Investigation of impact factors for various performances of passive UHF RFID system

In this paper, we present causes of variation in performance for passive UHF RFID tags with empirical results in two different environments: practical conditions and an anechoic chamber. We study the critical causes of RSSI ambiguity, such as a posture of tag, and variations among uniform tags. Moreover, in passive UHF RFID systems, Tag-to-Tag interferences affect performance of passive RF tags. When two tags are located close each other, an adjacent tag influences the other tags. This causes increase or decrease of the backscattering communication budgets. According to our empirical results, compared with non-interfered backscattering signal strength in an anechoic chamber, tag-to-tag interference affects the reader received signal strength, such as 5.8dB of excess decrease and 2.5dB of increase, depending on the distance between two tags. We present a new model of backscattered signal strength for passive UHF RFID system under tag-to-tag interference. The variation of excess power volume by the interference depends on an interference coefficient. In order to analyze the impacts of tag-to-tag interference, we show empirical results in the anechoic chamber, then, we model the change of the backscattered signal strength using the second order under-damped system for different tag-to-tag distances and angles.