通信原理课程设计——DS/CDMA 基带传输系统
一、 课程设计要求：
用Matlab 构造一个DS/CDMA 基带传输系统，各用户的二进制数据b 与扩频码c 进行扩频，用户数K 为4个，扩频增益取31，扩频码采用Gold 码，接收端假设理想同步，对各用户通过解扩恢复各自的信息数据。发端基带成型采用滚降因子为0.22的平方根升余弦滚降脉冲（用48阶的FIR 滤波器来实现，每个码片采样16个样点），接收机用码片第8个或第9个样点作为判决点，信噪比大小（SNR ）自设，如SNR 可取为20dB 或30dB 。
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二、 DS/CDMA 原理：
三、系统设计：
根升余弦滤波器设计：
irfn = 48; % 滤波器阶数
IPOINT = 4; % 码片速率过采样倍数（4倍
alfs = 0.22; % 滚降因子
[xh] = hrollfcoef(irfn,IPOINT,sr,alfs,1); %发送端根升余弦滤波器系数[xh2] = hrollfcoef(irfn,IPOINT,sr,alfs,0); %接收端根升余弦滤波器系数%根升余弦滤波器
figure('Name','根升余弦滤波器','NumberTitle','on');
% Tx
subplot(211);stem(xh);grid;
xlabel('Bits index');
title('发送端根升余弦滤波器');
% Rx
subplot(212);stem(xh2);grid;
xlabel('Bits index');
title('接收端根升余弦滤波器');
误码率-信噪比关系图
figure; % plot the BER vs. SNR
semilogy(SNR,r,'r-x'),grid;
xlabel('SNR');ylabel('BER');
title('BER vs. SNR');
原始数据，发送和接收的比较
figure('Name','Original Data','NumberTitle','on');
% plot data for a randomly selected user such as user no. 1 before the BPSK mapping Tx and Rx
% Tx
subplot(211);stem(data(cuser,1:20),'filled');grid;
xlabel('Bits index');
title('Transmitted Bits (showing only 20 bits)');
% Rx
subplot(212);stem(data_rm(cuser,1:20),'filled');grid;
xlabel('Bits index');
title('Received Bits (showing only 20 bits)');
BPSK编码后，发送和接收的比较
figure('Name','BPSK Symbols','NumberTitle','on');
% plot data for a randomly selected user such as user no. 1 after the BPSK mapping Tx and Rx
% Tx
subplot(211);stem(data_m(cuser,1:20),'filled');grid;
xlabel('Symbol index');
title('Transmitted BPSK Symbols (showing only 20 Symbol)');
% Rx
subplot(212);stem(data_rs(cuser,1:20),'filled');grid;
xlabel('Symbol index');
title('Received BPSK Symbols (showing only 20 Symbol)');
要发送的数据，各个用户对应位求和的结果
figure('Name','Combined signals','NumberTitle','on');%plot combined signals
%Tx
subplot(211);stem(data_f(1:50),'filled');
title('Combined signals (only 20 symbols)');
xlabel('Index of Combined symbols');
ylabel('Magnitude');
grid;
%Rx
subplot(212);stem(data_ros(1:50),'filled');
title('Combined noisy signals (only 20 symbols）');
xlabel('Index of Combined symbols');
ylabel('Magnitude');
四、程序代码：
% main_DS_CDMA.m
% DS/CDMA通信系统仿真
%扩频码：Gold码
%+++++++++++++++++++++++准备部分+++++++++++++++++++++++++++
clear all; close all; clc;
disp('--------------Calculate Start ...-------------------');
sr = 256000.0; % 符号速率
ml = 2; % 调制阶数
br = sr * ml; % 比特速率
nd = 1000; % 符号数
SNR=-5:1:10; % Eb/No:Eb是指平和比特能量，no是指白噪声的功率谱密度
cuser = 1; % 画图时要显示的用户
%+++++++++++++++++++++滤波器初值设定+++++++++++++++++++++++
irfn = 48; % 滤波器阶数
IPOINT = 4; % 码片速率过采样倍数（4倍
alfs = 0.22; % 滚降因子
[xh] = hrollfcoef(irfn,IPOINT,sr,alfs,1); %发送端根升余弦滤波器系数%%hrollfcoef指
[xh2] = hrollfcoef(irfn,IPOINT,sr,alfs,0); %接收端根升余弦滤波器系数
%++++++++++++++++++++++++扩频码初值设定+++++++++++++++++++
user = 4; % 用户数
%seq = 2; % 1:m序列2:Gold序列3:正交Gold序列
stage = 5; % 序列阶数
ptap1 = [2 5]; % 第一个线性移位寄存器的系数
ptap2 = [1 2 3 5]; % 第二个线性移位寄存器的系数
regi1 = [1 1 1 1 1]; % 第一个线性移位寄存器的初始化
regi2 = [1 1 1 1 1]; % 第二个线性移位寄存器的初始化
%移位寄存器级数3，码长7.
