Ultra Wideband

Ultra wideband (UWB) has advanced and merged as a technology, and many more people are aware of the potential for this exciting technology. The current UWB field is changing rapidly with new techniques and ideas where several issues are involved in developing the systems. Among UWB system design, the UWB RF transceiver and UWB antenna are the key components. Recently, a considerable amount of researches has been devoted to the development of the UWB RF transceiver and antenna for its enabling high data transmission rates and low power consumption. Our book attempts to present current and emerging trends in-research and development of UWB systems as well as future expectations

Feedback Mechanisms for Centralized and Distributed Mobile Systems

The wireless communication market is expected to witness considerable growth in the immediate future due to increasing smart device usage to access real-time data. Mobile devices become the predominant method of Internet access via cellular networks (4G/5G) and the onset of virtual reality (VR), ushering in the wide deployment of multiple bands, ranging from TVWhite Spaces to cellular/WiFi bands and on to mmWave. Multi-antenna techniques have been considered to be promising approaches in telecommunication to optimize the utilization of radio spectrum and minimize the cost of system construction. The performance of multiple antenna technology depends on the utilization of radio propagation properties and feedback of such information in a timely manner. However, when a signal is transmitted, it is usually dispersed over time coming over different paths of different lengths due to reflections from obstacles or affected by Doppler shift in mobile environments. This motivates the design of novel feedback mechanisms that improve the performance of multi-antenna systems. Accurate channel state information (CSI) is essential to increasing throughput in multiinput, multi-output (MIMO) systems with digital beamforming. Channel-state information for the operation of MIMO schemes (such as transmit diversity or spatial multiplexing) can be acquired by feedback of CSI reports in the downlink direction, or inferred from uplink measurements assuming perfect channel reciprocity (CR). However, most works make the assumption that channels are perfectly reciprocal. This assumption is often incorrect in practice due to poor channel estimation and imperfect channel feedback. Instead, experiments have demonstrated that channel reciprocity can be easily broken by multiple factors. Specifically, channel reciprocity error (CRE) introduced by transmitter-receiver imbalance have been widely studied by both simulations and experiments, and the impact of mobility and estimation error have been fully investigated in this thesis. In particular, unmanned aerial vehicles (UAVs) have asymmetric behavior when communicating with one another and to the ground, due to differences in altitude that frequently occur. Feedback mechanisms are also affected by channel differences caused by the user’s body. While there has been work to specifically quantify the losses in signal reception, there has been little work on how these channel differences affect feedback mechanisms. In this dissertation, we perform system-level simulations, implement design with a software defined radio platform, conduct in-field experiments for various wireless communication systems to analyze different channel feedback mechanisms. To explore the feedback mechanism, we then explore two specific real world scenarios, including UAV-based beamforming communications, and user-induced feedback systems

On geometry-base statistical channel models for MIMO wireles communications

El uso de sistemas de comunicación de banda ancha de múltiple entradamúltiple salida (Multiple Input Multiple Output MIMO) es actualmente objeto de un interés considerable. Una razón para esto es el reciente desarrollo de sistemas de comunicación móvil de tercera generación (3G) y superiores, tales como la tecnología de banda ancha Wideband Code Division Multiple Access (WCDMA, por sus siglas en inglés), la cual proporciona canales de radio de 5 MHz de ancho de banda. Para el diseño y la simulación de estos sistemas de radio móviles que usan propagación inalámbrica MIMO (como Wideband-CDMA por ejemplo), necesitamos modelos de canal que provean la requerida información espacial y temporal necesaria para el estudio de tales sistemas, esto es, los parámetros básicos de modelado en los dominios del espacio y el tiempo. Como ejemplo podemos mencionar, el valor cuadrático medio de la dispersión del retardo (Delay spread DS) el cual está directamente relacionado a la capacidad de un sistema de comunicación específico y nos da una idea aproximada de la complejidad del receptor. En esta tesis, se propone un modelo basado en geometría con enfoque en grupos (clusters) y es utilizado para el análisis en los dominios del espacio y el tiempo para condiciones estacionarias, y para representar los perfiles de potencia-angulo-retardo (Power Delay Angle Profiles PDAPs) de los componentes multi-trayectoria en ambientes urbanos. Además, se han derivado soluciones en formas cerradas para las expresiones en el dominio del ángulo (espacial) y del tiempo. La investigación previa sobre el modelado de canales cubre una amplia variedad de aspectos en varios niveles de detalle, incluyendo análisis para condiciones no estacionarias. Sin embargo el trabajo presentado en la literatura no incluye las relaciones entre los grupos (cluster) físicos y los PDAPs. El modelo propuesto basado en grupos (clusters) puede ser usado para mejorar aún más el desempeño en condiciones estacionarias de los sistemas de comunicaciones móviles actuales y futuros tales como los sistemas de comunicación MIMO de banda ancha. En la tesis también se presenta un análisis en el dominio del ángulo (espacial) y del tiempo respectivamente, a través de las funciones densidad de probabilidad (PDF) de la dirección de llegada (Direction of Arrival DOA) y el tiempo de llegada (Time of Arrival TOA) para el modelo basado en grupos. A fin de evaluar las funciones de probabilidad teóricas derivadas, éstas han sido comparadas con resultados experimentales publicados en la literatura. La comparación con estos resultados experimentales muestran una buena concordancia, no obstante la técnica de modelado presentada en esta tesis se encuentra limitada a condiciones estacionarias del canal. La condición de no estacionariedad se ubica más allá del alcance de esta tesis, es decir, el modelo propuesto no incorpora el efecto Doppler en los análisis

