1. THE READER COLLISION PROBLEM IN RFID SYSTEMS Kin Seong Leong Auto-ID Lab @ Adelaide School of Electrical & Electronic Engineering University of Adelaide Australia kleong@eleceng.adelaide.edu.au

2. Introduction on RFID What is RFID? RFID basic components:

3. Reader Collision Problem Definition Interrogation signal from a reader jams a reply of a tag to another reader EPCglobal Class 1 Generation 2 Using frequency hopping Our Focus: In-Channel Collision Listen Before Talk

4. In-Channel Collision (a) Path loss of path 1 and path 2, tag antenna gain, and tag efficiency loss (b) Path loss of path 3

5. Theoretical Background (1) Free Space Path Loss For 915 MHz, at 1 m away, PL = 31.6 dB

6. Theoretical Background (2) In-Building Path Loss d 0 = arbitrary reference distance n = environment factor

7. Our Model Propose piece-wise linear model based on Rappaport experiment result.

8. Our Model Equations

9. Our Experiment Results Approximately: Distance of Separation Between Antennae, d/m Model:

10. Calculation Results

11. Some Recommendations Proper Readers Arrangement (Reduce in-channel collision)

12. More Recommendations (Reduce in-channel collision) Reducing the power output. Use of external sensors. The use of RF opaque or RF absorbing materials

13. “Listen Before Talk” Introduction From ETSI 302 208 (European RFID Regulation) –Prior to Transmission, the interrogator must listen for the presence of another signal within its intended sub-band of transmission. The listen time shall comprise a fixed period of 5 ms plus a random time of 0 ms to 5 ms in 11 steps. If the sub-band is free the random time shall be set to 0 ms.

14. “Listen Before Talk” Limits

15. Recommendation Readers Synchronisation (to fulfil LBT)

16. 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

17. Sub-band 2 Sub-band 4 Sub-band 6 Sub-band 8 Sub-band 10 Synchronised LBT in Warehouse

18. Missing Truck 3

19. Limitations/ Challenges Model is just an approximation. –On-site measurement is needed for value n. –Case study yet to be tested in real life.

20. Conclusion