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Implementation of educational software

for analog modulation systems

Implementación del software educativo sistemas de

modulaciones analógicas

Neiser Ortiz Mosquera

Juan Duche Suárez

Ximena Trujillo Borja

Abstract

The use of new technological tools for the development of experimental

practices within the classrooms and laboratories has contributed to the

development of new skills by students in both the academic and

professional fields. For this reason, this research work aims to implement

a software Analogic Modulation System using the App Designer tool of

MATLAB. For the development of this research, the bibliographic,

experimental, and research method was used to cover the entire required

research field. In order to apply the research method, surveys were applied

by selecting the 36 students of the Analog and Digital Communications

subject in the seventh semester of the 2018-2019 academic period of the

Teleinformatic Engineering degree at the University of Guayaquil. The

results of the surveys indicate that the system is useful, intuitive, reliable,

and efficient but not as user-friendly because 81% of the respondents

believe that it is. It was also determined that the students who are taking an

experimental subject want to manipulate equipment that is available in the

laboratory because they have the perception that they can learn more even

if it takes longer to develop these experiments. In relation to the tests

* Magister, Universidad de Guayaquil, Guayaquil Ecuador,

neiser.ortizm@ug.edu.ec, https://orcid.org/0000-0002-

1051-6102

* Magister, Universidad de Guayaquil, Guayaquil Ecuador,

juan.duches@ug.edu.ec, https://orcid.org/0000-0001-

9673-8218

* Magister, Universidad de Guayaquil, Guayaquil Ecuador

, ximena.trujillob@ug.edu.ec, https://orcid.org/0000-0003-

2093-5906

Article

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carried out, it is deduced that they were successful because the signal

message can be recovered without error even though it was transmitted in

different media and also using different analog modulations. The only

discrepancy that existed was the time of transmission of the data.

Key words: Analogic Modulation System, App Designer, experimental

activities, students.

Resumen

El uso de las nuevas herramientas tecnologías para el desarrollo de

prácticas experimentales dentro de las aulas de clases y los laboratorios,

han contribuido a que los estudiantes desarrollen nuevas habilidades tanto

en el campo académico como profesional por este motivo el presente

trabajo de investigación tiene el objetivo de implementar un software de

Sistema de Modulaciones Analógicas utilizando la herramienta App

Designer del Software MATLAB. Para el desarrollo de esta investigación

se utilizaron el método bibliográfico, experimental y de indagación para

abarcar todo el campo investigativo requerido. Para la aplicación del

método de indagación se aplicó encuestas seleccionando a los 36

estudiantes de la materia de Comunicaciones Analógicas y Digitales del

séptimo semestre del periodo académico 2018-2019 CII de la Carrera

Ingeniería Teleinformática de la Universidad de Guayaquil. Los resultados

de las encuestas indican que el sistema es útil, intuitivo, fiable y eficiente

pero no tan amigable con el usuario debido a que el 81% de los encuestados

creen eso, además, se determinó que los estudiantes que están cursando una

materia experimental desean manipular equipos que están disponibles en

el laboratorio debido a que ellos tienen la percepción que pueden aprender

más, aunque tome más tiempo el desarrollar dichos experimentos. En

relación a las pruebas realizadas se deduce que fueron exitosas debido a

que se puede recuperar la señal mensaje sin ningún tipo de error, aunque

se haya transmitido en diferente medio de comunicación y usando también

diferentes modulaciones analógicas la única discrepancia que existió fue el

tiempo de transmisión de los datos.

Palabras clave: Sistemas modulaciones analógicas, App Designer,

prácticas experimentales, estudiantes.

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Introduction

The use of new technological tools in the classrooms and

laboratories of engineering careers in universities has helped

students to develop new skills both in the academic and professional

fields. As the authors indicate (Garcés, Garcés, & Alcívar, 2016) that

higher education institutions must adapt to the change of new

technological tools and teaching methodologies, in order to

encourage students to learn in new ways. The authors also agree

(Crispín, Gómez, Ramírez, & Ulloa, 2012). that teachers in higher

education institutions should increasingly seek to include practical

activities in the subjects they teach in the classroom, since students

can carry out simulations or activities similar to those carried out in

the professional field.

According to the author (Arias, 2012) indicates that it is necessary

to implement experimental practices and thus establish relationships

between theory and practice for better teaching, develop new skills

and create new knowledge in students, and the author Gomez (Maria,

2013) also agrees that the experimental practices that are performed

within the laboratory cannot be replaced with theoretical activities,

since the practices allow students to integrate into working groups

and be responsible for delivering individual results for the good of

the working groups.

