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Automatic Vehicle Identification using RFID-A first hand experience

* P.Butani, ** Dr. Joseph John & *** Major Akash Dhole

* P.Butani, Director Research (Mechanical), RDSO** Dr Joseph John, Prof. Electrical Engg., IIT, Kanpur

*** Major Akash Dhole, M.Tech student, IIT, Kanpur

Background:

Development of several wayside detection systems such as Wheel Impact Load Detector,Trackside Bogie Monitoring System and Hot Box, Hot Wheel Detector has been taken up withIIT Kanpur. In all these systems, vehicles with defects are identified using axle count startingfrom the locomotive. However, if there is a change in the direction of train or remarshalling ofvehicles, the axle count of the identified vehicle with defects no more remains valid.

Automatic Vehicle Identification (AVI) for identifying railway vehicles is being extensively usedworld over. This system in combination with wayside detection systems help in identifyingvehicles with defects and sending advise to the maintenance depot /owning authority for taking

corrective action. This has helped in introducing the concept of Predictive Maintenance.

In view of above, it was decided to develop the capability of identifying vehicles using RadioFrequency Identification (RFID) system along with the project of development of TracksideBogie Monitoring System.

Introduction:

Automatic identification, or auto ID for short, is the broad term given to a host of technologiesthat are used to help machines identify objects. Auto identification is often coupled withautomatic data capture. That is, companies want to identify items, capture information aboutthem and somehow get the data into a computer without having employees type it in. The aim ofmost auto-ID systems is to increase efficiency, reduce data entry errors, and free up staff toperform more value-added functions. There are a host of technologies that fall under the auto-IDumbrella. These include bar codes, smart cards, voice recognition, some biometric technologies(retinal scans, forinstance), optical character recognition, radio frequency identification (RFID)and others.

RFID (Radio Frequency Identification) is a means of identifying an item based on radiofrequency transmission. This technology can be used to identify, track and detect a wide varietyof objects. Communication takes place between a reader and a transponder (derived fromTRANSmitter/resPONDER - Silicon Chip connected to an antenna), usually called tag. Tagscome in many forms, such as smart labels that are stuck on boxes, smart cards and a box thatyou stick on your windshield to enable you to pay tolls without stopping. Tags can either be

passive (powered by the reader field), semi-passive or active (powered by battery). Active RFIDtags are powered by an onboard powering source and tend to be more expensive than passivetags that harvest power from the RF energy of the reader. On board power allows the activetags to have greater communication distance and faster response time. These tags are moreversatile and usually have larger memory capacity. Passive RFID tags have no internal powersource and use external power to operate. These tags are powered by the electromagneticsignal received from a reader. The received electromagnetic signal charges an internalcapacitor on the tags, which in turn, acts as a power source and supplies the power to the chip.

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RFID systems differentiation criteria depend on operating reader frequency, physical couplingmethod and communication distance (read range). The communication frequency used rangesfrom 135 KHz long wave to 5.8 GHz in the microwave range and are classified into four basicRanges: LF (low frequency, 30 - 300 kHz), HF (high frequency, 3 - 30 MHz), UHF (ultra highfrequency, 300 MHz 2 GHz) and Microwave (> 2 GHz). The physical coupling uses magneticand electromagnetic fields. The communication distance varies from few millimeters to above 3-5 meters (close coupling: 0 - 1 cm, remote coupling: 0 - 1 m, long range: > 1 m).

The following table shows an overview of RFID performances at various frequencies:

LF HF UHF MicrowaveFrequencyRange


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In the typical configuration tags are placed on the objects to be identified. Each tag is providedwith an internal memory, which is partially read-only and, optionally, rewritable, where theinformation (unique ID serial number, manufacture date, product composition etc.) about theobject is stored. When these tags pass through the field generated by a reader, they transmitthis information back to the reader, thus allowing the object identification.

The communication process between the reader and tag is managed and controlled by one ofseveral protocols, such as the ISO 15693 and ISO 18000-3 for HF or the ISO 18000-6, andEPC for UHF. The identification process begins when the reader is switched on; it starts

emitting a signal at the selected frequency band (typically 860 915 MHz for UHF or 13.56 MHzfor HF); the tags reached by the readers field will wake up (supplied by the field itself, ifpassive). Once the Tag has decoded the signal, it replies to the reader, by modulating thereader field (backscattering modulation). If many tags are present then they will all reply at thesame time. If this occurs, the reader detects a signal collision and an indication of multiple tags.In this case the reader uses an anti-collision algorithm designed to allow tags to be sorted andindividually selected. The number of tags that can be identified depends on the frequency andprotocol used, and typically ranges from 50 tags/s to 200 tags/s. Once one tag is selected, thereader can perform all the allowed operations such as read the tags identifier number, or alsowrite data in it (in case of a read/write tag). After operations on the first tag are finished, thereader starts processing the second one and so on until the last one.

