OFDM-MIMO多径信道的LS估计，绘制MSE与信噪比的关系图的代码

以下是基于MATLAB的OFDM-MIMO多径信道LS估计，绘制MSE与信噪比关系图的代码：

clear all;
close all;

% 设置参数
M = 4; % 调制阶数
Nt = 2; % 发射天线数
Nr = 2; % 接收天线数
SNR_dB = 0:5:30; % 信噪比范围
numIter = 1000; % 模拟次数
num_tap = 4; % 多径信道时延数
num_subcarrier = 64; % 子载波数

% 生成QPSK调制信号
data = randi([0 M-1], Nt, num_subcarrier);

% 构造发送信号
x = qammod(data, M);

% 构建MIMO多径信道
for i = 1:length(SNR_dB)
    SNR = 10^(SNR_dB(i)/10);
    h = zeros(Nr, Nt, num_tap);
    for j = 1:num_tap
        h(:,:,j) = (randn(Nr, Nt) + 1j*randn(Nr, Nt))/sqrt(2);
    end
    n = sqrt(1/SNR)*(randn(Nr, num_subcarrier, num_tap) + 1j*randn(Nr, num_subcarrier, num_tap))/sqrt(2);
    y_tmp = zeros(Nr, num_subcarrier, num_tap);
    for j = 1:num_tap
        y_tmp(:,:,j) = squeeze(h(:,:,j))*x(:,:,j) + squeeze(n(:,:,j));
    end
    y(:,:,i) = sum(y_tmp, 3);
    H(:,:,i) = squeeze(sum(h, 3));
end

% LS信道估计
H_LS = zeros(Nr, Nt, num_subcarrier, length(SNR_dB));
for i = 1:length(SNR_dB)
    for j = 1:num_subcarrier
        H_LS(:,:,j,i) = y(:,j,i)*x(:,j,i)'/(x(:,j,i)*x(:,j,i)');
    end
end

% 计算MSE
MSE_LS = zeros(length(SNR_dB), 1);
for i = 1:length(SNR_dB)
    for j = 1:num_subcarrier
        for k = 1:numIter
            noise = sqrt(1/SNR)*(randn(Nr, 1) + 1j*randn(Nr, 1))/sqrt(2);
            H_est = y(:,j,i)*x(:,j,i)'/(x(:,j,i)*x(:,j,i)');
            MSE_LS(i) = MSE_LS(i) + norm(H(:,:,i) - H_est, 'fro')^2;
        end
    end
end
MSE_LS = MSE_LS/numIter/num_subcarrier;

% 绘制MSE与信噪比关系图
figure;
semilogy(SNR_dB, MSE_LS, 'r-o');
title('LS信道估计MSE与信噪比关系图');
xlabel('信噪比 (dB)');
ylabel('MSE');
grid on;

该代码使用LS算法对OFDM-MIMO多径信道进行信道估计，并绘制了MSE与信噪比之间的关系图。