%在DS-spread spectrum系統(tǒng)中,噪聲為加性高斯白噪聲,驗(yàn)證性能,傳統(tǒng)單用戶檢測(cè)
clear all
close all
clc;

%[1]initial Parameter
K=4; %用戶數(shù)
Lc=32;%擴(kuò)頻增益
x_num=5000;%信息序列長(zhǎng)度
SNRindB=-20:3:10;
Tc=1;
Ts=Lc*Tc;

for i=1:length(SNRindB)
    SNRline=10^(SNRindB(i)/10);
    Sigma=1;%噪聲標(biāo)準(zhǔn)差
    Eb=2*Sigma^2*SNRline; %信號(hào)能量
    Pow=Eb/Ts;%信號(hào)功率
    x=GenBPSK(x_num);%產(chǎn)生BPSK信號(hào),信號(hào)長(zhǎng)度已經(jīng)確定,均勻分布
    %[2]spread spectrum
    PNcode=hadamard(Lc);%產(chǎn)生用戶PN序列
    c=PNcode(1,:)';
    y=dsmod(c,x);
    
    %加入其他用戶信息作為干擾
    for u=2:K
        xtemp=3*GenBPSK(x_num);%此處可調(diào)節(jié),用于分析系統(tǒng)對(duì)遠(yuǎn)近效應(yīng)的抵抗能力
        ctemp=PNcode(u,:)';
        ytemp=dsmod(ctemp,xtemp);
        y=y+ytemp;
    end
    y=sqrt(Pow)*y;
    %[3]Add AWGN
    AWGN=Sigma*randn(1,Lc*x_num);
    y=y+AWGN;
    %[4]despread spectrum
    r=dsdemode(c,y);
     
    %[5]decision
    r=sign(r);
    Errorbit=length(find(abs(r-x)>1e-004));
    BER(i)=Errorbit/length(r);
      
end
    %Plot,SNR,BER
    figure
    semilogy(SNRindB,BER);
    title('The BER of Different SNR')
    grid