In order to receive energy and communicate with a reader, passive tags use either one of thetwo following methods. These are near field, which employs inductive coupling of the tag to themagnetic field circulating around the reader antenna (like a transformer), and far field, whichuses similar techniques to radar (backscatter reflection) by coupling with the electric field. Thenear field is generally used by RFID systems operating in the LF and HF frequency bands, andthe far field for longer read range UHF and microwave RFID systems. The reason is that in thenear field, the field energy decreases, as a first approximation, proportionally to 1/R3 (where R is

the distance from the antenna), while in the far field the energy decreases proportionally to 1/R;the borderline between near and far field is at R = /2; as a result, in the far field the energy oflower frequencies waves will turn out to be much more reduced than that of higher ones, whoseuse is thus mandatory in that zone.

Passive technology is most widely used for RFID applications. Passive technology operates in arange of frequency bands, of which 860 956 MHz (ISM) band is most popular. Passive tagsoperating at UHF communicate with the reader through Amplitude Modulation (AM), and receivetheir power from the reader field, with energy transfer based on the far field properties.Communication from tag to reader is achieved by altering the antenna input impedance in timewith the data stream to be transmitted: in this way the power reflected back to the reader is

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modulated in time with the data. The use of far field backscatter modulation introduces problemsthat are not present in HF and lower frequency systems. One of the most important of suchundesired effects is due to the fact that the field emitted by the reader is not only reflected bythe tag antenna, but also by any objects with dimensions in the order of the wavelength used:these reflected fields could damp the readers and the back scattered field thus reducing thesystems efficiency; for this reason it is better to use more than just one antenna per reader. ISOdefines the Air interface communication between Reader->Tag and Tag->Reader, and includeparameters like Communication protocol, Signal Modulation types, Data coding and frames,Data Transmission rates and Anti-collision (detection and sorting of many tags in the Reader

field at the same time). The ISO standard list for Air Interface is as follows:

ISO 18000 RFID for Item Management: Air Interface-1 Generic parameters-2 below 135 kHz-3 at 13.56 MHz-4 at 2.45 GHz-5 at 5.8 GHz-6 at UHF frequency band

Electronic Product Code- 96 bits

EPC Global has released their UHF standards, which include class 0 and class 1 tag. Class 0

EPC tags have a factory programmed 96 bit data that cannot be altered, whereas class 1 allowsuser programmable data. EPC Global has proposed other classes of EPC tags that wouldprovide user memory beyond the ID code. It has also created detailed specifications for thestructure of the 96-bit code flexible enough to incorporate other coding standards currently inuse in the supply chain.

Operating Principle: Backscattering (UHF) Passive RFID: The major components, of abackscattering Passive (UHF) RFID system, are readers, tags and an application host. An RFIDreader mainly comprises of a set of antennae, a radio interface, a control unit and a poweringunit. The antenna performs the function of transmitting and receiving the electromagneticenergy used for communication and powering the tags, within its range. The radio interfaceperforms the job of detection, modulation and demodulation of the RF signal. The control unitexecutes the communication protocol with the tags and interprets the data received from thetags. In performing all the above-mentioned functionalities, the reader communicates with thetags within range as directed by the application host and reports the results to the host.

A common tag implementation consists of an electronic microchip that stores data and executesthe tags functionality, an antenna that performs the function of receiving and transmitting RFenergy, a tag powering circuit that utilizes the RF power from the reader to power up themicrochip, and a substrate on which the entire tag is built. Passive RFID tags, that utilize the RFenergy from the reader for its operation, come cheapest and have the largest commercialpotential.

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The tag Integrated Circuit (IC) controls the tag operations according to the readers commandsand the communication protocol. Tag antenna receives readers continuous wave during the

readers powering up phase. The tag powering up circuit rectifies this CW signal from the readerand further delivers it to its IC circuitry.

