RFID: A New Software Based Solution to Avoid Interference Syed S. Rizvi1, Eslam M. Gebriel2, and Aasia Riasat3
Computer Science & Engineering Department, University Of Bridgeport1, 2, Bridgeport, CT Department of Computer Science, Institute of Business Management3, Karachi, Pakistan {srizvi1, emahmoud2}@bridgeport.edu,
[email protected]
Abstract - RFID (Radio Frequency Identification) interference is one of the most important issues for RFID applications. The dense-reader mode in Class 1 Gen2 in EPC-global is one of the solutions which can reduce the interference problem. This paper presents a new software based solution that can be used for improving the performance of dense-reader mode through effectively suppressing the unwanted interference. We use two existing methods, Reva and Feig’s systems, to build a complete simulation program for determining the effectiveness of the new proposed software based solution. For the sake of our simulation results, we strictly follow the EPC-global Gen2 standard and use the Listen and Wait protocols [2]. Our simulation results demonstrate that the interference can be reduced significantly by using the proposed software based solution. Keywords - RFID, interference, dense-reader mode, listen and wait protocol
I.
INTRODUCTION
In this paper, we present a software based solution that can effectively reduce the interference between the RFID applications. Our designed approach addresses many issues related to RFID such as tag collision and interference. Our proposed solution is not only shown to reduce the interference but can also be used as an effective tool to analysis the interference among the RFID applications that are located within the closed proximity. RFID is an electronic barcode which can be used to track items under very harsh condition. RFID consists of three components: a tag, a reader and an antenna. In tag memory, the tags can be divided into read-only and read-write tag. With read-only tags, tags send data to the reader. With read-write tags, the tags send data to the reader where as the reader writes data to the tag. In tag power supply, the tags can be divided into passive and active tag. The passive tags contain no power supply and store very small amount of data. In addition, the passive tags need a transceiver signal in order to activate. The active tags, on the other hand, contain an internal battery and capable of storing large amount of data. At different frequencies, the tags have different read capability in the distance. At a frequency of 2.45 GHz, the tag can be read from 2 to 3 mm. The read distance can be
increased from 24 to 30 cm by adding a small booster antenna. At a frequency of 13.56 MHz, the tag can be read from 15 to 20 cm with the booster antenna and from 30 to 40 with the external antenna. In the UHF spectrum, the reading distance is up to 1 meter when use with the booster antenna where as up to 5 meters when use with the external antenna. The tags need both on-chip antenna and two external antennas to achieve the maximum read distances at the three common RFID frequencies (13.56 MHz, 868 to 956 MHz and 2.45GHz)[2]. The RFID could be considered as a dangerous source for spying on people [1, 4]. Since the tags can be read without being swiped or scanned, anyone with an RFID tag reader can read the tags embedded in your clothes and other consumer products without your knowledge [5]. II.
RELATED WORK
Dense-reader mode (DRM) reduces instances of interference between multiple readers. The power of signal is sent from reader is millionfold stronger than the tags. If the frequency is typically narrow bounded, the radio signals that are reflected from the tags will be covered. This implies that, in the dense reader mode, we need to separate the bandwidth use by each tag and limit the reader’s signal in a channel. The use of separate bandwidth strictly prevents the interference in the RFID applications [6]. Dense-reader mode reduces the bandwidth by getting the speed of signal slow and avoids the leak by filter. In the same time, they put the decode filter on tags to improve the anti-interference ability of tags. If the readers of DRM wants to send signal, it will listen first to be sure this channel is available. If it’s not, the reader switches (or hops) to another channel to avoid interfering with another reader on that channel [7]. Three widely used solutions were proposed by Hendrik van Eeden to avoid the interference in RFID applications [8]. In the first proposed solution, readers hop randomly between different frequencies in a particular portion of the UHF spectrum. However, it only works effectively in North America since united state (US) allows UHF tags to only jump between frequencies from 902 MHz to 928
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MHz. In their second solution, they use the concept of time division multiplexing (TDM) to provide synchronization between all the readers and assign them the time slots for transmission.. However, the time slots would become very small in a large installation based systems. When there are many readers in one location, the readers need more time to access tags that results longer delays. In their third solution, they enforce each tag and reader to use separate portion of the RF spectrum to minimize the chances of interference. In order to prevent the more powerful radio waves from the reader that may overwhelm the waves reflected back by the tags, readers send out energy at one separate frequency where as the tags reflect back a signal at a different frequency. This implies that a mutually compatible and standardized manner is required to avoid frequency hopping. In addition, to avoid interference caused by constantly emitting heavy energy signals from readers, the best solution is to enforce readers not to transmit data during the tag identification cycle. III.
