THz band multipath measurements and analysis

Abstract. The THz band is now becoming the core interest for many researchers as it offers massive bandwidth and high transmission rates. It is expected to be a solution to ongoing spectrum scarcity in the wireless communication world. Wave propagating through a channel is affected by various phenomena, especially in the case of non-line-of-sight (NLOS) condition. In this thesis work, measurement results on several NLOS propagation mechanisms such as reflection, diffraction, and penetration have been reported in the terahertz band ranging from 0.1 THz to 3 THz. Here, the primary focus is to measure the possible NLOS multipath, such as reflected, diffracted, and penetrated paths or a combination of multiple NLOS components. The goal is to evaluate and analyze the feasibility of those multipath in order to estimate the possibility to establish a communication link via such paths. The measurements have been conducted by using TeraView TeraPulse 4000, a measurement device that is based on THz time-domain spectroscopy (THz-TDS). Measurements were made under various NLOS propagation scenarios with several common indoor materials. Characteristics of the measured materials have also been reported. The results have been given as a function of frequency and measurement angles. Corresponding background theories and comparisons with the measurement results have also been investigated with subsequent analysis to check the relevance of the measurement results. The idea was to find possible multipath signals after various NLOS events while traveling through a channel and behavioural changes of the transmitted signal with the change of measurement scenarios. The measurement results agreed with the corresponding theories as expected. The THz band offers overall a decent NLOS wireless communication link between the receiver and transmitter at the lower angles

Towards 6G with THz Communications: Understanding the Propagation Channels

This article aims at providing insights for a comprehensive understanding of THz propagation channels. Specifically, we discuss essential THz channel characteristics to be well understood for the success of THz communications. The methodology of establishing realistic and 6G-compliant THz channel models based on measurements is then elaborated on, followed by a discussion on existing THz channel measurements in the literature. Finally, future research directions, challenges and measures to enrich the understanding of THz channels are discussed.Comment: 7 page

A proposed study of multiple scattering through clouds up to 1 THz

A rigorous computation of the electromagnetic field scattered from an atmospheric liquid water cloud is proposed. The recent development of a fast recursive algorithm (Chew algorithm) for computing the fields scattered from numerous scatterers now makes a rigorous computation feasible. A method is presented for adapting this algorithm to a general case where there are an extremely large number of scatterers. It is also proposed to extend a new binary PAM channel coding technique (El-Khamy coding) to multiple levels with non-square pulse shapes. The Chew algorithm can be used to compute the transfer function of a cloud channel. Then the transfer function can be used to design an optimum El-Khamy code. In principle, these concepts can be applied directly to the realistic case of a time-varying cloud (adaptive channel coding and adaptive equalization). A brief review is included of some preliminary work on cloud dispersive effects on digital communication signals and on cloud liquid water spectra and correlations

Terahertz Wireless Channels: A Holistic Survey on Measurement, Modeling, and Analysis

Terahertz (0.1-10 THz) communications are envisioned as a key technology for sixth generation (6G) wireless systems. The study of underlying THz wireless propagation channels provides the foundations for the development of reliable THz communication systems and their applications. This article provides a comprehensive overview of the study of THz wireless channels. First, the three most popular THz channel measurement methodologies, namely, frequency-domain channel measurement based on a vector network analyzer (VNA), time-domain channel measurement based on sliding correlation, and time-domain channel measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are introduced and compared. Current channel measurement systems and measurement campaigns are reviewed. Then, existing channel modeling methodologies are categorized into deterministic, stochastic, and hybrid approaches. State-of-the-art THz channel models are analyzed, and the channel simulators that are based on them are introduced. Next, an in-depth review of channel characteristics in the THz band is presented. Finally, open problems and future research directions for research studies on THz wireless channels for 6G are elaborated.Comment: to appear in IEEE Communications Surveys and Tutorial