Characterisation of MIMO radio propagation channels

Due to the incessant requirement for higher performance radio systems, wireless designers have been constantly seeking ways to improve spectrum efficiency, link reliability, service quality, and radio network coverage. During the past few years, space-time technology which employs multiple antennas along with suitable signalling schemes and receiver architectures has been seen as a powerful tool for the implementation of the aforementioned requirements. In particular, the concept of communications via Multiple-Input Multiple-Output (MIMO) links has emerged as one of the major contending ideas for next generation ad-hoc and cellular systems. This is inherently due to the capacities expected when multiple antennas are employed at both ends of the radio link. Such a mobile radio propagation channel constitutes a MIMO system. Multiple antenna technologies and in particular MIMO signalling are envisaged for a number of standards such as the next generation of Wireless Local Area Network (WLAN) technology known as 802.1 ln and the development of the Worldwide Interoperability for Microwave Access (WiMAX) project, such as the 802.16e. For the efficient design, performance evaluation and deployment of such multiple antenna (space-time) systems, it becomes increasingly important to understand the characteristics of the spatial radio channel. This criterion has led to the development of new sounding systems, which can measure both spatial and temporal channel information. In this thesis, a novel semi-sequential wideband MIMO sounder is presented, which is suitable for high-resolution radio channel measurements. The sounder produces a frequency modulated continuous wave (FMCW) or chirp signal with variable bandwidth, centre frequency and waveform repetition rate. It has programmable bandwidth up to 300 MHz and waveform repetition rates up to 300 Hz, and could be used to measure conventional high- resolution delay/Doppler information as well as spatial channel information such as Direction of Arrival (DOA) and Direction of Departure (DOD). Notably the knowledge of the angular information at the link ends could be used to properly design and develop systems such as smart antennas. This thesis examines the theory of multiple antenna propagation channels, the sounding architecture required for the measurement of such spatial channel information and the signal processing which is used to quantify and analyse such measurement data. Over 700 measurement files were collected corresponding to over 175,000 impulse responses with different sounder and antenna array configurations. These included measurements in the Universal Mobile Telecommunication Systems Frequency Division Duplex (UMTS-FDD) uplink band, the 2.25 GHz and 5.8 GHz bands allocated for studio broadcast MIMO video links, and the 2.4 GHz and 5.8 GHz ISM bands allocated for Wireless Local Area Network (WLAN) activity as well as for a wide range of future systems defined in the WiMAX project. The measurements were collected predominantly for indoor and some outdoor multiple antenna channels using sounding signals with 60 MHz, 96 MHz and 240 MHz bandwidth. A wide range of different MIMO antenna array configurations are examined in this thesis with varying space, time and frequency resolutions. Measurements can be generally subdivided into three main categories, namely measurements at different locations in the environment (static), measurements while moving at regular intervals step by step (spatial), and measurements while the receiver (or transmitter) is on the move (dynamic). High-scattering as well as time-varying MIMO channels are examined for different antenna array structures

