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MECA Electronics

1st-Generation UHF Standards for RFID
RFID is becoming as ubiquitous as printed bar codes. In fact, in many venues, optically scanned bar codes have been entirely replaced with embedded RFID tags. Clothing, high value electronics, packaged software, and even books have been using RFID (sometimes in the form of NFC - near field communications) for many years. Now, major retailers like Wal-Mart have made a commitment to making RFID ubiquitous. In the not-too-distant future, if you want to have your product sold by some of these retailers, you will be required to integrate RFID tags.

The magic price mark for RFID is a couple cents per tag. At that level, RFID can be added to every product and not represent more than a percent or two of the total cost.

This table summaries the protocols used in RID tags that operate in the 800/900 MHz band assigned for ISM (Industrial, Scientific & Medical) use.


  Key Parameters Auto-ID
Class 0 		Auto-ID
Class 1 		ISO18000-6 A ISO 18000-6 B
Forward
Link		 Operating Frequency 902 MHz - 928 MHz 902 MHz - 928 MHz 860 MHz - 930 MHz 860 MHz - 930 MHz
Air Interface AM PWM AM PWM Pulse Interval ASK Manchester ASK
Bit Period NA: 25 µs/12.5 µs
EU: 62.5 µs		 NA: 14.25 µs
EU: 66.67 µs		 Data ‘0’: 20 µs
Data ‘1’: 40 µs		 125 µs/25 µs
Data Rate NA: 40/80 kbps
EU: 16 kbps		 NA: 70.18 kbps
EU: 15.00 kbps		 33 kbps (1) 8/40 kbps
Worst-case
Duty Cycle		 52%
Data ‘1’ low for 6 µs		 62.5%
Data ‘1’ low for
3To/8		 50%
Data ‘0’ low for
10 µs		 50%
Manchester code
Modulation Depth
[Min, Max]		 [20%, 100%] [30%, 100%] [27%, 100%] Nom 15%:
 [13%, 17%
Nom 99%:
 [90%, 100%]
Reverse
Link		 Air Interface Passive Backscatter:
FSK		 Passive Backscatter:
Pulse Interval AM		 Passive Backscatter:
Bi-phase Space AM		 Passive Backscatter:
Bi-phase Space AM
Bit Period NA: 25 µs/12.5 µs
EU: 62.5 µs		 NA: 7.13 µs
EU: 33.33 µs		 25 µs 25 µs
Data Rate NA: 40/80 kbps
EU: 16 kbps		 NA: 140.35 kbps
EU: 30.00 kbps		 40 kbps (1) 40 kbps (1)
Forward-to-reverse
Link Turnaround		 Not Applicable (2) NA: 114 µs
EU: 534 µs		 Shall not exceed 100 µs Shall not exceed 100 µs
General Reset Signal Duration 800 µs (CW) 64 µs (CW) 300 µs (CW) 400 µs (CW)
Collision Arbitration Deterministic binary
tree search		 Deterministic/Slotted Adaptive Probabilistic binary
tree search (3)
Tag Read Speed Nom: 200 tags/sec
Max: 800 tags/sec		 Not specified Nom: 100 tags/sec
(~10 ms/tag)		 Nom: 100 tags/sec
(~10 ms/tag)
Tag Capacity Not limited by standard ~300 (4) ~300 (4) ~300 (4)
Memory Memory Type Read-only User programmable User programmable User programmable
Memory Organization EPC: 64/96 bits
Kill Code: 24 bits
Total: >=120 bits		 EPC: 64/96 bits
Kill Code: 8 bits
Total: >=104 bits		 Up to 256 blocks
w/256 bits/block (64 kBits)		 Up to 256 blocks
w/8 bits/block (2 kBits)
Security/
Privacy		 Features Moderate
D0/ID1 + 24 bit kill
passcode		 None
Reader broadcasts all or part of ID code.
Reader can request kill passcode.		 None
Reader broadcasts
UID/SUID. Production set block lock bits. No kill command.		 None
Reader broadcasts
UID/SUID. Production set block lock bits. No kill command.


(1) No mention of data rates specific to European operation. Reverse link is always 40 kbps.
(2) For Auto-ID class 0, the tag data response is always known a priori (i.e., nothing has to be computed based on the current bit).
(3) Probabilistic collision arbitration implies that tag selection speed will depend on the tag population size.
      This is a disadvantage.
(4) These standards are limited by the probabilistic nature of their collision arbitration protocols.
      Most of them assume a tag population of ~250 tags.



Source: RF Design, July 2005 , by Rob Glidden and John Schroeter. Click here for the full article.
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