Evsen Yanmaz

Survey on Unmanned Aerial Vehicle Networks for Civil Applications: A Communications Viewpoint

The days where swarms of unmanned aerial vehicles (UAVs) will occupy our skies are fast approaching due to the introduction of cost-efficient and reliable small aerial vehicles and the increasing demand for use of such vehicles in a plethora of civil applications. Governments and industry alike have been heavily investing in the development of UAVs. As such it is important to understand the characteristics of networks with UAVs to enable the incorporation of multiple, coordinated aerial vehicles into the air traffic in a reliable and safe manner. To this end, this survey reports the characteristics and requirements of UAV networks for envisioned civil applications over the period 2000-2015 from a communications and networking viewpoint. We survey and quantify quality-of-service requirements, network-relevant mission parameters, data requirements, and the minimum data to be transmitted over the network. Furthermore, we elaborate on general networking related requirements such as connectivity, adaptability, safety, privacy, security, and scalability. We also report experimental results from many projects and investigate the suitability of existing communication technologies for supporting reliable aerial networking.

The Mathematical Theory of Dynamic Load Balancing in Cellular Networks

While many interesting dynamic load balancing schemes have been proposed for efficient use of limited bandwidth and to increase the capacity of congested or hot spots (or cells) in wireless networks, to date, a comprehensive mathematical framework which encompasses all of these schemes does not exist. In this paper, we provide a unified mathematical framework for dynamic load balancing, which leads to closed-form performance expressions for evaluating the performance of some of the most important dynamic load balancing strategies proposed in the literature. To the best of our knowledge, this is the first generic theoretical framework that can be used to evaluate the performance of many different dynamic load balancing schemes with simple closed-form results. The accuracy of the results predicted by these analytical expressions derived from the theoretical framework is checked by comparing these results with simulation results provided in the literature for well-known schemes.

On the design of self-organized cellular wireless networks

It has been observed that complex networks such as the Internet, World Wide Web, social networks, and biological systems are self-organizing in nature and exhibit some common properties such as the power law degree distribution. Recently, two models (i.e., small world and scale-free network models) have been proposed and successfully used to describe the nature of such networks. In this article we investigate whether these concepts can also be applied to cellular wireless networks, which typically do not exhibit self-organizing or scalability properties due to the limited range of the wireless nodes. Our ultimate goal is to design robust, reliable, scalable, and efficiently utilized wireless networks via self-organizing mechanisms.

Application-driven design of aerial communication networks

Networks of micro aerial vehicles (MAVs) equipped with various sensors are increasingly used for civil applications, such as monitoring, surveillance, and disaster management. In this article, we discuss the communication requirements raised by applications in MAV networks. We propose a novel system representation that can be used to specify different application demands. To this end, we extract key functionalities expected in an MAV network. We map these functionalities into building blocks to characterize the expected communication needs. Based on insights from our own and related real-world experiments, we discuss the capabilities of existing communications technologies and their limitations to implement the proposed building blocks. Our findings indicate that while certain requirements of MAV applications are met with available technologies, further research and development is needed to address the scalability, heterogeneity, safety, quality of service, and security aspects of multi- MAV systems.

Achieving air-ground communications in 802.11 networks with three-dimensional aerial mobility

Increasing availability of autonomous small-size aerial vehicles leads to a variety of applications for aerial exploration and surveillance, transport, and other domains. Many of these applications rely on networks between aerial nodes, that will have high mobility dynamics with vehicles moving in all directions in 3D space and positioning in different orientations, leading to restrictions on network connectivity. In this paper, we propose a simple antenna extension to 802.11 devices to be used on aerial nodes. Path loss and small-scale fading characteristics of air-to-ground links are analyzed using signal strength samples obtained via real-world measurements at 5 GHz. Finally, network performance in terms of throughput and number of retransmissions are presented. Results show that a throughput of 12Mbps can be achieved at distances in the order of 300m.

Channel measurements over 802.11a-based UAV-to-ground links

We analyze unmanned aerial vehicle (UAV)-to-ground links for an 802.11a-based small quadrotor UAV network with two on-board antennas via a set of field experiments. The paper presents our first results toward modeling the uplink and downlink channel and provide the path loss exponents for an open field and a campus scenario. We illustrate the impact of antenna orientation on the received signal strength and UDP throughput performance for different heights, yaws, and distances. When both antennas are horizontal (parallel to the flight direction plane), yaw differences can be handled, whereas a vertical antenna can assist against signal loss due to tilting of the UAV during acceleration/deceleration. Further work is required to analyze fading as well as UAV-UAV links in a multi-UAV network.

Connectivity versus area coverage in unmanned aerial vehicle networks

We investigate the area coverage and connectivity of an autonomous, unmanned aerial vehicle (UAV) network, whose goal is to monitor and sense a given area of interest in an efficient manner. To this end, we propose a connectivity-based mobility model that aims to sustain connectivity between the UAVs and the ground station. We compare coverage and connectivity performance of the proposed scheme with a coverage-based mobility scheme in several scenarios. Results illustrate the trade-off between achieving good spatial coverage and staying connected.

Selecting a Spatially Efficient Cooperative Relay

Cooperative relaying is a communication technique in wireless networks where neighboring nodes assist communication pairs to mitigate the negative effects of multi-path fading. The resulting performance strongly depends on the selected relays. Although a cooperative relay provides benefits to a given source-destination pair, overall network performance might be degraded due to the increased level of interference. So far almost all relay selection mechanisms consider mainly channel conditions to the potential relays. In this paper we propose a contention-based relay selection mechanism that can take into account also spatial efficiency of potential relays. For that the degree as well as relative position of the nodes are used for selection. With the proposed method a high successful relay selection probability can be achieved, while significantly reducing the amount of additional spatial resources blocked by the cooperative relay.

An Autonomous Multi-UAV System for Search and Rescue

This paper proposes and evaluates a modular architecture of an autonomous unmanned aerial vehicle (UAV) system for search and rescue missions. Multiple multicopters are coordinated using a distributed control system. The system is implemented in the Robot Operating System (ROS) and is capable of providing a real-time video stream from a UAV to one or more base stations using a wireless communications infrastructure. The system supports a heterogeneous set of UAVs and camera sensors. If necessary, an operator can interfere and reduce the autonomy. The system has been tested in an outdoor mission serving as a proof of concept. Some insights from these tests are described in the paper.

Stationary and Mobile Target Detection Using Mobile Wireless Sensor Networks

In this work, we study the target detection and tracking problem in mobile sensor networks, where the performance metrics of interest are probability of detection and tracking coverage, when the target can be stationary or mobile and its duration is finite. We propose a physical coverage-based mobility model, where the mobile sensor nodes move such that the overlap between the covered areas by different mobile nodes is small. It is shown that for stationary target scenario the proposed mobility model can achieve a desired detection probability with a significantly lower number of mobile nodes especially when the detection requirements are highly stringent. Similarly, when the target is mobile the coverage-based mobility model produces a consistently higher detection probability compared to other models under investigation.