CHAPTER 2 RFID TECHNOLOGY AND ITS APPLICATIONS TO HUMAN TRACKING

Transcription

1 18 CHAPTER 2 RFID TECHNOLOGY AND ITS APPLICATIONS TO HUMAN TRACKING In this chapter, we briefly review some of the basic technical details pertaining to RFID Technology, its advantages and shortcomings and recent technological advances made in developing RFID technologies which would overcome the short comings. Figure 2.1 shows the basic RFID communication system which mainly consists of an application oriented host computer which controls a reader which in turn engages a group of preprogrammed tags. As explained in Chapter 1, a tag mainly consists of a microchip and an antenna. It transmits certain information to the reader via its antenna which in turn is forwarded to the host computer by the reader after processing the data. Efficient and reliable anti-collision protocols are required when dense RFID environment prevails and multiple tags are to be read simultaneously. Figure 2.1: Basic RFID Communication System

2 RFID PRINCIPLES RFID principles could be studied under two categories, namely (i) Near-field RFID and (ii) Far-field RFID. Some basic details about these two principles are given below Near-Field RFID System The near-field coupling between a reader and tag is better understood by applying Faraday s principle of magnetic induction. A large alternating current is passed through the antenna coil by the reader which results in an alternating magnetic field around the reader. This magnetic field couples with the smaller antenna coil of a tag present in the proximity of the reader and induces a voltage in the tag antenna coil which is rectified and used to charge an in-built capacitor connected across the antenna coil. This charge is used as a DC supply voltage to the tag chip. With reference to figure 2.2 (courtesy: RFID handbook), a resonant circuit is formed between the antenna coil of the tag and capacitor C1 whose frequency is equal to the transmission frequency of the reader. Figure 2.2: Near-field power/communication mechanism

3 20 Similarly, a capacitor Cr is shunted to the reader s antenna coil which behaves like a resonant circuit whose resonant frequency is equal to the transmission frequency of the reader. The functioning of the two antenna coils can be interpreted as a transformer (transformer coupling), where the reply given back by the tag can be interpreted as variable impedance ZT in the antenna s coil of the reader. As stated in section 1.2.1, half-duplex type of communication exists between the reader and the tag. Based on the information available in the tag memory, the load resistor (a simple diode) connected across the tag antenna coil is turned on and off. This in turn alters the impedance ZT and the voltage of the reader s antenna which if properly rectified and demodulated the information can be transmitted from the tag to the reader. This technique is called as transformer coupled modulation or load modulation. The efficiency of power transmission between the reader and the tag is dependent on four parameters. They are: (i) frequency of operation (ii) number of antenna coil windings of both reader and tag (iii) area of the antenna coil of the tag (iv) angle between the two antenna coils of the reader and the tag and (v) the separation between the reader and the tag.

4 21 Near-field coupling is the simplest way used in the implementation of a passive RFID system. But still it has some physical limitations especially with the range for which it can be used. The range of the magnetic induction is inversely proportional to the operating frequency, that is, one can see that the range of operation decreases as the frequency increases. A further limitation is the reduction in the RF energy available at the tag end to charge its capacitor C1 because the RF energy received by a tag is inversely proportional to the cube of the distance r between the tag and the reader. Now, one would appreciate the fact that real time RFID applications would certainly demand more number of tags with unique identification (ID) bits which in turn would pose the problem of discriminating one tag from the other present in the same vicinity in a constrained read time. In order to overcome this problem, one has to necessarily allot higher data rate for each tag which is possible only when the frequency of operation is considerably increased. These design constraints have led to the introduction of far-field RFID communication system Far-Field RFID System Far-field RFID communication system is required when the physical separation between the reader and the tag is greater than one

5 22 metre. In this case, UHF ( MHz) or Microwave ( GHz) frequencies are required to have an optimal performance of the system. Figure 2.3: Far-field power/communication mechanism As shown in Figure 2.3 (courtesy: RFID handbook), P1 is the power dissipated from the reader s antenna and only a very little amount of the transmitted power reaches the tag antenna because of the free space attenuation. The power P1 received by the tag induces an alternating voltage in the tags antenna coil and this voltage is rectified by the diodes D1 and D2 and fed to the devices of the tag chip as power supply. An FET transistor is connected across the dipole antenna of the tag which in turn is turned on and off based on the information stored in the tag s memory. The switching action of the FET transistor varies the impedance of the tag s antenna. Because of this impedance mismatch a portion of the received power P1 is backscattered as P2. Thus, the backscattering of the tag s antenna is dependent on the switching action of the FET transistor connected across the tag s antenna which in turn controlled by the data stream of the tag to be transmitted.

