SIMULATING TELEROBOTICS BY CELLULAR TELEPHONY

Rodrigo Montúfar-Chaveznava, Crisóforo Paisano

Computer Science Department,INAOE, Luis Enrique Erro 1, Tonantzitla,Puebla, Mexico

José María Cañas

Robotic Labs (GSyC), ESCET, Universidad Rey Juan Carlos, C/Tulipán s/n, Móstoles, Madrid, Spain.

Keywords: Telerobotics, GS

M, Simulation, Cellular telephony.

Abstract: In this work we present a simulation system to control a mobile robot using a cell phone. We exploit the

cellular telephony technology to communicate and command a robot provided with a modem in a simulation

environment. The system considers telerobotics can be performed using phone tones or sending text

messages via SMS. Due the cellular telephony is expensive, the simulation system give us the possibility to

experiment infinitely this novel way of telerobotics without expending a lot of economical resources. We

design all components required for a basic cellular telephony system and we employ a robotics simulator for

the Pioneer mobile robot, expecting to translate the system primitives to real systems in a near future. The

idea comes up due that cellular telephony has an enormous covering, and taking advantage of such situation,

telerobotics could be performed in places where wireless networking and power sources are not available at

all such as the country.

1 INTRODUCTION

Telerobotics is related to robot autonomy. In this

field, humans have to execute several tasks, such as

planning, world perception and manipulation. This

mean, there is somebody acting in real-time as part

of the robot control system. However, we need to

satisfy some requirements in the control system and

they are not always available, especially when we

are working with mobile robots.

Telerobotics is a response of the necessity of

carry ou

t operations where it is difficult to put a

human being due to constraints such as cost, safety

or time. Besides, telerobotics demands reliable

navigation because the environment where robots

operate is usually unknown, dynamic or unstructured

and the erratic navigation can guide us to an

unpredictable performance and system failures or

accidents. Telerobotics also requires of the efficient

generation of action commands because the success

on the task depends on the robot behavior.

Moreover, telerobotics claims for localized sensor

information, particularly when activities such as map

construction and registration are necessary.

Actually, telerobotics has extended to Internet

and it is acces

sible to almost everybody, it provides

user interfaces easy to use. However, networking is

not available everywhere, and this fact limits the

telerobotics expansion.

Considering that cellular telephony has a bigger

verage than Internet, the introduction of this kind

of technology in robotics is considered an alternative

to continue expanding the use of telerobotics to

places where it is considered a solution or assistance.

In this work, we present a simulation system to

carry ou

t telerobotics using a cell phone. Actually,

we have not found any reference about the use of

cell telephony in robotics. During the development

of the work, we have considered all aspects related

to communication in cellular telephony and we have

considered the use of a Pioneer robot simulator, the

idea is to translate the primitives of the system to

real Pioneer robots very soon.

2 CELLULAR TELEPHONY

In last years, we have been witness of the birth and

development of wireless technologies. Cellular

telephony is the one that has had the most important

development. At the beginning, cellular telephony

was conceived for voice communication; however,

329

Montúfar-Chaveznava R., Paisano C. and María Cañas J. (2005).

SIMULATING TELEROBOTICS BY CELLULAR TELEPHONY.

In Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics - Robotics and Automation, pages 329-334

DOI: 10.5220/0001167703290334

 SciTePress

nowadays it is able to provide a diversity of services,

such as data, audio and video transmissions with

some restrictions. At present, we identify five

generations of development in cellular telephony

(Ibrahim, 2002).

First Generation (1G). It was designed in 1970, but

implemented until 1984. It was completely analog

and employed for voice communication.

Second Generation (2G). 2G was designed in 1980,

and introduced in 1991. It was digital instead of

analog. The 2G system employs sophisticated

coding protocols and actually is in use.

Second and half Generation (2.5G). It was

designed in 1985 and introduced in 1999. 2.5G has a

higher capacity than previous versions and employs

packetized data.

