Access Control System using an Embedded System and Radio FrequencyIdentification Technology

Mario Alberto Ibarra-Manzano, Dora Luz Almanza-OjedaJose Josias Aviles-Ferrera and Juan Gabriel Avina-Cervantes

Universidad de GuanajuatoFacultad de Ingenierıa Mecanica, Electrica y ElectronicaCarretera Salamanca - Valle de Santiago Km 3.5 + 1.8,

Comunidad de Palo Blanco, Salamanca, Guanajuato, Mexico{ibarram, luzdora, avina}@salamanca.ugto.mx

Abstract

The radio frequency identification technique has beenknown since decades ago, however due to some importantadvances in technology, the amount of micro devices built-in on a chip and the cost of manufacturing, this technologyhas been implemented in many applications nowadays. Aradio frequency identification system used to security checkin a University is presented in this work. In this systemseveral autonomous embedded sub-systems are included,which are placed at different entrances at school. Everyembedded sub-system has a link up to a master control thatregisters every event at the entrance. This master controlhas the command to close or open any entry at any time if acase of emergency is occurred.

A detailed analysis about the elements that are includedin this autonomous access control is presented. Some im-portant aspects of this system are also presented. Conclu-sions and perspectives are presented at the end of this work

1. Introduccion

The Radio Frequency Identification (RFID) techniqueuses radio waves to transfer data between the reader andany mobile element in order to identify, to categorize andto track such element [3, 11, 9, 2]. The RFID systems arefast and reliable; also, their components do not need to be incontact or to use physical signals [1, 5]. A RFID system iscomposed by a radiofrequency reader, one or several anten-nas, a control unit (a PC, a microprocessor or other), at leastone transponder (tag) and optionally by a battery charger foractive transponders [11, 5, 8, 12, 6].

The radiofrequency identification process starts with the

emission of pulses from the reader’s antenna. So, if atleast one transponder is inside of signal detection range andif the transponders operation frequency is equal to readerfrequency then the transponder sends its code number toreader. After that, the reader de-codify this code num-ber [11, 7, 1, 5].

There are several types of transponders, nevertheless,the most known classification is based on their powersupply, their operating frequency and their type of mem-ory [10, 11, 6]. According to the power supply of the RFIDtransponders, these can be classified as passives and actives.An active transponder has his own energy system, normallya battery. This kind of transponders are useful to transmitinformation across long distances. The communication be-tween the reader and active transponders reaches distancesfrom 20 to 100 meters [10, 1, 5, 11].

On the other hand, passive transponders do not have apower supply, therefore they are smaller and cheaper. Also,this characteristic give transponders the possibility to setthem almost in anyplace or on anything, without need tocarry on a battery [11, 10, 5]. Instead of a battery, pas-sive transponders use an electromagnetic signal emitted byreader. This signal is reached by transponders only if theyare inside of the reader signal’s range. The power of theelectromagnetic field received from the reader is the onlypower used for the data transmission between transponderand reader. This power is stored into a capacitor throughprocess called inductive coupled. When the capacitor hasenough energy, he feeds the transmiting circuit and send thestored memory information to the reader [10, 3]. Anothertype of transponders is sometime considered: semi-passivetransponders. These kind of transponders have a batterypower supply as the actives, however, serves exclusively tosupply the transponder’s main elements (the microchip) andfor the retention of stored data [5].

Electronics, Robotics and Automotive Mechanics Conference 2008

978-0-7695-3320-9/08 $25.00 © 2008 IEEE

DOI 10.1109/CERMA.2008.31

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According to memory type, the transponders have readonly memory or read/write memory. In read only transpon-ders, usually a simple (serial) number is incorporated whenthe chip is manufactured and cannot be altered thereafter.In writable transponders, the reader can write data to thetransponders from 100 000 to 1 000 000 times. Sometimes,writable transponders have an access key to their informa-tion [5, 3].

The different transmission frequencies of passivetransponders are classified into three basic ranges, LF (LowFrequency, 30-300kHz), HF (High Frequency, 3-30 MHz),UHF (Ultra High Frequency, 300MHz-3 GHz) and mi-crowaves (> 3 GHz) [3, 1, 5]. Some advantages of LFtransponders are: well suited for applications which requireto read small amounts of data at slow speeds and mini-mal distances. Also they penetrate well material such aswater, tissue, wood and aluminum. In the other side, thedisadvantage that we can find are: they do not penetrateor transmit across metals, they handle a small quantity ofdata at low read speeds. Also, they use larger antennas thanHF transponders and their operating range is minimal. TheHF transponders are preferred for short distance’s rangesand small quantity of data. The main advantages of HFtransponders are: their transmission range is larger thantransponders LF range, antennas’ design is simpler and fi-nally these transponders are thinner. The main disadvan-tages of HF transponders are: their frequency range is con-trolled by federal government, their signal does not pene-trate metals, their reading range is 70 cm approximately,and finally, chip manufacturing process used to need morethan one surface. The UHF transponders are preferred forhigher transmission speeds and longer operating distances.The main advantages of these transponders are: their fre-quency range let us to reach greater distances (> 1m) andhigher quantity of data. Furthermore, UHF antennas aresmaller than LF and HF antennas and it is possible to con-trol the reading zone thanks to directional antennas. Thedisadvantages of UHF transponders are: signal does notpenetrate water nor tissues, we need to adapt severals as-pects such as frequency, channels, power and duty cycle. Fi-nally, microwave transponders are preferred for their smallsize and their higher data transmission speed. Among thedisadvantages we find: low distance transmission and lowsignal/noise ratio [3, 1, 5].

