Separation of overlapping RFID signals by antenna arrays

Radio frequency identification (RFID) is a technology to wirelessly transmit the identity of tagged objects. For long-range (UHF) systems with multiple tags, the tag replies may overlap. Current solutions are based on collision avoidance using MAC protocols (e.g. slotted ALOHA and binary tree algorithms). This can be a time-consuming process. In this paper, it is shown how an antenna array in combination with blind source separation techniques can be used to separate multiple overlapping tag signals. The source signals are modeled as Zero Constant Modulus (ZCM) signals, and the corresponding ZCM algorithms are tested on synthetic and measured data sets.