550 GHz bandwidth photodetector on low-temperature grown molecular-beam epitaxial GaAs

in Electronics Letters (1998), 34(1998), 119-120

The authors demonstrate that a 550GHz bandwidth photodetector can be fabricated on low-temperature grown MBE GaAs. The pulse response shows 0.4 and 0.6ps rise and fall times, respectively. The bandwidth ... [more ▼]

The authors demonstrate that a 550GHz bandwidth photodetector can be fabricated on low-temperature grown MBE GaAs. The pulse response shows 0.4 and 0.6ps rise and fall times, respectively. The bandwidth is in agreement with a value calculated using a carrier lifetime of 0.2ps, measured by femtosecond time-resolved reflectivity, and a capacitance of 0.014fF/um2, determined from microwave measurements. The device bandwidth is RC limited. [less ▲]

§§ 58 bis 62 WpHG betreffend Datenbereitstellungsdienste

in Kapitalmarktrechtskommentar (2020)

5D Super Yang-Mills on Y p,q Sasaki-Einstein manifolds

E-print/Working paper (2013)

On any simply connected Sasaki-Einstein five dimensional manifold one can construct a super Yang-Mills theory which preserves at least two supersymmetries. We study the special case of toric Sasaki ... [more ▼]

On any simply connected Sasaki-Einstein five dimensional manifold one can construct a super Yang-Mills theory which preserves at least two supersymmetries. We study the special case of toric Sasaki-Einstein manifolds known as Y p,q manifolds. We use the localisation technique to compute the full perturbative part of the partition function. The full equivariant result is expressed in terms of certain special function which appears to be a curious generalisation of the triple sine function. As an application of our general result we study the large N behaviour for the case of single hypermultiplet in adjoint representation and we derive the N 3-behaviour in this case. [less ▲]

5G AND BEYOND NETWORKS WITH UAV: TRAJECTORY DESIGN AND RESOURCE ALLOCATION

Doctoral thesis (2021)

Over the past few years, unmanned aerial vehicle (UAV)-enabled wireless communications have attracted considerable attention from both academia and industry due to their high mobility, low cost, strong ... [more ▼]

Over the past few years, unmanned aerial vehicle (UAV)-enabled wireless communications have attracted considerable attention from both academia and industry due to their high mobility, low cost, strong light-of-sight communication links, and ease of deployment. Specifically, UAVs can be deployed to serve as aerial base stations (BSs), relays, power sources, etc., to support ground users (GUs) in various scenarios such as surveillance missions, search and rescue, crop monitoring, delivery of goods, data collection, emergency communications, secrecy communications, space-air-ground communications, etc. Despite many advantages, UAV-enabled communications are not without limitations. The limitations of UAVs have imposed technical restrictions on weight, size, and energy capability, thereby affecting the durability and performance of UAVs. The key goal of this dissertation is to propose and develop new frameworks and efficient optimization algorithms to solve novel challenging problems, facilitate the design and deployment of UAV-enabled communications. Consequently, these proposed algorithms can become one of the foundations for deploying UAVs in future wireless systems. Specifically, this dissertation investigates different UAV communication systems by addressing several important research problems through four emerging scenarios: 1) Design UAV trajectory based on traveling salesman problem with time window (TSPTW); 2) Full-duplex (FD) UAV relay-assisted emergency communications in Internet of Things (IoT) networks; 3) Backscatter- and cache-assisted UAV communications; and 4) Satellite- and cache-assisted UAV communications in 6G aerial networks. In the first scenario, we provide the coarse trajectory for the UAV based on TSPTW, which has not been investigated in UAV communications yet. Concretely, we propose two trajectory design algorithms based on TSPTW, namely heuristic algorithm and dynamic programming (DP)-based algorithm, and they are compared with exhaustive search and traveling salesman problem (TSP)-based methods. Based on the feasible path obtained from proposed algorithms, we minimize the total UAV’s energy consumption for each given path via a joint optimization of the UAV velocities in all hops. Simulation results show that the energy consumption value of DP is very close to that of the exhaustive algorithm with greatly reduced complexity. Based on this work, an efficient TSPTW-based algorithm can be used as an initialized trajectory for designing a joint problem of UAV trajectory and other communications factors (e.g., communication scheduling, transmit power allocation, time allocation), which are challenges. We then study the case of a FD UAV relaying system in IoT networks. Specifically, a UAV can be deployed as a flying base station (BS) to collect data from time-constrained IoT devices and then transfer it to a ground gateway (GW). Especially, the impact of latency constraint for the uplink (UL) and downlink (DL) transmission utilizing FD or half-duplex (HD) mode is investigated. Using the proposed system model, we aim to maximize the total number of served IoT devices subject to the maximum speed constraint of the UAV, total traveling time constant, UAV trajectory, maximum transmit power at the devices/UAV, limited cache size of the UAV, and latency constraints for both UL and DL. Next, we attempt to maximize the total throughput subject to the number of served IoT devices. The outcome of this work will motivate a new framework for UAV-aided communications in disaster or emergency communications. Next, a novel system model that considers SWIPT, backscatter and caching in UAV wireless networks is developed. Based on this model, we aim to maximize the system throughput by jointly optimizing the dynamic time splitting (DTS) ratio and the UAV’s trajectory with caching capability at the UAV. This is the first work that jointly considers wireless power transfer (WPT), caching, and BackCom in UAV communications, which provides a potential solution for a battery-free drone system that can fly for a long period in the sky to support the terrestrial communication systems. Finally, a novel system model for effective use of LEO satellite- and cache-assisted UAV communication is proposed and studied. Specifically, caching is provided by the UAV to reduce backhaul congestion, and the LEO satellite assists the UAV’s backhaul link. In this context, we aim to maximize the minimum achievable throughput per ground user (GU) by jointly optimizing cache placement, the UAV’s transmit power, bandwidth allocation, and trajectory with a limited cache capacity and operation time. The outcomes of this work can provide a new design framework for Satellite-UAV-terrestrial communications that includes two tiers, i.e., the backhaul link from satellite to UAV and the access link from UAV to ground users, which imposes new challenges and was not investigated before. [less ▲]

