Coherent Cooperative Relaying In Low Mobility Wireless Multiuser Networks
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Coherent Cooperative Relaying in Low Mobility Wireless Multiuser Networks
In this thesis, several important aspects of cooperative wireless multiuser networks are investigated. The focus lies on coherent two-hop relaying networks where several amplify-and-forward (AF) relays assist the communication between multiple source-destination pairs. First, the impact of local oscillator (LO) imperfections and I/Q imbalance at the relays on two-hop relaying is investigated. A special focus lies on the comparison between frequency division duplexing (FDD) and time division duplexing (TDD) relays. Based on the observation that the direction in which a channel between two wireless nodes is measured has an impact on the estimate, phase synchronization requirements for coherent relaying networks are then found. Several channel estimation protocols that differ in the direction in which the single-hop channels are measured are furthermore identi'ed and their performance is compared. Next, a very simple phase synchronization scheme is presented that provides a set of relays with a common LO phase. Two coherent beamforming schemes, namely multiuser zero-forcing (MUZF) and multiuser minimum mean squared error (MMSE) relaying, are then investigated. Finally, a real-world demonstrator for distributed wireless communication networks (called RACooN Lab) is presented. It was used to implement coherent cooperative communication schemes on a practical two-hop relaying network.
Localization and Posture Recognition via Magneto-Inductive and Relay-Aided Sensor Networks
Author: Henry Ruben Lucas Schulten
language: en
Publisher: Logos Verlag Berlin GmbH
Release Date: 2022-12-15
Body-centric wireless sensor networks are expected to enable future technologies such as medical in-body micro robots or unobtrusive smart textiles. These technologies may advance personalized healthcare as they allow for tasks such as minimally invasive surgery, in-body diagnosis, and continuous activity recognition. However, the localization of individual sensor nodes within such networks or the determination of the entire network topology still pose challenges that need to be solved. This work provides both theoretic and simulative insights to enable the required sub-millimeter localization accuracy of such sensors using magneto-inductive networks. It identifies inherent localization issues such as the asymmetry of the position estimation in magneto-inductive networks and outlines how such issues may be addressed by using passive relays or cooperation. It further proposes a novel approach to recognize the entire structure of a magneto-inductive network using simple impedance measurements and clusters of passive tags. This approach is evaluated extensively by simulation and experiment to demonstrate the feasibility of low-cost human body posture recognition.
Magneto-Inductive Communication and Localization
Author: Gregor Dumphart
language: en
Publisher: Logos Verlag Berlin GmbH
Release Date: 2022-06-15
Utilizing magnetic induction for wireless communication, wireless powering, passive relaying, and localization could enable massive wireless sensor applications with tiny nodes in challenging media, foremost biomedical in-body sensor networks. This work investigates the performance limits of these unique wireless systems with hardly any assumptions. As a foundation, a general system model and an interface to communication theory are developed. A major part of this work identifies two crucial magneto-inductive fading channels: that between randomly oriented coils and that caused by a nearby swarm of resonant passive relay coils. The analysis yields important technological implications. Based thereon, an investigation of wirelessly-powered in-body sensors is conducted, revealing their active and passive data transmission capabilities. Finally, a treatise of magneto-inductive node localization develops algorithms that perform near identified accuracy limits in theory and practice.