Empirical study of post-envelope detection receive diversity combining for passive UHF RFID tags

The concept of incorporating receive diversity combining schemes into UHF RFID tags is presented in this work. The inclusion of the said schemes into RFID tags is employed as a possible solution to the effects of multipath propagation on the reader-to-tag (R→T) wireless link which reduce the read range and degrade the read reliability of current passive RFID systems. To explore this concept, the authors constructed reader and tag emulation platforms using National Instruments PXI hardware modules and LabVIEW software programs for modeling the R→T communications link. The reader emulation platform was used to model the transmit section of an RFID reader and is capable of transmitting user-predetermined sequences of RFID commands. The tag emulation platform was used to model the receive section of a single-or multi-antenna RFID tag. These two platforms were utilized as a testbed for developing and testing the following 2-channel diversity combining schemes for UHF RFID tags: (1) selection diversity combining (SDC), (2) post-detection direct additive combining (DACP), and (3) post-detection ratio squared combining (RSCP). Experiments were conducted to determine the read range and read reliability performance. Results of these experiments show that a maximum of 26.67% improvement in the read range and a maximum of 16.64% improvement in the read reliability of UHF RFID systems can be obtained by integrating receive diversity schemes into RFID tags. Improvements were recorded even for tag antenna spacings as low as 0.05?.