juanji_test.m

实现了信道编码

%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%  卷积码模块的性能测试  %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clear all;
close all;
% 信噪比测试范围为-4~+6dB
snr_in_dB1=[-4:1:6];
snr_in_dB2=[-4:0.1:6];
E=1;    % 噪声功率
for i=1:length(snr_in_dB1)
    snr(i)=10^(snr_in_dB1(i)/10);         % 转化单位
    sgma(i)=sqrt((E/snr(i))/2);           % 噪声方差
    bit_err_num1=0;   
    bit_err_num2=0;
    N=20;     % 帧数
    for n=0:(N-1)
        sequence=round(rand(1,224));          % 随机产生外编码后的得到的224bits序列
        input=[sequence,zeros(1,4)];          % 加尾比特0000
        viterbi_enc=SDC_IN_EN(input);         % 卷积码编码，编码后输出序列长度456bits
        
        % 经过高斯信道传输
        A=2*sequence-1;                       % 将单极性信号转化为双极性信号
        A=sign(A+sgma(i)*randn(size(A))+eps); % 未经过卷积编码的信号加高斯噪声并进行接收判决
        A=(A+1)/2;
        B=2*viterbi_enc-1;                    % 将单极性信号转化为双极性信号
	    B=sign(B+sgma(i)*randn(size(B))+eps); % 经过卷积编码后的信号加高斯噪声并进行接收判决
	    B=(B+1)/2;
        
        viterbi_out=SDC_IN_DE(B);             % Viterbi译码，输出序列长度228bits
        viterbi_dec=viterbi_out(1:224);       % 去掉四位尾比特
        
        original_bit_err_num=length(find(sequence~=A));            % 找出原始误码个数
        current_bit_err_num=length(find(sequence~=viterbi_dec));   % 找出有编译码改善后的误码个数
        if original_bit_err_num~=0
            bit_err_num1=bit_err_num1+original_bit_err_num;        % 累计每一帧的原始误码个数
        end
        if current_bit_err_num~=0
            bit_err_num2=bit_err_num2+current_bit_err_num;         % 累计每一帧改善后的误码个数
	    end
    end
    bit_err_rate1(i)=bit_err_num1/(N*224)  % 计算并显示原始误码率
    bit_err_rate2(i)=bit_err_num2/(N*224)  % 计算并显示改善后的误码率
end
for i=1:length (snr_in_dB2)
    SNR=exp(snr_in_dB2(i)*log(10)/10);
    theo_err_rate(i)=(1/2)*erfc(sqrt(2*SNR)/sqrt(2));    % 理论误码率
end

% 绘制曲线图
semilogy(snr_in_dB1,bit_err_rate1,'r*-');
hold on
semilogy (snr_in_dB1,bit_err_rate2,'g*-');
semilogy (snr_in_dB2,theo_err_rate);
xlabel('信噪比（dB）')
ylabel('误码率')
title('在高斯信道下原始误码特性、卷积码改善后的误码特性及理论误码特性比较')
hold off