Ralf Kernchen

Analytical Study of the IEEE 802.11p MAC Sublayer in Vehicular Networks

This paper proposes an analytical model for the throughput of the enhanced distributed channel access (EDCA) mechanism in the IEEE 802.11p medium-access control (MAC) sublayer. Features in EDCA such as different contention windows (CW) and arbitration interframe space (AIFS) for each access category (AC) and internal collisions are taken into account. The analytical model is suitable for both basic access and the request-to-send/clear-to-send (RTS/CTS) access mode. Different from most of existing 3-D or 4-D Markov-chain-based analytical models for IEEE 802.11e EDCA, without computation complexity, the proposed analytical model is explicitly solvable and applies to four access categories of traffic in the IEEE 802.11p. The proposed model can be used for large-scale network analysis and validation of network simulators under saturated traffic conditions. Simulation results are given to demonstrate the accuracy of the analytical model. In addition, we investigate service differentiation capabilities of the IEEE 802.11p MAC sublayer.

Performance study of a Green Light Optimized Speed Advisory (GLOSA) application using an integrated cooperative ITS simulation platform

This paper proposes a Green Light Optimized Speed Advisory (GLOSA) application implementation in a typical reference area, and presents the results of its performance analysis using an integrated cooperative ITS simulation platform. Our interest was to monitor the impacts of GLOSA on fuel and traffic efficiency by introducing metrics for average fuel consumption and average stop time behind a traffic light, respectively. For gathering the results we implemented a traffic scenario defining a single route through an urban area including two traffic lights. The simulations are varied for different penetration rates of GLOSA-equipped vehicles and traffic density. Our results indicate that GLOSA systems could improve fuel consumption and reduce traffic congestion in junctions.

CLWPR — A novel cross-layer optimized position based routing protocol for VANETs

In this paper, we propose a novel position-based routing protocol designed to anticipate the characteristics of an urban VANET environment. The proposed algorithm utilizes the prediction of the nodes position and navigation information to improve the efficiency of routing protocol in a vehicular network. In addition, we use the information about link layer quality in terms of SNIR and MAC frame error rate to further improve the efficiency of the proposed routing protocol. This in particular helps to decrease end-to-end delay. Finally, carry-n-forward mechanism is employed as a repair strategy in sparse networks. It is shown that use of this technique increases packet delivery ratio, but increases end-to-end delay as well and is not recommended for QoS constraint services. Our results suggest that compared with GPSR, our proposal demonstrates better performance in the urban environment.

Application of vehicular communications for improving the efficiency of traffic in urban areas

This paper studies the impacts of vehicular communications on efficiency of traffic in urban areas. We consider a Green Light Optimized Speed Advisory application implementation in a typical reference area and present the results of its performance analysis using an integrated cooperative intelligent transportation systems simulation platform. In addition, we study route alternation using vehicle-to-infrastructure and vehicle-to-vehicle communications. Our interest was to monitor the impacts of these applications on fuel and traffic efficiency by introducing metrics for average fuel consumption, average stop time behind a traffic light and average trip time, respectively. For gathering the results, we implemented two traffic scenarios defining routes through an urban area including traffic lights. The simulations are varied for different penetration rates of application-equipped vehicles, drivers compliance to the advised speed and traffic density. Our results indicate that Green Light Optimized Speed Advisory systems could improve fuel consumption, reduce traffic congestion in junctions and the total trip time. Copyright

Throughput Analysis of the IEEE 802.11p Enhanced Distributed Channel Access Function in Vehicular Environment

This paper proposes an analytical model for the throughput of the Enhanced Distributed Channel Access (EDCA)mechanism in IEEE 802.11p MAC sub-layer. Features in EDCA such as different Contention Windows (CW) and Arbitration Interframe Space (AIFS) for each Access Category (AC), and internal collisions are taken into account. The analytical model is suitable for both basic access and the Request-To-Send/Clear-To-Send (RTS/CTS) access mode. The proposed analytical model is validated against simulation results to demonstrate its accuracy.

Multimedia adaptation in ubiquitous environments: benefits of structured multimedia documents

This paper demonstrates the advantages of using structured multimedia documents for session management and media distribution in ubiquitous environments. We show how document manipulations can be used to perform powerful operations such as content to context adaptation and presentation continuity. When consuming media in ubiquitous environments, where the set of devices surrounding a user may change, dynamic media adaptation and session transfer become primary requirements. This paper presents a working system, based on a representative scenario, in which multimedia content is distributed and adapted to a movable user to best suit his/her contextual situation. The implemented scenario includes the following scenes: content selection using a personal mobile phone, content distribution to the most suitable device according to the users context, and presentation continuity when the user moves to another location. This paper introduces the underlying document manipulations that turn the scenario into a working system.

Multimodal user interfaces for context-aware mobile applications

This paper introduces a generic architecture that enables the development and execution of mobile multimodal applications proposed within the EU IST-511607 project MobiLife. Mobi Life aims at exploiting the synergetic use of multimodal user interface technology and contextual information processing, with the ultimate goal that the two together can provide a beyond-the-state-of-the-art user experience. And this led to an integrated concept, components of the underlying architecture are described in detail and the interfaces towards the application back-end as well as towards context aware resources are discussed. The paper also positions the current work against existing standardisation efforts and it pinpoints technologies required to support the implementation of a device and modality function within the MobiLife architecture

Asynchronous Multi-Channel MAC for Vehicular Ad Hoc Networks

This paper presents a new multi-channel MAC protocol for Vehicular Ad Hoc Networks, namely, Asynchronous Multi-Channel MAC (AMCMAC). The AMCMAC supports simultaneous transmissions on different service channels, as well as, allowing other nodes to make rendezvous with their provider/receiver or broadcast emergency messages on the control channel. We compare the performance of the proposed protocol with that of IEEE 1609.4 and Asynchronous Multichannel Coordination Protocol (AMCP), in terms of throughput on control and service channels, channel utilization, and the penetration rate of successfully broadcast emergency messages. We demonstrate that AMCMAC outperforms IEEE 1609.4 and AMCP in terms of system throughput by increasing the utilization of control channel and service channels. In addition, AMCMAC mitigates both the multi-channel hidden terminal and missing receiver problems which occur in asynchronous multichannel MAC protocols.

Intelligent Multimedia Presentation in Ubiquitous Multidevice Scenarios

This intelligent multimedia adaptation and delivery framework tailors to ubiquitous environments, so that users can experience multimedia content using multiple devices in various mobility situations. Multidevice environments offer the potential to enhance the user experience in terms of flexibility and interactivity and will enable novel applications in education, entertainment, collaboration, and communication. We analyzed the different processing steps and defined related framework functionalities such as the generation of the presentation schedule, the computation of the presentation-environment matches, personalization through situation learning, and device(s)-tailored presentation delivery.

Device discovery in future service platforms through SIP

This paper proposes an extension to Session Initiation Protocol (SIP) for contextualized service delivery in a service delivery platform (SDP) that enables device specific multimedia delivery. SIP separates between session establishment and description and is thus, amenable to be extended for advanced implementations which make it an ideal platform for service creation. Device specific multimedia delivery needs rich and flexible device descriptions, and our approach proposes advanced device descriptions through semantic technologies. The proposed SIP extensions have been implemented on a SIP Application Server which functions as SDP in IP Multimedia Subsystem (IMS). The validation of the proposed extensions is shown through an Android SIP client application that acts as a device browser and recommender for different multimedia services to users. An example device user agent (UA) application has also been implemented on a laptop.