二、數字信号調制系統簡介
二進制數字信号調制原理
數字調制是指用數字基帶信号對載波的某些參量進行控制, 使載波的這些參量随基帶信号的變化而變化。在通信系統中, 作為載波的正弦波有幅度、頻率和相位3個參數, 對應的也就有3種基本的調制方式:調幅、調頻和調相。由于數字信号不同與模拟信号的特殊性, 在數字載波通信中, 這3種基本的調制方式分别被稱為幅移 (ASK) 、頻移鍵控 (FSK) 和相移鍵控 (PSK) 。調制信号是二進制數字基帶信号時, 這種調制稱為二進制數字調制。在二進制數字調制中, 載波的幅度、頻率和相位隻有兩種變化方式。
1 ASK調制
振幅鍵控是利用載波的幅度變化來傳遞數字資訊, 而其頻率和初相位保持不變。二進制幅度鍵控 (2ASK) 方式是數字調制方式中出現最早也是最簡單的一種方法。這種方法最初用于電報系統, 二進制振幅鍵控常常作為研究其它數字調制方式的基礎。2ASK調制信号隻有0或1兩個電平相乘的, 結果相當于将載頻或者關斷, 或者接通, 它的實際意義是當調制的數字信号為“1”時, 傳輸載波;當調制的數字信号為“0”時, 不傳輸載波。
2ASK信号的一般表達式為:
其中
2 FSK調制
頻移鍵控是利用載波的頻率變化來傳遞數字資訊。在2FSK中, 載波的頻率随二進制基帶信号在f1和f0的兩個頻率點變化。它的實際意義是當調制的數字信号為“1”或“0”時傳輸f1或f2頻率的載波。
其中ω1=2nf1, ω0=2nf0, θn為頻率為f1的載波的初始相位, φn為頻率為f0的載波的初始相位。令 為Dn的反碼, 即
則2FSK信号可表示為:
3 PSK調制
相移鍵控是利用載波的相位變化來傳遞數字資訊, 而振幅和頻率保持不變。PSK調制時, 載波的相位随調制信号狀态不同而改變。如果兩個頻率相同的載波同時開始振蕩, 這兩個頻率同時達到正最大值, 同時達到零值, 同時達到負最大值, 此時它們就處于“同相”狀态;如果一個達到正最大值時, 另一個達到負最大值, 則稱為“反相”。一般把信号振蕩一次 (一周) 作為360度。如果一個波比另一個波相差半個周期, 我們說兩個波的相位差180度, 也就是反相。當傳輸數字信号時, “1”碼控制發0度相位, “0”碼控制發180度相位。相移鍵控有很好的抗幹擾性, 在有衰落的信道中也能獲得很好的效果。
三、部分源代碼
function varargout = display_signal(varargin)
% DISPLAY_SIGNAL MATLAB code for display_signal.fig
% DISPLAY_SIGNAL, by itself, creates a new DISPLAY_SIGNAL or raises the existing
% singleton*.
%
% H = DISPLAY_SIGNAL returns the handle to a new DISPLAY_SIGNAL or the handle to
% the existing singleton*.
%
% DISPLAY_SIGNAL('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in DISPLAY_SIGNAL.M with the given input arguments.
%
% DISPLAY_SIGNAL('Property','Value',...) creates a new DISPLAY_SIGNAL or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before display_signal_OpeningFcn gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to display_signal_OpeningFcn via varargin.
%
% *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help display_signal
% Last Modified by GUIDE v2.5 20-Dec-2020 17:01:23
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', @display_signal_OpeningFcn, ...
'gui_OutputFcn', @display_signal_OutputFcn, ...
'gui_LayoutFcn', [] , ...
'gui_Callback', []);
if nargin && ischar(varargin{1})
gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before display_signal is made visible.
function display_signal_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% varargin command line arguments to display_signal (see VARARGIN)
% Choose default command line output for display_signal
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes display_signal wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = display_signal_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes on selection change in type.
function type_Callback(hObject, eventdata, handles)
% hObject handle to type (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: contents = cellstr(get(hObject,'String')) returns type contents as cell array
% contents{get(hObject,'Value')} returns selected item from type
% --- Executes during object creation, after setting all properties.
function type_CreateFcn(hObject, eventdata, handles)
% hObject handle to type (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: popupmenu controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
function Fb_Callback(hObject, eventdata, handles)
% hObject handle to Fb (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'String') returns contents of Fb as text
% str2double(get(hObject,'String')) returns contents of Fb as a double
% --- Executes during object creation, after setting all properties.
function Fb_CreateFcn(hObject, eventdata, handles)
% hObject handle to Fb (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: edit controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
function Fc_Callback(hObject, eventdata, handles)
% hObject handle to Fc (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'String') returns contents of Fc as text
% str2double(get(hObject,'String')) returns contents of Fc as a double
% --- Executes during object creation, after setting all properties.
function Fc_CreateFcn(hObject, eventdata, handles)
% hObject handle to Fc (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: edit controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
function Bit_Callback(hObject, eventdata, handles)
% hObject handle to Bit (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'String') returns contents of Bit as text
% str2double(get(hObject,'String')) returns contents of Bit as a double
% --- Executes during object creation, after setting all properties.
function Bit_CreateFcn(hObject, eventdata, handles)
% hObject handle to Bit (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: edit controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
% --- Executes on button press in pushbutton2.
function pushbutton2_Callback(hObject, eventdata, handles)
% hObject handle to pushbutton2 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
tempobj=findobj(gcbf,'tag','type');
modu_type=get(tempobj,'value');
fc=eval(get(handles.Fc,'String')); %可選參數設定
B=str2double(get(handles.Fb,'String'));
DisBit=str2double(get(handles.Bit,'String'));
switch(modu_type)
case 1
nper=B/fc; %一個碼元中所包含的載波周期數
nsamp=128; %過采樣率
fs=nsamp*B; %采樣率
Ts=1/fs; %采樣周期
NumBit=1024; %資料位數
%數字基帶信号産生
Data=randint(1,NumBit);
NumSample=NumBit*nsamp; %總采樣點數
signal=zeros(1,NumSample);
start=1;
for i=1:NumBit
if(Data(i))
signal(start:start+nsamp-1)=1;
end
start=start+nsamp;
end
t=0:Ts:Ts*(NumSample-1);
ASK_signal=signal.*sin(2*pi*fc*t); 四、運作結果
五、matlab版本及參考文獻
1 matlab版本
2014a
2 參考文獻
[1] 沈再陽.精通MATLAB信号處理[M].清華大學出版社，2015.
[2]高寶建,彭進業,王琳,潘建壽.信号與系統——使用MATLAB分析與實作[M].清華大學出版社，2020.
[3]王文光,魏少明,任欣.信号處理與系統分析的MATLAB實作[M].電子工業出版社，2018.