A list,
Introduction modulation: the message signal is placed on a parameter of the carrier to form a modulated signal. Demodulation: The reverse process of modulation in which a message signal is recovered from a modulated signal.
2 modulation in the target wireless communication, matching channel characteristics, improving the frequency of transmitted signals, reducing antenna size; Spectrum shifting, a channel in the simultaneous transmission of multiple signals, multiplexing, improve channel utilization; Expand signal bandwidth and improve anti-interference ability of the system; Bandwidth and signal-to-noise ratio interchange (validity and reliability); Using telephone lines to connect a PC to the Internet requires the translation of analog/digital signals.
Signal signal, also known as modulation signal, baseband signal; Carrier: carrier, usually a sine wave or pulse train; Modulated signal: Modulated carrier, a message carrying a message signal, in various forms. 3.2 The modulated signal can be classified from different angles by type of modulation: analog/digital modulation By spectral structure of modulated signal: linear modulation/nonlinear modulation By modulated parameters of sinusoidal carrier: amplitude modulation/frequency modulation/phase modulation By type of carrier signal: continuous wave modulation/pulse modulation
4 Amplitude modulation 4.1 General model (1) Theoretical basis: Fourier transform (2) General model Amplitude modulation: the message signal controls the amplitude of the sinusoidal carrier. Method: The message signal is multiplied by the carrier signal through the multiplier, and then through the band-pass filter (time-domain convolution filter characteristics). For example, AM, DSB, SSB, VSB.
4.2 Conventional bilateral band amplitude modulation AM T domain: modulated signal waveform, modulation/demodulation method F domain: modulated signal spectrum, bandwidth B THE envelope of AM signal is proportional to the law of message signal, so simple envelope detection method (incoherent demodulation) can be used ** demodulation; The spectrum consists of a carrier wave, USB at the top and LSB at the bottom. Bandwidth BAM = 2 fh; Amplitude modulation is also called linear modulation; Application: medium and short wave AM broadcast. Disadvantages: Low power utilization, up to 50%
4.3 Suppressed Carrier The DSB spectrum of bilateral band is composed of USB at the top and LSB at the bottom, without carrier component. Bandwidth BDSB = BAM = 2 fh; The modulation efficiency can reach 100%. Using coherent demodulation: Method: the message signal is multiplied by the coherent carrier signal through the imager, and then through a low pass filter (time-domain convolution filter characteristics). Requirements: Carrier synchronization (coherent carrier and carrier signal in the same frequency and phase)
4.4 Single sideband modulation SSB transmits only one sideband and has high frequency utilization rate. Bandwidth BSSB = BAM / 2 = fH; In spectrum crowded communications, such as shortwave communications, multicarrier telephone systems. Low power consumption. For use in mobile communication systems. Disadvantages: complex equipment, there are technical difficulties, need coherent demodulation.
4.5 Residual sideband modulation VSB residual sideband filter characteristics: complementary symmetry at carrier frequency; A scheme between SSB and BILoba.
The angular modulation sinusoidal carrier has three parameters: amplitude, frequency and phase. Can carry message signals. Both frequency (FM) and phase (PM) are called angular modulation. The frequency modulation (FM) amplitude is constant, and the instantaneous phase is differentiated with respect to T to obtain the instantaneous angular frequency. The frequency spectrum of FM is composed of numerous side frequencies wc± NWM on both sides of carrier frequency component, whose amplitude depends on MF. Theoretically, the bandwidth of FM is infinite; In practice, Carson formula is used to calculate FM bandwidth: BFM=2(MF +1) FM. FM is the highest frequency of the modulation signal. FM modulation is nonlinear modulation. FM demodulation, also known as frequency discrimination, is realized by differential circuit + envelope detection. Characteristics and application of FM: constant amplitude, constant envelope. Advantages: Strong anti-noise ability; Cost: occupy a large channel bandwidth, low spectrum utilization; Application: high quality or channel noisy occasions. Such as satellite communication, mobile communication, microwave communication and so on.
6 Anti-noise performance Performance indicators: output SNR, system gain input SNR: Ni=n0B. N0 is the unilateral power spectral density of noise, and B=2fH is the bandwidth, which is twice the baseband bandwidth.
AM DSB SSB VSB (amplitude modulation) coherent demodulator: Linear demodulation, signal and noise can be processed separately. The anti-noise performance of bilateral and single side band modulation is the same. When the SNR is small, the signal is interfered into noise and the threshold effect is produced. The reason is the nonlinear demodulation of envelope detection. Fixed SNR. FM (Angular modulation) AN FM system can improve its anti-noise performance (signal-to-noise ratio) by increasing the transmission bandwidth.
Summary Spectrum utilization SSB>VSB>DSB/AM>FM Anti-noise performance: FM>DSB/SSB>VSB>AM Device complexity: AM is the simplest, DSB/FM is the second, SSB is the most complex
Two, some source code
function varargout = digital_modulation(varargin)
%DIGITAL_MODULATION
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', @digital_modulation_OpeningFcn, ...