6 23 A small portion of power P2 radiated by the tag is received by the reader s antenna which in turn is transmitted to the receiver input of the reader through the direction coupler and the data is retrieved. The operational range of the Far-field RFID system has mainly two constraints. They are: (i) The amount of energy transferred between the tag and the reader (ii) Receiver Sensitivity of the reader to the reflected signal. The RF energy received by the tag is inversely proportional to fourth power of r, where r is the physical separation between the tag and the receiver TYPES OF RFID TAGS AND READERS RFID tags are mainly classified into three types: (i) active tags (ii) passive tags and (iii) semi passive tags (i) Active tags have an integrated battery which provides the power required for its functionality. The price, shape, size and life time of the active tags are dependent on the batteries provided in these tags. One example where active tags are used is the device attached to the cars which works on GPS and Cellular technology used to locate if the car is stolen. (ii) Passive tags don t have in built power supply. The operational life is infinite and the size of the tag is very small which can be fit into any of the product for which an RFID label is required. Passive tag mainly consists of a microchip and an antenna encapsulated in a glass or a

7 24 plastic substrate as shown in figure 2.4 (a) and figure 2.4 (b). The purpose of encapsulating the tag is to protect from external varying ambience conditions. Figure 2.4 (a): RFID tags encapsulated in a small glass vial Figure 2.4 (b): RFID tags encapsulated in a laminar plastic substrate Semi passive tags have an integrated battery used to maintain the memory in the tag. It communicates in the same manner just like passive tags. Based on memory type used, tags are further classified into two types: (i) Read only tag and (ii) Read/Write tag Based on coupling between the tag and reader, tags can also be classified into two types: (i) Inductive coupling based tags (ii) Propagation coupling based tags

8 25 RFID readers are mainly classified into two types: (i) Read only readers (ii) Read /write readers. Read only readers read data from the tag. They are usually embedded with a microcontroller, transceiver, antenna, power supply unit. Read/write readers are capable of reading and writing the tags. Based on their fixation, they can also be classified as (i) Stationary readers and (ii) Mobile readers SHORTCOMINGS OF PRESENT DAY RFID TECHNOLOGY The following are the short comings that are identified of the present day RFID technology. But still, one could refer to standard literature to know more especially about the hardware associated with the system Standard norms and regulations. Standard Organizations like International Standard Organization (ISO), Electronic Product Code (EPC) global and European Article Numbering (EAN) define the norms and regulations to be followed which some times become problem in implementing for certain applications. Based on the characteristics of the ambience where the RFID system is being implemented, corresponding protocols, norms and standards are to be selected which is not feasible for some applications Economy The economy of the RFID system is mainly dependent on the price of readers and price of the tags which in turn depends on type of tag required and application.

9 26 By using the tags, the labor cost may decrease by 3-30 %, but still it requires a maximum of 20 cents per tag for high-end products, and 5 cents for common items. Prices of active or semi-passive tags (at least $1 per tag) are high which will be an obstruction, allowing their usage to high-value goods over long ranges only Collision Avoidance Depending on the application where multiple tags are involved, efficient collision avoidance protocols are required which identifies and enumerates the tags at very fast rate. For specific application like Human tracking where security is of prime concern selection of efficient and reliable collision avoidance protocols is of prime concern and one of the short comings of present RFID systems [17] Operational Frequency The selection of optimal frequency depends on several factors. a) Type of coupling between reader and tags There are two kinds of data transmissions used by RFID tags based on the coupling between them and the reader. On the other hand, the selection of coupling is dependent on the operational frequency. For low frequency ranges (such as khz or MHz) inductive coupling is used whereas for higher frequency ranges (such as

10 27 MHz and 2.45 GHz), propagation coupling is used. Finally, the reading range of the tags gets affected based on the coupling used. b) Ambience and content of the tagged goods Based on the material used for encapsulating the tags, the data transmission may get corrupted due to absorption or by reflection by the surroundings in which the RFID system is implemented. c) Regulations with respect to frequency allocation Federal Communication Committee (FCC) is the standard organization which allocates frequencies for various applications. It has divided the entire world into three regions and accordingly the frequency is allocated. Region 1 consists of Europe, Africa, the Middle East and Soviet Union member states. Frequencies assigned are: 125 khz, MHz, MHz. Region 2 consists of North America, South America and a part of the east pacific of the GWM. Frequencies assigned are: 125 khz, MHz, MHz. Region 3 comprises of Asia, Australia and west pacific of the GWM. Frequencies assigned are 125 khz, MHz, MHz. The industries which make use of RFID systems do exert pressure to go in for a regulation in the allotment of RFID frequencies. Yet, there seems to be technical and political differences between the three regions in the frequency allotment and this drives companies to employ different tags in different regions which ultimately lead complex logistics and

