Item level characterization of mm-wave indoor propagation

According to the current prospect of allocating next generation wireless systems in the underutilized millimeter frequency bands, a thorough characterization of mm-wave propagation represents a pressing necessity. In this work, an “item level” characterization of radiowave propagation at 70 GHz is carried out. The scattering properties of several, different objects commonly present in indoor environment are investigated by means of measurements carried out in an anechoic chamber. The measured data have been also exploited to tune some parameters of a 3D ray tracing model

On-Body Channel Measurement Using Wireless Sensors

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The high frequency flexural ultrasonic transducer for transmitting and receiving ultrasound in air

Flexural ultrasonic transducers are robust and low cost sensors that are typically used in industry for distance ranging, proximity sensing and flow measurement. The operating frequencies of currently available commercial flexural ultrasonic transducers are usually below 50 kHz. Higher operating frequencies would be particularly beneficial for measurement accuracy and detection sensitivity. In this paper, design principles of High Frequency Flexural Ultrasonic Transducers (HiFFUTs), guided by the classical plate theory and finite element analysis, are reported. The results show that the diameter of the piezoelectric disc element attached to the flexing plate of the HiFFUT has a significant influence on the transducer's resonant frequency, and that an optimal diameter for a HiFFUT transmitter alone is different from that for a pitch-catch ultrasonic system consisting of both a HiFFUT transmitter and a receiver. By adopting an optimal piezoelectric diameter, the HiFFUT pitch-catch system can produce an ultrasonic signal amplitude greater than that of a non-optimised system by an order of magnitude. The performance of a prototype HiFFUT is characterised through electrical impedance analysis, laser Doppler vibrometry, and pressure-field microphone measurement, before the performance of two new HiFFUTs in a pitch-catch configuration is compared with that of commercial transducers. The prototype HiFFUT can operate efficiently at a frequency of 102.1 kHz as either a transmitter or a receiver, with comparable output amplitude, wider bandwidth, and higher directivity than commercially available transducers of similar construction

Empirical multi-band characterization of propagation with modelling aspects for communictions

Diese Arbeit präsentiert eine empirische Untersuchung der Wellenausbreitung für drahtlose Kommunikation im Millimeterwellen- und sub-THz-Band, wobei als Referenz das bereits bekannte und untersuchte sub-6-GHz-Band verwendet wird. Die großen verfügbaren Bandbreiten in diesen hohen Frequenzbändern erlauben die Verwendung hoher instantaner Bandbreiten zur Erfüllung der wesentlichen Anforderungen zukünftiger Mobilfunktechnologien (5G, “5G and beyond” und 6G). Aufgrund zunehmender Pfad- und Eindringverluste bei zunehmender Trägerfrequenz ist die resultierende Abdeckung dabei jedoch stark reduziert. Die entstehenden Pfadverluste können durch die Verwendung hochdirektiver Funkschnittstellen kompensiert werden, wodurch die resultierende Auflösung im Winkelbereich erhöht wird und die Notwendigkeit einer räumlichen Kenntnis der Systeme mit sich bringt: Woher kommt das Signal? Darüber hinaus erhöhen größere Anwendungsbandbreiten die Auflösung im Zeitbereich, reduzieren das small-scale Fading und ermöglichen die Untersuchung innerhalb von Clustern von Mehrwegekomponenten. Daraus ergibt sich für Kommunikationssysteme ein vorhersagbareres Bild im Winkel-, Zeit- und Polarisationsbereich, welches Eigenschaften sind, die in Kanalmodellen für diese Frequenzen widergespiegelt werden müssen. Aus diesem Grund wurde in der vorliegenden Arbeit eine umfassende Charakterisierung der Wellenausbreitung durch simultane Multibandmessungen in den sub-6 GHz-, Millimeterwellen- und sub-THz-Bändern vorgestellt. Zu Beginn wurde die Eignung des simultanen Multiband-Messverfahrens zur Charakterisierung der Ausbreitung von Grenzwert-Leistungsprofilen und large-scale Parametern bewertet. Anschließend wurden wichtige Wellenausbreitungsaspekte für die Ein- und Multibandkanalmodellierung innerhalb mehrerer Säulen der 5G-Technologie identifiziert und Erweiterungen zu verbreiteten räumlichen Kanalmodellen eingeführt und bewertet, welche die oben genannten Systemaspekte abdecken.This thesis presents an empirical characterization of propagation for wireless communications at mm-waves and sub-THz, taking as a reference the already well known and studied sub-6 GHz band. The large blocks of free spectrum available at these high frequency bands makes them particularly suitable to provide the necessary instantaneous bandwidths to meet the requirements of future wireless technologies (5G, 5G and beyond, and 6G). However, isotropic path-loss and penetration-loss are larger with increasing carrier frequency, hence, coverage is severely reduced. Path-loss can be compensated with the utilization of highly directive radio-interfaces, which increases the resolution in the angular domain. Nonetheless, this emphasizes the need of spatial awareness of systems, making more relevant the question “where does the signal come from?” In addition, larger application bandwidths increase the resolution in the time domain, reducing small-scale fading and allowing to observe inside of clusters of multi-path components (MPCs). Consequently, communication systems have a more deterministic picture of the environment in the angular, time, and polarization domain, characteristics that need to be reflected in channel models for these frequencies. Therefore, in the present work we introduce an extensive characterization of propagation by intensive simultaneous multi-band measurements in the sub-6 GHz, mm-waves, and sub-THz bands. Firstly, the suitability of the simultaneous multi-band measurement procedure to characterize propagation from marginal power profiles and large-scale parameters (LSPs) has been evaluated. Then, key propagation aspects for single and multi-band channel modelling in several verticals of 5G have been identified, and extensions to popular spatial channel models (SCMs) covering the aforementioned system aspects have been introduced and evaluated

