Radio communication via near vertical incidence skywave system

Abstract. While the overall picture of our cutting-edge communication framework is one of high unwavering quality, the practical experience could be completely different during catastrophic situations, when communication services are disrupted due to damages in the communications infrastructure. Moreover, wireless connectivity in remote areas of the works is still a highly significant problem, with an estimated two billion people being outside of the connected world. This thesis studies the use of high frequencies communications as a way to address the abovementioned cases. High frequency (HF) communication utilizes radio waves between 3 and 30 MHz with the wavelengths of 100 to 10 m. The dominant means of long-distance communication in this band is skywave propagation, in which radio waves that are directed at an angle into the sky are reflected on Earth by the ionized layers of the atmosphere. HF ionospheric reflection technique is commonly used specifically for military, maritime, aeronautical, and emergency communication in remote areas, and as backup system. Factors such as season, sunspot cycle, solar activity, as well as polar aurora plays significant roles in the sustainability of HF radio communications. Propagation plays the most significant role while designing a communication network. Radio waves propagates with an objective of transmitting signal successfully without having an error. So, studies on wave propagation mechanisms, channel and noises are equally important. This thesis focuses on high frequency near vertical incidence skywave (HF NVIS) technology. NVIS, exploiting a frequency range of 2–10 MHz, can provide continuous coverage up to a couple of hundred kilometres from the transmitter without skip zone. NVIS operation is considered during disaster relief operations when infrastructure is severely damaged or where tactical communication is needed in military operations. NVIS operation requires the presence of substantial ionization in the ionosphere directly above the transmitter. For optimizing a NVIS communication system, the most important parameters to consider are elevation angle, fading, noise and polarization. Furthermore, NVIS operation requires careful selection of antennas, operating frequency, maximum usable frequency (MUF), lowest usable frequency (LUF), as well as frequency of optimum transmission (FOT) for successful communication. At the time of emergency, low data services such as voice and text could be easily established with NVIS system. A comprehensive overview of NVIS based on number of research articles is given which highlights ionospheric propagation, antennas, the operational use of HF communications, as well as applications. Further, we highlight the challenges with possible solutions, and future research direction to ensure NVIS system sustainability. From this literature review, the significant relationship between NVIS antenna and NVIS propagation mechanism is discussed. Furthermore, thesis provides a reference text to understand various elements of NVIS system and demonstrate how modern technology can be used to solve HF issues. We believe that this article will encourage more interests in addressing the technical challenges on the research and development of future HF radio communication systems

Advanced HF Communications for Remote Sensors in Antarctica

The Antarctica is a continent mainly devoted to science with a big amount of sensors located in remote places for biological and geophysical purposes. The data from these sensors need to be sent either to the Antarctic stations or directly to the home country. For the last 15 years, La Salle has been working in the application of HF communications (3–30 MHz) with ionospheric reflection for data collection of remote sensors in Antarctica. We have developed and tested the several types of modulations, the frame structure, the radio-modem, and the antennas for two different scenarios. First, a long-range transequatorial (approximately 12,800 km) and low-power communication system is used as an alternative to satellites, which are often not visible from the poles. This distance is covered with a minimum of four hops with oblique incidence in the ionosphere. Second, a low-power system using near vertical incidence skywave (NVIS) communications provides coverage in a surface of approximately 200–250 km radius, a coverage much longer than any other systems operating in either the VHF or UHF band without the need of line of sight

CO(J = 1-0) Imaging of M51 with CARMA and the Nobeyama 45 m Telescope

We report the CO(J = 1-0) observations of the Whirlpool Galaxy M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45 m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (rms) noise in the maps, (3) the sensitivity and uv coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the rms noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, should be applicable to grids in uv space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single-dish baselines only up to 4-6 kλ (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between the synthesized beam and convolution beam. The superior uv coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical Hubble Space Telescope image and polycyclicaromatichydrocarbon emission in a Spitzer 8 μm image. The total molecular gas masses of NGC 5194 and 5195 (d = 8.2 Mpc) are 4.9 × 10^9 M_⊙ and 7.8 × 10^7 M_⊙, respectively, assuming the CO-to-H_2 conversion factor of X _(CO) = 1.8 × 10^(20) cm-2(K km s^(–1))^(–1). The presented images are an indication of the millimeter-wave images that will become standard in the next decade with CARMA and NRO45, and the Atacama Large Millimeter/Submillimeter Array

