Christian Wietfeld

Bio: Christian Wietfeld is an academic researcher from Technical University of Dortmund. The author has contributed to research in topics: Smart grid & Cellular network. The author has an hindex of 35, co-authored 430 publications receiving 5242 citations. Previous affiliations of Christian Wietfeld include Information Technology University & RWTH Aachen University.

Using Public Network Infrastructures for UAV Remote Sensing in Civilian Security Operations

Abstract: IntroductionAs a result of advances in communication, computation, sensor and energy storage technologies, as well as carbon fiber-reinforced plastic materials, micro unmanned aerial vehicles (UAV) are available at affordable prices. On this basis many new application areas, such as the in-depth reconnaissance and surveillance of major incidents, will be possible. Uncontrolled emissions of liquid or gaseous contaminants in cases of volcanic eruptions, large fires, industrial incidents, or terrorist attacks can be analyzed by utilizing UAV (Figure 1). Hence, the use of cognitive Unmanned Aerial Systems (UAS) for distributing mobile sensors in incident areas is in general a significant value added for remote sensing, reconnaissance, surveillance, and communication purposes.1Figure 1: Deployment Scenario: Chemical Plume Detection with an Autonomous Micro UAV Mesh Network.In the near future police departments, fire brigades and other homeland security organizations will have access to medium- and small-size UAV and will integrate them in their work flow. The use of non-military frequencies and civil communication technologies gains in importance for purposes of safety and security missions, since the frequency pool is limited and nearly exhausted. In particular, regionally organized public authorities and small rescue organizations like fire brigades often have insufficient access to frequencies and expensive communication equipment. Thus, using civil mobile communication systems is often the only effective workaround for homeland security organizations.This is also one of the major issues for wireless communication in the area of unmanned aerial systems (UAS). Besides flight regulation, wireless communication is an important aspect of UAS as telemetry information (navigation, control, guidance) and sensor data usually have to be transmitted to a mission control center (MCC) in nearly real-time. Today, there is no viable alternative for this type of transmission besides using civil mobile communication networks. Unfortunately, there is no foreseeable solution in terms of frequency assignment for UAS. For efficient sensor coverage of large industrial and incident areas, fast and flexible strategies for collecting sensor data through an autonomous, reliably connected UAV need to be developed. In this article we focus on the civilian concepts of operations (CONOPS) for UAV, in particular for small-scale UAV. Viable concepts on the system level for leveraging public wireless communication networks for UAV-based cognitive remote sensing are presented with respect to both existing constraints and user requirements.The article is structured as follows: we first present the current state of the art and related research activities in the area of UAS communication. Civilian concepts of operations (CONOPS) for purposes of homeland security are discussed in the next section. Subsequent sections address the requirements, concepts and solutions for Air-to-Air (A2A), Air-to-Ground (A2G), and UAS-backend communication. On this basis we then show a methodology for agent-based UAV-mobility for areas with insufficient communication. The article ends suggestions for future research.Related Work and ProjectsSeveral research investigations have been done in the area of UAS. However, UAS communication aspects mostly address proprietary communication systems and usually do not consider public wireless infrastructures since these systems have been mostly deployed by military organizations in the past. Hence, we identify a demand for more in-depth contributions for UAS communication by means of public wireless networks.Tiwari and others have studied the placement planning problem of an airborne network.2 They offer a toolbox to optimize the ground coverage while maintaining a certain degree of reliability and connectivity. By introducing practical scenarios for deployment, the interaction between communication design and mobility planning is shown. …

Investigation of Air-to-Air Channel Characteristics and a UAV Specific Extension to the Rice Model

Abstract: One of the key challenges while operating multiple unmanned aerial systems (UAS) is to maintain reliable air-to-ground (A2G) and air-to-air (A2A) communication links. In previous works, the authors have introduced a communication-aware mobility behavior which takes communication constraints and overall mission goals into account. In order to further improve the mobility behavior with the help of a channel estimator, accurate models of the dynamic A2A channel are a necessity. In this work, we extend the Rice channel model to account for multipath effects introduced by the flight altitude of unmanned vehicles on an IEEE 802.11 communication link. Based on laboratory measurements and several experimental flights the influence on the channel is evaluated and exemplary model parameters are derived.

