| 简介 |
PROBLEM TO BE SOLVED : To prevent the communication collision problem that occurs when two tags enter simultaneously an RF field in a non-contact proximity automated data collection system, including tags, targets and hosts.
SOLUTION : Each time a first response from a tag is received, a target checks whether the response has an appropriate message format. First responses from a plurality of tags are designed to generate an inappropriate message format, when they interfere with each other. When the inappropriate message format is received, the target notifies to the tag that the message is invalid. The tag then performs retry, after a while. Although it is rare, the target may not be able to detect collision, even though a collision exists. At such a time, the host executes collision detection of a second level. This surely prevents two or more tags from simultaneously accessing the same target. |
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