Trustworthiness Mechanisms for Long-Distance Networks in Internet of Things

Aquesta tesi té com a objectiu aconseguir un intercanvi de dades fiable en un entorn hostil millorant-ne la confiabilitat mitjançant el disseny d'un model complet que tingui en compte les diferents capes de confiabilitat i mitjançant la implementació de les contramesures associades al model. La tesi se centra en el cas d'ús del projecte SHETLAND-NET, amb l'objectiu de desplegar una arquitectura d'Internet de les coses (IoT) híbrida amb comunicacions LoRa i d'ona ionosfèrica d'incidència gairebé vertical (NVIS) per oferir un servei de telemetria per al monitoratge del “permafrost” a l'Antàrtida. Per complir els objectius de la tesi, en primer lloc, es fa una revisió de l'estat de l'art en confiabilitat per proposar una definició i l'abast del terme de confiança. Partint d'aquí, es dissenya un model de confiabilitat de quatre capes, on cada capa es caracteritza pel seu abast, mètrica per a la quantificació de la confiabilitat, contramesures per a la millora de la confiabilitat i les interdependències amb les altres capes. Aquest model permet el mesurament i l'avaluació de la confiabilitat del cas d'ús a l'Antàrtida. Donades les condicions hostils i les limitacions de la tecnologia utilitzada en aquest cas d’ús, es valida el model i s’avalua el servei de telemetria a través de simulacions en Riverbed Modeler. Per obtenir valors anticipats de la confiabilitat esperada, l'arquitectura proposada es modela per avaluar els resultats amb diferents configuracions previ al seu desplegament en proves de camp. L'arquitectura proposada passa per tres principals iteracions de millora de la confiabilitat. A la primera iteració, s'explora l'ús de mecanismes de consens i gestió de la confiança social per aprofitar la redundància de sensors. En la segona iteració, s’avalua l’ús de protocols de transport moderns per al cas d’ús antàrtic. L’última iteració d’aquesta tesi avalua l’ús d’una arquitectura de xarxa tolerant al retard (DTN) utilitzant el Bundle Protocol (BP) per millorar la confiabilitat del sistema. Finalment, es presenta una prova de concepte (PoC) amb maquinari real que es va desplegar a la campanya antàrtica 2021-2022, descrivint les proves de camp funcionals realitzades a l'Antàrtida i Catalunya.Esta tesis tiene como objetivo lograr un intercambio de datos confiable en un entorno hostil mejorando su confiabilidad mediante el diseño de un modelo completo que tenga en cuenta las diferentes capas de confiabilidad y mediante la implementación de las contramedidas asociadas al modelo. La tesis se centra en el caso de uso del proyecto SHETLAND-NET, con el objetivo de desplegar una arquitectura de Internet de las cosas (IoT) híbrida con comunicaciones LoRa y de onda ionosférica de incidencia casi vertical (NVIS) para ofrecer un servicio de telemetría para el monitoreo del “permafrost” en la Antártida. Para cumplir con los objetivos de la tesis, en primer lugar, se realiza una revisión del estado del arte en confiabilidad para proponer una definición y alcance del término confiabilidad. Partiendo de aquí, se diseña un modelo de confiabilidad de cuatro capas, donde cada capa se caracteriza por su alcance, métrica para la cuantificación de la confiabilidad, contramedidas para la mejora de la confiabilidad y las interdependencias con las otras capas. Este modelo permite la medición y evaluación de la confiabilidad del caso de uso en la Antártida. Dadas las condiciones hostiles y las limitaciones de la tecnología utilizada en este caso de uso, se valida el modelo y se evalúa el servicio de telemetría a través de simulaciones en Riverbed Modeler. Para obtener valores anticipados de la confiabilidad esperada, la arquitectura propuesta es modelada para evaluar los resultados con diferentes configuraciones previo a su despliegue en pruebas de campo. La arquitectura propuesta pasa por tres iteraciones principales de mejora de la confiabilidad. En la primera iteración, se explora el uso de mecanismos de consenso y gestión de la confianza social para aprovechar la redundancia de sensores. En la segunda iteración, se evalúa el uso de protocolos de transporte modernos para el caso de uso antártico. La última iteración de esta tesis evalúa el uso de una arquitectura de red tolerante al retardo (DTN) utilizando el Bundle Protocol (BP) para mejorar la confiabilidad del sistema. Finalmente, se presenta una prueba de concepto (PoC) con hardware real que se desplegó en la campaña antártica 2021-2022, describiendo las pruebas de campo funcionales realizadas en la Antártida y Cataluña.This thesis aims at achieving reliable data exchange over a harsh environment by improving its trustworthiness through the design of a complete model that takes into account the different layers of trustworthiness and through the implementation of the model’s associated countermeasures. The thesis focuses on the use case of the SHETLAND-NET project, aiming to deploy a hybrid Internet of Things (IoT) architecture with LoRa and Near Vertical Incidence Skywave (NVIS) communications to offer a telemetry service for permafrost monitoring in Antarctica. To accomplish the thesis objectives, first, a review of the state of the art in trustworthiness is carried out to propose a definition and scope of the trustworthiness term. From these, a four-layer trustworthiness model is designed, with each layer characterized by its scope, metric for trustworthiness accountability, countermeasures for trustworthiness improvement, and the interdependencies with the other layers. This model enables trustworthiness accountability and assessment of the Antarctic use case. Given the harsh conditions and the limitations of the use technology in this use case, the model is validated and the telemetry service is evaluated through simulations in Riverbed Modeler. To obtain anticipated values of the expected trustworthiness, the proposal has been modeled to evaluate the performance with different configurations prior to its deployment in the field. The proposed architecture goes through three major iterations of trustworthiness improvement. In the first iteration, using social trust management and consensus mechanisms is explored to take advantage of sensor redundancy. In the second iteration, the use of modern transport protocols is evaluated for the Antarctic use case. The final iteration of this thesis assesses using a Delay Tolerant Network (DTN) architecture using the Bundle Protocol (BP) to improve the system’s trustworthiness. Finally, a Proof of Concept (PoC) with real hardware that was deployed in the 2021-2022 Antarctic campaign is presented, describing the functional tests performed in Antarctica and Catalonia