interference between the READERs that operate within 10 channels of UHF range. We use 4-channel approach where four channels are dedicated to the readers and six are allocated for the TAGs. Moreover, for our program, we assume that the interference may occur between the READERs which may exist in the same or in the neighboring CELL. Therefore, each CELL can have at least 4 or more READERs. In other words, four READERs can be activated and worked simultaneously. In this case, each of one works on a specific channel where as the rest has to wait until they find a clear channel. By doing this, we can avoid the possibility that any two READERs can work simultaneously over the same frequency/channel or on the same/neighboring cell(s).
INTERFERENCE AVOIDANCE VIA SOFTWARE BASED SOLUTION
The main purpose of the proposed software based solution is to improve the dense-reader mode to reduce instances of interference. RFID uses EPC protocol for communication though Class 1 Gen 2 networks. It includes three modes: single reader, multi-reader and dense-reader. The dense-reader mode can reduce the interference problem [2]. Dense-reader mode (DRM) reduces (but not solves) instances of interference between multiple readers. In 2006, a European Tele-communications Standards Institute (ETSI) demonstrated two synchronization techniques designed to enable many readers which were operating close to each other and shared frequency simultaneously. These two techniques are Reva system and Feig’s method. Reva System implements a RFID management system to control the interference between multi-reader and tags [3]. On the other hand, in Feig’s system, the reader synchronization instructs the first interrogator to emit a unique pre-pulse RF signal immediately before to its interrogation process [4]. A.
The Proposed Software Based Solution In the proposed technique, we first connect all the readers which are operating in the same area to a single centralized reader controller. Once the reader connects to the controller, it uses Feig’s method to emit a unique prepulse RF signal to the controller. The controller stores the available channel. If there are two reader’s channels overlapped, the controller rejects the later reader and the reader has to change the channel range until the controller accepts. Likewise, the active readers must follow the standard. Instead of using equipments to test performance in a real environment, we provide a software based solution to reduce the interference. Our approach reduces the
Fig.1. Flow Chart for the proposed software approach to resolve interference
RFID: A NEW SOFTWARE BASED SOLUTION TO AVOID INTERFERENCE
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The proposed approach for avoiding interference is shown in Fig.1. It should be noted in Fig. 1 that the entire proposed approach is based on the concept of closed loop solution where a constant feedback is provided periodically by the system to the requester reader. B.
Basic Scenario Initially, a user starts searching for a specific tag or a list of tags using the controller. On the other hand, the controller sends a signal to the READERs which are located within the close proximity of these tags as shown in Fig.2. Once the Reader receives a signal, it can then check the availability of the four UHF channels as shown in Fig. 3. Once we successfully pass this step, there are two possibilities that we address though our proposed solution: If the Reader finds that all the channels are currently busy, the Reader starts searching the channels. Once it finds a free channel, the Reader broadcasts a READY signal to all the neighboring Readers in order to announce that this specific channel is occupied at this point of time. The Reader will then wait for a specific amount of time to ensure that no other Reader wants to use the same channel. For instance, if another Reader wants to use exactly the same channel, that Reader is required to send the READY signal to request the same channel. In this case, our Reader releases the channel gracefully and starts searching for the other available channel. This cycle of searching goes on unless the Reader successfully occupied the channel. One obvious advantage of this approach is that our proposed solution avoids unnecessary collisions from the other active Readers. On the other hand, if none of the active Readers are interested to use the same channel, the Reader can immediately occupy the desired channel and broadcasts a
The simulating program has three main parts: Controller, Reader, and the Environment. We use a TCP connection between these three parts in which the Environment program works as a TCP Server whereas both Controller
Fig.2. Controller program with testing the availability of Tags
Fig.4 Setting dialog for Reader Program
Fig.3. Reader program with frequency and channel usage
BUSY signal on the line, so that all the neighboring READERs know that this specific channel is fully occupied and currently unavailable. Once the Reader has finished using the channel (BUSY time), the Reader broadcasts a RELEASE signal to announce that the channel is released gracefully. II.
