Communications and Network, 2013, 5, 78-80
doi:10.4236/cn.2013.51B018 Published Online February 2013 (http://www.scirp.org/journal/cn)
Sound Card Based ASK Communication System for
Teaching Communication Principle Course
Ming Jin, Yang Pu
College of Information Science & Engineering, Ningbo University, Ningbo, China
Received 2012
ABSTRACT
This paper deals with the issue of using the MATLAB tool in teaching the course of communication principles via con-
structing an Amplitude Shift Keying (ASK) communication system. Different from conventional MATLAB based si-
mulations, the constructed system transmits modulated signals through a wire audio channel by exploiting sound card.
Synchronization is required before the received signal being demodulated. Many practical problems should be consid-
ered as in real system. The designed system can be extended easily, and not only stimulates students’ interest in com-
munication course, but also helps them understanding the principles from system viewpoints.
Keywords: Sound Card; Communication Principles; ASK; Communication System
1. Introduction
Communication principles course is one of basic courses
of electronic engineering (EE) related specialties. Com-
munications technology is one of the most rapidly grow-
ing technologies in the telecommunications industry. As
a kernel course in EE, Communication principles course
plays an important role. Many universities [1-7] have
established hardware laboratory wh ich can implement all
experiments involved in the course. However, to estab-
lish such labs is very expensive. With the shortage of
supplement, computer aided simulations is an option.
Many Matlab/simulink based simulation program
packages for communication principles course are avail-
able online. However, some packages consist of many
independent script files; it is difficult for students to op-
erate it. And some program packages are designed based
on GUI or simulink. We found that these kinds of pack-
ages may not work in different computer platform or
software versions. Moreover, most of available simula-
tions are based on the ideal environment. Many practical
problems, which may be encountered in hardware labo-
ratory or real communication systems, are skipped. In [8],
sound card is used in a demo of communication system.
However, it is not shared for everyone.
Following the idea of [8], in this paper, we present a
MATLAB based Amplitude Shift Keying (ASK) com-
munication system which is realized by transmitting the
modulated signal through a wire audio channel by ex-
ploiting sound card. Hence, it is different from the soft-
ware only based simulations. And many practical prob-
lems, such as synchronization, may be encountered. In
addition, the simple ASK communication system can be
extended easily, and will not only stimulate students’
interest in communication course, but also help them
understanding the principles from system viewpoints.
2. Basic Principle of ASK
This section describes the modulation and demodulation
principles of ASK digital signals. Assumed that a binary
digital data 0
n
a

or 1, , need to be trans-
mitted through ASK modulation of car rier frequency
1, 2,n
c
f
.
Then, the transmission digital data sequence is given as
()( )
n
n
dtagtnT



 (1)
where ()
g
t and T are the pulse shape of each transmis-
sion digital data and the bit duration, respectively.
When ()
g
t is trailing rectangular pulse, it is given
that
1,
() 2
0, otherwise
TT
t
gt





2

(2)
The digital data sequence is modulated by multiplying
a carrier frequency signal and then transmitted. The
transmitted signal is given by

()()cos 2c
s
tdt ft   (3)
The transmitted signal is contaminated by multi path
fading and AWGN, and at the receiver it is received as

M. JIN, Y. PU 79
()()()()rtstht nt (4)
where is the impulse response of the radio chann el
and is the receiver noise.
()ht
()nt
If there is no multi path, the received signal is given by
()()() ()rt sttnt

  (5)
Without multi path, non-coherent demodulation method
can be applied. Figure 1 shows the ASK signal genera-
tion and demodulation scheme.
3. ASK Communication System via Sound
Card
In this section, the ASK communication system with
MATLAB using sound card is introduced. The digital
data is generated randomly, and modulated to a carrier
frequency of below 22.05 kHz which is the one a half of
the maximum sampling frequency in most sound card.
Then the modulated signal is transmitted through sound
card, and received also through the same sound card. For
example, the random digital data of 10 bits is [1, 1, 1, 1,
0, 1, 0, 1, 0, 1]. The transmitted and received modulated
signal with carrier frequency 4 kHz is shown in Figure 2.
The received modulated signal is rectifier with a full
wave rectifier and filtered with low pass filter. The fre-
quency spectrums of the received signal before and after
the full wave rectifier are shown in Figure 3.
cos(2 )
c
f

Figure 1. ASK signal generation and demodul ation scheme.
00.05 0.10.15 0.20.250.3
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
trans m it ted s i gnal
(a) time/s
00.05 0.10.15 0.20.250. 3
-0.4
-0.3
-0.2
-0.1
0
0. 1
0. 2
0. 3
0. 4
Rec e i v e d s i gn al
(b) time /s
Figure 2. The modulated signal at (a) transmitter and (b)
receiver.
-20 -15 -10 -505 10 15 20
0. 02
0. 04
0. 06
0. 08
0. 1
0. 12
rec eived s ig nal
(a) frequency/k Hz
-20 -15 -10 -5 05 10 15 20
0. 02
0. 04
0. 06
0. 08
0.1
0. 12
0. 14
0. 16
rec eived s i gnal af t er rec t ifier
(b) frequenc y/kHz
Figure 3. Frequency spectrums of received signal (a) before
and (b) after a full wave rectifier.
It is shown in Figure 3 that the signal after full wave
rectifier will cause twofold frequencies. What we need is
the direct-current component, which can be obtained via

M. JIN, Y. PU
80
REFERENCES
00.05 0.10.15 0.2 0.25 0.3
0
0.05
0. 1
Low pas s fi l t ered signal
time/s
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Figure 4. Low pass filtered signal.
low pass filter. The low pass filtered signal is shown in
Figure 4. The original digital data can be recovered from
the low pass filtered signal if we have its bit synchroni-
zation.
[5] L. DaSilva, S. Midkiff and I.-R. Chen, “A Laboratory
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4. Conclusions [6] Virginia Polytechnic Institute and State University, “New
Course Gives Students Hands-On Experience with Net-
work Interface,” Wireless Networking, Virginia Tech
ECE Annu. Rep.. [Online]. Available:
http://www.ecpe.vt.edu/news/ar03/newcourse.html
In this paper, we present a novel approach to teach
communication principle course by designing a commu-
nication system with MATLAB platform via sound card
in computer. In the design, many practical problems are
encountered. Through this system, the students can per-
ceive and have better understanding the points of princi-
ples.
[7] A. Helmy, “EE-599 Wireless and Mobile Networks De-
sign and Labor a tory,” [Online]. Available:
http://nile.usc.edu/~helmy/ee599
[8] X. Li, “Integration of System Design and Standard De-
velopment in Digital Communication Education,” Pro-
ceedings of the 2002 American Society for Engineering
Education Zone I Conference, United States Military
Academy, West Point, New York, 2002, pp. 1-9.
5. Acknowledgements
This work was supported by Ningbo key construction
service-oriented professionals (Sfwxzdzy200903).