Hannes Hartenstein

Bio: Hannes Hartenstein is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Vehicular ad hoc network & Wireless ad hoc network. The author has an hindex of 55, co-authored 234 publications receiving 14515 citations. Previous affiliations of Hannes Hartenstein include University of Mannheim & University of Freiburg.

Bug Fixes on the IEEE 802.11 DCF module of the Network Simulator ns-2.28

Abstract: The Network Simulator 2 (ns-2) is largely the most used simulator in the Ad Hoc research community. However, the 802.11 DCF module implemented in the default distribution of ns-2 presents some bugs, i.e., discordances with the IEEE 802.11 Standard specifications. We present in this Technical Report the result of an extensive analysis of both the IEEE 802.11 DCF specification and the ns-2 module. We first describe the discordances found with respect to the different DCF.s procedures. Second, we describe the different behavior corresponding to the physical layer capture model that current wireless interfaces present. Finally we provide in the Appendix all source code modified in the different ns-2.28 files. All modified source code files can be found for download at http://dsn.tm.uni-karlsruhe.de/ns-2.28-DCF-PHY-UKA.php.

Lossless acceleration of fractal image compression by fast convolution

Abstract: In fractal image compression the encoding step is computationally expensive. We present a new technique for reducing the computational complexity. It is lossless, i.e., it does not sacrifice any image quality for the sake of the speedup. It is based on a codebook coherence characteristic to fractal image compression and leads to a novel application of the fast Fourier transform-based convolution. The method provides a new conceptual view of fractal image compression. This paper focuses on the implementation issues and presents the first empirical experiments analyzing the performance benefits of the convolution approach to fractal image compression depending on image size, range size, and codebook size. The results show acceleration factors for large ranges up to 23 (larger factors possible), outperforming all other currently known lossless acceleration methods for such range sizes.

Statistical Analysis of the FleetNet Highway Movement Patterns

Abstract: The major objective of the FleetNet project [5, 2] was to develop a platform for inter-vehicle communication based on the principles of ad-hoc communication. In its process, unicast datagram routing served as one of the research focuses to identify and conquer the challenges of data forwarding in vehicular scenarios. Among others, car movement on highways was a scenario we paid attention to. To serve as a basis for network simulation, DaimlerChrysler provided realistic highway movement traces resulting from their own vehicular movement research [3]. This document is the complement to the Technical Report [4] where we describe the work done on the DaimlerChrysler traces in order to: a) model bidirectional scenarios, b) obtain Tcl scenarios compatible with the ns-2 simulator, and c) understand the vehicle distribution and movement of the resulting scenarios from a connectivity point of view. This report consists of the whole statistical evaluation of the basic set of scenarios listed in [4] and available to the VANET (Vehicular Ad-Hoc Network) community at [1]. We highly recommend the reading of [4], which describes the structure of this document and all parameters being analyzed.

Analysis of a Location Service for a Position-based Routing in Mobile Ad Hoc Networks

Abstract: Position-based routing in a mobile ad hoc network requires geographic addresses. Thus, a node that wants to send a packet to some target node has to know the target's (approximate) current position. In order to provide each node's position to the other network nodes, a distributed location service has to be used. J. Li et al. recently put forward a promising approach called the Grid Location Service' (GLS). In this paper we provide some analyses and evaluations of GLS by means of simulation with ns-2 beyond the results of the original paper. We present quantitative results with respect to location query failure rate and bandwidth consumption. We analyze in detail why queries failed and how the query failure rate can be decreased for scenarios with a low density of nodes.

Lossless acceleration of fractal image encoding via the fast Fourier transform

Abstract: In fractal image compression the encoding step is computationally expensive. We present a new technique for reducing the encoding complexity. It is lossless, i.e., it does not sacrifice any image reconstruction quality for the sake of speedup. It is based on a codebook coherence characteristic of fractal image compression and leads to a novel application of the fast Fourier transform-based cross correlation. The proposed method is particularly well suited for use with highly irregular image partitions for which most traditional (lossy) acceleration schemes lose a large part of their efficiency. For large ranges our approach outperforms other currently known lossless acceleration methods.

Random graphs

Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Spray and wait: an efficient routing scheme for intermittently connected mobile networks

Abstract: Intermittently connected mobile networks are sparse wireless networks where most of the time there does not exist a complete path from the source to the destination. These networks fall into the general category of Delay Tolerant Networks. There are many real networks that follow this paradigm, for example, wildlife tracking sensor networks, military networks, inter-planetary networks, etc. In this context, conventional routing schemes would fail.To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention, which can significantly degrade their performance. Furthermore, proposed efforts to significantly reduce the overhead of flooding-based schemes have often be plagued by large delays. With this in mind, we introduce a new routing scheme, called Spray and Wait, that "sprays" a number of copies into the network, and then "waits" till one of these nodes meets the destination.Using theory and simulations we show that Spray and Wait outperforms all existing schemes with respect to both average message delivery delay and number of transmissions per message delivered; its overall performance is close to the optimal scheme. Furthermore, it is highly scalable retaining good performance under a large range of scenarios, unlike other schemes. Finally, it is simple to implement and to optimize in order to achieve given performance goals in practice.

Dedicated Short-Range Communications (DSRC) Standards in the United States

Abstract: Wireless vehicular communication has the potential to enable a host of new applications, the most important of which are a class of safety applications that can prevent collisions and save thousands of lives. The automotive industry is working to develop the dedicated short-range communication (DSRC) technology, for use in vehicle-to-vehicle and vehicle-to-roadside communication. The effectiveness of this technology is highly dependent on cooperative standards for interoperability. This paper explains the content and status of the DSRC standards being developed for deployment in the United States. Included in the discussion are the IEEE 802.11p amendment for wireless access in vehicular environments (WAVE), the IEEE 1609.2, 1609.3, and 1609.4 standards for Security, Network Services and Multi-Channel Operation, the SAE J2735 Message Set Dictionary, and the emerging SAE J2945.1 Communication Minimum Performance Requirements standard. The paper shows how these standards fit together to provide a comprehensive solution for DSRC. Most of the key standards are either recently published or expected to be completed in the coming year. A reader will gain a thorough understanding of DSRC technology for vehicular communication, including insights into why specific technical solutions are being adopted, and key challenges remaining for successful DSRC deployment. The U.S. Department of Transportation is planning to decide in 2013 whether to require DSRC equipment in new vehicles.

PORs: Proofs of Retrievability for Large Files

Abstract: In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

Securing vehicular ad hoc networks

Abstract: Vehicular networks are very likely to be deployed in the coming years and thus become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness and efficiency.