'gui_OutputFcn', @digital_modulation_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 digital_modulation is made visible.
function digital_modulation_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 digital_modulation (see VARARGIN)
hold off;
axes(handles.axes1);
h=[1 1 0 1 0 0 1 1 1 0];
hold off;
bit=[];
for n=1:2:length(h)- 1;
if h(n)= =0 & h(n+1) = =1
se=[zeros(1.50) ones(1.50)];
elseif h(n)= =0 & h(n+1) = =0
se=[zeros(1.50) zeros(1.50)];
elseif h(n)= =1 & h(n+1) = =0
se=[ones(1.50) zeros(1.50)];
elseif h(n)= =1 & h(n+1) = =1
se=[ones(1.50) ones(1.50)];
end
bit=[bit se];
end
plot(bit,'LineWidth'.1.5); grid on; axis([0 500 1.5 1.5]);
%*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-
axes(handles.axes3)
hold off;
fc=30;
g=[1 1 0 1 0 0 1 1 1 0]; %modulante
n=1;
while n<=length(g)
if g(n)==0
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(1) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on;else
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(2) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on; end n=n+1;
end
% Choose default command line output for digital_modulation
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes digital_modulation wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = digital_modulation_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 button press in random.
function random_Callback(hObject, eventdata, handles)
% hObject handle to random (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
a=round(rand(1.10)); %genarar bits aleatorios
ran=[a(1),a(2),a(3),a(4),a(5),a(6),a(7),a(8),a(9),a(10)];
set(handles.bit1,'String',ran(1));
set(handles.bit2,'String',ran(2));
set(handles.bit3,'String',ran(3));
set(handles.bit4,'String',ran(4));
set(handles.bit5,'String',ran(5));
set(handles.bit6,'String',ran(6));
set(handles.bit7,'String',ran(7));
set(handles.bit8,'String',ran(8));
set(handles.bit9,'String',ran(9));
set(handles.bit10,'String',ran(10));
%*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
handles.bits=ran;
h=handles.bits;
axes(handles.axes1)
hold off;
bit=[];
for n=1:2:length(h)- 1;
if h(n)= =0 & h(n+1) = =1
se=[zeros(1.50) ones(1.50)];
elseif h(n)= =0 & h(n+1) = =0
se=[zeros(1.50) zeros(1.50)];
elseif h(n)= =1 & h(n+1) = =0
se=[ones(1.50) zeros(1.50)];
elseif h(n)= =1 & h(n+1) = =1
se=[ones(1.50) ones(1.50)];
end
bit=[bit se];
end
plot(bit,'LineWidth'.1.5); grid on; axis([0 500 1.5 1.5]);
%*-*-*-*-*-*-*-*-*-*-*-*-
hold off;
axes(handles.axes3);
cod=get(handles.select_mod,'Value');
switch cod
%*-*-*-*Modulation ASK*-*-*-*-*-*-*-*-*
case 1
hold off;
axes(handles.axes3)
fc=30;
g=handles.bits; %modulante
n=1;
while n<=length(g)
if g(n)==0
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(1) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on; % axis([0 n*2/fc - 3 3]);
else
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(2) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on; end n=n+1;
end
%*-*-*-*-*-*-*-Modulation OOK*-*-*-*-*-*-*-*-*-
case 2
hold off;
axes(handles.axes3);
t=0:0.001:1;
m=1;
fc=30;
g=handles.bits; %modulante
n=1;
while n<=length(g)
tx=(n- 1) *1/length(g):0.001:n*1/length(g);
p=(g(n))*sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5);
hold on;
axis([0 (n)*1/length(g) 1.5 1.5]);
grid on;
n=n+1;
end
%*-*-*-*-*-*-*-Modulation BPSK*-*-*-*-*-*-*-*-*-*-*-
case 3
axes(handles.axes3)
hold off;
g=handles.bits;
fc=10;
n=1;
while n<=length(g)
if g(n)==0 %0 is - 1
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(- 1) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on;else
tx=(n- 1) *0.1:0.1/100:n*0.1;
p=(1) *sin(2*pi*fc*tx);
plot(tx,p,'LineWidth'.1.5); grid on; hold on; end n=n+1;
end
Copy the code3. Operation results
Matlab version and references
1 matlab version 2014A
2 Reference [1] Shen Zaiyang. Proficient in MATLAB Signal Processing [M]. Tsinghua University Press, 2015. [2] GAO Baojian, PENG Jinye, WANG Lin, PAN Jianshou. Signal and System — Analysis and Implementation using MATLAB [M]. Tsinghua University Press, 2020. [3] WANG Wenguang, WEI Shaoming, REN Xin. MATLAB Implementation of Signal Processing and System Analysis [M]. Publishing House of Electronics Industry, 2018.