% 5 31
%+++++++++++++++++扩频码的产生+++++++++++++++++
m1 = mseq(stage,ptap1,regi1);
m2 = mseq(stage,ptap2,regi2);
code = [goldseq(m1,m2,user),zeros(user,1)]; %正交Gold序列
code = code * 2 - 1; %双极性
clen = length(code);
data = rand(user,nd) > 0.5;
dlen = length(data);
data_m = data.*2 -1; %QPSK;
data_s=zeros(user,dlen*(2^stage));
for i1=1:1:user %扩频
data_s(i1,:)=kron(data_m(i1,:),code(i1,:));
end
data_os = compoversamp2(data_s,IPOINT); % 过采样
data_f1 = compconv2(data_os,xh); % 滤波
if user == 1
data_f = data_f1;
else
data_f = sum(data_f1);
end
disp('--------------Send Data ...-------------------');
loo=0;
for kk=1:1:length(SNR)
data_n=awgn(data_f,SNR(kk),'measured');%在信号data_f中加入高斯白噪声data_rf = compconv2(data_n,xh2); % 滤波
sampl = irfn * IPOINT + 1;
data_ros = data_rf(:,sampl:IPOINT:IPOINT*nd*clen+sampl-1); %减采样
%++++++++++解扩++++++++
data_rs=zeros(user,dlen);
scused=ones(1,dlen);
for i2=1:1:user
bds=kron(scused,code(i2,:)); %将Gold码矩阵的i2行，复制scused次
ds=bds.*data_ros(1,:); %反哈达玛变换（解扩）
rds=reshape(ds,clen,length(data_ros(1,:))/clen);%对ds重新排列成hl行，length(s)/hl。
%注：(reshape数据排列顺序：从上往下，从左往右)
ou=sum(rds); %对每列求和
t=length(ou);
en=zeros(1,t);
for a=1:t
if ou(a)>1 %抽样判决
en(a)=1;
else
en(a)=-1;
end
end
data_rs(i2,:)=en;
end
%++++++++++++++++++
data_rm=(data_rs+1)./2;%BPSK解调
loo=loo+1;
[n(loo),r(loo)]=symerr(data_m,data_rs); %[number,ratio] = symerr(x,y) end
disp('----------------Calculate Finished-------------------');
disp('----------------Start Plot-------------------');
%根升余弦滤波器
figure('Name','根升余弦滤波器','NumberTitle','on');
% Tx
subplot(211);stem(xh);grid;
xlabel('Bits index');
title('发送端根升余弦滤波器');
% Rx
subplot(212);stem(xh2);grid;
xlabel('Bits index');
title('接收端根升余弦滤波器');
%误码率-信噪比关系图
figure; % plot the BER vs. SNR
semilogy(SNR,r,'r-x'),grid;
xlabel('SNR');ylabel('BER');
title('BER vs. SNR');
%原始数据，发送和接收的比较
figure('Name','Original Data','NumberTitle','on');
% plot data for a randomly selected user such as user no. 1 before the BPSK mapping Tx and Rx
% Tx
subplot(211);stem(data(cuser,1:20),'filled');grid;
xlabel('Bits index');
title('Transmitted Bits (showing only 20 bits)');
% Rx
subplot(212);stem(data_rm(cuser,1:20),'filled');grid;
xlabel('Bits index');
title('Received Bits (showing only 20 bits)');
%BPSK编码后，发送和接收的比较
figure('Name','BPSK Symbols','NumberTitle','on');
% plot data for a randomly selected user such as user no. 1 after the BPSK mapping Tx and Rx
% Tx
subplot(211);stem(data_m(cuser,1:20),'filled');grid;
xlabel('Symbol index');
title('Transmitted BPSK Symbols (showing only 20 Symbol)');
% Rx
subplot(212);stem(data_rs(cuser,1:20),'filled');grid;
xlabel('Symbol index');
title('Received BPSK Symbols (showing only 20 Symbol)');
%要发送的数据，各个用户对应位求和的结果
figure('Name','Combined signals','NumberTitle','on');%plot combined signals
%Tx
subplot(211);stem(data_f(1:50),'filled');
title('Combined signals (only 20 symbols)');
xlabel('Index of Combined symbols');
ylabel('Magnitude');
grid;
%Rx
subplot(212);stem(data_ros(1:50),'filled');
title('Combined noisy signals (only 20 symbols）');
xlabel('Index of Combined symbols');
ylabel('Magnitude');
grid;
disp('----------------Plot Finished-------------------');