A data transmission system includes a reader transceiver and one or more tag transceivers. The reader transmits an activation signal to a tag. The tag selectively transmits a response signal to the reader at a specific time determined by a detected level of communications channel activity. The detector...http://www.google.com/patents/US6034603?utm_source=gb-gplus-sharePatent US6034603 - Radio tag system and method with improved tag interference avoidance
