请帮我对下面的代码添加注释：copyfile('commlteMIMO_params_QAM16.m','commlteMIMO_params.m'); commlteMIMO_params; [prmLTEPDSCH, prmLTEDLSCH, prmMdl] = commlteMIMO_initialize(txMode, ... chanBW, contReg, modType, Eqmode,numTx, numRx,cRate,maxIter, fullDecode, chanMdl, corrLvl, ... chEstOn, numCodeWords, enPMIfback, cbIdx, snrdB, maxNumErrs, maxNumBits); clear txMode chanBW contReg modType Eqmode numTx numRx cRate maxIter fullDecode chanMdl corrLvl chEstOn numCodeWords enPMIfback cbIdx snrdB maxNumErrs maxNumBits %% disp('Simulating the LTE Mode 4: Multiple Tx & Rx antrennas with Spatial Multiplexing'); zReport_data_rate(prmLTEPDSCH, prmLTEDLSCH); hPBer = comm.ErrorRate; snrdB=prmMdl.snrdB; maxNumErrs=prmMdl.maxNumErrs; maxNumBits=prmMdl.maxNumBits; %% Simulation loop tic; nS = 0; % Slot number, one of [0:2:18] Measures = zeros(3,1); %initialize BER output while (( Measures(2)< maxNumErrs) && (Measures(3) < maxNumBits)) [dataIn, dataOut, txSig, rxSig, dataRx, yRec, csr] = ... commlteMIMO_SM2_step(nS, snrdB, prmLTEDLSCH, prmLTEPDSCH, prmMdl); % Calculate bit errors Measures = step(hPBer, dataIn, dataOut); % Visualize constellations and spectrum if (visualsOn && prmLTEPDSCH.Eqmode~=3) zVisualize( prmLTEPDSCH, txSig, rxSig, yRec, dataRx, csr, nS); end; % Update subframe number nS = nS + 2; if nS > 19, nS = mod(nS, 20); end; end disp(Measures); toc;

% 复制参数文件
copyfile('commlteMIMO_params_QAM16.m','commlteMIMO_params.m');

% 加载参数
commlteMIMO_params;

% 初始化LTE参数，包括物理下行共享信道(PDSCH)和下行共享信道(DLSCH)的参数，以及模型参数
[prmLTEPDSCH, prmLTEDLSCH, prmMdl] = commlteMIMO_initialize(txMode, chanBW, contReg, modType, Eqmode, numTx, numRx, cRate, maxIter, fullDecode, chanMdl, corrLvl, chEstOn, numCodeWords, enPMIfback, cbIdx, snrdB, maxNumErrs, maxNumBits);

% 清空参数变量
clear txMode chanBW contReg modType Eqmode numTx numRx cRate maxIter fullDecode chanMdl corrLvl chEstOn numCodeWords enPMIfback cbIdx snrdB maxNumErrs maxNumBits

% 输出模拟信息
disp('Simulating the LTE Mode 4: Multiple Tx & Rx antrennas with Spatial Multiplexing');

% 报告数据速率
zReport_data_rate(prmLTEPDSCH, prmLTEDLSCH);

% 初始化误码率计算器
hPBer = comm.ErrorRate;

% 从模型参数中获取信噪比和最大误码数、比特数
snrdB=prmMdl.snrdB;
maxNumErrs=prmMdl.maxNumErrs;
maxNumBits=prmMdl.maxNumBits;

% 初始化模拟循环参数
tic;
nS = 0; % 子帧编号，取值为[0:2:18]
Measures = zeros(3,1); % 初始化误码率输出

% 开始模拟循环
while ((Measures(2) < maxNumErrs) && (Measures(3) < maxNumBits))
    % 调用commlteMIMO_SM2_step()函数模拟信号传输和接收过程
    [dataIn, dataOut, txSig, rxSig, dataRx, yRec, csr] = commlteMIMO_SM2_step(nS, snrdB, prmLTEDLSCH, prmLTEPDSCH, prmMdl);

    % 计算误码率
    Measures = step(hPBer, dataIn, dataOut);

    % 可视化星座图和频谱
    if (visualsOn && prmLTEPDSCH.Eqmode ~= 3)
        zVisualize(prmLTEPDSCH, txSig, rxSig, yRec, dataRx, csr, nS);
    end;

    % 更新子帧编号
    nS = nS + 2;
    if nS > 19, nS = mod(nS, 20); end;
end

% 输出误码率
disp(Measures);

% 停止计时
toc;

这段代码是用于模拟LTE Mode 4的多个发射和接收天线的空间复用。首先进行了参数初始化，然后进入模拟循环。在循环中，通过调用commlteMIMO_SM2_step()函数，模拟信号传输和接收过程，并计算误码率(Measures)。同时，如果visualsOn为真且Eqmode不等于3，则可视化星座图和频谱。最后输出误码率(Measures)。