Powering up phase of the reader transmission is followed by the command transmission phasein which modulated RF is sent by the reader as command signal. The powered up tag ICexecutes the readers command. After the reader has transmitted its command, it starts tobroadcast a continuous field again which the tag will modulate and backscatter again as itsresponse to the readers command. The modulation is produced by switching the tags antennamatching. The schematic of this operation is depicted in figure:

Fig. Communication Principle

The response of the tag to the readers query ID command depends on whether reader isoperating in global scroll or inventory mode. The query ID command format from the readerdepends upon these modes and depending upon which format is used in the reader data field,the tag response will take one of the two possible forms. The global scroll command isintended to identify one tag at a time and the tag response to this command is generated in theform of tag's identification code in whole, which includes both the tag's EPC and CRC. In caseof inventory mode of the reader, several tags in its identification range can be identifiedsimultaneously. The reader goes through all possible code combinations with the minimumnumber of readings using an anti-collision algorithm. Each reply of the tags includes a 15-bitpart of its EPC defined in the reader's command code.

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The complete identification procedure takes a certain amount of time. This time takes intoaccount the maximum and minimum time intervals of each modulation window that is defined inthe concerned specification. Besides this, the data processing also takes a certain amount oftime. The identification time required for identification of tags one at a time using the Globalscroll technique is very less as it takes a single round trip of one command and its response.On the other hand Inventory command used for multiple tag identification consists of severalread cycles. The exact number of read cycles required depends on the number of tags presentwith in the identification range of the reader and their closeness in EPC codes in the binary tree.

It indicates that the inventory command should only be used with very low velocities to achievereliable identification accuracy, and for higher velocities, Global scroll command and reading ofthe tags one at a time is advisable.

Acquisition Modes: Acquisition Mode defines the method used to read tags in the field.There are two distinct methods for reading tags, "Global Scroll" and "Inventory. The choice ofone method over another depends on the application at hand.

Global Scroll: Global Scroll is the most primitive of tag ID reading operations. When a globalscroll command is issued, the RFID Reader sends a single command over the air to each andevery tag. This command is simply a request for any tag to immediately send back its ID to theRFID Reader.

The simplicity of this command is both its advantage and its downfall. The command is veryquick to execute as it involves only one round trip between the reader and the tag. However,because the command is so simple, problems may arise if there is more than one tag in thefield. At this point, multiple tags will all receive the same command, and will all send back theirIDs to the reader at virtually the same time. A situation such as this makes it difficult for thereader to discern individual IDs among the general noise. Typically one or two of the closesttags will be decoded, but the majority will not be discerned. There are many applications whereglobal scroll is the best tag reading method to use. These applications typically expect just oneor two tags in the field of view at any one time, such as conveyor belt or tollbooth applications.For these systems, global scroll outperforms a full inventory by a factor of three as far asindividual read rates are concerned.

Inventory: Inventory command is a full-featured system for discerning the IDs of multiple tags inthe field at the same time. This single high-level command transforms itself into a complexseries of reader-tag interrogations that eventually resolve themselves into a single list of tag IDsseen by the RFID Reader. This method of interrogation and evaluation of multiple tags is knownas an anti-collision search. These algorithms are far more complex than the global scrollalgorithm, requiring many more reader-tag instructions.

Class 1 Gen 1 Inventory uses deterministic inventory algorithm which involves a rigorousmethod of "walking the tree" through all possible bit combinations that make up Tag IDs. Incontrast, the Class 1 Gen 2 protocol is "probabilistic". In the Class 1 Gen 2 inventory, the readertells all the tags to roll a random number, and the population is subdivided into a number of"bins" (determined by the "Q" parameter). Only those tags that chose a random number in bin

#1 get to talk. After the reader finishes with this first group of tags, it tells the rest of the tags tomove down a bin, and it then talks to the next group of tags. Picking the starting Q parameterthat is right for the expected tag population size is important in achieving good inventoryperformance.

In case of railway application the tags will be placed far enough from each other to ensure thatno two tags will be in the RF field at any given time. In such a scenario use of Global Scrollmode of acquisition is possible and it will enhance the performance of the system drastically.However it has to be ensured that the tags are spaced apart adequately to avoid any collision.

