直接序列扩频通信仿真

1、function dscdmamodem(user,snr_in_dbs %建立模型:用户信息,snr_in_dbs为信噪比%设置初始参数user=0 1 0 1 1 0 1;close all%定义步长变量%length_user=length(user; %改变用户数据中的0为-1for i=1:length_userif user(i=0;user(i=-1;endend%用户传输前设置fc=3; %载频eb=2; %每个字符的能量tb=1; %每个信息比特所占的时间%用户输入的数据信息t=0.01:0.01:tb*length_user;basebandsig=;for i=1:len

2、gth_user;for j=0.01:0.01:tb;if user(i=1;basebandsig=basebandsig 1;elsebasebandsig=basebandsig -1;endendendfigure(1plot(basebandsigaxis(0 100*length_user -1.5 1.5;title('用户输入的信息'Y=fft(basebandsig;figure(2plot(abs(Yaxis(0 100 0 300;title('扩频前的频域图'%用户的BPSK调制过程bpskmod=;for i=1:length_use

3、r;for j=0.01:0.01:tb;bpskmod=bpskmod sqrt(2*eb*user(i*cos(2*pi*fc*j; endendlength(bpskmodW=fft(bpskmod;%用户BPSK调制后的波形图输出figure(3plot(bpskmodaxis(0 100*length_user -3 3;title('用户经BPSK调制之后的波形'%扩频%PN码发生器seed=1 -1 1 -1; %设PN码初始值为1000 spreadspectrum=;pn=;for i=1:length_userfor j=1:10; %PN码和数据比特码的比

4、率设为10:1pn=pn seed(4;if seed(4=seed(3 temp=-1;else temp=1;endseed(4=seed(3;seed(3=seed(2;seed(2=seed(1;seed(1=temp;endspreadspectrum=spreadspectrum user(i*pn;end%扩频过程pnupsampled=;len_pn=length(pn;for i=1:len_pnfor j=0.1:0.1:tbif pn(i=1pnupsampled=pnupsampled 1;elsepnupsampled=pnupsampled -1;endendend

5、%扩频码波形输出figure(4plot(pnupsampledaxis(0 100*length_user -2 2;title('PN码波形图'%扩频后的波形图输出figure(5plot(sigtxaxis(0 100*length_user -3 3;title('用PN码扩频后的波形图'composite_signal=sigtx;%扩频后的频域波形图Z=fft(sigtx;figure(6plot(abs(Zaxis(0 100 0 300;title('扩频后的频域图'%高斯白噪声信道传输snr_in_dbs=20; %设信噪比为2

6、0composite_signal=awgn(composite_signal,snr_in_dbs;%从信道中解扩出用户的信息plot(rxtitle('用户解扩后的波形'%BPSK解调过程demodcar=;for i=1:length_userfor j=0.01:0.01:tbdemodcar=demodcar sqrt(2*eb*cos(2*pi*fc*j;endendbpskdemod=rx.*demodcar;figure(8plot(bpskdemodtitle('用户经BPSK解调之后的波形'len_dmod=length(bpskdemod;

7、sum=zeros(1,len_dmod/100;for i=1:len_dmod/100for j=(i-1*100+1:i*100sum(i=sum(i+bpskdemod(j;endend%检波过程rxbits=;for i=1:length_userif sum(i>0rxbits=rxbits 1;elserxbits=rxbits 0;endendlength_rxbits=length(rxbits;t=0.01:0.01:tb*length_rxbits;savbandsig=;for i=1:length_rxbitsfor j=0.01:0.01:tbif rxbits(i=1savbandsig=savbandsig 1;elsesavb