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ETSI Tests Show EPC Scaleable in Europe
The second hard-wired approach, which Falck calls the "floating master," uses no single centralized controller. When a tag enters the any of the interrogation fields of a bank of readers, the first one that senses the tag reads it and acts as the master for all the other interrogators to which it is linked, coordinating their transmissions to ensure they all use only available channels.
To synchronize readers wirelessly, Feig Electronics demonstrated a system by which the first reader to be triggered sends out a pre-pulse, a signal prior to its main transmission on an unoccupied channel. All other readers in the vicinity that are programmed to decode this pre-pulse may join the group and transmit on the same channel, says Falck. The current proposal is to define a pre-pulse with fully specified parameters, thereby standardizing the signal and ensuring interoperability between vendors.
The readers all use the dense-reader mode of operation, which separates the interrogator's signals from the tag's backscatter replies onto separate but adjacent channels so that they don't interfere with each other. By coordinating a group of adjacent interrogators operating in dense-reader mode, a signal-synchronization scheme enables all the interrogators in that group to transmit simultaneously on the same frequency channel.
"We can run a lot of readers at once if we coordinate them such that in the aggregate, they obey the rules," says Reva Systems' cofounder and chief technology officer, David Husak. "Once a reader is on a channel, you can add more readers to that channel."
The TG34 tests were conducted over a two-week period at a distribution center operated by European retail giant and RFID user Metro Group, in Unna, Germany. The testing period consisted of three parts: First, TG34 needed to settle on which of two proposed channel-allocation schemes to use. There are 10 UHF channels—4 through 13—that ETSI says can carry 2-watt RF transmissions. One proposed channel-allocation scheme, called the four-channel approach, would let the interrogators use channels 4, 7, 10 and 13 to interrogate the tags, which would send their response signals over a pair of adjacent channels—either 5 and 6, 8 and 9 or 11 and 12—as instructed by the interrogator's signal.
To synchronize readers wirelessly, Feig Electronics demonstrated a system by which the first reader to be triggered sends out a pre-pulse, a signal prior to its main transmission on an unoccupied channel. All other readers in the vicinity that are programmed to decode this pre-pulse may join the group and transmit on the same channel, says Falck. The current proposal is to define a pre-pulse with fully specified parameters, thereby standardizing the signal and ensuring interoperability between vendors.
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| John Falck, TG34 |
"We can run a lot of readers at once if we coordinate them such that in the aggregate, they obey the rules," says Reva Systems' cofounder and chief technology officer, David Husak. "Once a reader is on a channel, you can add more readers to that channel."
The TG34 tests were conducted over a two-week period at a distribution center operated by European retail giant and RFID user Metro Group, in Unna, Germany. The testing period consisted of three parts: First, TG34 needed to settle on which of two proposed channel-allocation schemes to use. There are 10 UHF channels—4 through 13—that ETSI says can carry 2-watt RF transmissions. One proposed channel-allocation scheme, called the four-channel approach, would let the interrogators use channels 4, 7, 10 and 13 to interrogate the tags, which would send their response signals over a pair of adjacent channels—either 5 and 6, 8 and 9 or 11 and 12—as instructed by the interrogator's signal.
