RFID systems have to operate in the spectrum allocated for this application by each country. This allocation takes into account other demands on usage of the spectrum for that country. Balancing these demands means that in many countries, the maximum that the RFID industry can hope for is just 200 kHz in the 860-960 MHz band. Some countries have found 500 kHz and some hope for 2 MHz. In the US, this allocation can be as wide as 26 MHz.
The purpose of the RFID technology for global trade, is to have a system that operates in all countries and therefore the minimum allocations need to be used as the guidelines for getting an operating system working.
Recently, a partner of Trolley Scan's exhibited the scanner at a tradeshow in France. Trolley Scan makes tag-talks-first (TTF) equipment that uses just 10 kHz of bandwidth for operation and can allow multiple readers to operate at spacings as close as 4 m. Trolley Scan is one of many manufacturers that produce TTF-based equipment. The equipment currently embodied in the EPC specifications uses a reader-talks-first protocol (RTF) which results in the reader calling out continuously for any tags in the vicinity to respond - using the full power of the reader. This uses up 200 kHz of bandwidth - whether or not a transponder is present, and interferes with other readers within a 1 km radius.
At the show, Trolley Scan found that the reader produced by one North American supplier was generating such interference in the allocated spectrum, that other RFID reader manufacturers could not operate at the same time. The reader on show by that manufacturer met the requirements for the use of the RFID spectrum and was typical of those specified by EPC in Class 0 and Class 1. Eventually an agreement was reached whereby the offending supplier would switch off for half an hour each hour, to allow the other exhibitors to demonstrate their equipment.
The generation of this interference zone is acknowledged by the EPC in that its current specification for Generation 2 readers provides three levels of certification:
* Level 1 readers will be certified to work only when there are no other readers within a 1 km radius.
* Level 2 will be for readers capable of being deployed with several readers within a 1 km radius.
* Level 3 will be certified to work alongside 50 or more readers within a 1 km radius.
In a retail environment, one would expect many more than 50 readers to be present in a 1 km radius. Switching to a TTF type protocol, more than 6200 readers can be made to operate within the 1 km radius.
The requirements of countries with only a limited spectrum available for RFID, and the desire of the EPC to have a system that is accepted internationally, especially through ISO recognition, will force the development of a Gen 3 version shortly, which will need to be based on TTF principles in order to cater for high reader density.
For more information contact Mike Marsh, Trolley Scan, +27 (0)11 648 2087.
| Tel: | +27 10 237 0675 |
| Fax: | 086 617 8002 |
| Email: | [email protected] |
| www: | www.trolleyscan.com |
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