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Tag read mode: There are two methods of reading the tags, Interactive Mode andAutonomous Mode. In Interactive Mode the controlling application issues commands to thereader to read tags. This command will always immediately return with a list of tags in thereader's field of view. On the other hand in case of Autonomous Mode, the reader constantlyreads tags, and may initiate a conversation with a network listener when certain events arise.While both methods are equally useful, the choice will ultimately be determined by the needs ofthe controlling application. Although it may be easier and require less coding to work inInteractive Mode, a little investment in programming effort lets the user set up Auto Mode.Readers that spend less time communicating with the host can spend more time looking fortags.

Interactive Mode: Reading tags in Interactive Mode is as simple as issuing a single commandto the reader. This causes the reader to initiate a tag search, and report back the current TagList.

Autonomous Mode: Autonomous Mode is a configuration and operation mode that enablesautomated monitoring and handling of tag data. A series of configuration commands are issuedinitially to the reader which specify how and when to read tags, and optional ly what to do withthe tag data. Once configured in this mode, the reader can be left to opera te on its own. Anapplication on a host computer can then be set up to listen for notification messages from thereader containing any tag data that it has read.

Fundamentally, a reader operating in Auto Mode moves between several states: Waiting,Working, Evaluation, and Notification. Movement from one state to the next may be initiated byan expiration of a timer, a triggered event on the digital input lines, or changes to the Tag List.Autonomous mode has a feature by which the Tag List delivered has time stamps indicating theinstants at which the tags were detected. These can then be used to correlate the Tag IDs withthe corresponding sensor data.

Antenna Sequence: The readers can invariably support the use of multiple antennas andallow selecting which antenna port(s) to use and in what sequence. The reader cycles throughall the antennas, in the order specified in the Antenna Sequence. The Readers may be Mono-Static Systems orMulti Static Systems. Mono-Static System Readers have the ability to transmit

and receive RF signals on the same antenna port. Multi Static System Readers, on the otherhand, transmit and receive RF signals on separate antennas, providing significantly bettersensitivity to weak tag backscatter signals. These readers may allow fixed antenna pairingscheme or more flexible arbitrary combinations of transmit/receive antennas, giving better RFcoverage over a larger area in front of the reader, with fewer antennas.

Initial Hurdles in Implementation:

RFID is a relatively new technology and is yet to find widespread application in India. Earlierthere was no frequency allotted by Wireless Planning and Coordination Wing for this purpose.However vide its notification G.S.R 168(E), dated 11 th March, 2005, 865-867 MHz was allottedfor Radio Frequency Identification (RFID) with a maximum transmitter power of 1 Watt (4 WattsEffective Radiated Power) with 200 KHz carrier band width. Also 2.4 GHz to 2.4835 GHz. bandwas de-licensed vide notification no. G.S.R. 45 (E) dated 28th January 2005.

Although the frequency band was allotted for RFID application, no equipment working in thisband was available. For railway applications, the American railroads are using 902-928MHzwhile in Europe 2.4GHz band is being used. In Europe, 869.4-869.65MHz band with 500mWpower was also being used for general RFID applications. Subsequently, in October 2004, withgradual increase in use of RFID in Europe, ETSI 302208 was adopted with a frequency band of865-868 MHz. As a result, RFID equipment working in this frequency range became available inthe later half of 2005.

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It was decided to purchase a RFID system with a small quantity of tags for trials. The option wasto either go in for a proven system for Railway Vehicle Identification or to purchase a general-purpose system and adapt it for railway application. Offers were received from M/s Transcore,USA for their RFID system comprising of AI 1200 Reader, AR2200 RF module, AntennaAA3110, AP4118 Tag Programmer & 100 nos. of AT5118 tag and M/s Tag Master, Sweden fortheir Heavy Duty Reader S1566 and 100 nos. of Script tags S1450. Although they were offeringa proven system for Railway Vehicle Identification, they were offering their standard productworking on frequencies allotted for RFID in their countries, i.e, 902-928 MHz & 2.4 GHz

respectively. Also the systems were expensive (~ Rs 10 lakhs). The only company, which wasoffering equipment in the desired frequency band of 865-867 MHz in 2005, was CAEN, Italy.Although they were offering a general-purpose system not tried for railway applications, thesystem was cheaper (~ Rs 2 lakhs).

It was decided to purchase a general-purpose system, which, besides being cheaper will giveample scope for experimentation and learning. A development kit A948DKEU working on ISOprotocol was purchased from CAEN, Italy along with 100 nos of A918 tags for conducting trials.Subsequently, in the later half of 2006, more such equipments working on the desired frequencybecame available. Development kit ALR-8800 Dev C working on a different protocol, EPC,was purchased from Alien Technologies, USA. This system was also in the range of ~ Rs 2lakhs.

