conv_demo.m

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%clear all;
%clc;
tic

%(2, 1, 7)卷积码生成多项式O(133, 171)
%(n, k, N)即1个信息比特生成2个编码比特，约束长度N为7比特
%O(133, 171)为用八进制表示的生成多项式，即[1 0 1 1 0 1 1;1 1 1 1 0 0 1 ]
ConvCodeGenPoly = [1 0 1 1 0 1 1;1 1 1 1 0 0 1 ];
codeRate=1/2;

%初始化Viterbi译码
global prev_state;
global prev_state_outbits;

prev_state = zeros(64, 2);
prev_state_outbits = zeros(64, 2, 2);

for state = 0:63
   state_bits = de2bi(state, 6);
   input_bit = state_bits(1);
   for transition = 0:1
      prev_state_bits = [state_bits(2:6) transition];
      prev_state(state+1, transition+1) = bi2de(prev_state_bits);

      %对应映射为0->-1 1->+1的bpsk调制
      prev_state_outbits(state+1, transition+1, 1) = 2*(rem(sum(ConvCodeGenPoly(1,:).* ...
         [input_bit prev_state_bits]),2)) - 1;
      prev_state_outbits(state+1, transition+1, 2) = 2*(rem(sum(ConvCodeGenPoly(2,:).* ...
         [input_bit prev_state_bits]),2)) - 1;
   end
end

%单次仿真的信息长度
slen=64;

number_rows = size(ConvCodeGenPoly,1);
number_bits = size(ConvCodeGenPoly,2)+slen-1;
uncoded_bits = zeros(number_rows, number_bits);

%每种信噪比仿真迭代次数
simNum=1000;

%bpsk调制，每符号用1比特表示
k=1;

%信噪比矩阵，单位为dB
EbNo=2:0.5:5;
SNR=EbNo-10*log10(1/codeRate)+10*log10(k);

%初始化BER矩阵
BER=zeros(1, length(SNR));

for snrloop=1:length(SNR)

    disp(['EbNo(' num2str(snrloop) ')=' num2str(EbNo(snrloop))]);

    %计算噪声方差σ^2（bpsk调制后信号均值为0，平均功率为1）
    noise_var=1/(10^(SNR(snrloop)/10));

    totErr=0;

    for simcnt=1:simNum

        % Set Random number generators initial state
        % reset random number generators based on current clock value
        rand('state',sum(100*clock));
        randn('state',sum(100*clock));

        %产生取值为0或1的均匀分布的随机序列作为信息序列
        s=round(rand(1,slen));

        %卷积编码
        for row=1:number_rows
         uncoded_bits(row,:)=rem(conv(s,ConvCodeGenPoly(row,:)),2);
        end

        coded_bits=uncoded_bits(:)';

        %bpsk调制，映射为0->-1 1->+1
        bpsk_mod=coded_bits*2-1;

        %接收信号为bpsk调制信号加上噪声
        rx_waveform=awgn(bpsk_mod,SNR(snrloop),'measured');

        %Viterbi译码
        vtb_dec_out=rx_viterbi_decode(rx_waveform);
        uhat=vtb_dec_out(1:slen);

        %误码统计
        [errNum errRat]=biterr(s,uhat);
        totErr=errNum+totErr;

    end

    BER(snrloop)=totErr/simNum/slen;

end

result=[EbNo; SNR; BER]
save noInterleave_simNum1000_result result;

%绘制误码率曲线
semilogy(EbNo,BER,'m-');
title('Convolution coded bpsk simulation');
xlabel('Eb/No (dB)');
ylabel('BER');
legend('noInterleave Convolution BER',0);
grid on;

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