
96 CHAPTER FOUR
EPC UHF Class I Gen2
The latest revision of the EPC UHF Class I air interface is called the “Gen2 protocol.” Gen2
addresses some of the limitations of the first UHF protocol standard by defining protocol
variations that are able to work under European (CEPT) and North American (FCC) RF
regulations. It also specifies variations in the protocol for operating environments where
more than one reader is within another’s receiving range, including a special set of proto-
col requirements for environments where the number of readers is equal to the number of
available communication channels.
The EPC Gen2 protocol supports much faster tag singulation than the previous protocol,
with tag reads rates as fast as 1,600 tags per minute in North America and 600 tags per
minute under the more constrained power and frequency ranges in Europe. One of the
primary concerns it addresses is added security for the protocol. Key to the solution Gen2
offers is the recognition that signals the reader transmits may be received over a far greater
distance than signals generated by the tags. The specification considers two readers to be
in the same operating environment if they are within one kilometer of each other.
The protocol describes three procedures for communication between readers and tags. A
reader may select tags by asking tags to compare themselves to a bitmask, or it may inven-
tory tags by singulating ...