Performance of low power RFID tags based on modulated backscattering

Abstract :

This work takes place in the context of real time localization systems (RTLS) made as a system of RFID tags and a set of readers. Although some systems have already existed for several years, the double challenge of a low consumption for the tags (ideally fully passive, i.e. without any local source of energy) and of a high spatial resolution for the localization capability is very hard to achieve. An approach has been pursued within a few years, which consists of a system of four readers at the corners of a parallelepiped (‎Figure 1. ), and of tags operating according to a modulated backscattering principle ‎[1]. The benefit lies in the low energy requirement within the tag, since for responding to the interrogation signal, it only needs to modify the impedance seen by the antenna port, according to a certain digital code. This process does not require an RF transmitter in the tag, with the associated energy consumption. At the reader, the modulated backscattered signal is received and can be detected by making use of the processing gain provided by the code. An extra code can be used by the reader itself, so to discriminate between its own backscattered signals from those coming from the other readers. In other words, among the system parameters that require careful design in order to control the link budget and the effect of interference, the coding strategy is essential ‎[1]. Although some local energy source remains necessary, it can be much smaller than for an active transmitter and making use of a very small battery. Technologies are currently developed in order to cope with such needs, e.g. with supercapacitors ‎[2]. In this work, we address the system performance from the point of view of the radio channel between the readers and the tags. Typically, the backscattered signal is similar to that of a radar, meaning that it decays as the 4th power with the distance, which is extremely fast. In addition, since the technology is ultra wide band, the power spectral density is severely limited (typically well below 1 mW) and is much smaller than the power limitation for UHF RFID readers (typically 2 W). These facts are highly constraining in terms of detection range. However, since not only the propagation but also the antennas are involved in the link budget, it is possible to play with antenna characteristics in order to improve it somewhat. In this paper, we concentrate on attenuation measurements between reader antennas and tags, which depend on the reader antenna characteristics and the tag antenna characteristics, including the polarization. We show that, by appropriately tuning the reader antenna characteristics, the 4th power distance dependence can be reduced, hence providing an enhanced detection range.

Type de document :
Communication dans un congrès
Journées scientifiques 2016 d'URSI-France, Mar 2016, Rennes, France. Journées scientifiques 2016 d'URSI-France, 2016
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Soumis le : mardi 16 août 2016 - 18:50:51
Dernière modification le : jeudi 11 janvier 2018 - 06:23:39

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  • HAL Id : hal-01354010, version 1

Citation

Zeinab Mhanna, Alain Sibille, Richard Contreras. Performance of low power RFID tags based on modulated backscattering. Journées scientifiques 2016 d'URSI-France, Mar 2016, Rennes, France. Journées scientifiques 2016 d'URSI-France, 2016. 〈hal-01354010〉

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