Trials with the systems:RFID tags may be placed on the rail vehicles, and the reader with antenna can be placedsuitably, along with other wayside detection systems. The antennae may be placed on thetrackside and the tags may be fixed on the sides of the rail vehicle, or alternatively, the tags maybe mounted on the undercarriage of the rail vehicle and the antennae may be placed betweenthe tracks looking up. The setup may take one of the forms shown in figure. However on IR, atpresent, the toilet discharge from the passenger coaches is allowed to fall directly on the tracks.As such, the tag placed on the side of the vehicles is the only option.

Tag

ReaderAntenna

(a) Transponder attached to theundercarriage of vehicle

(b) Transponder attached to theside of vehicle

Trials with CAEN System: The CAEN development kit came with demo application software inJAVA and Visual C++. As the equipment was to be used along with the Trackside BogieMonitoring System working on LabVIEW, fresh program in LabVIEW was developed. Thesystem works on ISO-18000-6b protocol. The tag can store 2k bits of data (256 bytes). Theequipment was tested on running trains. It could read tagID+10 characters of data (vehicle no.)from tags fixed on the vehicles moving up to 75kmph. However at higher speeds it could read

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only the tagID. The speed of the vehicle had to be reduced when no. of characters of data to beread increased. The system first interrogates the tag for its ID and in the next interrogationreads the data. The tag should be available in the reading range for sufficient time for theReader to read the tag ID + data. This double interrogation cycle limits the speed of the vehiclefor automatic identification.

For using this system for vehicle identification at higher speeds, the option is to read only tag IDand link it to a computer database to find the vehicle no.

A948 Reader

A918 Tag

Tag IC Tag Antenna

A 948 Dev Kit

Antenna

Reader

Antenna

Reader

Field trials with CAEN System

Tag ID TagData

Tag ID TagData

Antenna-1 Antenna-2

Screenshot of LabVIEW program front panel used with the CAEN hardware

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During the trials numbering of 111... , 222, etc (10 alphanumeric characters) was used as Tagdata instead of actual vehicle no. for ease to find out which tag data was missed.

Speed: 50 kmph

S No. Tag ID Tag Data Time Delay (ms)

1 E004C9BD2C010000 1111111111 12:59:25 PM 129

2 E004C9BD2C010000 12:59:25 PM 148

3 E004C4B52C010000 2222222222 12:59:26 PM 126

4 E004C4B52C010000 2222222222 12:59:26 PM 1245 E0043BAD2C010000 3333333333 12:59:27 PM 1286 E0043BAD2C010000 3333333333 12:59:27 PM 124

7 E0043BAD2C010000 12:59:27 PM 1458 E004A5CD2C010000 4444444444 12:59:29 PM 101

9 E004FEC82C010000 5555555555 12:59:30 PM 128

10 E004FEC82C010000 12:59:30 PM 13011 E0042ACD2C010000 6666666666 12:59:31 PM 124

12 E0042ACD2C010000 6666666666 12:59:31 PM 12713 E0043BF82C010000 7777777777 12:59:32 PM 129

14 E0043BF82C010000 12:59:32 PM 123

15 E00463C12C010000 8888888888 12:59:34 PM 127

16 E00463C12C010000 8888888888 12:59:34 PM 126

17 E00463C12C010000 8888888888 12:59:34 PM 127

18 E00463C12C010000 8888888888 12:59:34 PM 124

19 E00463C12C010000 12:59:34 PM 14620 E00401D82D010000 9999999999 12:59:35 PM 126

21 E00401D82D010000 9999999999 12:59:35 PM 12322 E00401D82D010000 9999999999 12:59:35 PM 123

23 E00401D82D010000 12:59:35 PM 135

24 E00458B12C010000 10101010101 12:59:36 PM 112

25 E00458B12C010000 10101010101 12:59:36 PM 11726 E00458B12C010000 10101010101 12:59:36 PM 12127 E00458B12C010000 10101010101 12:59:36 PM 115

28 E00458B12C010000 10101010101 12:59:36 PM 107

Data acquired during field trials of CAEN equipment at speed of 50 kmph

Speed: 75 kmph

S No. Tag ID Tag Data Time Delay (mS)

