An Experimental Study on the Feasibility of a Frequency Diverse UHF RFID System

Ultra high frequency radio frequency identification (UHF RFID) is seen as a key technology for future sensor and actuator devices in the Internet of Things. Therefore, improvements of read range and reliability of this technology is highly demanded. In this paper a novel reader is proposed to work on two frequencies simultaneously, intended to improve multipath fading behavior and gain immunity to narrowband disturbance. The current legal situation is reviewed for the proposed device in the European Union and it is compared to existing multifrequency systems. The developed system is based on a software defined radio platform from National Instruments. In the measurement setup a commercially available transponder chip has been connected to the custom built reader which transmits a "Query'' command on two frequencies - 868 MHz and 915 MHz. The results show, that the transponder replies on both channels. Further measurements in a real world multipath environment show the different fading behaviour of the chosen frequencies. Furthermore, it is demonstrated how dead zones can be avoided by using two different frequencies. Additionally, within the reader software a bitwise error correction for FM0 encoded data is implemented, which employs the redundant information on the two carriers. We are able show that a multicarrier system can be implemented with commercially available tags without restrictions in the European Union. Such a system could be used to improve successful read rates in harsh environments or increase reliability in critical applications. When upgrading from an existing UHF RFID system, only the interrogator needs to be exchanged by a new device working on multiple frequencies.