a Promoter; b Researchers Wireless Personal Computer-Based Digital Communication Simulator Joe Arthur R. Agustin a , Francis Kevin D. Abuan b , Michael Vincent S. Aganon b , Jeremy Raphael B. Garcia b , Jan Darren D. Sanchez b , Ricco Gabriel D. Yabes b , Bryan Anthony C. Zacarias b , Ruth Chris C. De Vera b , Jeselyn D. Macalanda b ABSTRACT The study aims to demonstrate and simulate the signaling of digital communications through wireless (FM) transmission using Scilab, a freeware which eliminates the costly license acquisition problems of universities. More specifically, the study aims to show and apply the modulation techniques discussed in Digital Communications subject of Electronics Engineering Department of Saint Louis University. The system allows users to input desired information (recorded audio/textual/ generated waveform) and select modulation techniques (character coding, PCM, error coding, line coding, and channel coding) with the use of buttons, check boxes, and blank spaces; and to display graphs of sampled, line coded, and channel coded signal simultaneously with the output bit stream. The output of the transmit program, digital audio, is fed through the computer audio out into the FM transmitter, then propagated wirelessly by the FM transmitter. The FM receiver captures the propagated signal, demodulates it and feeds it to the receiving program through the computer audio in. The receive program decodes the signal based on the desired parameters similar in the transmit program and plots it. KEYWORDS Wireless, Digital, Communications, Simulator, PC-based, Personal, Computer, Based INTRODUCTION Improvements on digital communications are the main game in today‟s technology. Frontrunners in the industry boast their innovations and upgrades for digital communications. But for a student pursuing electronics engineering, understanding the concepts of digital communication is vital, especially its hands-on applications. Digital communications is defined as the electronic transmission of information that has been encoded digitally, for storage and processing of computers (The Free Dictionary). Also, digital communications is the transfer of discrete messages. The messages are either represented by a sequence of pulses by means of a line code, or by a limited set of continuously varying wave forms, using a digital modulation method (Clark, 1983). Digital communications is applied in telephony, internet, broadcast systems, control systems, television, radio systems, and even in navigation. Digital communications challenges the analog communications to improvements and efficiency on transmission and reception of data. The revolution set by digitalization of communication paved way to upgrades and shift of media used in communications, hardware and software equipment, and even data analyses, processes and interpretations. The high cost of commercially available Digital Communication Simulators imposes a problem in better understanding of concepts and topics in Digital Communications by ECE
Transcript
a Promoter; b Researchers
Wireless Personal Computer-Based Digital Communication Simulator
Joe Arthur R. Agustina, Francis Kevin D. Abuanb, Michael Vincent S. Aganonb, Jeremy Raphael B. Garciab, Jan Darren D. Sanchezb, Ricco Gabriel D. Yabesb, Bryan Anthony C. Zacariasb,
Ruth Chris C. De Verab, Jeselyn D. Macalandab
ABSTRACT
The study aims to demonstrate and simulate the signaling of digital communications
through wireless (FM) transmission using Scilab, a freeware which eliminates the costly license acquisition problems of universities. More specifically, the study aims to show and apply the modulation techniques discussed in Digital Communications subject of Electronics Engineering
Department of Saint Louis University. The system allows users to input desired information (recorded audio/textual/ generated
waveform) and select modulation techniques (character coding, PCM, error coding, line coding, and channel coding) with the use of buttons, check boxes, and blank spaces; and to display graphs of sampled, line coded, and channel coded signal simultaneously with the output bit
stream. The output of the transmit program, digital audio, is fed through the computer audio out into the FM transmitter, then propagated wirelessly by the FM transmitter. The FM receiver
captures the propagated signal, demodulates it and feeds it to the receiving program through the computer audio in. The receive program decodes the signal based on the desired parameters similar in the transmit program and plots it.
KEYWORDS
Wireless, Digital, Communications, Simulator, PC-based, Personal, Computer, Based
INTRODUCTION
Improvements on digital communications are the main game in today‟s technology. Frontrunners in the industry boast their innovations and upgrades for digital communications. But for a student pursuing electronics engineering, understanding the concepts of digital
communication is vital, especially its hands-on applications. Digital communications is defined as the electronic transmission of information that has
been encoded digitally, for storage and processing of computers (The Free Dictionary). Also, digital communications is the transfer of discrete messages. The messages are either represented by a sequence of pulses by means of a line code, or by a limited set of continuously varying
wave forms, using a digital modulation method (Clark, 1983). Digital communications is applied in telephony, internet, broadcast systems, control
systems, television, radio systems, and even in navigation. Digital communications challenges the analog communications to improvements and efficiency on transmission and reception of data. The revolution set by digitalization of communication paved way to upgrades and shift of
media used in communications, hardware and software equipment, and even data analyses, processes and interpretations.