Cooperative Techniques for Next Generation HF Communication Systems

The high frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. For decades, the HF band has been recognized as the primary means of long-range wireless communications. When satellite communication first emerged in 1960s, HF technology was considered to be obsolete. However, with its enduring qualities, HF communication survived through this competition and positioned itself as a powerful complementary and/or alternative technology to satellite communications. HF systems have been traditionally associated with low-rate data transmission. With the shift from analog to digital in voice communication, and increasing demands for high-rate data transmission (e.g., e-mail, Internet, FTP), HF communication has been going through a renaissance. Innovative techniques are required to push the capacity limits of the HF band. In this dissertation, we consider cooperative communication as an enabling technology to meet the challenging expectations of future generation HF communication systems. Cooperative communication exploits the broadcast nature of wireless transmission and relies on the cooperation of users relaying the information to one another. We address the design, analysis, and optimization of cooperative HF communication systems considering both multi-carrier and single-carrier architectures. As the multi-carrier HF system, we consider the combination of the orthogonal frequency division multiplexing (OFDM) with the bit interleaved coded modulation (BICM) as the underlying physical layer platform. It is assumed that cooperating nodes may use different HF propagation mechanisms, such as near-vertical-incidence sky wave (NVIS) and surface wave, to relay their received signals to the destination in different environmental scenarios. Diversity gain analysis, optimum relay selection strategy and power allocation between the source and relays are investigated for the proposed cooperative HF system. For single-carrier HF systems, we first derive a matched-filer-bound (MFB) on the error rate performance of the non-regenerative cooperative systems. The results from the MFB analysis are also used for relay selection and power allocation in the multi-relay cooperative systems. To overcome the intersymbol interference impairment induced by frequency-selectivity of the HF channel, equalization is inevitable at the destination in a single-carrier system. In this work, we investigate the minimum-mean-square-error (MMSE) based linear/decision-feedback frequency domain equalizers (FDEs). Both symbol-spaced and fractionally-spaced implementations of the proposed FDEs are considered and their performance is compared under different channel conditions and sampling phase errors at the relay and destination nodes.1 yea