Third Generation (3G). It was designed in 1990

and implemented in 2002. 3G has the ability to

contain high voice and data convergence with

wireless access to Internet; and consequently it is

suitable for multimedia. 3G protocols produce high-

speed data transmission; they are designed for

specialized applications such as MP3 audio, video in

movement, videoconference and high-speed access

to Internet.

Fourth Generation (4G). The 4G design began in

2000 and we expect it will be totally implemented in

2010. 4G will be completely IP-oriented, with higher

capacity, multimedia and transmissions of hundreds

of megabits.

2.1 The Cell Phone

Cell phones are considered very sophisticated radios

(Yucatan, 2001). We can compare the cell phone

with the short-wave radio to figure out such

sophistication. A short-wave radio allows

communicating two persons using the same

frequency, and only a person can talk in turn.

Whereas a cell phone is dual, it uses a frequency to

talk and other to listen. A short-wave radio has 40

channels. A cell phone can use 1664 channels. Cell

phones operate in regions named cells, which can be

alternated following the phone displacement. The

cells provide a high scope to phones, considering a

short-wave radio can only transmit until five miles.

The great idea concerning cell phones is that a

region can be divided in small cells extending the

communication frequency to the entire region.

2.2 Telephone Tones

The Dual-Tone Multi-Frequency (DTMF), also

known as touch tone dialing, is employed to transmit

telephone signals over the voice frequency band.

Previous to DTMF, the telephone systems

employed a sequence of clicks to dial numbers

(pulse dialing). The clicks were the beginning or end

of a connection on the line phone, and they were

equivalent to turn on or off a switch.

DTMF was developed in Bell laboratories to use

long distance numbers and establish wireless

connections via microwaves or satellite. Encoders

and decoders were included in the terminals to

translate standard pulses in DTMF tones and vice

versa. The touch-tone system introduced a standard

keyboard. The DTFM designers considered the

possible use of phone lines for computer access, then

they included some additional keys such as # and *.

The DTMF keyboard is a 4×4 matrix, each row

corresponds to a specific low frequency, and each

column to a specific high frequency. When a key is

pushed, a sinusoidal tone is produced containing

high and low frequencies. The tones are evaluated to

determine the pressed key. Frequencies were

designed using a ratio of 21/19, which is barely

lower than an entire tone, to avoid harmonics or

natural frequencies that could appear when two

tones are transmitted. Table 1 presents the keyboard

correspondence to DTMF values (Fogelklou, 1999).

Table 1: DTMF Frequencies

1 2 3 A 697 Hz

4 5 6 B 770 Hz

7 8 9 C 852 Hz

* 0 # D 941 Hz

1209 Hz 1336 Hz 1477 Hz 1633 Hz

2.3 Global System for Mobile (GSM)

GSM has some characteristics, which makes it

different in the mobile communications universe

(Rahnema, 1993). It was created in 80’s as result of

the cooperation between many European countries.

GSM shares common elements with other mobile

communication technologies as voice and data

digital transmission, or the cellular topology. A

GSM network has three basic elements: the terminal

or cell phone, the base station and the network or

node subsystem. Additionally, there are centers of

operation established to monitor the network status.

The terminal has the subscriber identity module

card (SIM), employed to identify a terminal when it

connects to the network. The SIM gives mobility to

the user, allowing the access to the network services,

independently of the terminal or location. There is a

unique number to identify every terminal, the

international mobile equipment identity (IMEI),

which is independent of the SIM.

The base station controls the connection between

terminal and network. It is known as the cell,

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because it covers a certain geographic region. The

base station subsystem (BSS) has a base transceiver

station (BTS), and a base station controller (BSC).

Every BSS has one or more BTSs. The BTS houses

the equipment for transmission and reception and

negotiate the protocols with the terminal. There are

more BTS in urban zones than in the country, and

some times broadcast equipment is employed to

guarantee the service. The stations use digital

techniques to allow many users connect to the

network; this negotiation is called multiplexing.

