function demod_out = demodulation(demod_in,mod_mode)
%%*************************************************************************
%%Function information:
%%由信道信号的复数值解调对应的二进制序列(In this program,the channel value are demodulated.)
%%-------------------------------------------------------------------------
%%First time : 3/25/2002
%%Newest modified time:6/20/2002
%%Programmer:Xuewei Mao
%%Version: 0.2
%%-------------------------------------------------------------------------
%%*************************************************************************
%%*************************************************************************
%% Reference:
%%-------------------------------------------------------------------------
%%
%%-------------------------------------------------------------------------
%% Note:
%%-------------------------------------------------------------------------
%% Here,the method for the four modulation modes is the same ,so see the note
%%for QPSK, and the note for the other three is omitted.
%%-------------------------------------------------------------------------
%% Function discription:
%%-------------------------------------------------------------------------
%% 由信道信号的复数值找出对应的二进制序列。方法如下：由信道值，
%%求出该值与星座图中所有点的距离，找出距离最小的点，该点对应的
%%二进制序列及为该信道对应的解调结果。
%% In this program,the channel value are demodulated.
%% The process: firstly,calculate the distance between the channel value
%% and all the constellation points.then,find the shortest distance,thus ,the point
%% is the one.At last,put out the binary sequence symbolizing the point.
%%-------------------------------------------------------------------------
%% Input:
%%-------------------------------------------------------------------------
%% demod_in :输入信道值 (the input channel value)
%%-------------------------------------------------------------------------
%% Output:
%%-------------------------------------------------------------------------
%% demod_out:解调结果 (demodulation output(binary) )
%%-------------------------------------------------------------------------
%% Global Variable:
%%-------------------------------------------------------------------------
%% g_RT
%%-------------------------------------------------------------------------
%%*************************************************************************
%system_parameters
switch (mod_mode)
case 2
%BPSK modulation
demod_out=zeros(1,length(demod_in));
for i=1:length(demod_in)
if abs( demod_in(i)-1)-abs( demod_in(i)+1)<=0 %demod_in(i)-1:接收点到1的距离; demod_in(i)+1:接收点到-1的距离
demod_out(i)=1;
else
demod_out(i)=0;
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
case 4
%QPSK modulation
d=zeros(4,length(demod_in)); % 'd ' is the distance between the channel value and the constellation point
m=zeros(1,length(demod_in));
temp=[-1-j -1+j 1-j 1+j]/sqrt(2);
for i=1:length(demod_in)
for n=1:4
%下面的demod_in(i)为啥要乘以sqrt(2)? --yzh
d(n,i)=(abs(demod_in(i)*sqrt(2)-temp(n))).^2;%由信道值，求出该值与星座图中所有点的距离
end %calculate the distance between the channel and the constellation points
[min_distance,constellation_point] = min(d(:,i)) ; %D(:,i)=sort(d(:,i));%排序 (sort the distance in ascending order.)
m(i) = constellation_point;
end
A=de2bi([0:3],'left-msb');%写出0到N-1(N为星座图点数)
%(converts a nonnegative decimal vector [0,3] to a binary matrix A.)
for i=1:length(demod_in)
DEMOD_OUT(i,:)=A(m(i),:); %matrix:length(demod_in)*2 --yzh
% 最小值对应的星座点序号的二进制表示即为解调结果
end
demod_out=reshape(DEMOD_OUT',1,length(demod_in)*2);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
case 16
d=zeros(16,length(demod_in));
b=ones(1,length(demod_in));
m=zeros(1,length(demod_in));
temp=[-3-3*j -3-j -3+3*j -3+j ...
-1-3*j -1-j -1+3*j -1+j ...
3-3*j 3-j 3+3*j 3+j ...
1-3*j 1-j 1+3*j 1+j]/sqrt(10);
for i=1:length(demod_in)
for n=1:16
%下面的demod_in(i)为啥又不需要乘以sqrt(10)? --yzh
d(n,i)=(abs(demod_in(i)*sqrt(10)-temp(n))).^2; %加上sqrt(10)，与其他解调对应 --yzh
end
[min_distance,constellation_point] = min(d(:,i)) ; %D(:,i)=sort(d(:,i));%排序 (sort the distance in ascending order.)
m(i) = constellation_point;
end
A=de2bi([0:15],'left-msb');
for i=1:length((demod_in))
DEMOD_OUT(i,:)=A(m(i),:);
end
demod_out=reshape(DEMOD_OUT',1,length(demod_in)*4);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
case 64
%64_QAM
d=zeros(64,length(demod_in));
D=zeros(64,length(demod_in));
m=zeros(1,length(demod_in));
temp=[-7-7*j -7-5*j -7-j -7-3*j -7+7*j -7+5*j -7+j -7+3*j...
-5-7*j -5-5*j -5-j -5-3*j -5+7*j -5+5*j -5+j -5+3*j...
-1-7*j -1-5*j -1-j -1-3*j -1+7*j -1+5*j -1+j -1+3*j...
-3-7*j -3-5*j -3-j -3-3*j -3+7*j -3+5*j -3+j -3+3*j...
7-7*j 7-5*j 7-j 7-3*j 7+7*j 7+5*j 7+j 7+3*j...
5-7*j 5-5*j 5-j 5-3*j 5+7*j 5+5*j 5+j 5+3*j...
1-7*j 1-5*j 1-j 1-3*j 1+7*j 1+5*j 1+j 1+3*j...
3-7*j 3-5*j 3-j 3-3*j 3+7*j 3+5*j 3+j 3+3*j ]/sqrt(42);
for i=1:length(demod_in)
for n=1:64
d(n,i)=(abs(demod_in(i)*sqrt(42)-temp(n))).^2;
end
[min_distance,constellation_point] = min(d(:,i)) ; %D(:,i)=sort(d(:,i));%排序 (sort the distance in ascending order.)
m(i) = constellation_point;
end
A=de2bi([0:63],'left-msb');
for i=1:length(demod_in)
DEMOD_OUT(i,:)=A(m(i),:);
end
demod_out=reshape(DEMOD_OUT',1,length(demod_in)*6);
otherwise
disp('Error! Please input again');
end
