Understanding RFID Counting Protocols.ppt
- 1. Understanding RFID Counting Protocols Authors: Binbin Chen, Ziling Zhou, Haifeng Yu MobiCom 2013 Presenter: Musab Hameed
- 2. Many applications need counting RFID technology enables large-scale counting 2
- 3. RFID counting problem (a simple single-set version) • One reader and 𝑛 tags • They run a protocol to get an ≈ 𝑛 – Getting the exact 𝑛 is expensive • Guarantee: − 𝑛 ≤ 𝜀𝑛 holds (say, with 90% probability) – Here, 𝜀 bounds the relative error See paper for generalizations: e.g., a reader moves around to extend coverage Legends: RFID tag RFID reader 3
- 4. Existing RFID counting research • An impressive arsenal of techniques • The central design goal: Reduce time overhead & provide the guarantee 4
- 5. despite the resulting complexity? Novel statistical gauges Optimization of parameters Adaptive iterations …… 5 Call for fundamental understanding • Diverse views on which design aspects are important Should we combine all these techniques
- 6. 𝜀2 Our central thesis for RFID counting The overlooked key is to have two phases: 6 2nd phase 1 O 1st phase 𝑂(log𝑛) Final estimate Rough estimate Other techniques proposed in the literature are less important than originally thought Note: • the log𝑛 term can be reduced to a loglog𝑛 term
- 7. incurring o loglog𝑛 + 2 The inspiration • Novel lower bounds for RFID counting protocols: Theorem: For single-set RFID counting, no protocol can estimate with < 𝜀 relative error while 1 1 overhead 𝜀 𝑙𝑜𝑔𝜀 7
- 8. Validating our thesis • Examine the importance of other techniques • Apply our thesis to design better protocols 8
- 9. Existing literature: diverse views about what are important Optimization of parameters Adaptive iterations …… 9 Novel statistical gauges
- 10. 10 Let us step back, and take an asymptotic view of existing protocols Such a comparison has not been done before
- 11. 𝑂 log𝑛 𝑂 log𝑛 + Multiplicative overhead: 1 𝜀2 Additive overhead: 1 𝜀2 Two distinct groups Enhanced Note: • Some protocols reduce the log𝑛 term to a loglog𝑛 term
- 12. 13 How they achieve additive overhead? • Despite their many differences (as originally emphasized), they all have a two-phase design: 2nd O phase 1 𝜀2 1st phase 𝑂(log𝑛) Final estimate Rough estimate
- 13. Enhanced FNEB(’10) Use of a novel gauge: The indices of the first non-empty slots ART(’12) Use of a novel gauge: The average run length of non-emptyslots ZOE(’13) i)Unique design about the gauge: Each trial has a single slot ii)Two-phasedesign Our thesis has not been discovered They also employ other interesting techniques: – involved optimizations, adaptive iterations …
- 14. 15 Are these other techniques important? Let us focus on the gauges
- 15. An old gauge of the early EZB (’07) protocol • # of empty slots – More empty slots ⟹ less tags 16 1 6 3 2 4 5
- 16. The novel gauges • ART: average run length of non-empty slots – In the example: (1+2+1)/3 • FNEB: index of the first non-empty slot • ZOE: still # of empty slots, but each slot is independent 17 1 6 3 2 4 5
- 17. Let us examine ART’s (’12) performance gain (over the early EZB (’07) protocol) 18
- 18. Replace ART’s (’12) gauge by the old EZB’s (’07) gauge We keep everything else unmodified 19
- 19. Similarly … • FNEB’s gauge seems not help • Neither does ZOE’s 20
- 20. Validating our thesis • Examine the importance of other techniques • Apply our thesis to design better protocols 21
- 21. 22 SRC𝑆: a Simple RFID Counting protocol for single-set counting • The design of SRC𝑆 is solely driven by our thesis: – It applies the 2-phase design – It uses simple & basic building blocks in all other aspects we claim no novelty for these building blocks SRC𝑆 pseudo-code: 1: Invoke a simple early protocol (LOF ’08) to get a rough estimate 𝑛; 2.1: calculate tag-responding probability according to 𝑛; 2.2: Use a simple early gauge (EZB ’07) to obtain the final estimate;
- 22. SRC𝑆 is ≥ 100% faster 23 SRC𝑆 Note: We have done extensive experiments under different settings Please see our paper for more details
- 23. How about multiple-set RFID counting? • Consider a reader sequentially visits multiple locations to count # of tags in a large space – Here 𝑛 = |𝑆1 ∪ 𝑆2 ∪ 𝑆3|: the sets can overlap 𝑆1 𝑆2 𝑆3
- 24. Apply our thesis • Unlike single-set case, no one happens to use 2 phase – All existing protocols incur multiplicative overhead – Our thesis hints that big improvement might be possible • Applying our thesis needs to overcome a challenge – The reader has no rough estimate of 𝑛 until the last location • Our SRC𝑀 protocol uses some interesting techniques to overcome the challenge – It achieves additive overhead, and is ≥ 500% faster • Knowing the thesis is critical – It guides us to identify & focus on the key challenge 25
- 25. Summary • Inspired by our RFID counting lower bound results, we find the overlooked key is a 2-phase design • All other techniques are less important • Our thesis leads to better protocols 26 2nd O phase 1 𝜀2 1st phase 𝑂(log𝑛) Final estimate Rough estimate