Roberto Magueta

RFID passive tag antenna for cork bottle stopper

In this paper we propose a possible design for a RFID tag antenna embedded into cork. The antenna is small and conformal and intended to be used into bottle stoppers for tracking and logging purposes of wine or other beverages. The proposed design is based on a inductive ring and an added resistance in order to modify the current distributions of the antenna. The resulting antenna has a relatively directive radiation pattern and despite the small efficiency it is able to operated with a commercial RFID reader at a reasonable distance.

RFID tags on cork stoppers for bottle identification

This paper presents the design of two UHF RFID tags in cork substrate. The RFID tags are designed to be compact and conformal to fit within the size and shape of the bottle and barrel stoppers. In a first step, the selected cork material is characterized taking into account the anisotropic properties of cork substrates and after the characterization two RFID tags are designed and optimized to cover a certain read range when placed inside bottle and barrel corks.

RFID-Based Wireless Passive Sensors Utilizing Cork Materials

This paper presents the design of low-cost, conformal UHF antennas and RFID tags on two types of cork substrates: natural cork and agglomerate cork. Such RFID tags find an application in wine bottle and barrel identification, and in addition, they are suitable for numerous antenna-based sensing applications. This paper includes the high-frequency characterization of the selected cork substrates considering the anisotropic behavior of such materials. In addition, the variation of their permittivity values as a function of the humidity is also verified. As a proof-of-concept demonstration, three conformal RFID tags have been implemented on cork, and their performance has been evaluated using both a commercial Alien ALR8800 reader and an in-house measurement setup. The reading of all tags has been checked, and a satisfactory performance has been verified, with reading ranges spanning from 0.3 to 6 m. In addition, this paper discusses how inkjet printing can be applied to cork surfaces, and an RFID tag printed on cork is used as a humidity sensor. Its performance is tested under different humidity conditions, and a good range in excess of 3 m has been achieved, allied to a good sensitivity obtained with a shift of >5 dB in threshold power of the tag for different humid conditions.

UHF RFID tag antenna for bottle labeling

In this paper we present a possible design for a passive RFID tag antenna on paper substrate to be integrated into bottle labels. Considering the application scenario, we verified and determined the permittivity and dissipation factor of the materials in order to simulate all the possible sources that would influence the antenna performance. The measured results reported a maximum reading range of 1.45 m even though the efficiency obtained with the antenna integrated into the bottle was only of 3%.

Iterative Multiuser Equalization for Subconnected Hybrid mmWave Massive MIMO Architecture

Millimeter waves and massive MIMO are a promising combination to achieve the multi-Gb/s required by future 5G wireless systems. However, fully digital architectures are not feasible due to hardware limitations, which means that there is a need to design signal processing techniques for hybrid analog-digital architectures. In this manuscript, we propose a hybrid iterative block multiuser equalizer for subconnected millimeter wave massive MIMO systems. The low complexity user-terminals employ pure-analog random precoders, each with a single RF chain. For the base station, a subconnected hybrid analog-digital equalizer is designed to remove multiuser interference. The hybrid equalizer is optimized using the average bit-error-rate as a metric. Due to the coupling between the RF chains in the optimization problem, the computation of the optimal solutions is too complex. To address this problem, we compute the analog part of the equalizer sequentially over the RF chains using a dictionary built from the array response vectors. The proposed subconnected hybrid iterative multiuser equalizer is compared with a recently proposed fully connected approach. The results show that the performance of the proposed scheme is close to the fully connected hybrid approach counterpart after just a few iterations.

Nonlinear Equalizer for Multi-User Hybrid mmW Massive MIMO Systems

The aim of this manuscript is to propose a new hybrid nonlinear block space-time receiver structure for millimeter wave (mmW) systems, to efficiently separate the spatial streams. We consider a fully connected analog-digital architecture. We assume that both the transmitter and the receiver are equipped with a large antenna array and the number of radio frequency (RF) chains is lower than the number of antennas. The analog and digital parts of the equalizer are jointly optimized using as a metric the mean square error (MSE) between the transmitted data vector and its estimate after the digital equalizer. The specificities of the analog domain impose several constraints in the joint optimization. To efficiently deal with the constraints the analog part is selected from a dic-tionary based on the array response vectors. The performance results have shown that the performance of our hybrid nonlinear space-time equalizer is close to the fully digital counterpart after only a few iterations. Moreover, it clearly outperforms the linear receivers recently proposed for hybrid mmW massive MIMO architectures.

