Asynchronous power-saving event-delivery protocols in mobile USN

Recently, Radio Frequency IDentification(RFID) technology has come to maturity such that numerous applications in many industries have been devised and implemented in the real world, In the conventional RFID application, the reader is located at some place without motion, periodically polling the nearby RFID tags. However, the emerging Mobile RFID technology[l] provides the user with the mobile RFID reader function by installing it into the portable wireless device like cellular phone or PDA so that he can access the spontaneous RFID-attached object information by approaching the device to RFID tag and triggering the information acquisition operation. Since the information service is immediately offered at any time and place, the whole service domain of mobile RFID is broader than that of conventional RFID. Currently, many commercial applications and their service senarios are developed and standardized in the mobile RFID Forum[1]. In this paper, we propose a new concept called as mobile USN (Ubiquitous Senser Network), the next-generation version of the newly emerging ubiquitous technologies like mobile RFID and NFC(Near Field Communication) [2]. The effective working range of mobile RFID(NFC) is limited within 1m(10cm) from the mobile(NFC) phone. This problem can be relieved by adopting RF transmission chip like CC2420 ZigBee RF Tranceiver[3] into the phone. By this upgrade, the effective working range is enlarged to 30-100m, so as to invite much more diverse ubiquitous services into realization. Then, we study energy saving issue in the data delivery from USN tag to phone. In mobile USN, USN phone is in charge of collecting the sensing and event data occuring at the nearby USN tags(that are USN version of RFID tags). However, since USN tag must be equipped with battery to support the active data acquisition, power-saving becomes the fundamental problem in achieving the commercial success of mobile USN. In particular, we introduce three asynchronous power-saving communication protocols. Finally, we study the energy efficiency and QoS aspects of three protocols.