Venting in the comparative study of flexural ultrasonic transducers to improve resilience at elevated environmental pressure levels

The classical form of a flexural ultrasonic transducer is a piezoelectric ceramic disc bonded to a circular metallic membrane. This ceramic induces vibration modes of the membrane for the generation and detection of ultrasound. The transducer has been popular for proximity sensing and metrology, particularly for industrial applications at ambient pressures around 1 bar. The classical flexural ultrasonic transducer is not designed for operation at elevated pressures, such as those associated with natural gas transportation or petrochemical processes. It is reliant on a rear seal which forms an internal air cavity, making the transducer susceptible to deformation through pressure imbalance. The application potential of the classical transducer is therefore severely limited. In this study, a venting strategy which balances the pressure between the internal transducer structure and the external environment is studied through experimental methods including electrical impedance analysis and pitch-catch ultrasound measurement. The vented transducer is compared with a commercial equivalent in air towards 90 bar. Venting is shown to be viable for a new generation of low cost and robust industrial ultrasonic transducers, suitable for operation at high environmental pressure levels

Effect of antenna element properties and array orientation on performance of MIMO systems

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A Study on mm-Wave Propagation In and Around Buildings

mm-waves are envisaged as a key enabler for 5G and 6G wireless communications, thanks to the wide bandwidth and to the possibility of implementing large-scale antenna arrays and advanced transmission techniques, such as massive MIMO and beamforming, that can take advantage of the multidimensional properties of the wireless channel. In order to analyze in depth the peculiar characteristics of mm-wave propagation, joint measurement and simulation campaigns in indoor and outdoor microcellular environments have been carried out. The investigation highlights that the assumption that mm-wave NLoS connectivity is hardly feasible is not necessarily true as significant reflections, scattering and even transmission mechanisms can provide good NLoS coverage in the considered indoor and outdoor scenarios. This is also reflected in the limited angle-spread differences between LoS and NLoS locations in some cases. Finally, the contribution of different propagation mechanisms (reflection, diffraction, scattering and combination of them) to the received signal is analyzed in the paper with the help of ray tracing simulations. These outcomes can be helpful to predict the performance of mm-wave wireless systems and for the development of deterministic and geometric-stochastic mm-wave channel models