1 E004C9BD2C010000 01:29:12 PM 141

2 E004C4B52C010000 2222222222 01:29:12 PM 116

3 E004C4B52C010000 01:29:12 PM 125

4 E0043BAD2C010000 01:29:13 PM 125

5 E004A5CD2C010000 4444444444 01:29:13 PM 1216 E004FEC82C010000 01:29:13 PM 120

7 E0042ACD2C010000 6666666666 01:29:14 PM 1298 E0043BF82C010000 01:29:14 PM 113

9 E00463C12C010000 8888888888 01:29:14 PM 120

10 E00463C12C010000 8888888888 01:29:14 PM 12111 E00463C12C010000 01:29:15 PM 123

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12 E00401D82D010000 9999999999 01:29:15 PM 12613 E00401D82D010000 9999999999 01:29:16 PM 113

14 E00401D82D010000 9999999999 01:29:16 PM 123

15 E00458B12C010000 10101010101 01:29:16 PM 112

16 E00458B12C010000 10101010101 01:29:17 PM 114

17 E00458B12C010000 10101010101 01:29:17 PM 112

18 E00458B12C010000 01:29:17 PM 122

Data acquired during field trials of CAEN equipment at speed of 75 kmph

Around 75kmph, although all TagIDs could be read, tag data of some of the tags highlightedabove was missed. These tags were fixed on wagons and the stiffeners surrounding the Tagsresulted in reflections, causing nulls in the RF field.

Trials with System supplied by Alien Technologies: The system works on EPCprotocol. The tags can store 96 bits of user programmable data. A separate program inLabVIEW was developed for this system. The equipment was tested up to 150 kmph by movingtwo vehicles, one with tags and the other with reader, in opposite direction. The system,however, was not tested on a wagon, wherein the limitation of reading the tags due to stiffeners,is experienced.

AntennaTag

Field trials with Alien System

Tag ID -16 alphanumericcharacters

Date Time No. ofReads

ReadingAntenna

Tag Type

0000000000000000 2007/03/02 09:19:08. 677 1 1 Class 1 Gen 2

0000000000000000 2007/03/02 09:19:08. 852 1 0 Class 1 Gen 21111111111111111 2007/03/02 09:19:10.936 1 1 Class 1 Gen 2

1111111111111111 2007/03/02 09:19:11.251 1 0 Class 1 Gen 22222222222222222 2007/03/02 9:19:12.337 1 1 Class 1 Gen 22222222222222222 2007/03/02 9:19:12.471 3 0 Class 1 Gen 23333333333333333 2007/03/02 09:19:14.257 1 1 Class 1 Gen 23333333333333333 2007/03/02 9:19:14.352 3 0 Class 1 Gen 24444444444444444 2007/03/02 9:19:16.077 1 1 Class 1 Gen 2

4444444444444444 2007/03/02 09:19:16.192 3 0 Class 1 Gen 25555555555555555 2007/03/02 9:19:18.297 1 1 Class 1 Gen 26666666666666666 2007/03/02 9:19:19.897 3 1 Class 1 Gen 26666666666666666 2007/03/02 9:19:20.052 3 0 Class 1 Gen 27777777777777777 2007/03/02 9:19:21.817 1 1 Class 1 Gen 27777777777777777 2007/03/02 9:19:21.992 3 0 Class 1 Gen 2

8888888888888888 2007/03/02 9:19:23.657 1 1 Class 1 Gen 29999999999999999 2007/03/02 9:19:26.013 3 0 Class 1 Gen 2

Data acquired at speed of 60 kmph with Alien System

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Screenshot of LabVIEW program front panel used with the ALIEN Hardware

ALR 8800 Dev kit

MINIMUMPROGRAMMINGCYCLES:Gen 2 tags 10,000write/erase cycles

MEMORY: Gen 2 tags240 bits NVMEPC size 96 bits

Protocol Control bits 16bitsLock Bits 10 bitsKill Bit 1 bitAccess Code 32 bitsKill Code 32 bitsReserved 53 bits

Setup for trials at 150 kmph for ALIEN system(Two vehicles moving in opposite direction to get a relative speed of 150 kmph)

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Tag ID Date Time No. ofReads

ReadingAntenna

Tag Type

TAG 1 2007/05/03 11:12:45.459 1 0 Class 1 Gen 2TAG 2 2007/05/03 11:12:45.735 3 0 Class 1 Gen 2

Data acquired during trials of ALIEN system at speed of 150 kmph

Comparison of the two systems

A comparison of the two systems is shown below:System CAEN, Italy Alien Technologies, USAReader Model A948 EU long range reader ALR 8800 Gen2Tag Universal tag A918- encapsulated -

@ 7.00. The cost may reduce ifthe quantity of tags increases.

