This paper proposes “group coding” of RFID tags. With our
group coding, we can verify the integrity of a group of RFID
tagged objects without an external database or verifier. In this
paper, fundamental group coding and general group coding are
introduced. Fundamental group coding can verify the integrity
of the group using a group ID as a checksum of the group.
General group coding can determine the number of RFID tags
missing from the group by using multiple subgroups which are
constructed by the fundamental group coding. The determination
accuracy of 10 RFID tags’ missing out of 20 is 99% with
writing 96 bits of checksum data to each RFID tag’s memory.
The performance of general group coding, the accuracy of the
determination, can be adjusted by controlling the size of the
checksum data. The performance increases in proportion to the
number of subgroups. When the high performance is not required,
we can reduce the memory consumption for each RFID
tag. In addition, even if the memory consumption of RFID tags
is the same, the coding strength of general group coding can be
affected by the structure of group codes. The parameter of group
coding should be determined with considering these characteristics.
This group coding can be done within a few seconds with a
laptop PC and a commercial RFID interrogator. While the computation
of the group encoding and the group decoding can be
done within a few milliseconds, most of the time duration is consumed
by the inventory and reading and writing of RFID tags.