The Precision Array for Probing the Epoch of Reionization: 8 Station Results

We are developing the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21cm emission from the early Universe, when the first stars and galaxies were forming. We describe the overall experiment strategy and architecture and summarize two PAPER deployments: a 4-antenna array in the low-RFI environment of Western Australia and an 8-antenna array at our prototyping site in Green Bank, WV. From these activities we report on system performance, including primary beam model verification, dependence of system gain on ambient temperature, measurements of receiver and overall system temperatures, and characterization of the RFI environment at each deployment site. We present an all-sky map synthesized between 139 MHz and 174 MHz using data from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5 steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that indicates what would be achievable with better foreground subtraction. We calculate angular power spectra ($C_\ell$) in a cold patch and determine them to be dominated by point sources, but with contributions from galactic synchrotron emission at lower radio frequencies and angular wavemodes. Although the cosmic variance of foregrounds dominates errors in these power spectra, we measure a thermal noise level of 310 mK at $\ell=100$ for a 1.46-MHz band centered at 164.5 MHz. This sensitivity level is approximately three orders of magnitude in temperature above the level of the fluctuations in 21cm emission associated with reionization.Comment: 13 pages, 14 figures, submitted to AJ. Revision 2 corrects a scaling error in the x axis of Fig. 12 that lowers the calculated power spectrum temperatur

Medium-resolution multispectral data from sentinel-2 to assess the damage and the recovery time of late frost on Vineyards

In a climate-change context, the advancement of phenological stages may endanger viticultural areas in the event of a late frost. This study evaluated the potential of satellite-based remote sensing to assess the damage and the recovery time after a late frost event in 2017 in northern Italian vineyards. Several vegetation indices (VIs) normalized on a two-year dataset (2018-2019) were compared over a frost-affected area (F) and a control area (NF) using unpaired two-sample t-test. Furthermore, the must quality data (total acidity, sugar content and pH) of F and NF were analyzed. The VIs most sensitive in the detection of frost damage were Chlorophyll Absorption Ratio Index (CARI), Enhanced Vegetation Index (EVI), and Modified Triangular Vegetation Index 1 (MTVI1) (-5.26%,-16.59%, and-5.77% compared to NF, respectively). The spectral bands Near-Infrared (NIR) and Red Edge 7 were able to identify the frost damage (-16.55 and-16.67% compared to NF, respectively). Moreover, CARI, EVI, MTVI1, NIR, Red Edge 7, the Normalized Difference Vegetation Index (NDVI) and the Modified Simple Ratio (MSR) provided precise information on the full recovery time (+17.7%, +22.42%, +29.67%, +5.89%, +5.91%, +16.48%, and +8.73% compared to NF, respectively) approximately 40 days after the frost event. The must analysis showed that total acidity was higher (+5.98%), and pH was lower (-2.47%) in F compared to NF. These results suggest that medium-resolution multispectral data from Sentinel-2 constellation may represent a cost-effective tool for frost damage assessment and recovery management

Estudio, diseño e implementación de la capa física para comunicaciones remotas utilizando tecnología NVIS

