awgn_1213.m

这是个扩频系统中的PN码仿真程序

%通信信号处理作业
%
%百噪声情况下CDMA误码率
%
%
% clear;clc;%close all;
function pe_awgn=awng_cdma_pe(SNR)
err_num=0;
data_bit_length=0;
while
   err_num<10
    N=200;
    Lc=15%扩频增益;
    fd=5.6;
    rate=2400;%码片速率
    if_frequency=1800;%数字上变频1800Hz
    fs=14400;%抽样频率14400Hz
    j=sqrt(-1);
    d=1;
    rand('state',sum(100*clock));
    data_bit=round(rand(1,N));
    modula_data=QPSK_Modulate(data_bit);
    modua_data_I=real(modula_data);
    modua_data_Q=imag(modula_data);
    
    code_type=2;  %0 = random 1 = hadamard 2 = gold生成扩品吗
    code_seed=rand('state'); 
    codes=(cdma_codes(1,0,code_type,Lc,code_seed))'; %cdma_codes(K_in,K_out,code_type,L,code_seed) 
    % codes=[1 1 0 0 0 0 1 0 1 1 0 1 1 1 0];
    I_spread=kron(modua_data_I,codes);%kron函数是张量积生成一个更大的矩阵这里是生成扩频码我想也应该可以用相乘的形式
    Q_spread=kron(modua_data_Q,codes);
    over_sample=[1 0 0 0 0 0];%过抽样，消除isi
    I_spread_samp=kron(I_spread,over_sample);
    Q_spread_samp=kron(Q_spread,over_sample);
    % num=rcosine(2400,14400,'sqrt',0.2);
    num=rcosfir(0.2,6,6,1/rate,'sqrt');%成型滤波
    I_rcosed_delay=conv(I_spread_samp,num);
    Q_rcosed_delay=conv(Q_spread_samp,num);
    
    for i=1:length(I_spread_samp)%产生周期为36的信号
        I_rcosed(i)=I_rcosed_delay(i+36);
        Q_rcosed(i)=Q_rcosed_delay(i+36);
    end

    % % plot(I_rcosed(1:10));
    i=1:length(I_rcosed);
    IF_fre_I=cos(2*pi*if_frequency*(i-1)*(1/fs));%上变频 data_f=14.4/522,所以1.8*522/14.4＝65.25就是中心载波所在的位置
    IF_fre_Q=sin(2*pi*if_frequency*(i-1)*(1/fs));
    I_if=I_rcosed.*IF_fre_I;
    Q_if=Q_rcosed.*IF_fre_Q;
    S_I_Q=I_if+Q_if;
    % 
    % % channel=rayleigh2(fd,fs,ns);
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    %信道
    %加入噪声
    % SNR=0;
    E=1;%归一化符号号能量
    E_chip=1;
    E_bit=E/2;
    snr=10^(SNR/10);
    sigma=sqrt(E_chip/(2*snr*4/15));%noise variance  (snr_in bit=E_bit/(N0))
    randn('state',sum(100*clock)+50);
    Noise=sigma*randn(size(S_I_Q));
    S_I_Q=S_I_Q+Noise;
    
    % %数字下变频
    I_down=S_I_Q.*IF_fre_I;
    f1=2*rate/fs;
    low_filter=fir1(34,f1);
    after_low_tem=conv(I_down,low_filter);
    for i=1:length(I_down)
        after_low_I(i)=after_low_tem(i+16);
    end
    % I_down_fft=fft(after_low);%比较滤波前后的频谱
    % figure(1);
    % plot(abs(I_down_fft));
    % figure(2);
    %plot(abs(fft(I_down)));
    Q_down=S_I_Q.*IF_fre_Q;
    after_low_tem=conv(Q_down,low_filter);
    for i=1:length(Q_down)
        after_low_Q(i)=after_low_tem(i+16);
    end
    % Q_down_fft=fft(Q_down);
    
    I_gr=conv((after_low_I),num);
    Q_gr=conv((after_low_Q),num);
    for i=1:length(I_spread_samp)
        I_after_gr(i)=I_gr(i+36);
        Q_after_gr(i)=Q_gr(i+36);
    end
    % I_down_samp=decimate(I_after_gr,6);
    % Q_down_samp=decimate(Q_after_gr,6);
    
    i=1;%和上两句完成的功能一样
    while (i*6)<=length(I_spread_samp)
        I_down_samp(i)=I_after_gr((i-1)*6+1);
        Q_down_samp(i)=Q_after_gr((i-1)*6+1);
        i=i+1;
    end
    
    % %验证
    % aa=fft(I_rcosed);
    % dd=fft(Q_rcosed);
    % bb=fft(I_down);
    % cc=fft(Q_down);
    % figure(1);
    % plot(abs(aa));
    % figure(2);
    % plot(abs(bb));
    % figure(3);
    % plot(abs(cc));
    % figure(4);
    % plot((abs(dd)));
    data_length=length(I_down_samp);
    length_symbol=round(data_length/Lc);
    for i=1:length_symbol
        tem=I_down_samp((i-1)*(Lc)+1:(i-1)*(Lc)+15);
        tem_sum=sum(tem.*codes);
        symbol_I(i)=tem_sum*2/Lc;
        tem=Q_down_samp((i-1)*(Lc)+1:(i-1)*(Lc)+15);
        tem_sum=sum(tem.*codes);
        symbol_Q(i)=tem_sum*2/Lc;
    end
    symbol=symbol_I+j*symbol_Q;
    
    symbol_demoulate=QPSK_Demodulate(symbol,d);
    err_num1=pe_bit(data_bit,symbol_demoulate);
    err_num=err_num+err_num1;
    data_bit_length=data_bit_length+length(data_bit);
end
pe_awgn=err_num/data_bit_length;
% pe_awgn=pe_bit(data_bit,symbol_demoulate);