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A proof of concept for ultra-wideband (UWB)-based ranging in passive UHF RF identification (RFID) is presented. The proposed method uses the tag's backscatter modulation and thus does not require processing of the UWB signal by the tag. It is evaluated using measurements in an indoor environment similar to a warehouse portal in terms of channel impulse responses. The ranging accuracy is comparable to classical UWB ranging and thus inherently robust to multipath propagation.
Introduction and motivation: Even though passive UHF RFID is now a widespread technology, reliable positioning is a feature that is not yet available. Foremost in the list of reasons for this are the need to keep the tag simple (power consumption, costs) and the bandwidth limits of the UHF RFID frequency bands. As a consequence, currently used ranging methods are based on narrowband parameters such as return link phases [1], which rely on a very dominant direct path in multipath environments. Channel measurements in a warehouse portal [2] have shown that UHF RFID channels are typically dominated by the indirect (non-line-of-sight, NLOS) paths and not the direct line-of-sight (LOS) path. This leads to large errors and biased estimates in narrowband ranging methods, which in general cannot extract the LOS signal (see [2]). It is well known that ultra-wideband systems are able to overcome this problem and are thus able to provide accurate ranging in dense multipath environments. A related FMCW-based ultra-wideband ranging method has recently been published [3].
Discussion of ranging method: Setup description: The proposed method augments conventional passive UHF RFID by adding a UWB radar system. The radar system operates in parallel to the UHF system, see Figs. 1 and 2. As in conventional UHF RFID systems, tag power supply and communication is performed by the UHF reader and protocol. The radar setup emits an ultra-wideband signal, which is reflected by the tag during normal operation. Separation from the generally time-variant environment (decluttering) is performed...