According to the author (Durango, 2015) indicates that laboratory

practices can be developed in two ways by the student, being in

physical contact and manipulating the equipment, instruments,

elements and materials required for experimental practices or using

interactive simulations programmed through computers. In addition,

the author (Cataldi, Lage, & Dominighini, 2013) agrees that

simulation in education is a powerful technique that teaches some

aspects of the real world through imitation or replication, which is

based on a model of a real world system or phenomenon in which

some elements have been omitted or simplified to facilitate learning,

with the purpose of understanding, recognizing, self-evaluating and

modifying strategies and acquiring new ones.

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The present research has the objective of implementing an analog

modulations system using the App Designer tool of MATLAB

software. Once the implementation of the system is done, it will be

possible to visualize each analog modulation technique, which will

allow the student to draw their own conclusions regarding the

practice performed. The analog modulation system will be a system

that will consist of features such as usability, reliability and

efficiency, which will ensure a proper functioning of the same to

measure these characteristics of the software will be conducted a

survey to students. This research project is part of the Research,

Development and Innovation Project of the Competitive Research

Fund FCI - 2018. (University of Guayaquil, 2018) with the central

theme "Development of a technological space in the area of

telecommunications through data processing systems that allow the

generation of communications systems".

The proposed research project is carried out in the classrooms of the

Universidad de Guayaquil in the Faculty of Industrial Engineering

of the Teleinformatics Engineering program in the Analog and

Digital Communications course.

Materials and methods

Within the development of this research, 3 types of research methods

were used to cover all the required research field, these methods are:

bibliographic, experimental and inquiry. The bibliographic method

was used for the collection of all the necessary information from

studies and research works carried out by different authors on topics

related to the present research work. The experimental method was

also used because the implementation of an analog modulation

system software was carried out through the App Designer

application of MATLAB software. (Gómez, 2016) application of

MATLAB software. Finally, the inquiry method was used to

determine the usability of the implemented system. (Reyes Vera,

Berdugo Torres, & Machuca Villegas, 2016) to determine the

usability of the implemented system, this method was applied

through surveys. For the development of the surveys of this research

process was selected as a population to the students of the career of

Engineering in Teleinformatics and as a sample was taken to the 36

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students of the seventh semester of the academic period 2018-2019

CII of the subject of Analog and Digital Communications, the

directly selected sample has the characteristics of interest within this

research work.

General outline of the proposal

To implement the system, two laptops were used as shown in Figure

1, one of which will be the transmitter and the other the receiver.

Two types of communication media were used: communication with

a guided medium (Ethernet network with UTP cat5 twisted pair

cable) and communication with an unguided medium (Wifi network

with IEEE 802.11n standard).

Figure 1. Graph of the functioning of the implemented system.

The analog modulations system that was designed using the App

Designer tool of MATLAB software were amplitude modulation and

frequency modulation. The output response of the system will be in

the time and frequency domain. The general scheme of the analog

modulation system design is shown in Figure 2 and consists of four

panels which are: input, modulation, configurations and finally

demodulation. The operation of each of them is explained below.

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Figure 2. General scheme of the Analog Modulation System

design.

In this panel of the analog modulation system is where the message

signal is entered through a microphone, to this signal the

digitalization process is performed to convert it into a . wav

extension file. Before converting the analog signal into digital, the

first thing to indicate is the sampling frequency (1), the most used

frequencies are 8 kHz, 11.025 kHz, 22.050 kHz, 44.1 kHz, 48 kHz

and 96 kHz. In addition, the number of bits (2) that the digital signal

to be converted will have must be indicated, this number must be

entered by the user, the possible values to be entered are 8, 16 and

24 bits. After setting the necessary parameters the system user can

start the recording process of the message signal through the start

button (3), in this button there are commands such as audirecorder,

TimerFcn, TimerPeriod. If the user wants to stop the recording he

has to use the stop button (4), commands such as Stop are used. Then

the process of converting the analog signal into digital is done, for

that the button load (5) is used, in this button there are commands

like file, path, uigetfile to define the file address and load it in the

application, in the button play (6) commands like soundsc are used

to play the recorded or loaded audio, in the button save (7) some

commands like file, path, uiputfile are used to define the file address,

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the name and type of file to save in this case they are type wav. To

visualize the message signal in preview (8) in the time domain and

enlarge (9) the signal, commands such as plot to show the graph and

xlabel ,ylabel to name the axes of the graph are used. Finally, if you

want to visualize the signal in the frequency domain you must use

the spectrum button (10), this button uses commands such as FFT to

perform the spectrum and xlabel, ylabel, plot to name the axes and

plot the spectrum. The input panel is shown in Figure 3.

Figure 3. Description of the input panel.

