function out=sq4QAM_Gray_map(input)

%%%--------example---------------------
%%% input=[0 0 0 1 1 1 1 0]
%%% out=[1+j
%%%     -1+j
%%%     -1-j
%%%      1-j]


%%%將輸入的信息比特流映射為方形4QAM星座點；輸出為并行復數序列，為表示星座點的復數
%%%輸入序列長度應為2的倍數；每2個比特映射為一個星座點

%%% 'input' is the inputed source bit sequence
%%% 'output' is the mapped constellations, and is still a serial sequence

K=length(input)/2;    %%% The number of symbols
d=1/sqrt(2);          %%% The minimum distance between constellations is 2*d
x=[d,-d];             %%% coordinate matrix
y=[d,-d];

for i=1:K             %%%將input變成K×2的矩陣，便于映射處理，每一行對應一個星座點
    for k=1:2
        temp(i,k)=input(2*(i-1)+k);
    end
end

%%% mapping --------------------------------
%%% Y-coordinate ---------------------------%%% 2個比特中的前一位決定縱坐標，后一位決定橫坐標
for i=1:K
    if temp(i,1)==0
        max(i,2)=y(1);
    else max(i,2)=y(2);
    end
end

%%% X-coordinate --------------------------
for i=1:K
    if temp(i,2)==0
        max(i,1)=x(1);
    else max(i,1)=x(2);
    end
end


clear i;
clear k;
clear temp;

%%% j=sqrt(-1);  %%%% if you have use j as a variable,then you must have to define j as a complex 
                 %%%%  if you want to use it as a complex sign

for i=1:K
    p_out(i,:)=max(i,1)+max(i,2)*j;   %%% generate complex constellations,and serial sequence
end
clear max;

out=p_out;     %%% parrallel complex constellations sequence