Design of an UWB indoor-positioning system for UAV navigation in GNSS-denied environments

Abstract: Commonly used unmanned aerial vehicle (UAV) platforms rely on the use of global navigation satellite system (GNSS) receivers for navigation. To enable the autonomous navigation of cooperative UAVs in GNSS-denied environments, the use of an ultra-wideband (UWB) positioning system is proposed. This paper discusses the design and evaluation of a practical and cooperative UWB positioning system using newly available integrated radio frequency hardware and antennas. Constellation-aware parameters, as well as other effects like antenna characteristics, are taken into consideration. A non-line-of-sight rejection is implemented based on the ratio of the first path compared to the power of the cumulated channel impulse response. An experiment covering a range of positions and orientations is conducted to gain a broad, representative set of results to assess the system accuracy in real-life usage. In a first experiment the system performance achieves a root-mean-square error of under 10 cm in the horizontal plane and under 20 cm in the three-dimensional space with a probability of 95 %. A GNSS emulation system is implemented to evaluate the real-time in-flight use of the UWB positioning system on an experimental UAV carrier. A proof of concept is given that the GNSS emulation may be used with commercially available UAV platforms to augment those systems with indoor navigation capabilities.

RF Mesh Systems for Smart Metering: System Architecture and Performance

Abstract: This paper describes the system architecture and the performance evaluation of a Radio Frequency (RF) mesh based system for smart energy management applications in the Neighborhood Area Network (NAN). The RF mesh system presented in this paper leverages the Industrial, Scientific and Medical (ISM) band at 902-928 MHz and is based on frequency hopping spread spectrum (FHSS). The performance evaluation is based on a geographical model of the deployment scenario and implements geographical routing combined with appropriate radio propagation models. The results show that the system is able to handle Smart Metering communication traffic with a high reliability provided potential coverage gaps are properly filled with repeater nodes. The proposed methodology allows the identification of coverage gaps, which may cause bottlenecks in the network, prior to deployment and therefore supports efficient and reliable deployment and operation of the system.

Role-Based Connectivity Management with Realistic Air-to-Ground Channels for Cooperative UAVs

Abstract: Ad-hoc aerial sensor networks leveraging MUAVs (Micro Unmanned Aerial Vehicles) are ideally suited to cost-efficiently explore unknown or hostile environments for example in case of incidents producing harmful gases or radiation In this manuscript we present results on the investigations of communication-aware steering algorithms for cooperative MUAV swarms The mission objective is to achieve a maximum spatial exploration efficiency with the simultaneous ability to self-optimize the communication links by exploiting controlled mobility While our previous work has mainly considered the performance of the Air-to-Air mesh network, in this paper we focus on the Air-to-Ground-link connectivity control To achieve appropriate communication links to a central sensor data sink even while exploring larger search areas, an agent-based role management strategy is used to provide suitable multi-hop connectivity The novel algorithms are investigated for static as well as dynamically changing environments Key results include a detailed realistic aerial channel characterization and network dimensioning analysis considering numbers of MUAVs and density of ground stations vs exploration speed and sensor data latency

Wireless communications with unmanned aerial vehicles: opportunities and challenges

Abstract: Wireless communication systems that include unmanned aerial vehicles promise to provide cost-effective wireless connectivity for devices without infrastructure coverage. Compared to terrestrial communications or those based on high-altitude platforms, on-demand wireless systems with low-altitude UAVs are in general faster to deploy, more flexibly reconfigured, and likely to have better communication channels due to the presence of short-range line-of-sight links. However, the utilization of highly mobile and energy-constrained UAVs for wireless communications also introduces many new challenges. In this article, we provide an overview of UAV-aided wireless communications, by introducing the basic networking architecture and main channel characteristics, highlighting the key design considerations as well as the new opportunities to be exploited.

Unmanned aerial systems for photogrammetry and remote sensing: A review

Abstract: We discuss the evolution and state-of-the-art of the use of Unmanned Aerial Systems (UAS) in the field of Photogrammetry and Remote Sensing (PaRS). UAS, Remotely-Piloted Aerial Systems, Unmanned Aerial Vehicles or simply, drones are a hot topic comprising a diverse array of aspects including technology, privacy rights, safety and regulations, and even war and peace. Modern photogrammetry and remote sensing identified the potential of UAS-sourced imagery more than thirty years ago. In the last five years, these two sister disciplines have developed technology and methods that challenge the current aeronautical regulatory framework and their own traditional acquisition and processing methods. Navety and ingenuity have combined off-the-shelf, low-cost equipment with sophisticated computer vision, robotics and geomatic engineering. The results are cm-level resolution and accuracy products that can be generated even with cameras costing a few-hundred euros. In this review article, following a brief historic background and regulatory status analysis, we review the recent unmanned aircraft, sensing, navigation, orientation and general data processing developments for UAS photogrammetry and remote sensing with emphasis on the nano-micro-mini UAS segment.

