Sound Card Based ASK Communication System for Teaching Communication Principle Course

doi:10.4236/cn.2013.51B018

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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

Email: mingjin141@gmail.com, [email protected]

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



or 1, , need to be trans-

mitted through ASK modulation of car rier frequency

1, 2,n

Then, the transmission digital data sequence is given as

()( )

dtagtnT







 (1)

where ()

t and T are the pulse shape of each transmis-

sion digital data and the bit duration, respectively.

When ()

t is trailing rectangular pulse, it is given

that

() 2

0, otherwise













(2)

The digital data sequence is modulated by multiplying

a carrier frequency signal and then transmitted. The

transmitted signal is given by



()()cos 2c

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 )



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

0.1

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. 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

REFERENCES

00.05 0.10.15 0.2 0.25 0.3

0.05

0. 1

Low pas s fi l t ered signal

time/s

[1] T. X. Brown, University of Colorado, TLEN 5320 Wire-

less Lab, [Online]. Available:

http://ece-www.Colorado.edu/~timxb/

[2] T. X. Brown, O. Notaros and N. Jadav, “Agilent Tech-

nologies Educator’s Corner,” Wireless Systems Lab, [On-

line], Available:

http://www.educatorscorner.com/index.cgi?CONTENT_I

D=2448

[3] C. Furse, R. Woodward and M. Jensen, “Laboratory Pro-

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tions on Education, Vol. 47, No. 1, 2004, pp. 18-25.

doi:10.1109/TE.2003.816066

[4] C. Furse, “Agilent Technologies Educator’s Corner,”

Utah State Univ., Wireless LAN Lab, [Online]. Available:

http://www.educatorscorner.

com/index.cgi?CONTENT_ID=2454

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

Course inWireless and Mobile Systems Design,” [Online ].

Available:

http://www.lan.ece.vt.edu/Presentations/dasilva_midkiff_

chen.pdf

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).