En els últims anys, les xarxes de comunicacions IoT han millorat significativament, tant respecte a la cobertura com a l'eficiència i el rendiment. Encara que aquestes millores són molt rellevants, no cobreixen la totalitat del territori mundial. Zones molt aïllades del món, com els pols o zones muntanyenques de difícil accés, no disposen d'aquesta mena de cobertura de dades, ja que les característiques del terreny limiten l'accés dels dispositius IoT en aquests entorns. Actualment, les solucions existents se centren en les comunicacions per satèl·lit que, si bé permeten la comunicació en aquests escenaris, tenen un cost econòmic molt elevat. D'altra banda, una possible solució seria l'ús de comunicacions HF. Gràcies a aquesta mena de comunicació es poden aconseguir velocitats de fins a 100 kbps, segons els estàndards i recerques prèvies. Una de les aplicacions de les comunicacions HF és la comunicació a través de la ionosfera. Aquest tipus d'enllaços proporcionen unes característiques ideals per a les comunicacions a llarga distància. En els últims quatre anys, el grup de recerca en tecnologies d'Internet (GRITS) de l'Escola d'Enginyeria de La Salle (Universitat Ramon Llull), s'ha centrat en les comunicacions ionosfèriques i, especialment, en la tecnologia NVIS (Near Vertical Incidence Skywave). En particular, ha posat el seu focus en les comunicacions amb la Base Antàrtica Joan Carles I. Aquest tipus de comunicació HF ofereix unes característiques ideals per a les comunicacions remotes de llarg abast, amb un radi de fins a 350 km i sense necessitat de visió directa entre els diferents transceptors. L'objectiu d'aquesta tesi és definir el millor escenari de comunicacions amb tecnologia NVIS per a una xarxa de cobertura IoT en entorns remots. Una de les principals metes és la disminució del consum en potència dels dispositius remots. Això proporcionarà una comunicació de llarg abast i maximitzarà el temps de vida de la bateria per a aquesta mena de dispositius, un factor primordial per a comunicacions IoT. A més, la solució proposada intenta mitigar el sobrecost econòmic que implicaria l'ús dels satèl·lits com a mitjà de comunicació, adaptant el desenvolupament de la tecnologia a dispositius de baix cost. Com a factor principal de millora, aquesta tesi se centra en la definició d'una capa física adaptada a l'entorn de comunicació NVIS. Per a optimitzar aquest enllaç, s'estudien les principals característiques d'un entorn wireless multicamí, el Doppler Shift, Doppler i Delay Spread, la qual cosa permet definir els temps de trama més adaptats a aquest canal. D'altra banda, es comparen les característiques de les modulacions QAM, PSK i FSK (d'ordre 2 a 32) en transmissions de molt baixa potència (de 0,5 W a 25 W) i en un entorn multicamí. Aquesta anàlisi permetrà definir la millor trama de comunicació, establint la capa física per a comunicacions NVIS en entorns remots. Finalment, i per a demostrar la viabilitat de la tecnologia desenvolupada en un entorn civil, es defineix i implementa un procés de transferència de coneixements del món acadèmic al món empresarial. S'estudien els diferents mercats on es podrien integrar aquest tipus de comunicacions, i es defineix una proposta de valor per al mercat de les comunicacions remotes, tot això amb la finalitat d'arribar a una conclusió tant de viabilitat econòmica com de necessitat de la tecnologia per a un escenari d'ús civil.En los últimos años, las redes de comunicaciones IoT han mejorado significativamente, tanto con respecto a la cobertura como a la eficiencia y el rendimiento. Aunque estas mejoras son muy relevantes, no cubren la totalidad del territorio mundial. Zonas muy aisladas del mundo, como los polos o zonas montañosas de difícil acceso, no disponen de este tipo de cobertura de datos, ya que las características del terreno limitan el acceso de los dispositivos IoT en estos entornos. Actualmente, las soluciones existentes se centran en las comunicaciones por satélite que, si bien permiten la comunicación en estos escenarios, tienen un coste económico muy elevado. Por otra parte, una posible solución sería el uso de comunicaciones HF. Gracias a este tipo de comunicación se pueden alcanzar velocidades de hasta 100 kbps, según los estándares e investigaciones previas. Una de las aplicaciones de las comunicaciones HF es la comunicación a través de la ionosfera. Este tipo de enlaces proporcionan unas características ideales para las comunicaciones a larga distancia. En los últimos cuatro años, el grupo de investigación en tecnologías de Internet (GRITS) de la Escuela de Ingeniería de La Salle (Universidad Ramon Llull), se ha centrado en las comunicaciones ionosféricas y, especialmente, en la tecnología NVIS (Near vertical incidence skywave). En particular, ha puesto su foco en las comunicaciones con la Base Antártica Juan Carlos I. Este tipo de comunicación HF ofrece unas características ideales para las comunicaciones remotas de largo alcance, con un radio de hasta 350 km y sin necesidad de visión directa entre los diferentes transceptores. El objetivo de esta tesis es definir