%- 2DPSK 调制与解调

%---------------------------------------------------

%>>>>>>>>>>>>>>>>>>Initial_Part>>>>>>>>>>>>>>>>>>>>> %--------------------------------------------------- function y=dpsk2() fs = 30000;

Time_Hold_On = 0.1;

Num_Unit = fs * Time_Hold_On; High_Level = ones ( 1, Num_Unit ); Low_Level = zeros ( 1, Num_Unit ); w = 300; A = 1;

%---------------------------------------------------

%>>>>>>>>>>>>>>>>>>Initial_The_Signal>>>>>>>>>>>>>>> %--------------------------------------------------- Sign_Set = [0,1,1,0,1,0,0,1]

Lenth_Of_Sign = length ( Sign_Set );

st = zeros ( 1, Num_Unit * Lenth_Of_Sign );

sign_orign = zeros ( 1, Num_Unit * Lenth_Of_Sign ); sign_result = zeros ( 1, Num_Unit * Lenth_Of_Sign ); t = 0 : 1/fs : Time_Hold_On * Lenth_Of_Sign - 1/fs;

%---------------------------------------------------

%>>>>>>>>>>>Generate_The_Original_Signal>>>>>>>>>>>> %--------------------------------------------------- for I = 1 : Lenth_Of_Sign if Sign_Set(I) == 1 sign_orign( (I-1)*Num_Unit + 1 : I*Num_Unit) = High_Level; else sign_orign( (I-1)*Num_Unit + 1 : I*Num_Unit) = Low_Level; end end

%---------------------------------------------------

%>>>>>>>>>>>>>>>>>>Modulation_Part>>>>>>>>>>>>>>>>>> %--------------------------------------------------- for I = 1 : Lenth_Of_Sign if Sign_Set(I) == 1 st( (I-1)*Num_Unit + 1 : I*Num_Unit) = A * cos ( 2 * pi * w * t( (I-1)*Num_Unit + 1 : I*Num_Unit ) + ( pi / 2 ) ); else st( (I-1)*Num_Unit + 1 : I*Num_Unit) = A * cos ( 2 * pi * w * t( (I-1)*Num_Unit + 1 : I*Num_Unit ) ); end end

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figure

subplot ( 2, 1, 1 ) plot(t, sign_orign);

axis( [ 0 , Time_Hold_On *( Lenth_Of_Sign + 1), - (A / 2), A + (A / 2) ] ); title ( '原始信号' ); grid

subplot ( 2, 1, 2 ); plot ( t, st );

axis( [ 0 , Time_Hold_On *( Lenth_Of_Sign + 1), - 3*(A / 2), 3*(A / 2) ] ); title ( '调制后的信号' ); grid

%---------------------------------------------------

%>>>>>>>>>>>>>>>>>>相乘>>>>>>>>>>>>>>>>>>>>>>>>>>>>> %--------------------------------------------------- dt = st .* cos ( 2 * pi * w * t );

figure

subplot(2,1,1) plot ( t, dt );

axis( [ 0 , Time_Hold_On *( Lenth_Of_Sign + 1), - 3*(A / 2), 3*(A / 2) ] ); title ( '相乘后的波形' ); grid

%---------------------------------------------------

%>>>>>>>>>>>>>>>>>>>低通滤波部分>>>>>>>>>>>>>>>>>>>> %---------------------------------------------------

[N,Wn] = buttord( 2*pi*50, 2*pi*150,3,25,'s'); %临界频率采用角频率表示 [b,a]=butter(N,Wn,'s');

[bz,az]=impinvar(b,a,fs); %映射为数字的

dt = filter(bz,az,dt);

subplot(2,1,2) plot ( t, dt );

axis( [ 0 , Time_Hold_On *( Lenth_Of_Sign + 1), - 3*(A / 2), 3*(A / 2) ] ); title ( '低通滤波后的波形' ); grid

%---------------------------------------------------

%>>>>>>>>>>>>>抽样判决 & 逆码变换部分>>>>>>>>>>>>>>> %--------------------------------------------------- for I = 1 : Lenth_Of_Sign

if dt((2*I-1)*Num_Unit/2) < 0.25

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sign_result( (I-1)*Num_Unit + 1 : I*Num_Unit) = High_Level; else sign_result( (I-1)*Num_Unit + 1 : I*Num_Unit) = Low_Level; end end

figure

plot ( t, sign_result );

axis( [ 0 , Time_Hold_On *( Lenth_Of_Sign + 1), - 3*(A / 2), 3*(A / 2) ] ); title ( '逆码变换后的波形' ); grid

3.2 2DPSK模拟调制和差分相干解调法仿真图

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图2.1 2DPSK模拟调制和差分相干解调法仿真图

3.2调试过程及结论

2DPSK信号经相关模块调试后的波形图如下：

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调制过后加入高斯白噪声，连接到带通滤波器，去除调制信号以外的在信道中混入的噪声，再连接到相乘器。此相乘器是一路延时一个码元时间后与另一路信号相乘。作用是去除调制信号中的载波成分。

信号经过低通滤波器后，去除高频成分，得到包含基带信号的低频信号。经过抽样判决，便还原成原始信号。

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