qpsk_baseband_ber.m

实现数字基带QPSK调制系统的误码率仿真

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% 仿真数字基带QPSK调制系统的误码率
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% 设置相关参数
Fd = 1;                      % 信号数据率
Fs = 1;                      % 调制信号的采样频率
N = Fs/Fd;
modulation = 'psk';
M = 4;                       % M元正交振幅调制参数，当M=2时为QPSK仿真
k = log2(M);
SNRpBit = 0:2:10;            % 设置仿真信噪比范围
SNR = SNRpBit + 10*log10(k);
symbPerIter = 4096;          % 设置每次迭代符合的次数
iters = 3;                   % 迭代次数                     
expSymErrs = 60;            % 设置预期误差符号数目
numSymbTot = symbPerIter * iters;
rand('state',123456789);   % 设置均匀随机数产生的“随机种子”
randn('state',987654321);   % 设置高斯噪声产生的“随机种子”
% 计算理论的比特误差和理论符号误差SER，并绘制BER和SER曲线
expBER = 0.5.* erfc(sqrt(10.^(SNRpBit(:).*0.1))); % 计算理论的比特误差BER
expSER = 1 - (1-expBER).^k;                       %  计算理论的比特误差和理论符号误差SER
semilogy(SNRpBit(:),expSER,'k-',SNRpBit(:),expBER,'k:');
legend('理论的SER','理论的BER',0);
title('基带QPSK调制性能仿真');
xlabel('SNR/bit(dB)');
ylabel('SER 与 BER');
hold on;
% 产生Gary码编码和解码序列
grayencod = bitxor([0:M-1],floor([0:M-1]/2));
[dummy graydecod] = sort(grayencod);graydecod = graydecod -1;
for(idx2 = [1:length(SNR)])         % 仿真不同SNR值时的BER和SER       
    idx = 1;
    while((idx<=iters)|(sum(errSym)<=expSymErrs))
        % 创建信号及Gary编码
        msg_orig = randsrc(symbPerIter,1,[0:M-1]);  % 产生[0,M-1]之间的信息序列
        % Gary编码
        msg_gr_orig = grayencod(msg_orig+1)';       % Gary编码
        % 数字基带调制
        msg_tx = dmodce(msg_gr_orig,Fd,Fs,modulation,M);
        % 对调制信号加高斯噪声
        msg_rx = awgn(msg_tx,SNR(idx2)-10*log10(1.*N),'measured',[],'dB');
        % 解调带通调制信号
        msg_gr_demod = ddemodce(msg_rx,Fd,Fs,modulation,M);
        % Gary码解码
        msg_demod = graydecod(msg_gr_demod+1)';
        % 计算本次迭代的BER、SER
        [errBit(idx) ratBit(idx)] = biterr(msg_orig,msg_demod,k);
        [errSym(idx) ratSym(idx)] = symerr(msg_orig,msg_demod);
        idx = idx + 1;    pause(.1); 
    end
    % 计算各次迭代后的平均BER、SER
    errors(idx2,:) = [sum(errBit), sum(errSym)];
    ratio(idx2,:) = [mean(ratBit), mean(ratSym)];
    % 绘制仿真的BER、SER曲线
    semilogy(SNRpBit([1:size(ratio(:,2),1)]),ratio(:,2),'k*',...
        SNRpBit([1:size(ratio(:,1),1)]),ratio(:,1),'ko');
    legend('理论的SER','理论的BER','仿真的SER','仿真的BER',0);
    pause(.1);
end
hold off;