Energy-Efficient UAV Communication With Trajectory Optimization

Abstract: Wireless communication with unmanned aerial vehicles (UAVs) is a promising technology for future communication systems. In this paper, assuming that the UAV flies horizontally with a fixed altitude, we study energy-efficient UAV communication with a ground terminal via optimizing the UAV’s trajectory, a new design paradigm that jointly considers both the communication throughput and the UAV’s energy consumption. To this end, we first derive a theoretical model on the propulsion energy consumption of fixed-wing UAVs as a function of the UAV’s flying speed, direction, and acceleration. Based on the derived model and by ignoring the radiation and signal processing energy consumption, the energy efficiency of UAV communication is defined as the total information bits communicated normalized by the UAV propulsion energy consumed for a finite time horizon. For the case of unconstrained trajectory optimization, we show that both the rate-maximization and energy-minimization designs lead to vanishing energy efficiency and thus are energy-inefficient in general. Next, we introduce a simple circular UAV trajectory, under which the UAV’s flight radius and speed are jointly optimized to maximize the energy efficiency. Furthermore, an efficient design is proposed for maximizing the UAV’s energy efficiency with general constraints on the trajectory, including its initial/final locations and velocities, as well as minimum/maximum speed and acceleration. Numerical results show that the proposed designs achieve significantly higher energy efficiency for UAV communication as compared with other benchmark schemes.

Survey of Important Issues in UAV Communication Networks

Abstract: Unmanned aerial vehicles (UAVs) have enormous potential in the public and civil domains. These are particularly useful in applications, where human lives would otherwise be endangered. Multi-UAV systems can collaboratively complete missions more efficiently and economically as compared to single UAV systems. However, there are many issues to be resolved before effective use of UAVs can be made to provide stable and reliable context-specific networks. Much of the work carried out in the areas of mobile ad hoc networks (MANETs), and vehicular ad hoc networks (VANETs) does not address the unique characteristics of the UAV networks. UAV networks may vary from slow dynamic to dynamic and have intermittent links and fluid topology. While it is believed that ad hoc mesh network would be most suitable for UAV networks yet the architecture of multi-UAV networks has been an understudied area. Software defined networking (SDN) could facilitate flexible deployment and management of new services and help reduce cost, increase security and availability in networks. Routing demands of UAV networks go beyond the needs of MANETS and VANETS. Protocols are required that would adapt to high mobility, dynamic topology, intermittent links, power constraints, and changing link quality. UAVs may fail and the network may get partitioned making delay and disruption tolerance an important design consideration. Limited life of the node and dynamicity of the network lead to the requirement of seamless handovers, where researchers are looking at the work done in the areas of MANETs and VANETs, but the jury is still out. As energy supply on UAVs is limited, protocols in various layers should contribute toward greening of the network. This paper surveys the work done toward all of these outstanding issues, relating to this new class of networks, so as to spur further research in these areas.

A Tutorial on UAVs for Wireless Networks: Applications, Challenges, and Open Problems

Abstract: The use of flying platforms such as unmanned aerial vehicles (UAVs), popularly known as drones, is rapidly growing. In particular, with their inherent attributes such as mobility, flexibility, and adaptive altitude, UAVs admit several key potential applications in wireless systems. On the one hand, UAVs can be used as aerial base stations to enhance coverage, capacity, reliability, and energy efficiency of wireless networks. On the other hand, UAVs can operate as flying mobile terminals within a cellular network. Such cellular-connected UAVs can enable several applications ranging from real-time video streaming to item delivery. In this paper, a comprehensive tutorial on the potential benefits and applications of UAVs in wireless communications is presented. Moreover, the important challenges and the fundamental tradeoffs in UAV-enabled wireless networks are thoroughly investigated. In particular, the key UAV challenges such as 3D deployment, performance analysis, channel modeling, and energy efficiency are explored along with representative results. Then, open problems and potential research directions pertaining to UAV communications are introduced. Finally, various analytical frameworks and mathematical tools, such as optimization theory, machine learning, stochastic geometry, transport theory, and game theory are described. The use of such tools for addressing unique UAV problems is also presented. In a nutshell, this tutorial provides key guidelines on how to analyze, optimize, and design UAV-based wireless communication systems.