el mejor escenario de comunicaciones con tecnología NVIS para una red de cobertura IoT en entornos remotos. Una de las principales metas es la disminución del consumo en potencia de los dispositivos remotos. Esto proporcionará una comunicación de largo alcance y maximizará el tiempo de vida de la batería para este tipo de dispositivos, un factor primordial para comunicaciones IoT. Además, la solución propuesta intenta mitigar el sobrecoste económico que implicaría el uso de los satélites como medio de comunicación, adaptando el desarrollo de la tecnología a dispositivos de bajo coste. Como factor principal de mejora, esta tesis se centra en la definición de una capa física adaptada al entorno de comunicación NVIS. Para optimizar este enlace, se estudian las principales características de un entorno wireless multitrayecto, el Doppler Shift, Doppler y Delay Spread, lo cual permite definir los tiempos de trama más adaptados a este canal. Por otra parte, se comparan las características de las modulaciones QAM, PSK y FSK (de orden 2 a 32) en transmisiones de muy baja potencia (de 0,5 W a 25 W) y en un entorno multitrayecto. Este análisis permitirá definir la mejor trama de comunicación, estableciendo la capa física para comunicaciones NVIS en entornos remotos. Finalmente, y para demostrar la viabilidad de la tecnología desarrollada en un entorno industrial, se define e implementa un proceso de transferencia de conocimientos del mundo académico al mundo empresarial. Se estudian los diferentes mercados donde se podrían integrar este tipo de comunicaciones, y se define una propuesta de valor para el mercado de las comunicaciones remotas, todo ello con el fin de llegar a una conclusión tanto de viabilidad económica como de necesidad de la tecnología para un escenario de uso civil.In the last years, IoT communications networks have improved significantly, both in terms of coverage and in terms of efficiency and performance. Although these improvements are very relevant, they do not cover the entire world territory. Very isolated areas of the world, such as the poles or mountainous areas that are difficult to access, do not have this type of data coverage, as the terrain characteristics limit the access of IoT devices in these environments. Currently, existing solutions are focused on satellite communications that, although they allow communication in these scenarios, have a very high economic cost. On the other hand, a possible solution would be the use of HF communications. Thanks to this type of communication, speeds of up to 100 kbps can be achieved, according to standards and previous research. One of the applications of HF communications is communication through the ionosphere. This type of link provides ideal characteristics for long distance communications. In the last four years, the research group on Internet technologies (GRITS) at the La Salle School of Engineering (Ramon Llull University), has focused on ionospheric communications and, especially, on NVIS technology (Near Vertical Incidence Skywave). In particular, it has focused on communications with the Juan Carlos I Antarctic Base. This type of HF communication offers ideal characteristics for long-range remote communications, with a radius of up to 350 km and without the need for direct vision between the different transceivers. The purpose of this thesis is to define the best NVIS technology communications scenario for an IoT coverage network in remote environments. One of the main goals is to decrease the power consumption of remote devices. This will provide long range communication and maximize battery life for these types of devices, a major factor for IoT communications. In addition, the proposed solution attempts to mitigate the economic over-cost that would be involved in using satellites as a means of communication, by adapting the development of the technology to low-cost devices. As a main improvement factor, this thesis focuses on the definition of a physical layer adapted to the NVIS communication environment. In order to optimize this link, the main characteristics of a multipath wireless environment, the Doppler Shift, Doppler and Delay Spread, are studied, allowing the definition of the most adapted frame times for this channel. Furthermore, the characteristics of QAM, PSK and FSK modulations (from order 2 to 32) in very low power transmissions (from 0.5 W to 25 W) and in a multipath environment are compared. This analysis will allow to define the best communication frame, establishing the physical layer for NVIS communications in remote environments. Finally, and in order to demonstrate the viability of the technology developed in an industrial environment, a process of knowledge transfer from the academic world to the business world is defined and implemented. The different markets where this type of communications could be integrated are studied, and a value proposal for the remote communications market is defined, all with the aim of reaching a conclusion on both the economic viability and the need for the technology for a non-military use scenario

Determining the electromagnetic constants of ground and analyzing HF propagation with the aid of a modern interferometric direction finder

Thesis (PhD)--University of Pretoria, 2018.Although high frequency (HF, 3 to 30 MHz) radio propagation (both skywave and ground wave) has been studied for more than a century and is a mature science at this point in time, some answers remain elusive and must be further investigated. The advent of modern, cost effective computers and especially Digital Signal Processing (DSP) techniques and hardware as implemented in an interferometric HF direction finder (DF) have opened exciting new opportunities to study and gain new insights into classic propagation phenomena that are due to the electromagnetic properties of an imperfect earth. These include the propagation loss and the tilt of a ground wave signal. An interferometric DF can also now add a new dimension to the study of the propagation of skywave HF signals through the ionosphere. Until recently it was challenging to analyse, in near real time, skywave ionospheric propagation modes between a transmitter and a receiver that monitors the signal. Received signal strength used to be one of the few available indicators of propagation conditions. During the course of this study, techniques were developed that utilises the elevation angle as measured by an interferometric DF and the output of a ray-tracing algorithm to study and identify propagation effects that the HF signal was subjected to. It is now possible to identify phenomena such as multi-hop and multi-layer propagation. The ionospheric layer(s) that refracted the received signal as well as the Optimum Working Frequency (OWF) for the circuit can now also be identified. The most stable region of the ionosphere for propagation over a specified circuit can also be determined with this new approach, thus helping to improve the reliability of HF communications. Accurate electromagnetic ground constants are required for applications such as the modelling of ground wave propagation of radio signals and determining the radiation characteristics of antennas above a real, imperfect earth. Accurate electromagnetic ground constants are thus paramount in any HF link planning or propagation study, but are not always available for a specific frequency and geographical location. A RF technique, Time Domain Reflectometry (TDR), implemented in modern, cost effective consumer equipment is used to determine the soil moisture content. With the aid of a previously published ground model, an easy to use method was developed to determine the electromagnetic ground parameters (conductivity and relative dielectric constant) at any radio frequency using the measured soil moisture content. This method offers significant advantages in terms of simplicity, speed and cost when compared with current techniques. It has been verified over the 2 to 30 MHz frequency range, but should be applicable up to 200 MHz, the upper frequency limit of the ground model used. An innovative application of an interferometric DF is to determine the forward wave tilt of a ground wave signal in the proximity of the DF antenna array. This application offers significant advantages in terms of simplicity and speed when compared to current manual techniques to determine wave tilt. The soil moisture content can be determined from the wave tilt and in conjunction with the ground model described above, an easy to use method was developed to determine the electromagnetic ground parameters with greater accuracy than is possible from the ITU publications. Having accurate ground electromagnetic constants in hand is very beneficial for the modelling of both ground wave and skywave propagation for the geographical location of the DF. Single Site Location (SSL) direction finding is a technique used to determine the origin (position of the transmitter) of a long-distance HF signal with the aid of a single, interferometric DF, an ionospheric model and a ray-tracing system. The elevation angle of the intercepted signal is used to calculate a ground range by modelling the path that the signal travelled through the ionosphere. With the measured direction (azimuth angle) and the calculated ground range, it is possible to determine the origin of the HF transmission. Simply being able to intercept (monitor) a signal and determining the wave angle (azimuth and elevation) with the aid of an interferometric DF does not guarantee the quality of the calculated SSL ground range. The reigning propagation conditions for the communications circuit must also be taken into consideration for optimum results. However, computing the performance of a SSL system is a complex problem with many variables to be considered. To overcome this difficulty, a quality factor, which only depends on the standard propagation metrics for HF communication links, was derived. Measured results are presented to demonstrate that this quality factor is a useful indicator of SSL performance.Electrical, Electronic and Computer EngineeringPhDUnrestricte