Reader Coverage Analysis for Multi-Carrier Passive UHF RFID Systems

Abstract

Applications of passive radio frequency identification (RFID) systems have gained considerable attentions in recent years. Because a passive tag must obtain its operating power from a continuous wave transmitted from a reader in a conventional RFID system, reader coverage is limited. Thus, expanding reader coverage is a current goal in RFID research. In this work, passive tags are provided with additional operating power via continuous waves in multiple frequency bands. In an interrogation region, continuous wave emitters, which provide additional operating power to passive tags, are deployed according to the base station configuration in a cellular phone system. Because transmission power of continuous wave emitters must consider the reader command demodulation constraint and minimum operating power required by a tag, transmission power of continuous wave emitters must be chosen carefully. A method for analyzing reader coverage in multi-carrier passive UHF RFID systems is derived in this work. Assuming all tags are uniformly distributed in an interrogation region, the optimal continuous wave emitter transmission power that achieves the largest reader coverage can be analytically determined. Simulation results verify that continuous wave emitters with suitable transmission power expand reader coverage in a multi-carrier passive UHF RFID system. Additionally, adjusting reader power in the forward (reader-to-tag) link duration can loosen the reader command demodulation constraint and thereby further expand reader coverage.