Towards 6G with THz Communications: Understanding the Propagation Channels

This article aims at providing insights for a comprehensive understanding of THz propagation channels. Specifically, we discuss essential THz channel characteristics to be well understood for the success of THz communications. The methodology of establishing realistic and 6G-compliant THz channel models based on measurements is then elaborated on, followed by a discussion on existing THz channel measurements in the literature. Finally, future research directions, challenges and measures to enrich the understanding of THz channels are discussed

306-321 GHz Wideband Channel Measurement and Analysis in an Indoor Lobby

The Terahertz (0.1-10 THz) band has been envisioned as one of the promising spectrum bands to support ultra-broadband sixth-generation (6G) and beyond communications. In this paper, a wideband channel measurement campaign in an indoor lobby at 306-321 GHz is presented. The measurement system consists of a vector network analyzer (VNA)-based channel sounder, and a directional antenna equipped at the receiver to resolve multi-path components (MPCs) in the angular domain. In particular, 21 positions and 3780 channel impulse responses (CIRs) are measured in the lobby, including the line-of-sight (LoS), non-line-of-sight (NLoS) and obstructed-line-of-sight (OLoS) cases. Multi-path propagation is elaborated in terms of clustering results, and the effect of typical scatterers in the indoor lobby scenario in the THz band is explored. Moreover, indoor THz channel characteristics are analyzed in depth. Specifically, best direction and omni-directional path losses are analyzed by invoking close-in and alpha-beta path loss models. The most clusters are observed in the OLoS case, followed by NLoS and then LoS cases. On average, the power dispersion of MPCs is smaller in the LoS case in both temporal and angular domains, compared with the NLoS and OLoS counterparts.Comment: 6 pages, 15 figure

THZ RF measurement techniques

Abstract. In this thesis, literature review on available methods, techniques and procedures for terahertz antenna measurement system and terahertz propagation measurement system are reported. The paper presented the terahertz frequency spectrum allocation by FCC, ITU, ETSI and its application in wireless communication system with advantage in obtaining terabits per second data rates. Terahertz antenna parameters are reported and measurement systems for measurement of these chapters are reviewed. Literature of three papers on terahertz antenna measurement system with their respective measurement setup, calibration techniques and measurement procedures are reviewed. An automated antenna measurement system is reviewed with stochastic and systematic measurements and has achieved terahertz antenna s-parameter measurements in far field region at frequency range of 220 GHz to 330 GHz. Another measurement system with single port short-open-load (SOL) calibration technique is reviewed. In this measurement of s-parameter of terahertz antenna is carried out, using receiver horn placed on 3 D positioner, which records the AUT 3D radiation pattern. The third paper reviewed, is a reconfigurable terahertz antenna measurement system, with capabilities of working on large bandwidths, with small change in work bench instrumentation. This setup contains the multiplexing stages for terahertz frequency generation. Beam pattern measurements are conducted at 1.37 THz supporting the simulations and the system stability for reconfigurations. In the later study, terahertz propagation parameters are studied and presented for review of available terahertz propagation measurement systems. Literature review of three papers describing different setup and procedures for terahertz propagation measurement system are reported. The first system with the setup to record path loss in LOS and NLOS links at 260 GHz to 400 GHz is presented. Propagation parameters containing reflections, shadowing is measured. LOS and NLOS channel capacity models are obtained based on data rates in terabits per second for using above 5G wireless communication systems. Another system with office architecture, indoor LOS link, viable for indoor wireless communication applications is reported. Propagation parameters containing power density profile (PDP) are measured and validated for 140 GHz to 220 GHz. A measurement system which reports effect of atmospheric pressure, temperature and humidity is reported in the last. The setup used short, offset-short, load and thru (SOLT) technique for calibration and PDP propagation parameter is measured for 0.5 THz to 0.75 THz. Terahertz antenna and wave propagation measurement system reviewed in the papers are vital for development of terahertz systems in wireless and mobile communication. Further the study can be extended for measurement of terahertz antennas and wave propagation parameters with models of use in wireless hand-held devices, connected devices, mobile backhaul system and more

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