基于MATLAB的2发1收空时分组码MIMO系统实现
本文介绍双发射天线单接收天线配置下的空时分组码MIMO系统实现，采用Alamouti编码方案。系统包含调制、编码、信道传输和解码全流程。
系统架构
系统核心参数配置：
- 发射端：2个天线
- 接收端：1个天线
- 编码方案：Alamouti空时编码
- 可配置调制方式：BPSK/QPSK/16QAM/64QAM
% 2Tx1Rx STBC-MIMO系统仿真
clear; clc;
%% 系统参数
txNum = 2; % 发射天线数
rxNum = 1; % 接收天线数
modType = 'QPSK'; % 调制类型
bitLength = 1e4; % 传输比特数
snrRange = 0:2:20; % 信噪比范围(dB)
frameCount = 100; % 每SNR仿真帧数
% 调制参数配置
switch modType
case 'BPSK'
bitsPerSym = 1;
symSet = [0, 1];
case 'QPSK'
bitsPerSym = 2;
symSet = 0:3;
case '16QAM'
bitsPerSym = 4;
symSet = 0:15;
case '64QAM'
bitsPerSym = 6;
symSet = 0:63;
end
% 比特数对齐
bitLength = ceil(bitLength/bitsPerSym) * bitsPerSym;
%% 主循环
errorRate = zeros(size(snrRange));
for idx = 1:length(snrRange)
errSum = 0; bitSum = 0;
for frm = 1:frameCount
% 生成随机比特
txBits = randi([0 1], bitLength, 1);
% 调制
modSyms = modulate(txBits, modType);
% Alamouti编码
encSyms = stbcEncode(modSyms);
% 瑞利信道
H = (randn(rxNum, txNum, length(encSyms)) + ...
1i*randn(rxNum, txNum, length(encSyms))) / sqrt(2);
% 加噪传输
rxSyms = transmit(encSyms, H, snrRange(idx));
% Alamouti解码
decSyms = stbcDecode(rxSyms, H);
% 解调
rxBits = demodulate(decSyms, modType);
% 误码统计
errSum = errSum + sum(txBits ~= rxBits);
bitSum = bitSum + bitLength;
end
errorRate(idx) = errSum / bitSum;
end
%% 结果可视化
figure;
semilogy(snrRange, errorRate, 'bo-', 'LineWidth', 1.5);
grid on;
xlabel('信噪比(dB)');
ylabel('误码率');
title([num2str(txNum) '发' num2str(rxNum) '收STBC-MIMO性能 (' modType ')']);
%% 调制函数
function out = modulate(bits, scheme)
switch scheme
case 'BPSK'
out = 1 - 2*double(bits);
case 'QPSK'
rebits = reshape(bits, 2, [])';
symIdx = bi2de(rebits, 'left-msb');
out = exp(1i*(pi/2*symIdx + pi/4));
case '16QAM'
rebits = reshape(bits, 4, [])';
symIdx = bi2de(rebits, 'left-msb');
out = qammod(symIdx, 16, 'UnitAveragePower', true);
case '64QAM'
rebits = reshape(bits, 6, [])';
symIdx = bi2de(rebits, 'left-msb');
out = qammod(symIdx, 64, 'UnitAveragePower', true);
end
end
%% 解调函数
function out = demodulate(syms, scheme)
switch scheme
case 'BPSK'
out = real(syms) < 0;
case 'QPSK'
phase = angle(syms);
symIdx = mod(round((phase - pi/4)/(pi/2)), 4);
out = de2bi(symIdx, 2, 'left-msb')';
out = out(:);
case '16QAM'
symIdx = qamdemod(syms, 16, 'UnitAveragePower', true);
out = de2bi(symIdx, 4, 'left-msb')';
out = out(:);
case '64QAM'
symIdx = qamdemod(syms, 64, 'UnitAveragePower', true);
out = de2bi(symIdx, 6, 'left-msb')';
out = out(:);
end
end
%% STBC编码器
function out = stbcEncode(syms)
out = zeros(2, length(syms));
for k = 1:2:length(syms)-1
s1 = syms(k);
s2 = syms(k+1);
out(1,k) = s1; % 时隙1: 天线1
out(2,k) = s2; % 时隙1: 天线2
out(1,k+1) = -conj(s2); % 时隙2: 天线1
out(2,k+1) = conj(s1); % 时隙2: 天线2
end
end
%% 信道传输
function out = transmit(txSyms, H, snr)
[~, symCount] = size(txSyms);
out = zeros(size(H,1), symCount);
noiseVar = 10^(-snr/10);
for t = 1:symCount
chOut = H(:,:,t) * txSyms(:,t);
noise = sqrt(noiseVar/2)*(randn(size(chOut)) + 1i*randn(size(chOut)));
out(:,t) = chOut + noise;
end
end
%% STBC解码器
function out = stbcDecode(rxSyms, H)
symCount = size(rxSyms, 2);
out = zeros(1, symCount);
for k = 1:2:symCount-1
y1 = rxSyms(:,k);
y2 = rxSyms(:,k+1);
h1 = H(:,1,k);
h2 = H(:,2,k);
% Alamouti组合
s1_hat = conj(h1).*y1 + h2.*conj(y2);
s2_hat = conj(h2).*y1 - h1.*conj(y2);
% 信道增益归一化
chGain = abs(h1).^2 + abs(h2).^2;
out(k) = s1_hat ./ chGain;
out(k+1) = s2_hat ./ chGain;
end
end信道估计增强实现
%% 带信道估计的STBC-MIMO
function ber = stbcMIMO_CE()
% 系统参数
txNum = 2; rxNum = 1;
modType = 'QPSK';
bitLen = 1e4;
snrVec = 0:2:20;
frameNum = 100;
% 导频配置
pilotSym = [1; -1j]; % QPSK导频
pilotInterval = 10;
% 调制参数
switch modType
case 'BPSK', symBits = 1;
case 'QPSK', symBits = 2;
case '16QAM', symBits = 4;
case '64QAM', symBits = 6;
end
% 主循环
ber = zeros(size(snrVec));
for snrIdx = 1:length(snrVec)
errCnt = 0; bitCnt = 0;
for frm = 1:frameNum
% 生成数据
dataBits = randi([0 1], bitLen, 1);
dataSyms = modulate(dataBits, modType);
% 插入导频
txSyms = [];
pilotPos = [];
for p = 1:pilotInterval:length(dataSyms)
txSyms = [txSyms; pilotSym];
pilotPos = [pilotPos, length(txSyms)-1, length(txSyms)];
endIdx = min(p+pilotInterval-1, length(dataSyms));
txSyms = [txSyms; dataSyms(p:endIdx)];
end
% STBC编码
encSyms = stbcEncode(txSyms);
% 信道传输
H_true = (randn(rxNum, txNum, size(encSyms,2)) + ...