2. Background.

The study of access control problem has started fewyears ago. The traditional access control method consistof human guard who verify, valid and include each personalinformation data. This method could fails when after 5 or 6hours of work the human error appears. It is to say, duringthe day a big quantity of users enters several time per day,

finally the guard accidentally avoid to enter somebody withauthorization or at the contrary, he approves the entranceof somebody without authorization. Another big problem isthe attendance time, which can be as long as the day. Differ-ent solutions to these problems have been proposed. One ofthem consist of magnetic cards which are mainly popular inhotels, nevertheless, this technique is not easy for the usersand many people have problems for use it. Another solu-tion propose the biometric features detection, such as iris,fingerprint. Unfortunately, these kind of systems are ex-pensive and complex, so that they are not commonly used.The RFID is an easy to use technology, and at the sametime it has high powerful applications. Its characteristicsdescribed above and its low cost of implementation give toRFID technology the capacity of using it almost in any auto-identification problem.

RFID technology give us a big gamma of new capaci-ties to well performing some daily task. Furthermore, RFIDtechnology let us to construct new kind of efficient identifi-cation systems [1]. In the last years, RFID technology hasmainly been using in security systems, but others interestingapplications had been proposing in [4].

3. The problem and its solution

The University of Guanajuato has several academic unitsaround to Guanajuato State, each one presents his own se-curity problem. The main objective of this work is to pro-pose a useful general solution to security access for eachacademic unit. In this paper we present the results of thefirst phase to this project. The results show the proposedsystem works only inside of one academic unit (Salamancaacademic unit). The Salamanca academic unit is located atPalo Blanco Community, 3.5 km off Salamanca, Guanaju-ato State. This Salamanca academic unit has just one park-ing access, two buildings with several access’ doors. Eachbuilding has different laboratories which we are interestedin controlling their entrance.

The proposed solution to this problem involves the use ofRFID systems for people identification. Multiples embed-ded systems are connected to verify and control the accessto different laboratories. The unit that verify and control theperformance of every system’s component (RFID system,sensors, actuator, etc) is called master control.

4. System’s Components Description

In this section we describe every proposed system’s com-ponents (figure 1). The system has mainly two types ofcomponents: embedded systems and a master control. Ev-ery embedded system controls personal access in an au-tonomous way, and also, each of them has a direct com-

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munication to master control. Following subsections de-scribe the elements of each autonomous embedded systemand also describes the interaction form among them in orderto reach an expected performance.

Figure 1. Block diagram of overall system.

4.1 Autonomous embedded systems

Every embedded system has six components: antenna,RFID reader, control element, actuator, sensor and dis-play element. Antenna sends and receives electromag-netic waves to transponders, thanks to that, it is possibleto obtain nearest transponders’ code. RFID reader demod-ulates transponder’s electromagnetic wave into digital sig-nal which contains the detected transponders’ code. Finally,RFID reader communicates this digital signal to control el-ement. The control element of every embedded systemsshould not be confused with master control; the last onecan be seen as total system’s heart and the control elementas embedded system’s heart. So that, control unit of embed-ded system performs all central tasks as an autonomous em-bedded unit, these central task can be seen as subtask withrespect to overall system task. Actuators consist of elec-trical AC motor controlled by power stage and electronicdoor locking systems for providing access to laboratoriesand work areas. Sensors verify if user has already crossedthe door and therefore, gives electrical signal to unit controlfor closing door.

4.1.1 Transponders

The identification process is done using LF transponderscards. This kind of cards are passive transponders (with-out battery power supply) with read only memory; they areoperated at 134 kHz of frequency. The passive transpondercard model RI-TRP-R4FF fulfills the requirements of secu-rity system so he was used to test this project (Figure 2).

Figure 2. Read-only transponder cards modelRI-TRP-R4FF.