In this panel the modulation process is carried out as shown in Figure

4. Within the panel configuration, the modulation type component

(1) is used, the addresses of functions such as @modularAM and

@modularFM are used, which point to the .m files where the

respective commands and functions for the modulation processes are

located. To determine the parameters of the carrier signal of the

modulated signal, the modulation frequency (2), the amplitude of the

carrier (3) and the type (4) of sine wave must be configured, these

components use the modulacion_prev function. The modular button

(5) is used to plot the respective modulation in the time domain, this

button uses the commands like hold, linspace, funModType, xlabel,

ylabel. The spectrum button (6) is used to plot the signal in the

frequency domain, this button uses commands like FFT, xlabel,

ylabel and plot. Finally, preview (7) is used to observe the modulated

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signal in the time or frequency domain, this button also uses

commands like plot, hold, xlabel and ylabel.

Figure 4. Description of the modulation panel.

To perform the different types of analog modulations in the

modulation panel, equation 1 for AM modulation and equation 2 for

FM modulation were used in the modular button:

𝑦

(

𝑡

)

= 𝑥

(

𝑡

)

∙ 𝑓𝑢𝑛(2𝜋𝐹

𝑡)

(1)

𝑦

(

𝑡

)

= 𝑓𝑢𝑛(.2𝜋𝐹

𝑡 + 𝑘

∫

𝑥

(

𝑡

)

𝑑𝑡.)

(2)

Where:

•

𝑦

(

𝑡

)

: Modulated signal.

•

𝑥(𝑡)

: Signal to modulate

•

𝐹𝑐

Carrier frequency

•

𝑓𝑢𝑛(𝑡)

: Function for modulation, can be sine or

cosine.

•

𝑘𝑓 =

∙

&'(

)

: Constant

•

𝐹

: Sampling frequency

In the Settings panel the transmission connection is configured, this

panel is shown in Figure 5. In the connection type section the internal

connection component (1) is selected to perform the transmission

process on the same laptop and if this component is not activated the

transmission can be done through Wifi or Ethernet using two

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laptops, this component makes use of commands such as enablecom

to enable data communication. In the Client/Server section it is

selected that the server is the transmitting computer and the client is

the receiving computer, for this purpose the NetworkRole (2)

component is used. To complete the data transmission configuration,

the communication port must be configured through the port

component (3), the IP address of the Server/Client is configured

through the IP component (4) and to determine the size of the

transmission buffer, the buffer component (5) is used, where the user

determines the port number, the IP address and the buffer size using

the keyboard and these are saved as default values. To start the

transmission process the start component (6) is used, this component

uses the fopen command to open the communication channel and to

stop the communication the stop component (7) is used, the fclose

command is used and in the send data component (8) some

commands were used such as fwrite to transmit the data, tic to count

the transmission time, toc to count the reception time.

Figure 5. Description of the configurations panel.

The following tasks are performed in this panel:

1. It splits the modulated signal into blocks of the buffer size.

2. Adds headers to identify the block number.

3. Transmits and waits for a response for each block.

4. Displays the progress of the transmission.

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5. When all blocks have been transmitted, the communication is

terminated.

Figure 6 shows the Demodulation panel, where the demodulation

process is performed and the message signal is recovered. Within the

panel there are components such as modulation type (1) that uses

function addresses such as @modularAM and @modularFM, which

point to the .m files where the respective commands and functions

are located to perform the demodulation processes. The modulation

frequency (2), sampling frequency (3) and type (4) components must

have the same values as configured in the transmitting computer.

The demodulate component (5) is used to perform the selected

demodulation process and uses commands such as hold, linspace,

funModType, xlabel, ylabel to plot the modulation in the received

data component (7). Finally, the play component (6) uses commands

such as soundsc to play the demodulated audio.

Figure 6. Description of the demodulation panel.

The receiver acts with the following steps:

1. Receive a block of information.

2. Remove the header.

3. If it is the first block of information, it creates a new buffer for

transmission, otherwise it only concatenates the blocks in the

existing buffer.

4. Responds to the transmitter.

5. When the last block has been received, the entire signal is

reconstructed.

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When all the information has been received in the Demodulation

panel, the demodulate button will be activated, which contains

equation 3 for AM demodulation and equation 4 for FM

demodulation, recovering the original signal:

𝑥

(

𝑡

)

= 𝑦

(

𝑡

)

∙ 𝑓𝑢𝑛(2𝜋𝐹

𝑡)

(3)

𝑥

(

𝑡

)

= 𝐻

[

𝑦

(

𝑡

)

]

∙ 𝑒𝑥𝑝(.−𝑖 ∙ 2𝜋𝐹

𝑡.)

(4)

Where:

•

𝑦

(

𝑡

)

: Modulated signal.

•

𝑥

(𝑡)

: Demodulated signal

•

𝐹𝑐

Carrier frequency

•

𝑓𝑢𝑛(𝑡)

: Function for modulation, can be sine or cosine.

