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.

Bridging the Gap between Physical Layer Emulation and Network Simulation

Abstract: Many of the simulations reported in wireless networking literature contain several abstractions at the physical layer and the corresponding channel models. In particular, the basic simulation unit assumed in such simulations is the frame (or packet), which omits considerations of the signal processing details at the physical layer, such as frame construction and reception. Due to this abstraction, available channel models for network simulators are applied to frames as a whole and cannot reflect properly the effects of fast fading or frequency-selective channels. Moreover, it is not possible to study the mechanisms of the physical layer and their impact on higher layers such as the MAC. Therefore, we propose to address the lack of accurate physical layer representation in modern network simulators by incorporating a physical layer emulator for OFDM-based IEEE~802.11 communications into the popular NS-3 simulator. In this paper, we outline the architecture of the physical layer emulator and present initial results which highlight the promise of the new architecture in providing more detailed simulations to the networking community. The additional memory and computational requirements of the new model are also discussed.

Internet on the Road via Inter-Vehicle Communications

Abstract: Driving means constantly changing location. This, in turn, means a constant demand for information on the current location and specifically for data on the surrounding traffic. In particular, there is a demand for sensor data from other cars such as data on braking sent from a preceding car, for data on the traffic flow on a route, and for information about sites located along a route. Although need for information pertaining to the close environment of the car is obvious, so far no intervehicle communications system for data exchange between vehicles and between roadside and vehicles has been put into operation. To promote the development of such an inter-vehicle communication system, the project “FleetNet – Internet on the Road” was set up by a consortium of six companies and three universities: DaimlerChrysler AG, GMD FOKUS, NEC Europe Ltd., Robert Bosch GmbH, Siemens AG, TEMIC TELEFUNKEN microelectronic GmbH, Universities of Mannheim and Hannover, and Technische Universität Hamburg-Harburg. The project is partly funded by the German Ministry of Education and Research. FleetNet started on September 1, 2000 and will end on December 31, 2003. FleetNet aims at the development and demonstration of a wireless ad hoc network for inter-vehicle communications. Key design requirements for FleetNet are the capability to distribute locally relevant data where generated and needed and to satisfy the vehicle drivers’ and passengers’ needs for location-dependent information and services. Location awareness and position data play a crucial role not only for FleetNet applications but also for the communication protocols deployed. This paper provides an overview of the FleetNet project: we describe FleetNet applications and services as well as Fleetnet’s technical challenges together with our current design choices.

Thoughts on a Protocol Architecture for Vehicular Ad-Hoc Networks

Abstract: In comparison to other communication networks, Vehicular Ad-hoc Networks (VANETs) have unique requirements with respect to applications, types of communication, self-organization and other issues. In order to meet these requirements, the structuring of functionalities into protocols and their interaction must be re-thought for VANETs. The traditional approach of decomposition of functionality into protocol layers (layered approach) and a protocol design specifically tailored to the needs of VANETs (unlayered approach) lead to two extreme and opposed manifestations of a potential VANET protocol architecture. From these two extreme approaches we derive a stack-based VANET protocol architecture that combines the strengths of both sides. Among the key features of this protocol architecture are VANET-specific protocol layers, a staircase approach for interaction among layers and the use of an information connector for cross-layer information exchange using the publisher/subscriber pattern. We believe that this protocol architecture provides a clear modular structure with flexibility for protocol interaction and information exchange at a reasonable complexity.

Optimal fractal coding is NP-hard

Abstract: In fractal compression a signal is encoded by the parameters of a contractive transformation whose fixed point (attractor) is an approximation of the original data. Thus fractal coding can be viewed as the optimization problem of finding in a set of admissible contractive transformations the transformation whose attractor is closest to a given signal. The standard fractal coding scheme based on the collage theorem produces only a suboptimal solution. We demonstrate by a reduction from MAXCUT that the problem of determining the optimal fractal code is NP-hard. To our knowledge, this is the first analysis of the intrinsic complexity of fractal coding. Additionally, we show that standard fractal coding is not an approximating algorithm for this problem.

Short Paper: An Empirical Analysis of Blockchain Forks in Bitcoin

Abstract: Temporary blockchain forks are part of the regular consensus process in permissionless blockchains such as Bitcoin. As forks can be caused by numerous factors such as latency and miner behavior, their analysis provides insights into these factors, which are otherwise unknown. In this paper we provide an empirical analysis of the announcement and propagation of blocks that led to forks of the Bitcoin blockchain. By analyzing the time differences in the publication of competing blocks, we show that the block propagation delay between miners can be of similar order as the block propagation delay of the average Bitcoin peer. Furthermore, we show that the probability of a block to become part of the main chain increases roughly linearly in the time the block has been published before the competing block. Additionally, we show that the observed frequency of short block intervals between two consecutive blocks mined by the same miner after a fork is conspicuously large. While selfish mining can be a cause for this observation, other causes are also possible. Finally, we show that not only the time difference of the publication of competing blocks but also their propagation speeds vary greatly.

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.