Wireless Communication Systems Based on Spatial Modulation MIMO

Spatial modulation (SM) is a unique single-stream, multiple-input multiple-output (MIMO) transmission technique. Unlike traditional MIMO schemes, SM sends out signals through a single active antenna, and achieves multiplexing gains by encoding information bits into the index of the currently active antenna. In contrast to multi-stream MIMO systems, this particular characteristic offers great superiority in two main aspects. Firstly, SM completely avoids inter-channel interference. Secondly, SM requires a single radio-frequency chain, regardless of the number of antennas used, and therefore exhibits a significant energy saving. However, the property of a single active antenna challenges the channel estimation process for SM: the transmit antennas have to be activated sequentially for sending pilot signals. As a result, the time consumed in pilot transmission is proportional to the number of transmit antennas. However, this fact has so far been neglected in related research. Also, published research on SM has focused on point-to-point communications, and few have covered a network perspective. In this thesis, a comprehensive study is undertaken on SM systems in single-user, multi-user and multi-cell scenarios. As a unique three-dimensional modulation scheme, SM enables a trade-off between the size of the signal constellation diagram and the size of the spatial constellation diagram. In this thesis, an optimum transmit structure is proposed for SM to employ an adaptive scale of antennas against channel correlations. Unlike traditional antenna selection methods, this new approach is not sensitive to fast fading, due to the exploitation of statistical channel state information (CSI) instead of instant CSI. The proposed transmit structure is demonstrated to have a near-optimal performance against exhaustive search, while achieving very low computational complexity. In addition, three novel methods are developed to improve the channel estimation process for SM. A first method estimates the entire MIMO channel by sending pilot signals through only one of the transmit antennas, among which the channel correlation is exploited. In a similar way but focusing on the receiver, a second method can improve the estimation accuracy without increasing the pilot sequence length. A third method balances the transmission power between pilot and data to minimise the bit error rate. A framework of combined channel estimation is also proposed, in which the three methods are jointly applied. Furthermore, the antenna allocation in multi-user SM is studied, in order to explore multi-user diversity gains. A method that jointly manages transmit antennas and receive antennas for all co-channel users is proposed. The aim of this new method is to maximise the channel capacity for each user, and the fairness among users is taken into account. It is demonstrated that the proposed method significantly improves the performance of multi-user SM, especially when serving a large number of users. Finally, a novel cooperative scheme is proposed for SM in a multi-cell scenario. Based on the concept of coordinated multi-point transmission (CoMP), this scheme enables the coordinated users to swap the base station antennas pertaining to them. A three-tier cellular architecture is further developed to switch between CoMP and the cooperative scheme

Multiscale Modeling of Inter-Vehicle Communication

Within this thesis, different modeling approaches at different scales in the domains of urban radio propagation, decentralized channel coordination, and information dissemination in inter-vehicle communication networks are investigated. The contributions reveal the suitability of existing models for network-oriented research, propose a novel information-centric modeling approach, and identify characteristics of inter-vehicle communication systems which determine key dependability aspects

Wireless energy harvesting for autonomous reconfigurable intelligent surfaces

In the current contribution, we examine the feasibility of fully-energy-autonomous operation of reconfigurable intelligent surfaces (RIS) through wireless energy harvesting (EH) from incident information signals. Towards this, we first identify the main RIS energy-consuming components and present a suitable and accurate energy-consumption model that is based on the recently proposed integrated controller architecture and includes the energy consumption needed for channel estimation. Building on this model, we introduce a novel RIS architecture that enables EH through RIS unit-cell (UC) splitting. Subsequently, we introduce an EH policy, where a subset of the UCs is used for beamsteering, while the remaining UCs absorb energy. In particular, we formulate a subset allocation optimization problem that aims at maximizing the signal-to-noise ratio (SNR) at the receiver without violating the RIS’s energy consumption demands. As a problem solution, we present low-complexity heuristic algorithms. The presented numerical results reveal the feasibility of the proposed architecture and the efficiency of the presented algorithms with respect to both the optimal and very high-complexity brute-force approach and the one corresponding to random subset selection. Furthermore, the results reveal how important the placement of the RIS as close to the transmitter as possible is, for increasing the harvesting effectiveness.This work was supported by the Luxembourg National Research Fund (FNR) under the CORE project RISOTTI (ref. 14773976), the European Commission’s Horizon 2020 research and innovation programme (ARIADNE) under grant agreement No. 871464, and the Digital Futures center.Peer ReviewedPostprint (published version