ALL-9460 Omni squiggle tags-label tags-free samplesEncapsulated tags cost thesame as A918 tag of CAEN

Cost of Dev kit 2970 US $ 3400Protocol ISO-18000-6b EPCInterrogation cycle Double interrogation - first for tag ID

and then for tag data.Single interrogation

Type of System Mono-static: transmits and receives

RF signals on the same antennaport.

Multi-static: has different

transmission and receptionantennaeNo. of Antenna Each antenna works independently. Work in pairs- each antenna

alternately transmits & receives;the first antenna transmits andthe other receives; then thesecond antenna transmits andthe first one receives.

Method of Tag dataacquisition-Global Scroll /Inventory

Does not give the option for Tagacquisition using global scroll

Global scroll & Inventory search-Global scroll is approximatelythree times faster than inventorysearch which uses anti-collision

algorithmMode of OperationAutonomous/Interactive

Does not have a provision forautonomous mode of operationusing external trigger. However withlittle modification in firmware thisoption can be made available in thesystem.

Provision for autonomous modeof operation using externaltrigger. Interactive mode ofreading spends too much time inthe communication betweenreader and the host PC.Autonomous mode saves thetime spent in communicationbetween the host and readerwhile the acquisition is on.

Power ERP 3.2 W@ 8dbi antenna - Can be

varied

2 W - Can be varied

Tag ID TagID is unique and is given at thetime of manufacture of tags- toprovide a user defined ID to the tagsit is necessary to use some amountof tag data. Reading 10alphanumeric characters of tag dataalong with tag ID doubles the readtime, making the applicationdrastically slower

Tag ID itself is user defined inthe EPC C1G2 tags.

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Tag Memory 2048 bits (256 bytes out of which216 bytes are user defined) inview of larger memory, maintenanceschedule dates may also be stored.

96 bits is user programmable. -16 alphanumeric characters canbe stored can be used only forvehicle identification

Reading speed(for 12 charactersof vehicle ID data)

~75kmph - limitation is on accountof wagons due to effect of stiffeners.

~150kmph not tried onwagons. However the system isfaster than CAEN as it is multi-static and can work in GlobalScroll mode.

Reading range ~ 6 metersPerformance is affected by metallicsurroundings

~ 6 metersPerformance is affected bymetallic surroundings

Trans./ Rec. RatesTX/RX

40/160 kbps 80/80 kbps

General Observations:

The operating environment plays a very important role while designing and implementing anRFID application. Metal objects and electrical noise in the vicinity of tags, extreme operatingtemperatures, presence of liquids and physical obstructions can seriously affect theperformance of the system. To have a reliable RFID system it is very important to do a detailedsite survey and carry out extensive trials. The following observations were made during thetrials: - As the performance of the system is affected by metallic surroundings, it was easier to read

the tags on a coaching vehicle than on a wagon with stiffeners.

AAR Manual of Standards and Recommended Practices Railway Electronics specifies aClear Zone surrounding the tags and towards the wayside. This clear zone must not beobstructed byany metallic objects or protrusions. To allow for unobstructed transmission ofdata, tags must be afforded horizontal and vertical clearance windowsof 2.5 cm on eachside. These windows radiate out at 45 from the ends of the tags, and at60 from the sidesof the tags asshown in the figure. No part of the rail vehicle structure orattachments may

xtend into theclear zones as depicted, to include 2.5 cm from the periphery of the tag.e

Tag mounting clearance zone

It was observed that the Reader had difficulty in reading some of the tags as compared toothers. These were the tags fixed on the goods wagon and for speeds around 75 kmph

reader failed to detect some of these tags. The stiffeners surrounding the Tags resulted inreflections, causing nulls in the RF field. Nulls are created due to interaction of incident RFwaves with those reflected from obstructions in the vicinity of the tag. These null are veryprominent when the tag, on the moving rail vehicle, enters the RF field of the reader, as thereflections from the obstruction preceding the tag in the RF field are very strong. Howeverthe effect diminishes as the tag moves towards the point where it is directly in front of theReader antenna. The net result is that the reading zone is reduced causing the reader tomiss the tags at high speeds.

