Tag-to-reader settings, Tag contention settings, Tag-to-reader settings tag contention settings – ThingMagic Mercury API v1.23.0 User Manual
Page 124: For details, Tag-to, Reader settings, Tag contention, Settings
How UHF RFID Works (Gen2)
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Performance Tuning
channels, but in the EU region where there are only 4 channels, this could become an
issue. In this case, you would want to try increasing the Tari to decrease the link rate and
see if the performance of the first reader improves.
Tag-to-Reader Settings
/reader/gen2/BLF
/reader/gen2/tagEncoding
The tag uses a slightly different signaling method to communicate back to the reader than
the reader uses to communicate with the tag. There are two settings that you can use to
control the tag-to-reader communication method, the link frequency (called “Backscatter
Link Frequency” to clearly distinguish it from the reader’s link rate) and “M” value. Both
the Backscatter Link Frequency (often abbreviated “BLF”) and “M” value modify the way
the tag communicates back to the reader. The BLF is the raw signaling rate. Data rates
supported by ThingMagic readers are 250 kHz and 640 kHz. The M value essentially
controls how many times a symbol is repeated. An M of 2 means that each symbol is
repeated twice. M values of 1 (FM0), 2, 4, and 8 are supported by ThingMagic readers.
When there is no repetition (M=1) this mode is referred to as “FM0” because of other
slight distinctions not relevant to this discussion. The Gen2 protocol provides this option
to repeat symbols to maximize the chances that the reader can decode a very weak
signal from the tag. Just as it is easier to understand someone who is whispering in a
noisy room if they repeat everything they say several times, so too, the RFID reader will
decode a weak signal more reliably if “M” is 2 or greater.
ThingMagic readers currently support a BLF of 640 kHz together with an “M” value of
FM0 to achieve the highest tag-to-reader data rate, around 400 tags per second.
Alternatively, a BLF of 250 kHz can be combined with “M” options of FM0, 2, 4, or 8. At
BLF=250 kHz and M=8 the tag read rate drops to around 100 tags per second, but the
increased sensitivity could nearly double the read distance compared to settings of 640
kHz/FM0 for sensitive battery-assisted tags. There is one additional tradeoff to consider
when selecting theses values. Just as higher data rates from reader-to-tag
communication increased the likelihood of reader-to-reader interference when many
readers are present, so too can higher rates from tag-to-reader cause unwanted adjacent
channel interference. How to balance these concerns will be addressed in the section on
optimization.
Tag Contention Settings