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Mitigating the Reader Collision Problem in RFID Networks with ...

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  • 1. Mitigating the Reader Collision Problem in RFID Networks with Mobile Readers
      • Presented By
      • Shailesh M. Birari
      • Guided By
      • Prof. Sridhar Iyer
  • 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
  • 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
    CTS CTS
      • A CTS from all the tags is required to ensure collision avoidance
    RTS RTS T 2 T 1 CTS CTS R 1 T 3 RTS T 1 RTS R 1 RTS RTS R 2 T 2
  • 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 T 1 Query Beacon Query Query Query Query Query Query Query Beacon R 2 T 2 T 3 R 1 Query Query Query Query R 1 ’s Read Range R 2 ’s Read Range
  • 13. PULSE Protocol Overview
    • Before communicating, a reader listens on the control channel for any beacon for T min time
    • If no beacon on the control channel for T min , 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
    T min T read 2 1 5 4 3 2 T read R 1 R 2 R 3 2 5 3 T min T min T min T min T min 3 2 5 1 T read R1 chooses 3BI
  • 15. Delay before beaconing R2 R1 R3 R 1 ‘s control channel Sensing range R 1 ‘s beacon range Wait for control channel to get idle and then send beacon R1, R2, R3 are not in each others beacon range Both R1 and R3 are communicating with tags Transmit beacon immediately R1, R2 & R3 are communicating with the tags Choose a small delay and then transmit
  • 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. System Efficiency (contd..)
    • Varying the number of readers
    • Unlike CSMA, Pulse remains to be efficient even in a network of 64 readers with mobility
  • 24. 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.
  • 25. Optimal BRF
    • Throughput Vs BRF (Static Readers)
    • BRF of 28 shows highest system throughput in almost all the networks
  • 26. Optimal BRF (contd..)
    • Throughput Vs BRF (Mobile Readers)
    • BRF of 28 shows highest system throughput in almost all the networks
  • 27. Optimal BRF (contd..)
    • Throughput Vs BRF (25 Reader Topology)
    • Height of the bars indicate total queries sent by all the readers
    • Total queries sent in the network decreases as BRF increases
  • 28. Optimal BRF (contd..)
    • Efficiency Vs BRF
    • BRF of 28 and above shows very high efficiency in almost all the networks
  • 29. 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
  • 30. 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
  • 31. Performance Modeling (contd..)
    • Cycle :
        • Duration between two successful T read 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
  • 32. Backoff Decrement Interval (BDI)
  • 33. System Throughput
  • 34. Comparison
    • Comparison results
  • 35. 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
  • 36. 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.
  • 37. Thank you
  • 38.  
  • 39.  
  • 40. 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
  • 41. Initial Results
  • 42. 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
  • 43.
    • 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.)
  • 44. 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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