Ultra-wide bandwidth backscatter modulation: processing schemes and performance

Future advanced radio-frequency identification (RFID) systems are expected to provide both identification and high-definition localization of objects with improved reliability and security while maintaining low power consumption and cost. Ultrawide bandwidth (UWB) technology is a promising solution for next generation RFID systems to overcome most of the limitations of current narrow bandwidth RFID technology, such as reduced area coverage, insufficient ranging resolution for accurate localization, sensitivity to interference, and scarce multiple access capability. In this article, the UWB technology is applied to passive RFID relying on backscatter modulation. A signaling structure with clutter and interference suppression capability is proposed and analyzed. The potential performance is investigated in terms of range/data rate trade-off, clutter suppression, and multiple access capability using experimental data obtained in both the controlled and realistic environments

Analysis of Secret Key Randomness Exploiting the Radio Channel Variability

A few years ago, physical layer based techniques have started to be considered as a way to improve security in wireless communications. A well known problem is the management of ciphering keys, both regarding the generation and distribution of these keys. A way to alleviate such difficulties is to use a common source of randomness for the legitimate terminals, not accessible to an eavesdropper. This is the case of the fading propagation channel, when exact or approximate reciprocity applies. Although this principle has been known for long, not so many works have evaluated the effect of radio channel properties in practical environments on the degree of randomness of the generated keys. To this end, we here investigate indoor radio channel measurements in different environments and settings at either 2.4625 GHz or 5.4 GHz band, of particular interest for WIFI related standards. Key bits are extracted by quantizing the complex channel coefficients and their randomness is evaluated using the NIST test suite. We then look at the impact of the carrier frequency, the channel variability in the space, time, and frequency degrees of freedom used to construct a long secret key, in relation to the nature of the radio environment such as the LOS/NLOS character

Single and Multiple Scattering in UWB Bicone Arrays

An analysis of interactions between radiators in a UWB biconical array, drawing attention to single and multiple scatterings, is carried out. The complementarity between electrical coupling and radiation scattering is argued. The point source approximation is discussed and shown to be insufficient. An approximation of radiation scattering based on angular averaging of the scattering coefficient is proposed. This approach yields a reduction of the problem complexity, which is especially interesting in UWB multiple antenna systems, because of the large bandwidth. Multiple scattering between radiators is shown to be a second-order effect. Finally, a time domain approach is used in order to investigate pulse distortion and quantify the exactness of the proposed scattering model

Statistical Modeling of Antenna: Urban Equipment Interactions for LTE Access Points

The latest standards for wireless networks such as LTE are essentially based on small cells in order to achieve a large network capacity. This applies for antennas to be deployed at street level or even within buildings. However, antennas are commonly designed, simulated, and measured in ideal conditions, which is not the real situation for most applications where antennas are often deployed in proximity to objects acting as disturbers. In this paper, three conventional wireless access point scenarios (antenna-wall, antenna-shelter, and antenna lamppost) are investigated for directional or omnidirectional antennas. The paper first addresses the definition of three performance indicators for such scenarios and secondly uses such parameters towards the statistical analysis of the interactions between the wall and the antennas

Performance of low-power RFID tags based on modulated backscattering

National audience<p>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 (&#8206;Figure 1. ), and of tags operating according to a modulated backscattering principle &#8206;[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 &#8206;[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 &#8206;[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.</p

Modeling and characterization of the uplink and downlink exposure in wireless networks

This paper deals with a new methodology to assess the exposure induced by both uplink and downlink of a cellular network using 3D electromagnetic simulations. It aims to analyze together the exposure induced by a personal device (uplink exposure) and that induced by a base station (downlink exposure). The study involved the major parameters contributing to variability and uncertainty in exposure assessment, such as the user's posture, the type of wireless device, and the propagation environment. Our approach is relying basically on the modeling of the power radiated by the personal device and the ambient electric field, while taking into account the effects of human body shadowing and the propagation channel fluctuations. The exposure assessment as well as the human-wave interactions has been simulated using the finite difference in time domain method (FDTD). In uplink scenarios, four FDTD simulations were performed with a child model, used in two postures (sitting and standing) and in two usage scenarios (voice and data), which aimed to examine the exposure induced by a mobile phone and a tablet emitting, respectively, at 900 MHz and 1940 MHz. In the downlink scenario, a series of FDTD simulations of an exposure to a single plane wave and multiplane waves have been conducted, and an efficient metamodeling of the exposure using the Polynomial Chaos approach has been developed

Characterization of far-field and near-field exposure of the population for RF-EMF in realistic configurations of ICT usages

International audienceThe study presented in this paper is part of a larger study within the European FP7 project LEXNET framework. The project LEXNET aims at considering new technologies and architectures for minimizing the global exposure of a population to radiofrequency electromagnetic fields. In the framework of the project a new exposure metric named Exposure Index (EI) is proposed. The EI quantifies the global exposure of a population induced by both mobile devices and base station antennas or wireless access points. The EI requires a set of SAR values (whole-body and local-body) for typical postures and usages of mobile devices in a population. In our study, we assessed these SAR values by 3D electromagnetic simulations. We used an adult and a child numerical model in two postures (sitting and standing) and in three usages (voice, data and laptop).The whole-body SAR for each exposure configuration was evaluated at four different frequencies (400, 900, 1940 and 2600MHz).</p

Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI