Terahertz (THz) band represents the unused frequency band between the microwave and optical bands and lies in the range of frequencies between 0.1 to 10 THz. As a result, the THz signal generation can be done using electronic or photonic circuits. Moreover, the channel gain has hybrid features from both microwave and optical bands allowing to reap the benefits of each band. Adopting such a technology can mitigate the spectrum scarcity and introduce a substantial solution to other systems such as visible light communications. Despite of the generous bandwidth, the THz communications suffer from high attenuation that increases with adopted frequency similar to the microwave frequency band. Furthermore, THz communications are subject to a different type of attenuation called Molecular Absorption, that depends on the chemical nature of the ambiance air. Thus, THz transmitters need to use extra power and high antenna gains to overcome signal loss and compensate the short distance range limitation. In this thesis, we investigate the pathloss model to compute the overall attenuation faced by the THz wave for different frequencies and weather conditions. Then, we use the THz technology to support the operation of uplink networks using directional narrow beams. We optimize the uplink communication network resource represented in the frequency bands and the assigned power in order to minimize the total power consumption while achieving a specific quality of service. Furthermore, we investigate the impact of weather conditions and the system’s requirements in order to guarantee a better performance.

Ultrawideband (UWB) is one of the most promising communication technologies in recent times with the promise of high data rates and spectral reuse. This work analyses the outdoor and outdoor-to-indoor propagating characteristics of the UWB pulse, which can be of the order of a few gigahertz in bandwidth. The aim of the thesis is to provide the parameters needed in order to develop a channel model for such cases. The channel model would then play an important role in determining physical layer (PHY) solutions to optimally exploit these characteristics. The measurements carried out on the Virginia Tech campus are used to compute parameters such as path loss, penetration loss and delay statistics. These are carried out in multiple frequency bands and the results are compared across frequency bands to determine effect of different frequency levels on the parameters. Finally the results are analyzed with respect to similar parameters obtained in other measurement campaigns in an attempt to evaluate the performance of Ultrawideband vis-à-vis narrowband systems. / Master of Science

Indoor use of wireless systems poses one of the biggest design challenges. It is difficult to predict the propagation of a radio frequency wave in an indoor environment. To assist in deploying the above systems, characterization of the indoor radio propagation channel is essential. The contributions of this work are two-folds. First, in order to build a model, extensive field strength measurements are carried out inside two different buildings. Then, path loss exponents from log-distance path loss model and standard deviations from log-normal shadowing, which statistically describe the path loss models for a different transmitter receiver separations and scenarios, are determined. The purpose of this study is to characterize the indoor channel for 802.11 wireless local area networks at 2.4 GHz frequency. This thesis presents a channel model based on measurements conducted in commonly found scenarios in buildings. These scenarios include closed corridor, open corridor, classroom, and computer lab. Path loss equations are determined using log-distance path loss model and log-normal shadowing. The chi-square test statistic values for each access point are calculated to prove that the observed fading is a normal distribution at 5% significance level. Finally, the propagation models from the two buildings are compared to validate the generated equations.

En esta Tesis Doctoral se realiza una caracterización experimental de las pérdidas de propagación del canal radio vehicular basada en una extensa campaña de medidas realizada en diferentes escenarios de propagación, todos ellos potenciales entornos de comunicaciones vehiculares. Se han realizado medidas en escenarios urbanos, suburbanos, rurales y de autovía, con condiciones reales de tráfico rodado, diferentes densidades de vehículos y condiciones de propagación. La sonda de canal empleada en las medidas ha sido diseñada e implementada con el propósito de realizar una caracterización en banda estrecha permitiendo analizar el efecto de las pérdidas de propagación y desvanecimiento multicamino. Las medidas se han realizado en la banda DSRC (Dedicated Short-Range Communications) a 5,9 GHz, adoptada en EEUU y Europa para comunicaciones vehiculares, y en la banda de 700 MHz propuesta por Japón para este tipo de comunicaciones. En este sentido, los resultados mostrados en esta Tesis Doctoral a 700 MHz son los primeros realizados en esta banda de frecuencia. Se han propuesto diferentes métodos de análisis de las medidas realizadas, permitiendo un extenso estudio de los parámetros que caracterizan las pérdidas de propagación. Se ha analizado el canal radio vehículo a vehículo (V2V, Vehicular-to-Vehicular) y el canal vehículo a infraestructura (V2I, Vehicular-to-Infrastructure), estableciendo un modelo lineal entre las pérdidas de propagación y el logaritmo de la distancia entre el transmisor y receptor. Se trata de un modelo sencillo, pero bastante exacto, que permite una fácil implementación en simuladores de redes vehiculares. A diferencia de otros trabajos previos, que solamente analizan valores medios de los parámetros del modelo de pérdidas, en esta tesis se presentan resultados que permiten conocer el rango de variación de dichos parámetros En la investigación realizada se ha analizado el impacto que las condiciones de propagación, en lo que respecta a línea de visión directa y obstrucción de la misma, tienen sobre el comportamiento de la atenuación introducida por el canal radio. Los resultados derivados de esta Tesis Doctoral pueden ser utilizados el diseño y evaluación de protocolos de comunicación bajo condiciones de propagación próximas a la realidad, así como en el diseño y planificación de las futuras redes vehiculares. / Fernández González, HA. (2014). Caracterización experimental de las pérdidas de propagación en comunicaciones vehiculares a 700 MHz y 5,9 GHz [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/40370 / TESIS

Cooperative wireless communication is an attractive technique to explore the spatial channel resources by coordination across multiple links, which can greatly improve the communication performance over single links. In this dissertation, we study the cooperative multi-link channel properties by geometric approaches in body area networks (BANs) and cellular networks respectively.<p><p>In the part of BANs, the dynamic narrowband on-body channels under body motions are modeled statistically on their temporal and spatial fading based on anechoic and indoor measurements. Common body scattering is observed to form inter-link correlation between links closely distributed and between links having synchronized movements of communication nodes. An analytical model is developed to explain the physical mechanisms of the dynamic body scattering. The on-body channel impacts to simple cooperation protocols are evaluated based on realistic measurements. <p><p>In the part of cellular networks, the cluster-level multi-link COST 2100 MIMO channel model is developed with concrete modeling concepts, complete parameterization and implementation methods, and a compatible structure for both single-link and multi-link scenarios. The cluster link-commonness is introduced to the model to describe the multi-link properties. The multi-link impacts by the model are also evaluated in a distributed MIMO system by comparing its sum-rate capacity at different ratios of cluster link-commonness. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished