Collision resolution in ISO 18000-6C passive RFID communication

According to the ISO 18000-6C passive RFID standard, the tags rely on limited energy harvested from the reader carrier wave rather than an internal power supply to perform logic functions and backscatter signals. The reader receives the tag's backscattered response, and then decodes the tag signal in order to access the tag information. However, in a tag intensive environment, when multiple tags receive the reader Query command and respond simultaneously, the reader may receive multiple responses giving what is termed a collision signal. Because the collision signal violates the encoding as specified in the standard, the reader is not able to decode it using its built-in circuitry that is designed for non-colliding tag responses. Therefore, the reader fails to complete the inventory for tags in the field in this case, which degrades the overall performance of the passive RFID system requiring retries.;This research focuses on resolving the two-tag collision signal with extensions to more tags. A preliminary tag data acquisition system has been developed along with an ISO 18000-6C conformance test platform, which consists of an FPGA-based software defined reader. The collision signal is obtained from the data acquisition system and processed by the FPGA in real time. Two types of collision resolving algorithms based on phase and amplitude characteristics of the collision signal are developed and simulated using LabVIEW on a host PC and then realized with a National Instruments FPGA development board NI5640R. These two algorithms deal with the two-tag collision situation with and without a distinct phase shift individually, and they can be unified. As an extension to multiple tag collision resolution, an advanced statistical signal processing method using Independent Component Analysis (ICA) is researched for the three-tag collision situation. The ICA simulation is performed using LabVIEW on the host PC, and then implemented on the target FPGA development board. Performance analysis and comparison are presented to prove the efficiency and timing conformance of the proposed methods to the standard. Finally, the collision signals acquired from moving tags are resolved using the amplitude mapping method to prove the method compatibility on dynamic tags.