main.m

程序实现了基带FM调制和解调

% %**************************************************************************
%                The Base band FM Modulate Algorithm
%--------------------------------------------------------------------------
%% ALGORITHM
% The base band modulation do not need carrier frequency and send the
% signal directly.The signal was separated into I and Q
% So the transmit signal S(t) is defined as follows.
%
% signal_I = cos(Kf / (2 * pi * fm) .* int_v);
% signal_Q = sin(Kf / (2 * pi * fm) .* int_v);
%
% v(t) = cos(2*pi*fm*t) is the signal for modulating
% int_v is the integral of v(t)  
%--------------------------------------------------------------------------
%% QUESTION I MEET
%--------------------------------------------------------------------------
clear all

%% parameter
fs = 16000;                  % the sampling rate.
ts = 1 / fs;
fm = 400;                    % the frequency of input signal v(t)
T = 0.02;                    % the duration of signal v(t)
Kf = 21000;                  % Defining the frequency modulation constant.

fai_v = 130 / 180 * pi;      % the initial phase of signal v(t)
fai_mod = 41 / 180 * pi;     % the phase delay at modulating moment
fai_de = 21 / 180 * pi;      % the phase delay vs signal_send at receiver

%--------------------------------------------------------------------------
% 引入基带信号v(t) = cos(2*pi*fm*t)
t = 0: 1 / fs : T;
v = v_cos(fs,fm,T,fai_v);

%--------------------------------------------------------------------------
%对音频信号进行基带调制,得到I,Q两路信号
[signal_I,signal_Q,int_v] = fm_modulate(fm,fs,Kf,v,fai_mod);

%--------------------------------------------------------------------------
%% 接收端收到I,Q两路基带信号为demod_I,demod_Q,
%  其与输出端I,Q两路的信号signal_I,signal_Q相位偏移fai_de

[demod_I,demod_Q] = fm_signal_received(signal_I,signal_Q,fai_de);

%--------------------------------------------------------------------------
%%对接收到的信号进行FM基带解调

% 求解调信号的瞬时相位
fai = atan2(demod_Q , demod_I);

% 对瞬时相位进行微分得到瞬时频率
m =1 / Kf .* unwrap(diff(fai)) .* fs;

%--------------------------------------------------------------------------
% figure(1)
% 
subplot(4,1,1);
plot(signal_I);
subplot(4,1,2);
plot(signal_Q);

subplot(4,1,3);
plot(demod_I);
subplot(4,1,4);
plot(demod_Q);
% 
% figure(2)

subplot(2,1,1);
plot(v);
subplot(2,1,2);
plot(m);