PERFORMANCE ANALYSIS OF THE PROPOSED SOFTWARE BASED APPROACH
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in Station Mode, Reader receives a list of Tag IDs which are randomly chosen and are located all around a particular cell. In Mobile Mode, Reader first sets the header, and then gets a list of Tag IDs which are all around the header of the cell. Since Reader is using four-channel approach, it is essential to display the Reader ID in each channel of the Operating Reader within the receivable distance at the bottom of the panel. The Environment program provides graph feature to view the status of the Readers as shown in Fig. 5. In the simulation, when Reader is operating, all Readers around operating Reader can receive the signal. Therefore, if any two Readers that exist within the same or neighboring cell and/or operating in the same frequency range, they might interfere each other. The size of cells can be changed by clicking the Setting in the menu bar. It can be changed from 3x3 to 10x10. Fig.5. Environment program and analysis the result of test run
and Reader work as TCP Clients. Therefore, the simulation can run on multiple machines. Controller program has a power switch button which will be operated by the Controller to connect to the Environment as shown in Fig. 4. Controller can make a query command by manual typing Tag ID, or open a file that stores a list of Tag IDs. After opening the file, the Controller will determine the total operating time of the commands for performance measure. Reader program also has a power switch button as shown in Fig. 3. When Controller is on, the Reader receives a unique Reader ID, and displays in the title. On the top of the panel, when the reader is operating, it displays the operating frequency, the header of the located tags, reader mode, and Station and Mobile. When Reader is
A.
Simulation Results
We set two scenarios. In the first case, we use 5 readers in one cell that share 4 channels. In the second case, we use 9 cells and use one reader in each cell. There are 27 commands for all readers. The execution time since the first command was sent by the Controller to the last result received by the Controller is like the chart. We notice that the execution time decreases when we get waiting time less with certain limitations. Even we set fewer waiting time, we can not get shorter execution time. Even we use Listenand-Wait protocol to avoid collision; the improvement depends on the choice of the random numbers. If the random number is closed, we get more collisions as shown in Fig. 6. III.
CONCLUSION
The proposed approach can avoid RFID interference efficiently. However, all readers have to follow EPCglobal Gen2 standard and use Listen and Wait protocol. We also need to setup one or more controllers in the working environment where all readers have to communicate with controller(s) before the initial operation that involves extra cost and time. Also, we need to put RFID tags by area as SDMA (Space Division Multiple Access). If we put tags too close, the readers might have more signal collisions which will consequently decrease the performance. For future, it will be interesting to implement this method for comparatively big work space like a warehouse or factory. REFERENCES [1]
Fig.6. Analysis the result of test run with process time (ms) versus waiting time (ms)
[2] [3]
Deal, III, Walter F., “RFID: A REVOLUTION IN AUTOMATIC DATA RECOGNITION,” Technology Teacher, 07463537, April 2004, Vol. 63, Issue 7 Rachel Wadham, “Radio Frequency Identification,” Library Mosaics; Sep/Oct2003, Vol. 14 Issue 5, p22, 1p, 1bw “RFID Big Picture” Microwave Journal; Jul2006, Vol. 49 Issue 7, p47-47, 1/3p
RFID: A NEW SOFTWARE BASED SOLUTION TO AVOID INTERFERENCE [4] [5] [6] [7] [8]
Lisa Smith, “Warrantless wiretaps and your EZ pass” Humanist, Mar/Apr2006, Vol. 66 Issue 2, p38-39, 2p. Erika Fricke, “Air wave interference a consideration,” Daily Planet Staff (12-20-00) Chris Diorio, “What is “dense reader” mode?,” RFID Journal, Available at: http://www.rfidjournal.com/faq/19/78 Alien Technology, “ALR-9800 Enterprise RFID Reader”, http://www03.ibm.com/solutions/businesssolutions/sensors/doc/cont ent/bin/sa_at_ds_9800_v3_web.pdf?g_type=pspot, p3 Hendrik van Eeden, “Why UHF RFID Systems Won’t Scale,” RFID Journal, http://www.rfidjournal.com/article/articleview/1056/1/82
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