Interference reduction scheme for UHF passive RFID systems using modulation index control

Performance of UHF-band passive RFID system in a dense multi-reader environment is limited by both the reader-to-reader interference and reader-to-tag interference. In this paper, we firstly propose a combination of a subcarrier modulation backscattering and a reduced carrier frequency offset among readers to reduce both the reader-to-reader interference and the reader-to-tag interference. Then, we propose a new distributed modulation index control scheme using a tag's SINR estimation at readers in order to further reduce the reader-to-tag interference. By adaptively controlling the each reader's transmission modulation index, the asymmetric reader-to-tag interference can be effectively controlled to satisfy the required SINR of tags. Computer simulations show that the proposed scheme can reduce the minimum required inter-reader distance or increase the number of concurrently operable readers in dense multireader environments, especially when there is large unbalance among the reader-to-tag interferences on tags. copyright