Sascha Schnaufer

Position-based unicast routing for city scenarios

In vehicular ad-hoc networks unicast packet forwarding can be separated into the one-dimensional highway case and the two-dimensional city case; in this paper, we deal with the latter. We survey existing position-based routing protocols and present GRANT, our own approach of greedy routing with an abstract neighbor table. We simulate each protocol in our city scenario of Karlsruhe, consisting of streets with a length of 66 km, 390 junctions, and radio obstacles derived from high-definition satellite images. We also simulate the protocols with a FACE-2- and a distance vector-based recovery strategy. As a result we propose GRANT as a routing protocol for unicast city scenarios.

Vehicular ad-hoc networks: from vision to reality and back

VANETs, or vehicular ad-hoc networks, have recently gained scientific and commercial interest. In fact, they have drawn many people from neighboring fields like general mobile ad-hoc networks (MANETs), into their wake. In this invited paper, we discuss the history of vehicular ad-hoc networks from our perspective. In detail, we will show the early vision of creating a huge MANET that would facilitate cheap and ubiquitous communication on the ISM bands, and how this vision was reduced to cars sending emergency information in a geographically limited area. Also, we will describe how new challenges emerge from these new constraints, and then argue that VANETs are still an interesting research area

Beacon-based short message exchange in an inner city environment

In this paper, we proposes a method to utilize the huge number of IEEE 802.11 access points in an inner city environment to distribute information such as local sensor values, votes or short text messages. Due to the overlapping channels on IEEE 802.11b/g it is possible to receive packets from neighboring channels by overhearing. This fact allows every access point to monitor a part of the frequency band without switching the current radio channel. Our novel idea is to add user data to network layer beacon packets which every access point continuously send on a user-selected radio channel. This method allows transferring small size messages between access points or an access point and a mobile device without any reconfiguration like disabling the WLAN encryption. We conduct a measurement in the inner city of Mannheim, Germany to evaluate the typical density and distribution of access points in such an environment. We then use the measured data to calculate for every access point the expected reception probability on the street segments around. Based on these statistics, we appraise the reception probabilities of the access points among each other and perform a simulation study to estimate the size of the dissemination area that can be reached. Additionally, we analyze the required time to distribute the information to all reachable access points. Based on the measurement and simulation results, we can conclude that the estimated connectivity of an ad-hoc network based on access points is sufficient to disseminate information in the proximity.

Automatic identification of fingerprint regions for quick and reliable location estimation

One of the drawbacks of location fingerprinting systems is the effort that is necessary to set up and update the fingerprint database. In this paper, we propose a novel approach to significantly reduce this effort. We split the area of operation into a grid of quadratic cells and then combine these cells into larger regions of similar signal properties using a clustering algorithm and a novel similarity measure. Thus, less training data is required, and it can be collected in a more efficient way: We move through the area of operation on predefined trajectories and interpolate the approximate position for each measurement. In addition, by storing only one fingerprint for each region, we reduce the computational requirements of the location fingerprinting algorithm considerably. Since the radio measurements are quite similar in such a region, it is hard to estimate the exact location within the region; thus we do not lose much accuracy by clustering. An evaluation of our approach shows that it achieves an accuracy that is sufficient for most location-based services and at the same time reduces the effort for the collection of the training data to a mere walk of the area of operation.

REWARD a Real World Achievement and record database

We propose a system for acquiring, maintaining, and communicating Real-World Achievements. The concept is based on virtual world systems that are in common use in current Massively Multiplayer Online Games (MMOG) like World of Warcraft or Warhammer Online. The system design is centered around a global database of achievement definitions and individual progress.

Achievement notification in a real-world achievement system

We propose a global system for acquisition, maintenance and communication of achievements in the real-world. The main focus of the proposal lies on a context-aware notification service for achievements. Users of the system can browse the achievement web application and will only get notifications of users within the same context. The definition of context is based on the network infrastructure of the client accessing the system. Our server utilizes information derived from IP-routing traces to build the notification groups.

Proximity Detection and Message Exchange in WLANs

We present a novel system that allows small handheld devices to detect other devices in the local proximity and to exchange messages with them. The client devices use WLAN to access the system via a web interface and do not require additional software or modification of the devices operating system. The physical closeness of client devices is estimated based on their signal strengths measured by the systems access points. A major advantage compared to indoor positioning systems is the fact that our system does not require a training phase. We conduct a comprehensive evaluation to demonstrate the practicability of our approach.

A real-world achievement system

We propose a system for the acquisition, maintenance, and communication of Real-World Achievements. The concept is based on online entertainment systems like Microsofts XBox Live or virtual worlds like World of Warcraft. The system design is centered around a global database of achievement definitions and individual progress. Focus is put on flexibility to track achievement-related actions and instantaneous notification of obtained achievements. We have tested our system at a major international conference, and conclude that our approach is suitable for implementing a Real World Achievement System.

BSMX: message exchange between unassociated WLAN devices

Beacon-based Short Message eXchange (BSMX) is a system to exchange small-sized messages between unassociated WLAN devices. We implemented BSMX for the Android operating system and developed several applications to demonstrate the potential of our novel approach.