The speci?¬?cation also caters for different modes of operation, Single Reader Use when
isolated readers are deployed in an environment, or Dense Reader Use, in which the
transmit spectrum masks are adjusted to allow for dense operation.
The commands that establish communication with tags also de?¬?ne the communication
parameters for the tag??™s response. Again, these choices are made by the reader,
based on local regulations, required application and noise performance of previous
communication techniques. Tags may respond to reader commands using one of two
tag backscatter modulation schemes, either ASK or PSK modulation, with the format
being selected by the tag vendor, and readers are capable of demodulating either
modulation type. Tags may be commanded by the reader to encode the backscattered
data as either FM0 base band or Miller modulation of a subcarrier at the data rate (either
2,4, or 8 cycles of subcarrier per bit). A variety of data rates can be selected by the reader
from 40 to 640 kbps.
Additionally, the speci?¬?cation details the reader commands and tag responses to those
commands. Most of those commands are concerned with reading or writing data to the
tag. Tags are identi?¬?ed (singulated) in a population of multiple tags, by the anticollision
protocol, which is called the Q protocol. This protocol is an ALOHA-based reply protocol,
in which tags receive anticollision parameters from the command by the reader and then
randomly self-select a period to respond.
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