cdma_1208看1.m

这是个扩频系统中的PN码仿真程序

%通信信号处理作业
%
%
%
%
clear;clc;%close all;
N=100;
Lc=15%括频增益;
fd=5.6;
rate=2400%码片速率;
if_frequency=1800%数字上变频;
fs=14400%抽样频率;
j=sqrt(-1);
d=1;
rand('state',50);%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GOLD扩频码
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);
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
%RCOSFIR(R, N_T, RATE, T)R是滚降因子N。。。。，
I_rcosed=conv(I_spread_samp,num);%时域卷积输出
Q_rcosed=conv(Q_spread_samp,num);%时域卷积输出
% % 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=-10;
E=1;%归一化符号号能量
E_bit=E/2;
snr=10^(SNR/10);
sigma=sqrt(E_bit/2/snr);%noise variance
randn('state',sum(100*clock)+50);
Noise=sigma*randn(size(S_I_Q));
S_I_Q_receive=S_I_Q+Noise;

% %数字下变频
I_down=S_I_Q_receive.*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_receive.*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+72);
    Q_after_gr(i)=Q_gr(i+72);
end
I_down_samp=downsample(I_after_gr,6);
Q_down_samp=downsample(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);
pe=pe_bit(data_bit,symbol_demoulate)