1i*randn(rxNum, txNum, size(encSyms,2)))/sqrt(2);
rxSyms = transmit(encSyms, H_true, snrVec(snrIdx));
% 信道估计
H_est = zeros(size(H_true));
for p = 1:2:length(pilotPos)-1
pos = pilotPos(p);
y1 = rxSyms(:,pos); y2 = rxSyms(:,pos+1);
h1 = (conj(pilotSym(1))*y1 + pilotSym(2)*conj(y2))/2;
h2 = (conj(pilotSym(2))*y1 - pilotSym(1)*conj(y2))/2;
H_est(:,:,pos:pos+1) = cat(3, h1, h2);
end
% 线性插值
for ant = 1:txNum
for rx = 1:rxNum
H_est(rx,ant,:) = interp1(pilotPos, ...
squeeze(H_est(rx,ant,pilotPos)), ...
1:size(H_est,3), 'linear');
end
end
% STBC解码
decSyms = stbcDecode(rxSyms, H_est);
decSyms(pilotPos) = []; % 移除导频
% 误码统计
rxBits = demodulate(decSyms, modType);
errCnt = errCnt + sum(dataBits ~= rxBits);
bitCnt = bitCnt + bitLen;
end
ber(snrIdx) = errCnt / bitCnt;
end
% 结果展示
figure;
semilogy(snrVec, ber, 'ms-', 'LineWidth', 1.5);
grid on;
xlabel('信噪比(dB)'); ylabel('误码率');
title('带信道估计的STBC-MIMO性能');
end系统性能对比
%% STBC-MIMO与SISO性能对比
function compareSystems()
modType = '16QAM';
bitLen = 1e4;
snrVec = 0:2:20;
frameNum = 50;
berMIMO = zeros(size(snrVec));
berSISO = zeros(size(snrVec));
for snrIdx = 1:length(snrVec)
errMIMO = 0; errSISO = 0; bitTotal = 0;
for frm = 1:frameNum
% 公共数据源
data = randi([0 1], bitLen, 1);
modSyms = modulate(data, modType);
%% MIMO分支
encSyms = stbcEncode(modSyms);
H_mimo = (randn(1,2,size(encSyms,2)) + ...
1i*randn(1,2,size(encSyms,2)))/sqrt(2);
rxMIMO = transmit(encSyms, H_mimo, snrVec(snrIdx));
decSyms = stbcDecode(rxMIMO, H_mimo);
rxBitsMIMO = demodulate(decSyms, modType);
errMIMO = errMIMO + sum(data ~= rxBitsMIMO);
%% SISO分支
H_siso = (randn(1,1,length(modSyms)) + ...
1i*randn(1,1,length(modSyms)))/sqrt(2);
rxSISO = zeros(size(modSyms));
for k = 1:length(modSyms)
rxSISO(k) = H_siso(:,:,k)*modSyms(k);
end
noise = sqrt(10^(-snrVec(snrIdx)/10)/2) * ...
(randn(size(rxSISO)) + 1i*randn(size(rxSISO)));
rxSISO = rxSISO + noise;
eqSyms = rxSISO ./ squeeze(H_siso);
rxBitsSISO = demodulate(eqSyms, modType);
errSISO = errSISO + sum(data ~= rxBitsSISO);
bitTotal = bitTotal + bitLen;
end
berMIMO(snrIdx) = errMIMO / bitTotal;
berSISO(snrIdx) = errSISO / bitTotal;
end
% 可视化对比
figure;
semilogy(snrVec, berMIMO, 'bd-', 'LineWidth', 1.5, 'DisplayName', 'STBC-MIMO');
hold on;
semilogy(snrVec, berSISO, 'r^--', 'LineWidth', 1.5, 'DisplayName', 'SISO');
grid on;
xlabel('信噪比(dB)'); ylabel('误码率');
title(['系统性能对比 (' modType ')']);
legend('Location', 'best');
end实现说明：
- 支持不同调制方式配置
- 包含基础实现和信道估计扩展
- 提供与SISO系统的性能对比
- 采用准静态平坦瑞利衰落信道模型
