% 這個(gè)函數(shù)返回調(diào)制以后的qpsk信號(hào)；
% 這里的調(diào)制考慮了載波發(fā)送的問題；
% 編程原則是先寫出基本功能，在逐步完善；



function [y_mod]=...
          qpsk_mod_ZiBian(x,fc,fs,symbol_t,theta,plot_flag)

% 注意把握好fc,fs,之間的關(guān)系，是一個(gè)四進(jìn)制碼元內(nèi)的載波信號(hào)點(diǎn)
% symbol_t表示的是一個(gè)調(diào)制符號(hào)的持續(xù)時(shí)間，
% 對(duì)于使用者來說，我知道的只是：載波頻率，抽樣頻率，調(diào)制以后的
% 符號(hào)持續(xù)時(shí)間；
% x表示的是輸入的二進(jìn)制序列碼，是列向量，
% fc是載波頻率，fs是采樣頻率，
% n是每一個(gè)四進(jìn)制碼元下?lián)碛械妮d波信號(hào)采樣點(diǎn)數(shù)；
% qpsk調(diào)制的原理很簡(jiǎn)單，第一步：完成星座圖對(duì)應(yīng)，
% 第二步：用這些星座圖上的點(diǎn)乘以載波；
% 畫圖標(biāo)志：plot_flag=1，就畫圖，否則不畫圖；

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
if nargin<6
    error('the input arguments are not complete');
end;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
if size(x,1)<=size(x,2)
    x=x';
else
    x=x;
end;   % 把x變換成列向量；
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 時(shí)間的設(shè)置要注意兩點(diǎn)：采樣點(diǎn)數(shù)和采樣間隔；
n=ceil(symbol_t*fs);
t=(0:n-1)/fs;
% 一個(gè)四進(jìn)制碼元下的載波：
signal_i=cos(2*pi*fc*t);
signal_q=sin(2*pi*fc*t);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% 注意信號(hào)的發(fā)送方向：------------------x(i+1)--x(i)---->

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 下面是調(diào)制部分：
signal_mod=[];     temp=[];
for i=1:2:(size(x,1)-1)
    % 首先是完成2，4進(jìn)制的轉(zhuǎn)換；
    if (x(i)==0) & (x(i+1)==0)
        signal_symbol=0;
    elseif (x(i)==1) & (x(i+1)==0)
        signal_symbol=1;
    elseif (x(i)==0) & (x(i+1)==1)
        signal_symbol=2;
    elseif (x(i)==1) & (x(i+1)==1)
        signal_symbol=3;
    else
        error('The input x are not apt to the function need');
    end;
    % 二進(jìn)制碼元轉(zhuǎn)化為四進(jìn)制符號(hào)；
    temp=[temp,signal_symbol];
    % 星座圖對(duì)應(yīng)；
    signal_constellation=pskmod(signal_symbol,4,theta);
    % 調(diào)制載波；
    signal_mod_i=real(signal_constellation).*signal_i;
    signal_mod_q=imag(signal_constellation).*signal_q;
    signal_mod_temp=signal_mod_i+signal_mod_q;
    signal_mod=[signal_mod,signal_mod_temp];
end;

symbol_base=temp;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    if size(signal_mod,1)<=size(signal_mod,2)
       signal_mod=signal_mod';
    else
        signal_mod=signal_mod;
    end;   % 把signal_mod變換成列向量；
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%    
% 在本函數(shù)的返回端得到調(diào)制好的信號(hào)；
y_mod=signal_mod;    
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%    
    
    
 if plot_flag==1
    
fft_signal_mod=abs(fftshift(fft(signal_mod)));

% 畫圖；

figure;
subplot(221);
plot((0:size(x)-1)/fs,x); title('基帶二進(jìn)制信號(hào)'); 
xlabel('時(shí)間(s)'); ylabel('信號(hào)幅度');

subplot(222);
plot((0:size(signal_mod,1)-1)/fs,signal_mod);
title('調(diào)制后的信號(hào)'); xlabel('時(shí)間(s)'); ylabel('信號(hào)幅度');

subplot(223);
f_n=size(fft_signal_mod,1);
plot(fs*(-f_n/2:f_n/2-1)/f_n,fft_signal_mod);
title('qpsk調(diào)制信號(hào)的頻譜'); 
xlabel('頻率(Hz)'); ylabel('幅度'); axis tight; grid on;

subplot(224);
plot(fs*(-f_n/2:f_n/2-1)/f_n,20*log10(fft_signal_mod));
title('qpsk調(diào)制信號(hào)的頻譜(單位(dB))'); 
xlabel('頻率(Hz)'); ylabel('幅度(dB)');  grid on; 
% 這里對(duì)dB圖的axis 不作限制；
 elseif plot_flag==0
 end;