•

𝐻

[

𝑦

(

𝑡

)

]

: Hilbert transform of the FM modulated signal.

•

𝑖

: Complex operator.

Then a butter filter is applied to the demodulated signal to obtain the

reconstruction of the original signal.

Results

After the development of the analog modulation system software,

the respective implementation was carried out using the same

information signal in the two tests performed and the same

configuration parameters were used to make the corresponding

comparisons. In the first test, Ethernet, AM modulation and

demodulation were used as the transmission medium and in the

second test, Wifi, FM modulation and demodulation were used as

the transmission medium. Table 1 shows the different output

response graphs of the AM and FM modulation and demodulation

systems using the analog modulation system software.

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Table 1.

Table of results of AM and FM modulations and demodulations

using the Analog Modulations System application.

General Conditions:

Sampling frequency = 44,100 KHz Number of Bits= 16

Modulated Frequency = 88.20 KHz Carrier amplitude = 1

Port = 30000 Buffer = 10 KB

AM modulation

FM modulation

Transmission medium: Ethernet

Transmission medium: Wifi

AM modulated signal output response

FM modulated signal output response

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AM modulated signal spectrum

FM modulated signal spectrum

AM Demodulated Signal Output

Response

FM Demodulated Signal Output

Response

As can be seen in Table 1, the message signal recovered in the two

tests are similar, even though they have been transmitted in two

communication media and used two different types of modulations.

The only difference is the transmission time, in the first test when

Ethernet was used as the communication media the transmission

time was 13.47 s and in the other test when Wifi was used the

transmission time was 15.48 s.

Finally, a survey of the usability of the analog modulation systems

software was conducted as shown in Table 2, the results of the

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usability of the software are favorable as all respondents indicated

that it is a useful, intuitive and efficient system. In addition, 81% of

the respondents indicated that the software is a user-friendly system.

The survey also determined that 97% of the respondents think it is a

reliable system.

Table 2.

Software Usability Survey Analog Modulation Systems

Question

Scale

Useful

Intuitive

Friendly

Efficient

Reliable

Totally agree

39%

14%

28%

64%

Agreed

61%

67%

72%

33%

Disagree

Strongly

disagree

Discussion

In the FCI project, Development of a technological space in the area

of telecommunications through data processing systems that allow

the generation of communications systems, different types of

research projects are being developed with the objective of providing

students of the eighth semester System Simulation subject with new

experimental practices with the use of existing equipment in the

Networking laboratory. Due to the number of students registered in

each semester in the subject of System Simulation the existing

equipment in the Networking laboratory are scarce for the demand,

for this reason in the 2018-2019 CII semester two projects were

developed for the creation in software of modulations systems

making use of the App Designer tool of the MATLAB software. The

modulation systems that were developed are Digital Modulation

Systems and the present work Digital Modulation System. (Wila

Espinoza, 2018) and the present work Analog Modulation System,

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these systems have similar characteristics in the process of

configuration and data transmission. For the implementation of each

of the modulation systems, it was decided to choose the Analog and

Digital Communications subject and the Systems Simulation

subject, these subjects are related because in the first one all the

theoretical content is given and in the second one the experimental

implementation of the communications systems is done. After

carrying out the respective implementations and obtaining the

corresponding results, we proceeded to conduct the surveys that

determined that the implemented systems met the needs of the

students, obtaining a favorable response on their use. After

conducting the surveys the students of the Analog and Digital

Communications course indicated that the Analog Modulation

System software helped to complement the knowledge that had been

explained in class and in the Systems Simulation course indicated

that although they obtained the expected results they did not like it

because they are students of an experimental subject, they prefer to

manipulate the elements and equipment that are available in the

Networking laboratory instead of a software that does everything

because they believe they can learn more even if it takes more time

to develop it. This is how the author's idea is expressed (Durango,

2015) The author's idea about the two ways of performing

experimental practices in the classroom is thus reflected, making it

clear that the practices developed in software should be used in the

theoretical subjects and that the use of electronic elements and

equipment to perform practices should be used exclusively in the

experimental subjects. By the opinions made by the students of the

subject of System Simulation, it was decided to carry out electronic

trainer modules in subsequent semesters. In the semester of the

2019-2020 CI academic period, four trainer modules were carried

out, such as the FM Modulation and Demodulation trainer module,

AM/ASK modulation, AM/ASK modulation and FM/ASK

demodulation trainer module. (Alvarado Nieves, 2019)AM/ASK

Modulation (Ramírez Macías, 2019)Modulation, QPSK/BPSK

Modulation (Pillasagua Oviedo, 2019) and finally the trainer module

QPSK Modulation and Demodulation. (Pacheco Santana, 2019).

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