Non linear space-time equalizer for single-user hybrid mmWave massive MIMO systems

The aim of this manuscript is to propose a new hybrid iterative block space-time receiver structure for millimeter wave (mmW) systems, to efficiently separate the spatial streams. We consider that both the transmitter and the received are equipped with a large antenna array and the number of radio frequency (RF) chains is lower that the number of antennas. The analog and digital parts of the equalizer are jointly optimized using as a metric the mean square error (MSE) between the transmitted data vector and its estimate after the digital equalizer. The specificities of the analog domain impose several constraints in the joint optimization. To efficiently deal with the constraints the analog part is selected from a dictionary based on the array response vectors. Our performance results have shown that the performance of the hybrid iterative space equalizer is close to the fully digital counterpart after only a few iterations. Moreover, it clearly outperforms the linear receivers recently proposed for hybrid mmW massive MIMO architectures.

Two-stage space-time receiver structure for multiuser hybrid mmW massive MIMO systems

This paper considers a hybrid two-stage space-time receiver structure for uplink millimeter wave (mmW) based systems, where the user terminals (UTs) and the base station (BS) are equipped with a large antenna array and the number of radio frequency (RF) chains is lower than the number of antennas. In the first stage the analog transmit and receive beam-formers/precoders are computed for each UT - BS pair considering multi-user interference free links, to maximize the desired signal power for each UT. In the second one, an iterative block space-time equalizer is designed to explicitly remove the multi-user interference. The designed space-time equalizer is optimized by using as a metric the mean square error (MSE) between the transmitted data vector and its estimate after the digital equalizer. Our performance results havye shown that the proposed iterative space-time equalizer outperforms the linear MMSE based receivers for hybrid mmW massive MIMO architectures.

IB-DFE based equalizer for constant envelop OFDM systems

Constant envelope OFDM (CE-OFDM) is a promising modulation technique for future millimeter wave (mmW) based wireless communications, since it allows low-cost and highly efficient power amplification based on strongly nonlinear amplifiers. The aim of this paper is to design a new iterative space-frequency equalizer, based on iterative block decision feedback equalization (IB-DFE) principle, for multiplexing MIMO CE-OFDM based systems. The equalizer is designed to take into account both inter-block and residual inter-carrier interferences by efficiently exploit the space-frequency diversity order inherent to these systems. The matrices for this iterative space-frequency equalizer are obtained by minimizing the overall mean square error (MSE) of all data streams at each subcarrier. Our iterative scheme significantly outperforms the linear frequency domain equalizers, recently considered for CE-OFDM, with only a few iterations.

Iterative Equalization and Interference Alignment for Multiuser MIMO HetNets with Imperfect CSI

In this paper we consider a scenario, where several small-cells work under the same coverage area and spectrum of a macrocell. The signals stemming from the small-cell (macrocell) users if not carefully dealt with will generate harmful interference into the macrocell (small-cell). To tackle this problem interference alignment and iterative equalization techniques are considered. By using IA all interference generated by the small-cell (macrocell) users is aligned along a low dimensional subspace, at the macrocell (small-cells). This reduces considerably the amount of resources allocated, to enable the coexistence of the two systems. However, perfect IA requires the availability of error-free channel state information (CSI) at the transmitters. Due to CSI errors one can have substantial performance degradation due to imperfect alignments. Since in this work the IA precoders are based on imperfect CSI, an efficient iterative space-frequency equalization is designed at the receiver side to cope with the residual aligned interference. The results demonstrate that iterative equalization is robust to imperfect CSI and removes efficiently the interference generated by the poorly aligned interference. Close to matched filter bound performance is achieved, with a very few number of iterations.