5G Space Communications Lab: Reaching New Heights

in Proceedings of the 18th International Conference on Distributed Computing in Sensor Systems (DCOSS) (2022)

5G-NTN GEO-based In-Lab Demonstrator using OpenAirInterface5G

in 11th Advanced Satellite Multimedia Conference (2022, September)

The integration of 5G with Non-Terrestrial Network (NTN) components is going through a series of technological advancements and soon satellites will be a part of the 5G ecosystem. Early demonstrators ... [more ▼]

The integration of 5G with Non-Terrestrial Network (NTN) components is going through a series of technological advancements and soon satellites will be a part of the 5G ecosystem. Early demonstrators, especially based on open-source implementations, are essential to support further research. In this work, we discuss the ongoing activities and developments related to the project 5G-Enabled Ground Segment Technologies OverThe-Air Demonstrator (5G-GoA) which has been funded under the ESA-ARTES program. The vision of 5G-GoA is developing and implementing suitable modifications in the 5G New Radio (NR) standard for enabling direct radio access to 5G services using a transparent GEO satellite. For this purpose, we have used OpenAirInterface(OAI) which is a Software Defined Radio (SDR) based open-source implementation of the 5G-NR protocol stack. We adapted it to address the challenges caused by the excessive round-trip delay in GEO satellites. Our solutions encompass all the layers of the 5G protocol stack: The physical layer (e.g. synchronization) up to upper layer implementations (e.g. timers and random-access procedure) of the Radio Access Network. Our modifications comply with the specifications mentioned for 5GNTN in the recently frozen 3GPP Release-17. An end-to-end demonstrator has been developed for in-lab validation over a satellite channel emulator prior to over-the-satellite testing. Our initial experiments show promising results and the feasibility of direct access to 5G services through transparent GEO satellites. [less ▲]

5G-SpaceLab

Poster (2021, April 19)

The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are ... [more ▼]

The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are concentrated and orbiting missions (single spacecraft or constellations) around the Earth, Moon or Mars will be particularly challenging. The standardization of the 5G Non-Terrestrial Networks (NTN) has already begun [1], and nothing prevents 5G from becoming a common communications standard supporting space resource missions [2]. The 5G Space Communications Lab (5G-SpaceLab) is an interdisciplinary experimental platform, funded by the Luxembourg Space Agency and is part of the Space Research Program of SnT. The lab allows users to design and emulate realistic space communications and control scenarios for the next-generation of space applications. The capabilities of the 5G-SpaceLab testbed combine the experience of different disciplines including space communications, space and satellite mission design, and space robotics. The most relevant include the demonstration of SDR 5G NTN terminals including NB-IoT, emulation of space communications channel scenarios (e.g. link budget, delay, Doppler…), small satellite platform and payload design and testing, satellite swarm flight formation, lunar rover and robotic arm control and AI-powered telerobotics. Earth-Moon communications is one of the scenarios demonstrated in the 5G-SpaceLab. Bidirectional communication for the teleoperation of lunar rovers for near real-time operations including data collection and sensors feedback will be tested. AI-based approaches for perception and control will be developed to overcome communication delays and to provide safer, trustworthy, and efficient remote control of the rovers. [1] 3GPP Release 17 Timeline. [Online]. Available: https://www.3gpp.org/release-17 [2] Nokia, Nokia selected by NASA to build first ever cellular network on the Moon. [Online]. Available: https://www.nokia.com/about-us/news/releases/2020/10/19/nokia-selected-by-nasa-to-build-first-ever-cellular-network-on-the-moon/ [less ▲]

5th international workshop on principles of engineering service-oriented systems (PESOS 2013)

in Proceedings of the 2013 International Conference on Software Engineering (ICSE '13), San Francisco, CA USA (2013)

§§ 6 bis 15 WpHG betreffend die Eingriffsbefugnisse der BaFin

in Kapitalmarktrechtkommentar (2019)

6-hydroxydopamine-induced Parkinson's disease-like degeneration generates acute micro- and astrogliosis in the nigrostriatal system but no Bioluminescence Imaging detectable alteration in adult neurogenesis

in European Journal of Neuroscience (2016)