4.1.2 RFID reader

The RFID reader model RI-STU-MB2A integrated to thisproject, developed by Texas Instruments company, is shownin Figure 3. The operating frequency of reader is the samefrequency as transponders; the power supply to the readeris 7 to 14 VDC at 1 A. Reader needs one antenna (at least)for working, so the antenna model RI-ANT-S01C was con-nected in the reader. With this antenna, reader has a maxi-mal range of 30 cm to detect passive tags. Despite of shortdetecting range, our security system does not need a widerrange because identification procedure is done near to door.Nevertheless, our system need two antennas, one of themdetects when user enters and the other one detects whenuser exits. The protocol communication of the reader tounit control is RS-232 protocol.

4.1.3 Control unit of embedded systems

Control unit is implemented into Field Programmable GateArrays (FPGA) which is a main component of Spartan-3Ecard. FPGA device belongs to family of ProgrammableLogic Device (PLD) which has between 100 000 and 1.6million of gates, also this family device has many attractiveand powerful features for control applications.

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Figure 3. RFID reader model RI-STU-MB2A.

Embedded system consist of a RS-232 communicationinterface that this is a module of communication withreader. This interface sends data to unit control to processreceived information and to search transponder code num-ber in the memory unit. The memory unit is a databasestored in the RAM internal memory of the FPGA. An-other component of embedded system is a display modulecomposed of Liquid Crystal Display (LCD), which displayuser information. Finally, communication between personalcomputer and FPGA is done using a Telnet communicationmodule with a reduced number of instructions, but enoughto verify, control and validate system performance in a re-mote way.

The performance of control system is showed as flow di-agram in figure 4. As we can see in the figure, the processstarts with the initialization of components, which consistof close laboratory’s door and turn on communication mod-ules and LCD. After initialization step, control unit checksif emergency button is active, if it is true, then he sendsalarm message to LCD and open access door. The secu-rity system remains in this state until he is re-initialized andthe button emergency is inactive. In the case of there isnot an emergency alert, system falls into detection state inwhich detects if there is any transponder close to the readzone. The system remains in this state until a transpon-der is detected or the emergency button is activated. Whenthe reader receives a sufficiently strong signal of a passivetransponder card, he sends a message with the transponder’scode to master control. Last one checks if the code numberis stored in database, if it does not, LCD shows a messageand system goes back to detection state. In the case of thecode number were stored in database, the systems opensdoor and waits until 10 seconds or until sensor sends a sig-nal indicating that user has crossed door, after that systemsclose door and he goes back to detection state.

Figure 4. Flow diagram of control system.

Embedded system has three basic instructions to com-municate with the master control. The first one is the emer-gency instruction, which is activated when a critical prob-lem is occurred and an evacuation process should be exe-cuted. The second one serves to send a detection signal atinstitution. The last instruction reprograms the memory inorder to update unit control database of the embedded sys-tem.

4.2 Master Control

The master control synchronizes different embeddedsystems, also verifies, registry and controls the correct per-formance of embedded system. This system consists of sixmain task: control interface, database, report generator, webserver, itinerary activities and communication interface.

4.2.1 Database

Database is developed in Microsoft Access; database hasthe unique identification number, user name, authorized ac-cess, photo identification, among other informations. Thisdatabase is linked with interface control by ODBC. AnODBC stores the information of connection which is onlyvisible and usable by authorized user and declared PC. Thisdatabase serves as a backup of others databases located inthe embedded systems. Also, with this database it is pos-sible to update by adding a new users, to do that, it is justenough to add it and give it required privileges. Automati-cally, the database of master control updates all embeddedsystems that it can access.

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4.2.2 Report Generator

The master control has also a formatted report generator thatmakes reports in printed or electronic form (as file). The re-port generator is able to save all events passed during theday. The importance of this report is to have an expedientof occurred actions if there were a security problem. Thegenerated report has a PDF, Word or html format, depend-ing on what user used to handle.

4.2.3 Itinerary activities

This module task let us to program different process suchas open or close door or activate an alarm. The main ad-vantage of this task is to have the possibility of controllingthe security system, for instance, if an special journey forall public is organized it is more convenient to inactivatesecurity system by programming the free access during allday.

4.2.4 Communication Interface

Communication interface is a Telnet module, that sends andreceives messages between each embedded system. Thismodule is very important because it let us to communicatedamong embedded systems and therefore to verify if theywell-done their function. Furthermore, it is possible to up-date existing database to each embedded system and acti-vate an alarm.

4.2.5 Control Interface

Control interface makes to work all master control, also heverifies if the database of embedded system has the lastupdates and if there are pending activities in the itinerary.Generated reports and active alarms in emergency cases aredone also by control interface. Another important activityto control interface is to supervise several access doors andto see laboratories affluence.

