C/A 码扩频与解扩实验代码

以下是一个使用 MATLAB 编写的 C/A 码扩频与解扩实验代码示例：

% C/A 码扩频与解扩实验

% 设置参数
fs = 10e6;          % 采样频率
fc = 1.023e6;       % GPS C/A 码载波频率
PRN = 1;            % GPS C/A 码 PRN 号
Tc = 1/fc;          % C/A 码周期
Ts = 1/fs;          % 采样周期
fc_t = 1/Tc;        % C/A 码周期数
fs_t = fs/fc_t;     % 采样周期数

% 生成 C/A 码
CA_code = generateCAcode(PRN);

% 生成载波信号
t = 0:Ts:Tc-Ts;
carrier = cos(2*pi*fc*t);

% 扩频
spread_code = repmat(CA_code, 1, fc_t);
spread_signal = carrier .* spread_code;

% 添加噪声
SNR = 10;    % 信噪比
noise = randn(size(spread_signal));
signal_power = norm(spread_signal)^2 / length(spread_signal);
noise_power = signal_power / 10^(SNR/10);
noise = noise * sqrt(noise_power);
noisy_signal = spread_signal + noise;

% 解扩
despread_signal = noisy_signal .* spread_code;

% 绘制图形
figure;
subplot(2,2,1);
plot(t, carrier);
title('原始载波信号');
subplot(2,2,2);
plot(t, spread_code);
title('C/A 码');
subplot(2,2,3);
plot(t, noisy_signal);
title('加噪声后的扩频信号');
subplot(2,2,4);
plot(t, despread_signal);
title('解扩后的信号');

% 生成 C/A 码的函数
function ca_code = generateCAcode(prn)
    % 生成 C/A 码
    G1 = [-1,-1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,1,-1,-1,-1,1,-1,-1,-1,-1,-1,1,-1,-1];
    G2 = [-1,-1,-1,-1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,-1,-1,-1,1,-1];
    code_length = length(G1);
    ca_code = zeros(1, code_length);
    LFSR1 = ones(1, 10);
    LFSR2 = ones(1, 10);
    for i = 1:code_length
        ca_code(i) = mod(LFSR1(end) + LFSR2(end), 2);
        G1_output = mod(sum(G1 .* LFSR1), 2);
        G2_output = mod(sum(G2 .* LFSR2), 2);
        LFSR1 = [G1_output, LFSR1(1:end-1)];
        LFSR2 = [G2_output, LFSR2(1:end-1)];
    end
    ca_code(ca_code == 0) = -1;
    ca_code = ca_code(prn+1:end);
end

上述代码中，首先生成了 C/A 码和载波信号，然后将载波信号与 C/A 码进行扩频，得到扩频信号。再添加噪声后，使用与发送端相同的 C/A 码进行解扩，得到解扩后的信号。最后绘制出原始载波信号、C/A 码、加噪声后的扩频信号和解扩后的信号的波形图。