Friday, November 23, 2007

Understanding what have been achieved so far

Constraints in RFID communication in particular:
i. Lack of internal power source in the passive tags. This requires the tag reader to powerupthese tags whenever it needs to communicate with them.
ii. Total number of tags is unknown.
iii. Tags cannot communicate with each other. Hence collision resolution needs to be doneat the tag reader.
iv. Limited memory and computational capabilities at the tag. Thus the resolution protocolmust be simple and incur minimum overhead from the tag’s perspective.

Measurement in RFID anti-collision performance:
a. Minimal Delay: Time taken for identification of all the tags should be low. From a userpoint of view, this should not be perceptible.
b. Power consumption: Due to the absence of an internal power source, power consumedby the tags should be minimal. The amount of power consumed is influenced by the totalnumber of replies sent by each of the tags. An efficient protocol will minimize themessages between the tag and tag reader.
c. Reliability and Completeness: All the tags in the range of the tag reader should getidentified correctly.
d. Line-of-sight Independence: The object attached with the tag can be located anywhereas long as they are in the range of the tag reading device.
e. Robustness: The protocol should work irrespective of environmental conditions.
f. Scalability: The protocol should be scalable to accommodate an increase in the numberof tags.

Four basic algorithms in RFID:

  • Splitting or Tree Search, use coin flipping or tag ID, needs feedback from reader, and counter

  • Memoryless or Query Tree, maximum number of tag assumed, prefix p, feedback each cycle, no counter. This algorithm sometimes is refered as Binary Tree in many literatures
  • I-Code or frame-slotted Aloha, not 100% detection of tag, need experimental measurement in refining protocol, particular in estimating number of tags

  • Contactless, special modulation: 00ZZ->0, ZZ00-> 1

C. Abraham, V. Ahuja, A.K. Ghosh, P. Pakanati, InventoryManagement using Passive RFID Tags: A Survey, Department ofComputer Science, The University of Texas at Dallas, Richardson,Texas, pp. 1–16, October, 2002.
This is a very good paper, which is almost the first part of
Taxonomy and survey of RFID anti-collision protocols DH Shih, PLSun, DC Yen, SM Huang - Computer Communications, 2006

Standard Protocols:

EPCglobal Bit-based Avg. : 200 tags/sCLASS 0 Binary tree Max. : 800 tags/s(UHF) (Deterministic)

EPCglobal Binary tree Not specifiedCLASS 1 (Bin slot)(UHF) (Probabilistic)

ISO 18000-6 Dynamic Avg. : 100 tags/sTYPE - A Framed ALOHA(UHF) (Probabilistic)

ISO 18000-6 Binary Tree Avg. : 100 tags/sTYPE - B (Probabilistic)(UHF)

Binary Tree and Dynamic Frame-Slot Aloha(DFSA) are two commonly implemented algorithms. Grouping is a major investigating area in improving DFSA.

SSim - a Simple Discrete-Event Simulation Library:

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