5. Results

Access control system was implemented and tested inDigital Signal Processing laboratory of Salamanca Aca-demic Unit belongs to University of Guanajuato. The em-bedded system is composed of several passive transponders,an antenna, RFID reader, Spartan 3E card (FPGA) and LCD(Figure 5). The system works in satisfactory way undercommon operating conditions.

When authorized or denied access message is showed inLCD (Figure 6 and 7 respectively) means that systems iswell performed in the case of known or unknown transpon-der, respectively. After severals days of test, we have ver-ified that if transponder code is known, effectively, system

Figure 5. Embedded system.

sends correct message to LCD, open door and wait for closeit. In contrary cases he never open door, but he sends deniedaccess to LCD. In both cases, any action that system do isadding to activity report.

Figure 6. Authorized access message.

The figure 8 shows the interface of master control sys-tem. In the image, Interface displays an identification num-ber and name of user. After that, another important infor-mation is shown, such as, photo, access hour and charge.

6. Conclusions

System has enough good performance, nevertheless, itsuffers embedded system’s disadvantages. The main disad-vantage is visible while we are updating the database mem-ory into master control, and this one is unable to detect anytransponder even if he is inside of the reading range. Thisdisadvantage can be solved using memory of double port

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Figure 7. Denied access message.

Figure 8. Master control interface.

and dividing control main task in two parts; first part willcontrol the identification and the second one will update thesystem. Another particular disadvantage of the proposedsystem is hundred of millisecond delay into LCD. One so-lution to this problem is to optimize LCD module until elim-inated the delay; another solution proposed is to change theLCD display.

Currently system is well-performed, but he depends onseveral devices connect to him. So that, in the next stage ofthis project, we propose to include RFID system into FPGA.This change will reduce such components as system price.

References

[1] D. L. Almanza-Ojeda, A. Hernandez-Gutierrez, and M. A.Ibarra-Manzano. Design and implementation of a vehicularaccess control using rfid. In IEEE, editor, 1st Multiconfer-

ence on Electronics and Photonics, pages 223–225, Novem-ber 2006.

[2] D. L. Almanza-Ojeda, A. Hernandez-Gutierrez, M. A.Ibarra-Manzano, and J. M. Lopez-Hernandez. Prototipo deun sistema de medicion de tiempos aplicado en carreras dedescenso de montana. In I. T. de Merida, editor, VII Con-greso Nacional de Ingenierıa Electrica y Electronica delMayab, pages 1–8, March 2007.

[3] K. Finkenzeller. RFID Handbook: Fundamentals and Appli-cations in Contactless Smart Cards and Identification. JohnWiley & Sons Ltd, West Sussex PO19 8SQ, England, 2ndedition, 2003.

[4] A. Graafstra. Hands on. how radio-frequency identificationand i got personal. IEEE Spectrum, 44(3):18–23, March2007.

[5] M. A. Ibarra-Manzano, D. L. Almanza-Ojeda,A. Hernandez-Gutierrez, J. J. Aviles-Ferrera, J. M.Lopez-Hernandez, and G. O. Burnham. Diseno e imple-mentacion de un administrador de bibliotecas utilizandoidentificacion por radio frecuencia. In IEEE, editor, IEEE5to. Congreso Internacional en Innovacion y DesarrolloTecnologico, pages 191–196, October 2007.

[6] B. Jiang, K. P. Fishkin, S. Roy, and M. Philipose. Un-obtrusive long-range detection of passive rfid tag motion.IEEE Transactions on Instrumentation and Measurement,55(1):187–196, February 2006.

[7] J. Landt. The history of rfid. IEEE Potentials, 24(4):8–11,October-November 2005.

[8] K. S. Leong, M. L. Ng, and P. H. Cole. Positioning analysisof multiple antennas in a dense rfid reader environment. InIEEE, editor, International Symposium on Applications andthe Internet Workshops, pages 1–4, January 2006.

[9] C. H. Quan, W. K. Hong, and H. C. Kim. Performanceanalysis of tag anti-collision algorithms for rfid systems.Emerging Directions in Embedded and Ubiquitous Comput-ing, 4097/2006:383–391, 2006.

[10] R. Weinstein. Rfid: A technical overview and its applicationto the enterprise. IT Professional, Technology Solutions forthe Enterprise, 7(3):27–33, May-June 2005.

[11] Y. Xiao, X. Shen, S. Bo, and L. Cai. Security and privacy inrfid and applications in telemedicine. IEEE CommunicationsMagazine, 44(4):64–72, April 2006.

[12] T. Yoshihisa, Y. Kishino, T. Terada, M. Tsukamoto,R. Sagara, T. Sukenari, D. Taguchi, and S. Nishio. A rule-based rfid tag system using ubiquitous chips. In IEEE, ed-itor, Proceedings of the 2005 International Conference onActive Media Technology, pages 423–428, May 2005.

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