Channel Simulators for MmWave and 5G Applications

Along with the tremendous growth of extremely high traffic demand, 5G radio access technology, is becoming the core component to support massive and multifarious connected devices and real-time, and to offer high reliability wireless communications with high data rate. And millimeter-wave (mmWave) range with a huge frequency spectrum from 3 GHz to 300GHz will perfectly meet the multi-gigabit communicative demand. However, mmWave usage also generally brings new challenges, such as coping with high attenuation or path losses. As an effective method to evaluate the performance of the new concept in communication networks, nowadays, several channel models and simulators have been proposed and developped, such as, WINNER, COST-2100, IMT-Advanced, METIS, NYU Wire-less and QuaDRiGa etc. The thesis goals have been to offer an overview of the advantages and disadvantages of various mmWave channel models existing in the literature, based on the published literature, and to compare based on simulations some of the main features of two selected open-source models, namely the WINNER 2 and QuaDRiGa channel models. In the future, more mmWave channel models are planned to be tested and simulated for a better understanding of their suitability for various mmWave applications

Wireless Friendliness Evaluation of Building Materials as Reflectors

The enormous popularity of wireless devices has prompted a rapid growth of indoor wireless traffic. To meet the high data demand and avoid inconvenient usages of a room, indoor base stations (BSs) and Wi-Fi access points (APs) with large-scale multiple-input multiple-output (MIMO) antenna arrays are likely to be deployed in the vicinity of a wall, which therefore results in non-negligible interactions between indoor electromagnetic (EM) wave propagations and building materials. The reflection characteristics of building materials, which depend on their intrinsic EM and physical properties, play a crucial role in indoor wireless communications. However, the relationship between the material properties and the indoor wireless performance has not been sufficiently studied. In this thesis, wireless friendliness is proposed as a new metric to measure the impact of a building material on indoor wireless performance as a function of its EM and physical properties. The main objectives are to develop wireless friendliness evaluation schemes for building materials as reflectors on indoor line-of-sight (LOS) MIMO communications, and to provide insights into the appropriate design and/or selection of building materials according to their wireless friendliness. To achieve these objectives, the thesis presents four major contributions. The first contribution is to propose a new two-ray channel model and a new multipath channel model that incorporate both the LOS path and the wall reflection (WR) path for indoor LOS MIMO downlink transmissions. For the first time, the relative permittivity (EM property) and thickness (physical property) of a building material are encapsulated into the channel models through the reflection coefficient of the building material, which provides theoretical prerequisites for the subsequent tractable analysis. The second contribution is to reveal the analytical relationship between the relative permittivity and thickness of building materials and the MIMO channel capacity. By exploiting the expressions of indoor wireless capacity and their asymptotic forms, four effective metrics for evaluating the wireless friendliness of building materials are proposed, i.e., the spatially averaged capacity, the spatially averaged logarithmic eigenvalue sum (LES), the spatially averaged logarithmic eigenvalue product (LEP), and the upper-bound outage probability, which are all over the room of interest. The third contribution is to develop the evaluation schemes for the wireless friendliness of building materials. The optimal values of the relative permittivity and thickness of a building material that maximise the indoor wireless capacity are obtained, shedding light on the selection and/or design of a building material accordingly, and thus paving the way for wireless friendly architectural design. The fourth contribution is to analyse the effects of the WR from building materials on the per-antenna power distribution across a precoded antenna array at a BS or an AP deployed near a wall. An uneven power distribution across antenna elements may reduce the efficiencies of their corresponding radio frequency (RF) power amplifiers. How the per-antenna power distribution changes with the building material’s relative permittivity and thickness is investigated, providing guidelines on the selection and/or design of a building material that alleviates the unevenness of per-antenna power distribution. Simulation results validate the correctness of analytical results as well as the effectiveness of the four proposed evaluation metrics, and demonstrate that the EM and physical properties of building materials have to be delicately selected or designed to avoid the risk of reducing indoor wireless capacity and RF power amplifier efficiency. More specifically, the inappropriate choices of relative permittivity and thickness of a building material may reduce the indoor wireless capacity by up to 13.5% or cause severe unevenness as large as 8 dB in the per-antenna power distribution across a precoded antenna array. The outcomes of this thesis would enable appropriate design and/or selection of building materials for building designers, e.g., civil engineers and architects, and provide wireless-friendliness information for communications engineers