Impact of RF Interference between a Passive RFID System and a Frequency Hopping Communications System in the 900 MHz ISM Band Michael R. Souryal 1 , David R. Novotny 2 , Daniel G. Kuester 3 , Jeffrey R. Guerrieri 2 , Kate A. Remley 2 National Institute of Standards and Technology 3 University of Colorado 1 Information Technology Laboratory 2 Electronics and Electrical Engineering Laboratory Electrical and Computer 100 Bureau Drive 325 Broadway Engineering Department Gaithersburg, MD 20899 Boulder, CO 80305 Boulder, CO 80309 {michael.souryal,david.novotny,daniel.kuester,jeffrey.guerrieri,kate.remley}@nist.gov Abstract—We present experimental measurements and anal- ysis of RF interference between a passive RFID system and a generic frequency hopping communications system in the 902 MHz to 928 MHz ISM radio band. Interference in both directions is considered, RFID to communications and vice-versa, and interference mitigation strategies are assessed. Variables of interest include transmission power, antenna locations and polarization, and frequency hopping channel bandwidth and dwell time. Among the findings are the susceptibility of the RFID backscatter link to sources operating within regulatory limits, characterization of the performance asymmetry between the systems, and the constructive effect of interference to RFID at low powers. I. I NTRODUCTION Passive radio frequency identification (RFID) in the ultra- high frequency (UHF) band is attractive due to the availability of low cost tags and adequate read range for supply chain and other applications. In the US, UHF RFID operates in an unlicensed radio frequency (RF) band, therefore RFID equipment must tolerate and be tolerated by other radiators sharing this band. As RFID becomes more commonly used in critical applications such as cargo and material identification, it is essential that system engineers and procurement officers understand under what circumstances various systems can be deployed reliably. This paper investigates the effects of RF interference be- tween a passive UHF RFID system and a communications sys- tem sharing the 902 MHz to 928 MHz industrial, scientific and medical (ISM) band. Communications devices in the ISM band are used for supervisory control and data acquisition (SCADA) applications, industrial automation and control, and wireless sensor networking. To comply with US regulatory rules for this band, the RFID and communications systems we have tested employ frequency hopping spread spectrum, whereby each device pseudo-randomly hops from one narrowband channel to another, transmitting for a given duration (or hop dwell time) on each channel. We measure and analyze the performance The Department of Homeland Security Science and Technology Directorate sponsored the production of this material under Interagency Agreement HSHQDC-09-X-00305 with NIST. US Government work not protected by US Copyright impact of the RFID system on the communications system and vice-versa, for varying transmission powers, antenna locations, antenna polarization, channel bandwidth and hop dwell time. Prior work on interference with passive UHF RFID systems includes the analysis of reader-to-reader interference by Kim et. al. [1]; however this work addressed fixed, not hopping, channels. The work by Hong et. al. [2] identified conditions under which UHF RFID disrupted a nearby GSM downlink channel, while the work by Arnaud-Cormos et. al. [3] mea- sured the effect of a GSM mobile device on the read range of a UHF RFID system. Novotny et. al. [4] analyzed the potential interference caused by UHF RFID emitters to nearby devices that satisfy standard minimum RF immunity levels. There have also been studies of interference with other types of RFID systems. Jiang and Ma [5] presented analytical and simulation results for the effect of microwave (2.4 GHz) RFID on an IEEE 802.11b link, and Chen et. al. [6] did the same for an IEEE 802.15.4 (Zigbee) link. Regarding high frequency (HF) RFID systems operating at 13.56 MHz, Novotny et. al. [7] investigated conditions under which continuous wave and modulated HF carriers can disrupt the RFID transaction. This study differs from the aforementioned studies in that we examine the mutual interference between frequency hop- ping RFID and communications systems in the UHF ISM band. Furthermore, in measuring the performance impact of interference, we utilize “soft” performance metrics—the read success rate and read throughput of RFID, and the packet reception rate of communications—rather than a hard on/off metric. Through experimental measurements, we find that, though the effects of interference are demonstrable in both systems, the RFID system is more sensitive to emissions of the communications system than vice-versa, likely owing to the greater susceptibility of the weaker backscattered tag-to-reader signal. However, we also find, interestingly, that under certain conditions RFID read performance can actually improve in the presence of another signal, as the communications signal appears to provide additional RF energy to help activate the passive tag. Interference mitigation through cross-polarization and strategic antenna location are also assessed. The remainder of the paper is organized as follows. Sec- 495 U.S. Government work not protected by U.S. copyright