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Planar antennas have a higher reading range than circularly polarized antennas for thesame power level although orientation of tags with respect to the antenna assumesimportance.

Cut Off Distances(cm) La

Identification Ranges (cm)Ra

Identification Distances (cm)Wa

Power(mW)

LinearAntenna

CircularAntenna

LinearAntenna

CircularAntenna

LinearAntenna

CircularAntenna

200 252 194 91.65 93.06 305.08 192.73300 286 226 104.02 108.41 346.25 224.52

400 399 251 145.12 120.40 483.05 249.36

500 414 277 150.57 132.87 501.21 275.19

600 488 308 177.49 147.74 590.80 305.98

700 533 332 193.86 159.25 645.28 329.83800 555 387 201.86 185.64 671.91 384.47

900 582 417 211.68 200.03 704.60 414.271000 627 434 228.05 208.18 759.08 431.16

Variation of identification distance as a function of radiated power

for CAEN System under ideal conditions

La is the max. distance at which the Reader was barely able to read the tagWa is the max. width of the reading zone along the direction of movement of vehicleRa is the distance from the Antenna at which the width of reading zone is maximum.

Cut Off Distances(cm) La

Identification Ranges(cm) Ra

Identification Distances(cm) Wa

PowerAttenuation (dB)

LinearAntenna

CircularAntenna

LinearAntenna

CircularAntenna

LinearAntenna

CircularAntenna

15 202 115 64.04 52.48 240.88 120.7414 246 127 78.99 57.96 293.35 133.3513 289 165 91.62 75.30 344.63 173.24

12 334 187 105.89 85.34 398.29 196.35

11 388 202 123.00 92.18 462.68 212.09

10 403 226 127.76 103.14 480.58 237.29

9 455 254 144.24 115.92 542.58 266.69

8 512 287 162.32 130.98 610.55 301.34

7 563 319 178.48 145.58 671.37 334.946 585 360 185.46 164.29 697.61 377.99

5 625 417 198.14 190.30 745.31 437.84

4 673 461 213.36 210.38 802.55 484.043 707 478 224.13 218.14 843.10 508.88

2 741 505 234.91 230.46 883.64 530.24

1 796 530 252.35 241.87 949.22 556.49

0 823 580 267.25 264.69 981.42 608.98

Variation of Identification distance as a function of radiated powerfor Alien Technology System under ideal conditions

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Linear Antenna - Radiation Pattern Circular Antenna - Radiation Pattern

Plot of equi-power points

Increasing power always does not result in increase in Reading range of the tags. Reflectionfrom rails & other metallic surroundings come into play.

The reading zone of antennas is around 70-75 degrees.

In CAEN RFID system, using more no. of antennas increases the zone for reading the tags.However, the system takes more time to read the tags. Also the reading time increases asthe size of data increases.

For One Antenna ID OnlyReading Time Required 62 ms

For Two Antenna ID OnlyReading Time Required 119 ms

Note: The readings are taken byallowing only one tag in front of anantenna. If more tags are present,delay will further increase

Delay When Data Is Also Read With IDs

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For railway vehicle identification, anti-collision algorithm is not required as more than onetag is never expected to be in the RF field of the reader.

Global scroll is approximately three times faster than inventory search, which uses anti-collision algorithm. For the system that we are trying to implement, more than one tag isnever expected to be in the RF field of the reader. In such a scenario sacrificing precioustime working with full inventory search is not advisable.

The tags will have to be placed on the metal surface of the rail vehicle and hence must beencapsulated with proper shielding.

A918 universal tags supplied by CAEN have an air gap of about 10-12mm between the tagcircuitry and the metal surface of the vehicle on which the tag is fixed. They areencapsulated using ABS (Acrylonitrile, Butadiene, Styrene). As the tags on Rail vehicles willbe subjected to heavy vibrations, an insulating material instead of air may be used whichmay also act as a support for the tag circuitry.

To improve the reliability in detection of tags, it is essential to build in redundancies in thesystem. Multiple antennas may be used to increase the zone of reading of tags, although itmay slow down the system.

Probable applications for Railways:

The RFID system can be used for the following applications on Railways:

Automatic Vehicle Identification

Parcel Tracking

Inventory Monitoring

Tracking of wheel sets

Schedule dates of Locomotives/Coaches can be stored - using larger memory tags

Monitoring of critical subassemblies in locomotives- using larger memory tags

As an alternative to storing all the information in the tag, a computer database linked to tag ID

may be used.

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