synchronization of rfid readers for dense rfid reader environments

1. 1 Synchronization of RFID Readers for Dense RFID Reader Environments Alfio R. Grasso Auto-ID Lab @ Adelaide School of Electrical & Electronic Engineering University of Adelaide Australia alf@eleceng.adelaide.edu.au

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3. 3 User Requirements † 100’s to 1000’s of readers possible Industrial Parks 2 km radius 100’s readers per DC DC ? 50 -100 dock doors 2 readers per door Cluster of DC in Industrial Parks

4. 4 Challenges in Dense RFID Reader Environments Performance Maximal coverage Minimal interference / data loss Regulations Frequency Hopping Spread Spectrum (USA) Listen Before Talk (Europe) Standards EPCglobal C1G2 the requested performance by end users. The current state of regulations around the world.the requested performance by end users. The current state of regulations around the world.

5. 5 FCC Environment FCC Part 15.247 UHF RFID Band (902 to 928 MHz) 4W EIRP 50 channels, 500 kHz wide 902.5 to 927.5 MHz Maximum dwell time 0.4 s (400 ms) Each channel used in 2.0 s interval

6. 6 Listen Before Talk (LBT) ETSI 302 208 865 to 868 MHz 200 kHz channels 2W ERP – only 10 channels LBT Listen for 5 ms Various thresholds 2W ERP, threshold is -96 dBm Use sub-band for 4s The current European regulation. A latest version is still in progress. The threshold value is very low, can be seen in next slide.The current European regulation. A latest version is still in progress. The threshold value is very low, can be seen in next slide.

7. 7 LBT Threshold

8. 8 EPCglobal C1G2 Dense Reader Mode (Annex G) Reader Transmissions in even channels Tag replies in odd channels

9. 9 Deployment Problems Distance between antennas, to be lower than -96 dBm threshold - An approximation for antenna safe distance. Notice that for an antenna to operate in a same channel with another antenna, they must be 1400m apart in front of each other, or 350m apart side by side.- An approximation for antenna safe distance. Notice that for an antenna to operate in a same channel with another antenna, they must be 1400m apart in front of each other, or 350m apart side by side.

10. 10 - The proposed solution to LBT area.- The proposed solution to LBT area.

11. 11 Reader SynchronizationThe Concept Readers start to “Listen” at the same time and start to “Talk” at the same time. can use physical link or wireless link. At this moment, not sure which is the best yet. Readers can be assigned channels dynamically, so that the spectrum management is optimised while the reader collision is minimised. can use physical link or wireless link. At this moment, not sure which is the best yet. Readers can be assigned channels dynamically, so that the spectrum management is optimised while the reader collision is minimised.

12. 12 Synchronisation Schemes Not a subject of the paper, but could be Hardwired Network Controlled NTP Protocol designed to synchronise the clocks of computers over a network Radio controlled Separate channel (use one of the 5 lower powered channels) Master reader, issues synchronisation pattern

13. 13 Case Study Warehouse Depot in Europe ETSI EN 302 208 865 to 868 MHz 15 sub-bands, 200 kHz wide Only 10 sub-bands at 2W ERP EPCglobal Class 1 Generation 2 Interrogator transmissions are located in even-numbered channels Tag backscatter located in odd-numbered channels

14. 14 Combining EN302-208 and C1G2 Interrogators can use 5 of the channels for Transmission If all readers in a facility are networked and configured to listen at the same time, then at the end of the listen period, they can all synchronously start Readers will then naturally stay synchronised, within the sub-band Even if different readers are on for different time, they will all start again in synchronism, once the last reader has finished. Thus we can have several readers occupying the same channel, even if they are close together. Readers assigned geographically to 1 of 5 sub-bands

15. 15 Dock Door Example The next slide depicts 6 dock doors, with each door requiring 2 readers Each reader is networked, and connected to some synchronisation device Each reader is assigned to operate in one of the 5 even numbered sub-bands Each reader listens for the required time, and if the sub-band is free, starts Transmissions Each transmission must terminate within 4 seconds, after which the reader releases the sub-band for at least 100 ms

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17. 17 Other Mechanisms Reducing the overall time for talking. While it is possible to talk for 4 seconds, readers and applications should be configured to talk for only the time necessary to capture tag data. Reducing the power output. While the maximum allowed 2W ERP can be useful in single or small population reader environments, in dense reader populations this higher power may not be necessary. Use of external sensors. The sensor determines that an object may be in the near vicinity, to turn on (enable) an RFID reader. The use of RF opaque or RF absorbing materials Dynamic Channel Assignments

18. 18 Example with sensorstruck 3 absent, so no RF

19. 19 RF Opaque / RF Absorbing Materials More expensive method. May still have leakage at the openings, but the antenna gain at the side is approximately 20dB lower than the gain at the front.More expensive method. May still have leakage at the openings, but the antenna gain at the side is approximately 20dB lower than the gain at the front.

20. 20 Switching Channel Assignments Switching of channel every cycle. Prevent jamming by external signal/ noise. May implement with high AI for better smarter switching.Switching of channel every cycle. Prevent jamming by external signal/ noise. May implement with high AI for better smarter switching.

21. 21 Conclusions Reader densities in Distribution Centres > 100’s ETSI EN302-208 LBT @ -96 dBm Threshold C1G2 Even channels for Tx => 5 sub bands Synchronisation