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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 3T_o/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	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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