigned int M;             // constellation size, M=2^m

    // Reference vector for demodulating linear arrays
    //
    // By storing these values in an array they do not need to be
    // calculated during run-time.  This speeds up the demodulation by
    // approximately 8%.
    T ref[MAX_MOD_BITS_PER_SYMBOL];

    // modulation