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Mitigating the Reader Collision Problem in RFID Networks with Mobile Readers

Presented By Shailesh M. Birari Guided By Prof. Sridhar Iyer. Mitigating the Reader Collision Problem in RFID Networks with Mobile Readers. Basic Working of RFID system. Uses radio frequency to identify & track items in supply chain and manufacturing RFID readers and tags

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Mitigating the Reader Collision Problem in RFID Networks with Mobile Readers

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  1. Presented By Shailesh M. Birari Guided By Prof. Sridhar Iyer Mitigating the Reader Collision Problem in RFID Networks with Mobile Readers

  2. Basic Working of RFID system Uses radio frequency to identify & track items in supply chain and manufacturing RFID readers and tags Active and Passive tags 2

  3. Motivation for Mobile Readers Cost : “Always on” Fixed reader may be an overkill Convenience : Easy, faster deployment No wiring installation hassles Example applications : Searching a particular book in library Counting the items on the shelves in a super market Showing the list of items in the vicinity of the customer in a super market

  4. Scenario under consideration Super market, library Each customer has a RFID reader Readers form an ad hoc network All readers have unrestricted mobility Readers often join and leave the network All tags are passive

  5. Reader Collision Problem (RCP) • Multiple Reader to tag Interference:

  6. RCP (contd..) • Reader to Reader Interference:

  7. RCP (contd..) • Hidden Terminal

  8. Why a new protocol ? TDMA : Interfering readers transmit in different timeslot Time synchronisation required Timeslot distribution is inefficient in a mobile network CSMA: Sense channel before transmitting RFID suffer from hidden terminal Collision happen at the tags and hence collision detection is not possible by carrier sensing at the readers alone

  9. Why a new protocol ? • FDMA : Interfering readers transmit at different frequency • Tags do not have tuning circuitry • Adding tuning circuitry to the tags will increase the cost • CDMA : • Requires complex circuitry at tags which will increase the cost of passive tags

  10. Why a new protocol ? (contd..) • RTS-CTS : • Additional collision avoidance for CTS from tags R1 T1 CTS RTS RTS CTS T2 • A CTS from all the tags is required to ensure collision avoidance R1 R2 CTS RTS RTS RTS RTS T1 T2 CTS T3

  11. PULSE Protocol Assumptions Dual channel : data and control channel Data channel : reader-tag communication Control channel : reader-reader communication A reader can receive simultaneously on both channels but transmit on only one channel at a time No inter-channel interference

  12. PULSE Protocol Example Beacon Beacon R1 R2 T1 T2 T3 Query Query Query Query Query Query Query Query Query Query Query Query R2’s Read Range R1’s Read Range

  13. PULSE Protocol Overview Before communicating, a reader listens on the control channel for any beacon for Tmintime If no beacon on the control channel for Tmin , start communication on the data channel Reader periodically transmits a beacon on the control channel while communicating with the tags

  14. Contend_backoff R1 chooses 2 BI, R2 chooses 5BI, R3 chooses 3BI 2 3 Tmin Tmin 1 2 2 R1 Tread Tread 5 Tmin Tmin 4 5 5 R2 3 Tmin Tmin 2 3 1 Tread R3 R1 chooses 3BI

  15. Delay before beaconing Wait for control channel to get idle and then send beacon Transmitbeaconimmediately R1, R2 & R3 are communicating with the tags Choose a small delay and then transmit Both R1 and R3 are communicating with tags R1, R2, R3 are not in each others beacon range R2 R3 R1 R1‘s beacon range R1‘s control channel Sensing range

  16. PULSE Protocol Flowchart

  17. Simulation in QualNet

  18. Simulation Setup

  19. Simulation Setup (contd..) • Performance Metrics: • Beacon Range Factor (BRF): • Beacon Interval (BI) : interval after which beacon is sent • Compared Protocols : CSMA, Colorwave, Aloha

  20. System Throughput 25 Reader Topology : • Pulse shows throughput improvement in both static and mobile networks

  21. System Throughput (contd..) • Varying the number of readers • Pulse shows throughput improvement even at dense network of 64 readers

  22. System Efficiency • 25 Reader Topology • Pulse has system efficiency of above 95% which means Pulse is able to detect and avoid most of the collisions successfully

  23. Optimal Beacon Interval (BI) • Effect of Beacon Interval on 25 reader topology • Variation in Beacon Interval does not show too much of difference in both system throughput and efficiency.

  24. Optimal BRF • Throughput Vs BRF (Static Readers) • BRF of 28 shows highest system throughput in almost all the networks

  25. Optimal BRF (contd..) • Throughput Vs BRF (Mobile Readers) • BRF of 28 shows highest system throughput in almost all the networks

  26. Optimal BRF (contd..) Effect of Density of readers on networks with different BRFs • Networks with BRF=28 maintain its efficiency above 95% even when the number of readers is increased to 64

  27. Performance Modeling • Assume a beacon transmission is heard by all the readers • Backoff Decrement Interval: Interval after which backoff value is decremented • May contain a successful transmission by other reader • May contain a collision • May be empty

  28. Performance Modeling (contd..) • Cycle : • Duration between two successful Tread transmission by a reader • Consists of BDIs • Calculate the average duration of a BDI • Calculate the average number of BDIs in a cycle • Calculate the average duration of a cycle

  29. Backoff Decrement Interval (BDI)

  30. System Throughput

  31. Comparison • Comparison results

  32. Conclusion • Mobile Readers reduce cost and improve convenience • Pulse shows an improvement in both the dimensions, system throughput and system efficiency • Pulse is effective even in dense mobile networks

  33. References [1] Daniel W. Engels. The Reader Collision Problem. Technical Report, epcglobal.org, 2002. [2] J. Waldrop, D. W. Engels, and S. E. Sarma. Colowave: An anticollision algorithm for the reader collision problem. In IEEE Wireless Communications and Networking Conference (WCNC), 2003. [3] QualNet Simulator 3.6. http://www.qualnet.com [4] O. Tickoo and B. Sikdar. Queuing Analysis and Delay Mitigation in IEEE 802.11 Random Access MAC based Wireless Networks. In IEEE INFOCOM, 2004.

  34. Thank you

  35. Existing Work • ETSI EN 302 208 (CSMA): • Sense the data channel for 100msec before communicating the with tags • Colorwave (TDMA) : • Readers randomly select a timeslot to transmit • Chooses a new timeslot if collision and announce it to neighbors • UHF Gen 2 Standard (FDMA): • Separate reader transmissions and tag transmissions spectrally • Readers collide with readers and tags collide with tags

  36. Initial Results

  37. Approaches Considered Registration at the access point (query response) Transmit Neighbour information to AP along with request to transmit AP scans the status of the neighbours and responds accordingly

  38. Centralised graph coloring at Access Point All nodes transmit neighbour information to the AP AP applies a graph coloring to allocate time-slots Approaches Considered (contd.)

  39. Interesting Features of RCP • Readers may not be in each others sensing range; • Tag cannot select a particular reader to respond(unlike cellular systems) • None of the readers can read the tag • The passive tags, where the collision may take place, are not able to take part in the collision resolution as in hidden terminal problem • Reduces the read rate of the RFID system

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