On Computation and Application of k Most Locally-Optimal Paths in Road Networks

For some applications, e.g. route planning services, it is desirable to answer a point-to-point shortest path query on a road network with a set of alternative paths. We discuss the general requirements for such sets of paths such as shortness, diversity, etcetera. As a measure to rank reasonable alternatives we propose the local optimality ratio, because it implicitly covers all of these requirements. We present an algorithm that computes the k best alternatives in terms of this measure

Efficient Communication Concepts for Low-Earth-Orbit Pico-Satellite Formations

Advances in miniaturization during the last decades have enabled the construction of small spacecraft with total masses reaching down to 1kg and below. At the same time standardization of components, interfaces, and platforms for the design of small satellites have further reduced their development costs. This trend has recently made formations of several small satellites in favor of one large unit an economically feasible alternative for university-scale organizations. While the satellite-formation approach provides new opportunities regarding Earth observation applications, it also poses new challenges to their communication system: the increased number of nodes at large distances and therefore propagation delays complicates the problem of medium access; the distributed collection of Earth observation data creates the necessity to gather the data over different links and possibly multiple hops. At the same time, the simultaneous operation of a number of identical satellites performing one task cooperatively can lead to redundancy in the data that needs to be communicated; exploiting this redundancy improves the overall efficiency of the communication system. In this work we discuss design approaches for communication protocols for Earth-observing satellite formations. In doing so we cover several layers from medium access control over network and transport up-to and including compression of payload data. Cooperative position awareness beaconing is nowadays required for vessels at the high seas and serves as a convenient example for the in-orbit reception of data from large terrestrial sensor networks. We demonstrate how a purpose-made medium access control protocol can improve both, terrestrial performance for cooperative awareness and in-orbit overhearing for the purpose of global tracking. Regarding higher network layers we discuss modern coding techniques like network coding and distributed source coding. These are less frequently used in terrestrial general-purpose communication networks like the Internet but can be employed to take advantage of the communication redundancy that is inherent to satellite formation operation. We show how use cases that differ in terms of kind of payload data and network topology each can benefit from their own, best-suited communication technique. We find that network coding is well-suited for over-the-air programming of satellite formations, that is, for ground-station-to-satellite broadcast transmissions. To adapt the concept of random linear network coding to typical topologies of satellite-and-ground-station networks, we introduce a novel decoding algorithm that enables protocols to use simpler feedback mechanism. Satellite-to-ground-station transmissions of multiple satellites' payload measurement data is often correlated across nodes. Here we demonstrate the applicability of distributed source coding techniques to increase the efficiency of communication resource utilization. As a common bottom line that applies to all of these subtopics we conclude in the end that in Earth-observing satellite formations, there is a plethora of different types of information redundancy across the satellites. The exploitation thereof allows tailored communication protocols to significantly outperform their state-of-the-art terrestrial counterparts

SUMO 2016 – Traffic, Mobility, and Logistics

Dear reader, You are holding in your hands a volume of the series „Reports of the DLR-Institute of Transportation Systems“. We are publishing in this series fascinating, scientific topics from the Institute of Trans- portation Systems of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt e.V. – DLR) and from his environment. We are providing libraries with a part of the circulation. Outstanding scientific contributions and dissertations are here published as well as projects reports and proceedings of conferences in our house with different contributors from science, economy and politics. With this series we are pursuing the objective to enable a broad access to scientific works and results. We are using the series as well as to promote practically young researchers by the publication of the dissertation of our staff and external doctoral candidates, too. Publications are important milestones on the academic career path. With the series „Reports of the DLR-Institute of Transportation Systems / Berichte aus dem DLR-Institut für Verkehrssystemtechnik“ we are widening the spectrum of possible publications with a building block. Beyond that we understand the communication of our scientific fields of research as a contribution to the national and international research landscape in the fields of automotive, railway systems and traffic management. With this volume we publish the proceedings of the SUMO Conference 2016 which was held from 23rd to 25th May 2016 with a focus on traffic, mobility, and logistics. SUMO is an open source tool for traffic simulation that provides a wide range of traffic planning and simulation functionalities.The conference proceedings offer an overview of the applicability of the SUMO tool suite as well as its universal extensibility due to the availability of the source code. The major topic of this fourth edition of the SUMO conference are the different facets of moving objects occurring as personal mobility and freight delivery as well as communicating networks of intelligent vehicles. Several articles cover heterogeneous traffic networks, junction control and new traffic model extensions to the simulation. Subsequent specialized issues such as disaster management aspects and applying agile development techniques to scenario building are targeted as well. At the conference the international user community exchanged their experiences in using SUMO. With this volume we provide an insight to these experiences as inspiration for further projects with the SUMO suite