The high cost of commercially available Digital Communication Simulators imposes a problem in better understanding of concepts and topics in Digital Communications by ECE
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students. Most of the available Digital Communications Simulators use MatLab which is a licensed application. The limits of MatLab-based Digital Communications Simulators are as
follows: the license is costly; the programming and interfacing requires knowledge on MatLab; and the application is to some extent cannot be customized to suit the manner of teaching of the
faculty. With these factors in mind, this study focuses on the design of low-cost Digital
Communications Simulator using Scilab as the programming software. Scilab is a freeware
alternative for MatLab programming software and is considerably easy to understand. According to the study by Güngör et al, the basic components of a digital communication
system are simulated with channel models and noise by using flexible antenna systems both at the transmitting and receiving ends. A digital communication system is made up of both analog and digital parts. The digital part consists of digital source, source encoder-decoder, channel
encoder-decoder and digital modulator-demodulator. Meanwhile, the analog part consists of analog source, transmitter and receiver antenna systems, channel models and noise models.
The developed simulation program is capable of inputting both digital and analog information. The simulation program allows the user to add other desired coding/decoding techniques and modulation/demodulation techniques easily.
METHODS
Materials and Equipment:
In this study, the researchers used two laptops which satisfy the requirements needed for
the programs to run, and FM transmitter and receiver purchased and assembled by the researchers. The transmitter module has an output power of 20mW (13dBm).
In addition, the researchers used Scilab 5.5 (minimum version requirement of Scilab 5.4.1) with Image Processing Design Toolbox and Portaudio Toolbox in programming.
To prevent overdriving the signal and the system, the laptop should be adjusted to the
The study is divided into four main components: transmitter program simulator,
transmitter module, receiver module, and the receiver program simulator. Both transmitter and receiver modules are purchased and set to a frequency of 88.5MHz.
The researchers used the frequency to avoid adjacent channel interference of any FM radio station (89.8MHz being the nearest) and other spectral uses (below 88MHz). The transmitter module is plugged at the speaker (audio out) of the computer with transmitter program simulator
while the receiver module is plugged at the microphone (audio in) of the computer with receiver program simulator.
For the programming parts of the study, the researchers first identified the required improvements: GUI design, separate program for transmit and receive parts, additional processes for digital communications, and simultaneous display of graphs. These improvements are the
core of the project study. The researchers made a block diagram of the system and flowchart of algorithms to make
programming systematic. (See Figure 1 for the Block Diagram and Figure 2 for the Flowchart.)
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After the researchers finalized the sequence of programs, they designed a layout for the GUI. GUIs for transmitter and receiver program simulator are shown in Figure 3.
Once the researchers decided on how the simulators look and function, they started programming the simulator software using Scilab.
Figure 1: Block Diagram of the System
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Figure 2-1: Flow Chart of Programs at the Transmit Side
No
Yes
No
Yes
Start
Load Parameters
Load Functions (Character Coding Functions, PCM Functions, Error Coding, Line
[A]The audio output is fed into the FM transmitter by the digitransmit function, for wireless propagation, which will then be processed and converted back to the original
information in the receive side.
Run „mainfunc.sce‟ in parallel
with „syscompute‟.
Bar
Plot
Line Coding
Plot
Channel Coding
Plot
Bit
Stream
A
Redo with different
input?
B
C
Audio[A]
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Figure 2-2: Flow Chart of Programs at the Receive Side
No
Yes
No Yes
Start
Load Parameters
Load Functions (Character Decoding Functions, PCD Functions, Error Decoding, Line
Note: Programs will terminate if and only if the Scilab is closed.
FINDINGS & DISCUSSION
Overview of the System
The wireless personal computer-based digital communication simulator has four main components: transmitter program simulator, transmitter module, receiver module, and the
receiver program simulator. The transmitter program simulator generates the desired information. In order for the
system to produce the GUI, the user must load all transmit functions/programs. The transmit
program simulator will run the default program parameter generator to continuously run the GUI with default values, which for the meantime is blank, waiting for the user input. The user then
inputs the desired input information either be it a generated waveform, textual information, or analog voice signal. The input information is supported by the input selector switch which enables the input information to be sampled, quantized, and encoded into a digital signal. The
encoded output is then processed by the character coding selector (which enables the ASCII or EBCDIC options), further processed by the pulse code modulator (which enables anti-aliasing,
anti-imaging, and analog/digital commanding methods), then by the error coding selector (which enables the CRC, LRC, VRC or LRC&VRC options), then by line coding selector (which
A
Bar
Plot
Line Coding
Plot
Channel
Coding Plot
Bit
Stream Audio
Run „mainfunc.sce‟ in parallel
with „syscompute‟.
Redo with different input?
B
C
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enables UPRZ, BPRZ, or other line coding techniques), and finally by a channel coding selector (with enables ASK, PSK, or other channel coding techniques). The output at the channel coding
selector will be the final output of the program through the audio out of computer. Also, a bar plot, bit stream plot, line coding plot and channel coding plot will appear on the graphical display
on the GUI. The output signal will then be fed into the FM transmitter module to convert the
electronic signal into an electromagnetic (EM) radio wave ready for wireless propagation. The
EM radio wave will then be received by the FM receiver module, which converts the EM radio wave back into a digital audio signal fed into the audio in of the second computer.
