function out = delay(data,n,sample_number)
%data:延迟的数据
%n:延迟码元个数
%sample_number:码元采样个数
out = zeros(1,length(data));
out(n*sample_number+1:length(data)) = data(1:length(data)-n*sample_number);
function [data_diff] = difference(data)
%差分编码
%**************************************************************************
%data 输入信号
%data_diff 差分编码后信号
%**************************************************************************
%--------------------------------------------------------------------------
data_diff = zeros(1,length(data));
data_diff(1) = 1 * data(1); %1为差分编码的初始参考值
for i = 2:length(data)
data_diff(i) = data_diff(i-1) * data(i);
end
%**************************************************************************
function [signal_out,I_out,Q_out] = mod_msk(data,data_len,sample_number,Rb)
%MSK基带调制
%**************************************************************************
% data 调制信号
% data_len 码元个数
% sample_number 每个码元采样点数
% Rb 码元速率
% signal_out 基带调制输出
% I_out I路输出
% Q_out Q路输出
%**************************************************************************
% data_len = 10; %码元个数
% sample_number = 8; %采样点数
% Rb = 16000; %码元速率
% data1 = randint(1,data_len);
% data = 2*data1-1; %传输的序列
Tb = 1/Rb; %码元时间
fs = Rb*sample_number; %采样速率
%--------------------------------------------------------------------------
%差分编码
[data_diff] = difference(data);
%**************************************************************************
%--------------------------------------------------------------------------
%并串转换，延时
I(1) = 1; %fai0 = 0,cos(fai0) = 1
for i = 1:2:data_len
Q(i) = data_diff(i);
Q(i+1) = data_diff(i);
end
for i = 2:2:data_len
I(i+1) = data_diff(i);
I(i) = data_diff(i);
end
for i = 1:sample_number
I1(i:sample_number:data_len*sample_number) = I(1:data_len);
Q1(i:sample_number:data_len*sample_number) = Q(1:data_len);
end
%**************************************************************************
%--------------------------------------------------------------------------
%乘加权函数
t=1/fs:1/fs:data_len*Tb;
I_out = I1 .* cos(pi*t/2/Tb);
Q_out = Q1 .* sin(pi*t/2/Tb);
%**************************************************************************
%--------------------------------------------------------------------------
%调制信号产生
signal_out = I_out + j*Q_out;
%**************************************************************************
% %--------------------------------------------------------------------------
% %画图
% subplot(221)
% plot(data,'.-');title('MSK传输的数据');xlabel('时间');ylabel('幅度')
% subplot(222)
% plot(data_diff,'.-');title('差分后的数据');xlabel('时间');ylabel('幅度')
% subplot(223)
% plot(I1,'.-');title('加权前I路');xlabel('时间');ylabel('幅度');
% subplot(224)
% plot(Q1,'.-');title('加权前Q路');xlabel('时间');ylabel('幅度');
%
% figure(2)
% subplot(221)
% plot(cos(pi*t/2/Tb),'.-');title('加权函数cos(πt/(2Tb))');xlabel('时间');ylabel('幅度')
% subplot(222)
% plot(sin(pi*t/2/Tb),'.-');title('加权函数sin(πt/(2Tb))');xlabel('时间');ylabel('幅度')
% subplot(223)
% plot(I_out,'.-');title('加权后I路');xlabel('时间');ylabel('幅度');
% subplot(224)
% plot(Q_out,'.-');title('加权后Q路');xlabel('时间');ylabel('幅度');
% %**************************************************************************
function [signal_out,I_out,Q_out,phase] = mod_msk2(data,data_len,sample_number,Rb)
%MSK基带调制
%**************************************************************************
% data 调制信号
% data_len 码元个数
% sample_number 每个码元采样点数
% Rb 码元速率
% signal_out 基带调制输出
% I_out I路输出
% Q_out Q路输出
%**************************************************************************
% data_len = 10; %码元个数
% sample_number = 8; %采样点数
% Rb = 16000; %码元速率
% data1 = randint(1,data_len);
% data = 2*data1-1; %传输的序列
Tb = 1/Rb; %码元时间
fs = Rb*sample_number; %采样速率
%--------------------------------------------------------------------------
%采样
for i = 1:sample_number
data_sample(i:sample_number:data_len*sample_number) = data;
end
%**************************************************************************
%--------------------------------------------------------------------------
%计算相位
phase = zeros(1,data_len*sample_number);
phase(1) = data_sample(1) * pi/2/sample_number;
for i = 2:data_len*sample_number
phase(i) = phase(i-1) + data_sample(i-1) * pi/2/sample_number;
end
%**************************************************************************
%--------------------------------------------------------------------------
%I/Q
I_out = cos(phase);
Q_out = sin(phase);
%**************************************************************************
%--------------------------------------------------------------------------
%调制信号产生
signal_out = I_out + j*Q_out;
%**************************************************************************
%MSK调制，差分解调方法一
clear all
close all
%--------------------------------------------------------------------------
%参数设置
data_len = 10000; %码元个数
sample_number = 8; %采样个数
Rb = 24000; %码元速率
fc = 96000; %载波频率
%**************************************************************************
%--------------------------------------------------------------------------
%随机产生传输信号
data=rand_binary(data_len);
%**************************************************************************
%--------------------------------------------------------------------------
%MSK基带调制
[signal_out,I_out,Q_out] = mod_msk(data,data_len,sample_number,Rb);
%**************************************************************************
%--------------------------------------------------------------------------
%中频搬移
multi = fc/Rb;
I_temp=interp(I_out,multi);
Q_temp=interp(Q_out,multi);
Fs=fc*sample_number;
t=1/Fs:1/Fs:length(I_temp)*1/Fs;
signal_i=I_temp.*cos(2*pi*fc*t);
signal_q=Q_temp.*sin(2*pi*fc*t);
signal_mod=I_temp.*cos(2*pi*fc*t)-Q_temp.*sin(2*pi*fc*t);
%**************************************************************************
%--------------------------------------------------------------------------
%加噪声
for SNR = 0:8
signal_mod1 = awgn(signal_mod,SNR);
%--------------------------------------------------------------------------
%去载波
N=300; % 滤波器的阶数为(N+1)
F=[0,fc-1000,fc+1000,Fs/2]*2/Fs;
A=[1,1,0,0];
lpf=firls(N,F,A);
[amp_lpf,w]=freqz(lpf);
I_dem=signal_mod1.*cos(2*pi*fc*t)*2;
I_dem=conv(I_dem,lpf);
I_dem=I_dem(N/2+1:N/2+length(I_temp));
Q_dem=signal_mod1.*sin(2*pi*fc*t)*2;
Q_dem=conv(Q_dem,lpf);
Q_dem=-Q_dem(N/2+1:N/2+length(I_temp));
I_dem_out=zeros(1,length(I_dem)/multi); % 抽取
Q_dem_out=zeros(1,length(Q_dem)/multi);
for i=1:length(I_dem_out)
I_dem_out(i)=I_dem(multi*(i-1)+1);
Q_dem_out(i)=Q_dem(multi*(i-1)+1);
end;
%**************************************************************************
%------------------------------------------------
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