Arquitectura de Sistemas de Comunicaciones Tierra-Tierra y Aire-Tierra con Multiplexación Espacial

Tesis (DCI)--FCEFN-UNC, 2017La interacción autómata de múltiples tipos de dispositivos inteligentes (Smart Devices - SD) conforman una red conocida como internet de las cosas (Internet-of-Things - IoT) la cual ofrece potenciales beneficios para incrementar efectivamente la calidad de vida de las personas. Los potenciales beneficios del paradigma de IoT se apoyan en la integración a la red de IoT de todos los SD, a través de redes de comunicaciones entre máquinas (Machine-to-Machine - M2M). Los SD exhiben rango de comunicaciones inalámbricas limitado, debido al bajo costo y consumo de energía impuesto por el paradigma M2M. Consecuentemente, las comunicaciones entre máquinas M2M dependen de alguna infraestructura de comunicaciones, por ejemplo las redes celulares, que otorgue soporte de transporte de datos para dichos dispositivos y así realizar la integración efectiva de todos ellos a la red IoT. No obstante, debido al rango de cobertura limitado de los SD no todos ellos pueden integrarse de manera efectiva, como aquellos que operan en zonas urbanas poco frecuentadas por personas y zonas alejadas de la infraestructura de redes celulares, limitando la proyección de funcionamiento óptimo de la red IoT. Como la proyección del volumen de SD operando en simultáneo se vislumbra masivo, la combinación de tecnologías que despliegan múltiples antenas (Multiple-Input Multiple-Output - MIMO) y la diversidad multiusuario (Multi-User Diversity - MUD), inherente a un conjunto masivo de SD, tiene el potencial para brindar solución al rango limitado de cobertura de los SD. En la primera parte de esta Tesis se proponen y analizan aspectos de implementación de distintos receptores multiusuarios operando en una arquitectura de comunicaciones con diversidad en transmisión a lazo cerrado (Closed-Loop Transmit-Diversity - CL-TD) en canales MIMO, conformación de haz lineal (Linear BeamForming - LBF), selección de usuarios en canales MIMO con múltiples usuarios (Multi-User MIMO - MU-MIMO) en base a información de estado del canal en transmisión parcial (Channel State Information at the Transmitter side - CSIT) y operando en enlaces de canal Tierra-Tierra. En base a estos estudios se determinan cuáles son las estrategias de recepción más conveniente para el problema de rango de cobertura de los SD. Por otro lado, para aquellos SD que operan en zonas alejadas de infraestructuras de soporte de comunicaciones, se propone una infraestructura de comunicaciones alternativa a bordo de un vehículo aéreo autónomo no tripulado (Unmanned Aerial Vehicles - UAV). Sin embargo, para evaluar alguna propuesta de arquitectura de comunicaciones es necesario conocer el comportamiento de canal configurado en este tipo de escenario. Dado que en la literatura, los modelos de canal existentes hasta el momento son insuficientes para describir las características de los nuevos escenarios configurados por los UAV (Zonas rurales, urbanas y sub-urbanas) en vuelos de baja altura, otra contribución fundamental de esta Tesis es la propuesta y extensión de un modelo de canal MIMO de tres dimensiones. La misma considera la existencia de la componente con línea de vista (Line-of-Sight - LOS), la componente sin línea de vista (Non Line-of-Sight - NLOS) con distribuciones de dispersores (Scatterers) no-isotrópicos y las características de movilidad en ambos extremos del enlace. En base a esta propuesta de canal se evalúa una arquitectura de comunicaciones con CL-TD para canales MIMO-3D, LBF y mecanismos de selección de usuarios para canales MU-MIMO con CSIT parcial operando en enlaces de canal Aire-Tierra. En base a estos estudios se evalúa el desempeño de la arquitectura para estos nuevos escenarios