In order for the system to produce the GUI, the user must load all receive functions/programs, preferably simultaneously with the computer on the transmit side. The transmit program simulator will run the default program parameter generator to continuously run
the GUI with default values, which for the meantime is blank, waiting for an input from the receiver module. When the computer detects an audio input signal, the system records for the
meantime. The recorded signal will then be processed back, after enabling the input switch selector, by the channel decoding selector, line decoding selector, error decoding selector, pulse code demodulator, character decoding selector, decoder and reverse quantizer into the
reconstruction circuit which will then be the output of the speakers as analog audio signal.
Graphic User Interface
Figure 3: Graphic User Interface of Transmit Program
The graphic user interface features three major portions: the parameter section, the plot
section, and the bit stream section. (See Figure 3 for a sample of GUI.) The parameter section is an improved version of the earlier PC-based digital communication simulator. Instead of drop-down menu/toolbar, the study made use of check
boxes, buttons, blank space for user inputs, and pop-up dialogue boxes.
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The plot section features the plot/graph of the input wave form (samples plot), line coding, and digital modulation output. All information is plotted in amplitude vs. time axes. Such
plots/graphs are discussed in the Digital Communications lecture subject. This section is essential so that students can visualize and verify the processes happening in the digital
communication transmitter/receiver. The bit stream section displays the transmit bit stream in binary. The shown bit stream is the integration of all modulation techniques and the user input signal.
Functions
Mainfunc.sce – The Main Function
The mainfunc.sce (mainfunction) is a looping program that monitors the GUI and sets
default variables while waiting for the user inputs. Once the user inputs information and parameters, the mainfunction runs simultaneously with the syscompute program.
Syscompute – Program Proper
The syscompute program is an integral part of the study. This program enables the
computing and plotting functions. Digisolve is the subprogram of syscompute which processes signal for digital transmission. This solves the necessary modulation techniques for the input to
result in the required digital signal. Meanwhile, the digiplot function, another subprogram of syscompute, is for retrieving and plotting the values in the plot section.
Digitransmit – The Computer-FM module interface
The digitransmit program functions as a temporary storage of processed data which will
then be played or fed in the transmitter module. It serves as the interface between the computer and the FM transmit/receive module.
In a sampling test done by the researchers, a second of analog sine wave produced 1
minute and 20 seconds of digital audio at the output of digitransmit due to the processing of 8000 samples per second with a total of 64,080 bits.
CONCLUSIONS & RECOMMENDATION
To demonstrate the processes in digital communications, the wireless personal computer-based digital communication simulator is a tool that students can use in their laboratories.
The study made use of the freeware Scilab 5.5 (minimum version requirement of Scilab 5.4.1) with Image Processing Design Toolbox and Portaudio Toolbox for programming. This resolves the Saint Louis University‟s problem on costly programming software.
The system, which is an example of simplex type of communication, features easy-access for input classification and information (analog audio, textual or generated waveform), character
coding/decoding, pulse code modulation, error coding/decoding, line coding/decoding, and channel coding/decoding. Drop-down boxes present in the previous version were replaced with push buttons, check boxes and text fields to simplify the selection of the user. The graphic user
interface also features graphical display for bar plot, input bit stream, line coding plot, and channel coding plot, which are essential in the demonstration of the theories in the lecture.
The programming includes of functions such as mainfunction (mainfunc.sce), which is a looping program that monitors the GUI and sets default variables while waiting for the user
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inputs; syscompute, which is the general program for information processing and plotting; digisolve, which is a syscompute subprogram to process signal for transmission; digiplot, which
is a syscompute subprogram for plotting values; digitransmit, which is the program for temporary storage of processed data to be played or fed in the transmitter module.
For future improvements of the project, the researchers recommend the addition of more digital modulation techniques such as QPSK and QAMs for channel coding, addition of Hamming bits for error coding, and others. Improvements in the application capacity such as
number of bits, limits on the number of samples, and processing time should also be considered for any future progress done on this study.
ACKNOWLEDGMENT
The researchers would like to thank the mighty and ever-powerful God for providing wisdom, resources, strength and attitude that they needed in making this project study. A warm
gratitude is given to basis of the study, Engr. Zenaida L. Agustin for her support and recommendations in improving her masteral thesis. Lastly, this project study will not be completed if not for the parents and families of each researcher who gave moral and financial
supports to the researchers. Forever appreciation is given to all people who have supported the researchers in any way possible. To God be the glory.
REFERENCES
Agustin, Zenaida L. “Computer-Based Simulator for Digital Communications.” Masteral Thesis,
Saint Louis University, Baguio City, Philippines, 2013.
Analog and Digital Communications Laboratory Manual. Department of Electronics &
Communications Engineering. 2012-2013: Madanapalle Institute of Technology and Sciences
Digital Communications Lab Manual. Department of ECE. 2012-2013: PVP Siddhartha Institute
of Technology. India.
“Digital Communications” The Free Dictionary. Date accessed: 24 October 2014