The BSC manage the resources of one or more

BTSs. Some functions of the BSC are the handoff,

the establishment of the channels to be employed

and the frequency switching. The BSC establishes

the connection between the cell phone and the

mobile service-switching center (MSC), which is the

core of the GSM system.

The MSC is the network core, where a cell phone

is connected to networks such as the public switched

telephone network or the integrated services digital

network. The node where the MSC is located has

equipment to control some functions such as

security, messenger service or service collecting.

2.4 Short Message Service (SMS)

GSM provides the transmission and reception of

short text messages (SMS), where two classes are

specified: Point to point (SMS/PP) and Cell

broadcast (SMS/CB).

SMS/PP allows sending a message form a GSM

phone to another. SMS/CB allows sending one or

more messages at the same time to all GSM phones

located in certain zone. SMS/CB can have at most

93 characters, but it can link up to 15 messages to

produce a macro message. Each SMS/CB message is

assigned to a category where the information and the

language employed are classified. In this way, it is

possible to read selectively or discard the messages.

SMS is a protocol with no-connection. In fact,

during transmission, a connection between

transmission and receptor is not produced.

Sending a SMS/PP message from a GSM phone

to another is considered a two steps operation: the

message transmission from the cell phone to a

special network entity, the short message service

center (SMSC), and from here to the cell phone

receptor. The first operation is called SMS mobile

originated (SMS-MO), and the second one is called

SMS mobile terminated (SMS-MT).

SMS-MT allows the reception of text messages

containing up to 160 characters in the screen of the

GSM cell phone. SMS-MO allows the transmission

of messages containing up to 160 characters to

another GSM terminal, fax, modem or e-mail

Internet address.

The success of SMS depends, in one hand, on the

simplicity and facility to use it and, in the other

hand, on the sensation of presence in the other side

of the phone. Both factors have produced such

success, in spite of the costs and limitations in

communication.

3 ROBOT SIMULATORS

Due the novelty that robotics was sometime ago;

actually we find many definitions for robot. Some

definitions, obtained form different sources are: (1)

Machinery controlled electronically, capable to

move and execute automatically different actions,

according an established program; (2) a machine,

which apparently mimics behaviors and actions of

people; (3) a machine, which acts automatically as a

response to its environment; (4) a handful of motors

controlled by computer software; or (5) a robot is a

computer with muscles. These definitions are very

different from the original meaning of robot

(robota): force or work.

The introduction of microprocessors in 70’s

makes possible the progress in robot technology.

The modern computers provide the brain to the

muscles of mechanic robots. Nowadays, robotics is

the symbiosis between electronics and mechanics

An acceptable robot for research is not usually

cheap. It is necessary to have resources to get one or

a colony and for maintaining. A robot is not always

accessible to anyone, and when programming,

sometimes the results can be unexpected. Then,

robot simulators are a solution to overcome these

problems.

At present, the robot Pioneer (Fig. 1) is one of

the most employed, and we can have access to some

Pioneer robot simulators to tests ideas, theories,

programs and algorithms, without necessity of the

robotic body. Some of the most common simulators

for the Pioneer are:

Saphira (Konolige, 1997). It is considered a mobile

robot control architecture. It was developed for

research purposes and programming in the robot

Flakey at SRI in 1994. Saphira is divided in two

modules. The low-level routines are organized and

implemented as individual software: Aria. Saphira is

designed and supported by ActivMedia Robotics

(ActivMedia, 2005). The system is based on a set of

C++ classes. The structure of classes makes easy to

expand and develop new programs adding new

sensors when it is required. Saphira and Aria are

considered two different architectures, one

constructed over the other. Aria consists of a set of

SIMULATING TELEROBOTICS BY CELLULAR TELEPHONY

331

communication routines programmed to control the

robot from the server in a computer. The system

architecture is designed to define easily robot

applications using programs. Saphira is an open

architecture, available to everyone who wishes to

write its own control system without worries about

complexities in hardware control. Communication is

an advantage of micro-task properties and reflex of

the architecture status.

