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    Angle Modulation

    Angle-modulation schemes, which include frequency modulation (FM) and phase modulation
    (PM), belong to the class of nonlinear modulation schemes. This family of 

    modulation schemes is characterized by high-bandwidth requirements and good performance
    in the presence of noise. These schemes can be visualized as modulation
    techniques that tradeoff bandwidth for power and, therefore, are used in situations
    where bandwidth is not the major concern and a high SNR is required. Frequency
    modulation is widely used in high-fidelity FM broadcasting, TV audio broadcasting,
    microwave carrier modulation, and point-to-point communication systems.

    In the frequency domain we have,

    Matlab Coding

     

      

     

     1 % MATLAB script for Illustrative Problem 3.10.
     2 % Demonstration script for frequency modulation. The message signal
     3 % is +1 for 0 < t < t0/3, -2 for t0/3 < t < 2t0/3, and zero otherwise.
     4 echo on
     5 t0=.15;                                  % signal duration
     6 ts=0.0005;                               % sampling interval
     7 fc=200;                                  % carrier frequency
     8 kf=50;                                   % modulation index
     9 fs=1/ts;                                 % sampling frequency
    10 t=[0:ts:t0];                             % time vector
    11 df=0.25;                                 % required frequency resolution
    12 % message signal
    13 m=[ones(1,t0/(3*ts)),-2*ones(1,t0/(3*ts)),zeros(1,t0/(3*ts)+1)];
    14 int_m(1)=0;
    15 for i=1:length(t)-1                      % integral of m
    16     int_m(i+1)=int_m(i)+m(i)*ts;
    17     echo off ;
    18 end
    19 echo on ;
    20 [M,m,df1]=fftseq(m,ts,df);               % Fourier transform
    21 M=M/fs;                                  % scaling
    22 f=[0:df1:df1*(length(m)-1)]-fs/2;        % frequency vector
    23 u=cos(2*pi*fc*t+2*pi*kf*int_m);          % modulated signal
    24 [U,u,df1]=fftseq(u,ts,df);               % Fourier transform
    25 U=U/fs;                                  % scaling
    26 pause % Press any key to see a plot of the message and the modulated signal. 27 subplot(2,1,1) 28 plot(t,m(1:length(t))) 29 axis([0 0.15 -2.1 2.1]) 30 xlabel('Time') 31 title('The message signal') 32 subplot(2,1,2) 33 plot(t,u(1:length(t))) 34 axis([0 0.15 -2.1 2.1]) 35 xlabel('Time') 36 title('The modulated signal')
    37 pause % Press any key to see plots of the magnitude of the message and the 38 % modulated signal in the frequency domain. 39 subplot(2,1,1) 40 plot(f,abs(fftshift(M))) 41 xlabel('Frequency') 42 title('Magnitude spectrum of the message signal') 43 subplot(2,1,2) 44 plot(f,abs(fftshift(U))) 45 title('Magnitude spectrum of the modulated signal') 46 xlabel('Frequency')


    The message and the modulated signal

     The message and the modulated signal in the frequency domain

    Reference,

      1. <<Contemporary Communication System using MATLAB>> - John G. Proakis

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  • 原文地址:https://www.cnblogs.com/zzyzz/p/13831830.html
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