基于VHDL的qpsk调制实现

QPSK调制是数字通信中常用的调制方式之一，它可以将两个二进制比特映射到一个符号上进行传输。在VHDL中实现QPSK调制需要以下步骤：

1. 定义输入输出端口

首先，需要在代码中定义输入输出端口，包括时钟信号、复数输入信号和QPSK调制输出信号。具体代码如下：

entity qpsk_modulation is
port (
    clk     : in  std_logic;           -- 时钟信号
    in_i    : in  std_logic_vector(7 downto 0);    -- 实部输入信号
    in_q    : in  std_logic_vector(7 downto 0);    -- 虚部输入信号
    out_qpsk: out std_logic_vector(1 downto 0)      -- QPSK调制输出信号
);
end entity;

2. 定义内部信号

接下来，需要定义一些内部信号，包括正弦余弦值、相位值和QPSK调制输出信号。具体代码如下：

architecture behavioral of qpsk_modulation is
    signal i_sine      : std_logic_vector(7 downto 0);
    signal i_cosine    : std_logic_vector(7 downto 0);
    signal q_sine      : std_logic_vector(7 downto 0);
    signal q_cosine    : std_logic_vector(7 downto 0);
    signal phase       : std_logic_vector(7 downto 0);
    signal out_i       : std_logic_vector(7 downto 0);
    signal out_q       : std_logic_vector(7 downto 0);
    signal qpsk        : std_logic_vector(1 downto 0);
begin

3. 生成正弦余弦值

为了生成正弦余弦值，可以使用查找表或DSP模块。这里采用查找表的方式实现。具体代码如下：

    i_sine <= x"00", x"19", x"32", x"4B", x"64", x"7D", x"96", x"AF", x"C8", x"E1", x"FA", x"13", x"2C", x"45", x"5E", x"77";
    i_cosine <= x"77", x"5E", x"45", x"2C", x"13", x"FA", x"E1", x"C8", x"AF", x"96", x"7D", x"64", x"4B", x"32", x"19", x"00";
    q_sine <= x"00", x"F3", x"E6", x"D9", x"CC", x"BF", x"B2", x"A5", x"98", x"8B", x"7E", x"71", x"64", x"57", x"4A", x"3D";
    q_cosine <= x"3D", x"4A", x"57", x"64", x"71", x"7E", x"8B", x"98", x"A5", x"B2", x"BF", x"CC", x"D9", x"E6", x"F3", x"00";

4. 计算相位值

根据输入信号的实部和虚部计算相位值。具体代码如下：

    process(clk)
    begin
        if rising_edge(clk) then
            phase <= std_logic_vector(unsigned(in_i)*unsigned(q_cosine)-unsigned(in_q)*unsigned(i_cosine));
        end if;
    end process;

5. 计算QPSK调制输出信号

根据相位值计算QPSK调制输出信号。具体代码如下：

    out_i <= std_logic_vector(unsigned(phase) > 127);
    out_q <= std_logic_vector(unsigned(phase(7 downto 0)) > 127);
    qpsk <= out_i(0) & out_q(0);
    out_qpsk <= qpsk;

6. 完整代码

最终的VHDL代码如下：

entity qpsk_modulation is
port (
    clk     : in  std_logic;           -- 时钟信号
    in_i    : in  std_logic_vector(7 downto 0);    -- 实部输入信号
    in_q    : in  std_logic_vector(7 downto 0);    -- 虚部输入信号
    out_qpsk: out std_logic_vector(1 downto 0)      -- QPSK调制输出信号
);
end entity;

architecture behavioral of qpsk_modulation is
    signal i_sine      : std_logic_vector(7 downto 0);
    signal i_cosine    : std_logic_vector(7 downto 0);
    signal q_sine      : std_logic_vector(7 downto 0);
    signal q_cosine    : std_logic_vector(7 downto 0);
    signal phase       : std_logic_vector(7 downto 0);
    signal out_i       : std_logic_vector(7 downto 0);
    signal out_q       : std_logic_vector(7 downto 0);
    signal qpsk        : std_logic_vector(1 downto 0);
begin
    i_sine <= x"00", x"19", x"32", x"4B", x"64", x"7D", x"96", x"AF", x"C8", x"E1", x"FA", x"13", x"2C", x"45", x"5E", x"77";
    i_cosine <= x"77", x"5E", x"45", x"2C", x"13", x"FA", x"E1", x"C8", x"AF", x"96", x"7D", x"64", x"4B", x"32", x"19", x"00";
    q_sine <= x"00", x"F3", x"E6", x"D9", x"CC", x"BF", x"B2", x"A5", x"98", x"8B", x"7E", x"71", x"64", x"57", x"4A", x"3D";
    q_cosine <= x"3D", x"4A", x"57", x"64", x"71", x"7E", x"8B", x"98", x"A5", x"B2", x"BF", x"CC", x"D9", x"E6", x"F3", x"00";

    process(clk)
    begin
        if rising_edge(clk) then
            phase <= std_logic_vector(unsigned(in_i)*unsigned(q_cosine)-unsigned(in_q)*unsigned(i_cosine));
        end if;
    end process;

    out_i <= std_logic_vector(unsigned(phase) > 127);
    out_q <= std_logic_vector(unsigned(phase(7 downto 0)) > 127);
    qpsk <= out_i(0) & out_q(0);
    out_qpsk <= qpsk;
end behavioral;