Stage/Player/Gazebo (Gerkey, 2003). Player was

developed in the Research Robotics Laboratories at

the University of Southern California. Player is a

free software; it is a multithread server of robot

devices, which provides a simple and complete

control of sensors and actions to execute in the

robot. When Player is running, the control program

client is connected to Player through a TCP socket,

and the communication is performed sending and

receiving messages translated as commands or status

information. Player is designed as an independent

language and platform. The program client can run

in any machine with network connection. The client

can be written in any language to open and control

TCP sockets. The client characteristics are available

in C, C++, TCL, LISP, Java and Python. Player is

designed to virtually support any quantity of clients.

Java Mobile Robots – JMR (Gallardo, 2003). JMR

is a client-server architecture, which can support

many robots. The robots are identified by an

independent name. JMR can run different processes

in any robot, and connect to the Saphira simulator to

communicate to a real robot. The client controls

devices such as sonars and cameras; it also controls

speed and reads the distance from the robot to any

obstacle; it is also possible to know the robot status,

and we can dictate the distance to travel and the

degrees to rotate. The server receives and simulates

the commands sent by the client. In the server we

can load the worlds where the robot will navigate,

and read the images captured by the robot cameras,

such images can be sent to the client and displayed.

Figure 1: The holonomic robot Pioneer 2DX

4 THE SYSTEM SIMULATOR

The system (Fig. 2) consists of the mobile robot

simulator (SimRobot), corresponding to a modified

version of JMR, and the basic GSM cellular

telephony simulator (SimGSM). SimGSM has three

modules: the GSM cell phone (M1), the GSM

modem (M2) and the SMS/Phone center (M3).

Figure 2: The SimGSM system

M1 is employed to communicate and control the

robot via the telephone network. The robot control

can be performed sending/receiving text messages or

tones. M2 is employed for communication and it is

attached to a specific robot in the JMR environment.

M3 receives and re-sends text messages and

establishes the connection between modules in the

telephone network.

4.1 Communication by tones

First, the connection is stablished dialing, from M1,

the number attached to M2. M3 determines the

connection. Once the connection is established, we

can send commands (sequences of tones) from M1

to SimRobot through M2, which is provided with a

command verifier (VeriCommand) to validate the

orders. If the command is correct, it is re-sent to

SimRobot where the robot executes the action.

The commands are defined as a sequence of

tones:

** Start/end command.

#**n Robot moves forward n centimeters.

#*#n Robot turns n degrees clockwise.

For example, to move the robot 20 cm forward,

we send the sequence: ** #**20 **

The robot status is always checked previous to

execute any command. The possible states are:

Collision: The robot has collided.

Moving: The robot is moving.

Stopped: The robot and motors are on, but it is

stopped.

No motors: The robot is on, but motors are off.

Disconnected: The robot is off.

If the status is No motors or Disconnected, then

the commands cannot be executed. If the status is

Collision, then it is only possible to execute turns. If

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the status is Stopped then any command can be

executed.

M2 can send tones to M1 depending the status of

the system, the tones are:

1 The connection is accepted.

2 The connection is denied.

3 The command has been executed successfully.

4 The robot has collided.

5 The robot is in an infinite loop.

6 The robot is executing a command.

4.2 Communication by SMS

The commands are written as a text message,

following the rules dictated for tone communication.

We employ the messages screen in M1. Once the

message is written, we send it providing the phone

number attached to M2. The message is processed in

the SMS center and re-sent to M2. When M2

receives the message, it is verified. If the command

in not valid, then M2 constructs an error message,

which is sent to M1. If the command is validated,

then it is passed to SimRobot and the robot executes

the order.

5 MODELING THE SYSTEM

We employ UML as a tool to develop the system.

UML determines a set of notations and diagrams to

model object-oriented systems and describe the

essential semantic respect the meaning of symbols

and diagrams (Popkin, 1998). UML is used to model

many kind of software and hardware systems, and

the real world organization.