11 28 operational difficulties. Figure 2.5 shows a global division of all these three regions. Figure 2.5: Major RFID markets by frequency Poor Quality of Tags The qualities of the tags that are manufactured are not of good quality and 100 % fault free. About 20 to 30 % of the tags have been found defective that are used by early RFID pilots [21] Poor Detection Capability of Tags Identification of the tags attached to any product is of prime concern for any RFID based application. Poor detection of tags will arise because of the following reasons: (i) Damage of the tags during usage (ii) Mishandling of the tagged goods

12 29 (iii) Problems associated with readers Fast Technology Adoption All the companies using RFID technology should keenly observe about the rapid development of the RFID technology. New protocol standards are available which are reliable, fast and fault-free. They have to replace with the latest available well equipped RFID readers and tags to have an efficient RFID based system Issues related to Security and Privacy In RFID based Human Tracking System where security is of prime concern, it is necessary to restrict unauthorized persons. Reliable and efficient encryption methods are to be adopted to ensure that no data can be transferred nor copied [21] Issues related to privacy are related to item level tagging. Most worried privacy issues are: (a) Secret placement of the tags (b) Reading the contents of the tags by a third person unknowingly. (c) Link between the item and the user (d) Reading range of the tags, especially with UHF tags. (e) Including personal details without the consent of the individual

13 Virus and Hacking Attacks Much care has to be taken with respect to the software that is used in readers and tags with back end database. Virus attacks can perform spiteful operations on the database contents. Similarly the contents available at the backend will be hacked if no proper care is taken RECENT RFID TECHNOLOGIES TO OVERCOME THE SHORTCOMINGS. With more research on RFID technology, the drawbacks and limitations can be nullified. With latest software and anti-collision protocols available, RFID technology can be made available for variety of applications like supply chain management, library, transport, jewellery and transport businesses. Microelectronics can be used for anti-counterfeiting devices. Identification technologies can be implemented by using digital signatures of very high degree of accuracy. Microelectronics based devices can be used if price is not a major issue [18]. The use of RFID systems for authentication purpose is discussed in various papers [19, 20]. Two approaches are defined in the literature. (i) Using unique numbers assigned to tagged goods which can be tracked and traced to know the history of the goods. Efficient bulk reading capacity of the RFID readers is the main advantage over the other methods like bar codes etc., (ii) Using cryptographic approaches to prevent duplication of the similar tags. The complexity involved with

14 31 respect to cryptographic approach is similar to smart cards. The only problem with this approach is requirement of larger chip size and thus higher costs. The power consumption will be high which is not suitable for the RFID systems which deploy passive tags since large amounts of data to be sent between reader and the tags. The above mentioned approaches are very useful with respect to security aspect, verification process and possibilities to conduct large number of tests. However the drawbacks associated are high cost and authentication is done only for the tags but not for the products. 2.5 HUMAN TRACKING USING RFID TECHNOLOGIES Now-a-days, personnel working in an organization and various things handled by them are subjected to a very high level of security risk due to threat escalations from antisocial elements and terrorists. Hence it has become almost a necessity for any organization to pay more attention to various security measures which would considerably reduce the risk factors. RFID based Human Tracking is one such security measure recommended and practiced in various risk prone installations. The purpose behind this kind of security measure is of three fold; one to monitor movement of all personnel working or visiting a risk prone site, two to categorize the personnel as (i) security cleared, (ii) suspicious and (iii) unknown and three to take corrective and defensive or offensive action on those who fall under the second category.

15 32 A reliable Human tracking system which uses RFID technology should consist of the following: 1. Reliable hardware comprising a control panel, computers, RFID readers, tags and other accessories. 2. Application oriented software preferably with artificial intelligence built in. 3. Trained security personnel who can handle the RFID gear efficiently 4. Continuous upgrading of technology and updating of intelligence gathered. Figure 2.7 shows a hypothetical site where RFID technology has been installed. Figure 2.6: Hypothetical site for Human activity tracking RFID system In the next chapter 3, we proceed with the study of important lacunae called collision of tags that invariably prevails in the existing RFID communication system and some of the current corrective measures taken to prevent collisions and their success indicators.