MSII_Cvičení_4
Práce se signály:
řízené generátory
modulace (AM, FM, PM, PWM)
>> t=0:0.001:2;
>> y=chirp(t,0,1,2); % Start at 0Hz, go up to 2Hz, at t=1 sec
>> plot(t,y)
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Př.: 2
>> t=0:0.001:2;
y=chirp(t,0,1,2,'quadratic');
plot(t,y)
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Př.: 3.
>>
>>
>>
>>
>>
x=zeros(1,1000);
x(1,[1:500])=-0.8;
x(1,[501:1000])=0.8;
y=vco(x,2,90);
plot(y)
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
100
200
300
400
500
600
700
800
900
1000
Př.: 4.
>>
>>
>>
>>
t=-3*pi:6*pi/1000:3*pi;
y=sinc(t);
plot(t,y)
grid on
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-10
-8
-6
-4
-2
0
2
4
6
8
10
MODULATE Signal modulation for communications simulations.
Y = MODULATE(X,Fc,Fs,METHOD,OPT) modulates the message signal X
with a
carrier frequency Fc and sampling frequency Fs, using the
modulation
scheme in METHOD. OPT is an extra sometimes optional parameter
whose
purpose depends on the modulation scheme you choose.
Fs must satisfy Fs > 2*Fc + BW, where BW is the bandwidth of the
modulated signal.
METHOD
MODULATION SCHEME
'am',
Amplitude modulation, double side-band, suppressed
carrier
'amdsb-sc' OPT not used.
'amdsb-tc' Amplitude modulation, double side-band, transmitted
carrier
OPT is a scalar which is subtracted from X prior to
multiplication by the carrier cosine. It defaults
to
min(min(X)) so the offset message signal is positive
and
has a minimum value of zero.
'amssb'
Amplitude modulation, single side-band
OPT not used.
'fm'
Frequency modulation
OPT is a scalar which specifies the constant of
frequency
modulation kf. kf = (Fc/Fs)*2*pi/max(max(abs(X)))
by
default for a maximum frequency excursion of Fc
Hertz.
'pm'
Phase modulation
OPT is a scalar which specifies the constant of
phase
modulation kp. kp = pi/max(max(abs(x))) by default
for a
maximum phase excursion of +/-pi radians.
'pwm'
Pulse width modulation
If you let OPT = 'centered', the pulses are centered
on the
carrier period rather than being "left justified".
'ppm'
Pulse position modulation
OPT is a scalar between 0 and 1 which specifies the
pulse
width in fractions of the carrier period. It
defaults to .1.
'qam'
Quadrature amplitude modulation
OPT is a matrix the same size as X which is
modulated in
quadrature with X.
If X is a matrix, its columns are modulated.
[Y,T] = MODULATE(...) returns a time vector the same length as
Y.
See also demod, vco in the signal Processing Toolbox, and
PAMDEMOD,
QAMDEMOD, GENQAMDEMOD, FSKDEMOD, PSMDEMOD, MSKDEMOD in the
Communications Toolbox.
Reference page in Help browser
doc modulate
Př 5. Modulace AM
fc=1000; fs=4000;t=0:1/fs:1;
>> x=sin(2*pi*50*t);
>> y=modulate(x,fc,fs,'am');
>> plot(t([1:160]),y([1:160]))
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.005
0.01
0.015
0.02
>> hold on
>> plot(t([1:160]),x([1:160]),'r')
0.025
0.03
0.035
0.04
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
Př. 6.: FM
fc=400; fs=4000;t=0:1/fs:1;
>> x=1-10*sin(2*pi*20*t);
>> y=modulate(x,fc,fs,'fm');
>> subplot(2,1,1), plot(t([1:400]),x([1:400]),'r')
subplot(2,1,2), plot(t([1:400]),y([1:400]))
15
10
5
0
-5
-10
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
1
0.5
0
-0.5
-1
Další modulace
fc=100;fs=2000;
x=[0.1 0.3 0.5 0.7 0.9];
y=modulate(x,fc,fs,'pwm');plot(y), axis([-Inf Inf 0 1.1)
y=modulate(x,fc,fs,'pwm');plot(y), axis([-Inf Inf 0 1.1])
fc=400; fs=4000;t=0:1/fs:1;
x=0.5-0.5*sin(2*pi*20*t);
y=modulate(x,fc,fs,'pwm');
subplot(2,1,1), plot(t([1:400]),x([1:400]),'r')
subplot(2,1,2), plot(t([1:400]),y([1:400]))
axis([-Inf Inf -0.1 1.1])
clc
fc=100;fs=2000;
x=[0.1 0.3 0.5 0.7 0.9];
y=modulate(x,fc,fs,'pwm');plot(y), axis([-Inf Inf
y=modulate(x,fc,fs,'ppm');plot(y), axis([-Inf Inf
x=[0.1 0.3 0.5 0.7 0.9];
y=modulate(x,fc,fs,'ppm',0.3);plot(y), axis([-Inf
clc
fc=100;fs=2000;
x=[0.1 0.5 0.7 0.5 0.1];
y=modulate(x,fc,fs,'ppm',0.3);plot(y), axis([-Inf
0 1.1])
0 1.1])
Inf 0 1.1])
Inf 0 1.1])