An Energy Efficient Active RFID Protocol to Avoid Overhearing Problem

In this paper we describe an energy efficient protocol for active radio frequency identification (RFID) tags complying with the standard. The energy efficiency is a key requirement for the wider acceptance of the active RFID systems that use battery constrained tags. The existing active RFID protocols try to reduce energy consumption of tags by putting them into sleep mode when the reader is not interrogating. To start interrogation, a reader sends a special signal that wakes up its nearby tags in sleep mode. After wake up, a tag remains in active mode during the whole interrogation period until it receives a sleep command from the reader. However, the existing protocols do not consider ineffective energy consumption of tags during the interrogation period. Overhearing is a state of a tag in which it wastes energy for maintaining active RX state while there is no frame destined to it. According to our analysis, the amount of energy consumed by a tag due to overhearing is several times larger than that consumed for the effective communication. To eliminate overhearing, a tag has to know the time and the duration of its effective communication intervals in advance, and it has to maintain active mode only for those intervals while keeping sleep mode in other intervals of the interrogation period. But, a tag is hard to know the effective communication intervals in advance with the existing protocols. We propose Reservation Aloha for No Overhearing (RANO) that is designed to inform a tag of its effective communication intervals to eliminate overhearing problem in active RFID communication. We implement them on our own designed active RFID hardware to check its validity and efficiency. Using the hardware, the number of tags, the collection time of the tags and the data volume of the tags for the collection were varied in the performance test. The results show that RANO protocols saved the energy about several dozen times than the standard protocol when the number of tags increases.