We consider four stages to model SimGSM: (1)

Analysis, (2) Design, (3) Implementation and (4)

Testing.

The stages include a set of UML diagrams.

Analysis includes the diagrams of (1) Situation and

(2) Classes. Design comprises (1) Classes (detail),

(2) Sequence, (3) Interaction, (4) Status and (5)

Activities. Implementation has only the Members

diagram. Finally, the black box method was

employed for Testing.

6 THE OPERATION

SimGSM has two interfaces (modules): The cell

phone (Fig. 3) and the SMS/Phone center (Fig. 4).

The cell phone (M1) emulates the basic functions of

a real GSM cell phone and it is employed to send

commands and receive the status of the robot in

SimRobot. The SMS/Phone Center (M3) is in charge

of verify, validate, monitor and establish

communications and data transmission between

modules.

Figure 3: The cell phone interface

Figure 4: The SMS/Phone Center interface

The SimRobot interface is a modified version of

JMR, where we add the GSM modem (M2), which is

attached to the robot, and the VeriCommand module

(Fig. 5). The additional modules are employed to

monitor and verify commands, communication and

data transmission.

The robot control simulation was performed

employing the interfaces. The robot and the world

are initially loaded in SimRobot. Next, we send

several commands following the rules dictated in

section 4.1 and we receive the corresponding (text or

tone) message for every command sent. In SimRobot

we could observe the robot behavior, the execution

of commands and the robot status. During test we

observe an acceptable performance. We test the two

possibilities of control, considering all reasonable

possibilities because we expect to translate this

system to real world, using commercial cell phones,

the GSM network and a Pioneer mobile robot.

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7 CONCLUSIONS AND FUTURE

WORK

We have present a telerobotics system simulator as a

first approximation to control mobile robots using a

cell phone through the GSM network: Telerobotics

by cell phone.

The system was modeled employing UML to

consider all possibilities that can emerge during

operation. UML modeling includes analysis, design,

implementation and testing models, and every model

has different UML diagrams.

The system was developed in Java, including

JMR and JMF. It is a client-server architecture. We

expect some modifications and additions in future to

the system: (1) A module for speech recognition to

command the robot via voice, (2) a module for

speech creation to provide oral status information to

user, and (3) the robot control via Internet

considering that at present, cellular telephony

technology provides such service.

We also expect to evolve the system to real

world, using cell phones, the GSM network and a

mobile robot as Pioneer as soon as possible.

Finally, due latency, the control of the robot

using SMS messages is not recommended, but it is

just an alternative and possibility.

REFERENCES

ActivMedia Robotics. 2005. http://www.activrobots.com.

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Gallardo-Lopez, D. et al. 2003. Java Mobile Robots (JMR)

Manual del Programador. DCCIA, U. de Alicante.

Gerkey, B. P. et al. 2003. The Player/Stage Project: Tools

for Multi-Robot and Distribited Sensor Systems. In

Proc. of the International Conf. on Advanced Robotics

2003. Coimbra, Portugal, pp. 317-323.

Ibrahim, J. 2002. 4G Features. Bechtel Telcom. Technical

Journal. Vol. 1, No. 1, pp. 11-14.

Konolige, K. et al. 1997. The Saphira Architecture: A

Design for Autonomy. Journal of Experimental &

Theoretical AI. Vol. 9, No. 1, pp. 215-235.

Popkin, Software and Systems. 1998. Modeling Systems

with UML. A Popkin System White Paper.

Rahnema, M. 1993. Overview of the GSM System and

Protocol Architectura. IEEE Communications

Magazine. No. April 1993.

Yucatán, D. de. 2001. Teléfonos celulares ¿bendición o

pesadilla. Reportaje Especial del Diario de Yucatán.

http://www.yucatan.com.mx/especiales/celular/

Figure 5: SimRobot: A modified version of JMR. The additional modules corresponding to GSM modem and VeriCommand

are indicated at the bottom of image

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