Lothar Stibor

The IEEE 802.11 universe

The introduction of IEEEs 802.11 standards has enabled a mass market, with a huge impact in the home, office, and public areas. Today, laptops, PCs, printers, cellular phones, VoIP phones, MP3 players, Blu-Ray players, and many more devices incorporate wireless LAN technology. With low-cost chipsets and support for high data rates, 802.11 has become a universal solution for an ever increasing application space. As a direct consequence of its high market penetration, several amendments to the basic 802.11 standard have been developed or are under development. They fix technology issues or add functionality expected to be required by future applications. In this article we overview the emerging 802.11 standard and address the technical context of its extensions. The article highlights its finalized amendments and those under development.

An error model for inter-vehicle communications in highway scenarios at 5.9GHz

The design and evaluation of Inter-Vehicle Communication (IVC) protocols rely much on the accurate and efficient computational simulations. For simulations of Medium Access Control (MAC) and higher layers, the modeling work of underlying Physical layer (PHY) and wireless channel has impacts both on the computational efficiency of simulations and on the correctness of results. In this contribution, we discuss the modeling issues of the inter-vehicle wireless channel in highway scenarios and the packet error performance of Dedicated Short Range Communications (DSRC) PHY, which works at the newly allocated 5.9GHz Intelligent Transportation System (ITS) frequency band. A computationally efficient yet accurate enough error modeling approach used in our MAC layer simulator WARP2 is presented in this paper, together with simulation results. Both weaknesses and potential improvements of the proposed approach are discussed also in this work.

Evaluation of Communication Distance of Broadcast Messages in a Vehicular Ad-Hoc Network Using IEEE 802.11p

Current research for vehicular communication is largely driven by the allocation of 75MHz spectrum in the 5.9GHz band for dedicate short range communications (DSRC) in North America. The IEEE 802.11p physical (PHY) layer and medium access control (MAC) layer that is currently under standardization aim at communication distances of up to 1000m. In this paper we evaluate the maximum communication distance of an IEEE 802.11p vehicular ad-hoc network including mobility effects and multi-path propagation. Furthermore the communication distance for different path loss exponents is evaluated.

Towards Broadband Vehicular Ad-Hoc Networks - The Vehicular Mesh Network (VMESH) MAC Protocol

The current medium access control (MAC) protocol of the wireless access in vehicular environments (WAVE) system is based on IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which have drawbacks in supporting throughput-sensitive non-safety applications in vehicular ad-hoc network (VANET). In order to address the problem, we propose a novel MAC protocol, namely vehicular MESH network (VMESH), which is specifically designed for the control channel (CCH) and multiple service channels (SCHs) structure of WAVE. A synchronized and distributed beaconing scheme is employed in the VMESH protocol for the purposes of neighborhood awareness and dynamic resource reservation on SCHs. The advantages of the VMESH protocol in supporting the throughput-sensitive non-safety applications in VANET are shown through the theoretical analysis comparing to the current WAVE MAC.

A Novel MAC Protocol for Throughput Sensitive Applications in Vehicular Environments

The current medium access control (MAC) protocol of the wireless access in vehicular environments (WAVE) system is based on IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which have drawbacks in supporting throughput-sensitive applications in high density networks, e.g. future vehicular ad-hoc networks (VANET). In order to address the problem, we propose a novel MAC protocol, namely vehicular MESH network (VMESH), which is specifically designed for the control channel (CCH) and multiple service channels (SCHs) architecture of WAVE system. A synchronized and distributed beaconing scheme is employed by the VMESH protocol for the purposes of neighborhood awareness and dynamic channel resource reservation. In this paper, we present the advantage of VMESH protocol under saturated traffic load condition through theoretical analysis. For more realistic scenarios with mobility and unsaturated traffic loads, through the simulative study, we can also show that the VMESH protocol outperforms the WAVE protocol when the traffic load is heavy.

Wireless local danger warning using inter-vehicle communications in highway scenarios

In this paper we proposed a novel self-organized message dissemination algorithm, namely the cluster-based broadcast (CB), for the emergency electronic brake light (EEBL) application in vehicular ad-hoc networks (VANET). The proposed cluster-based broadcast algorithm converts multihop broadcast message forwarding into multiple of single-hop broadcast clusters, which offers higher reliability, lower channel usage and message propagation delay in comparison with the traditional Directional Flooding (DF). Furthermore, we study the depedence of EEBL application on the market penetration ratio of the VANET wireless communication nodes. An innovative idea of combining the VANET with nomadic devices is proposed in this work to mitigate the slow market penetration rate problem. The results show that the nomadic devices, like portable navigation devices with communication ability, will play an important role when the VANET technology is rolling out in our real life.

Opportunistic Wireless Internet Access in Vehicular Environments Using Enhanced WAVE Devices

In this paper we study the feasibility of providing automotive users the Internet access using C2C communication with help of roadside infrastructure and the novel Vehicular Communication Gateways (VCG), which is developed in the MYCAREVENT project. A technical solution of managing the opportunistic wireless links between On-Board Units (OB Us) and Road-Side Units (RSUs), as well as between OB Us and VCGs, is developed based on WA VE system. To further enhance the performance of WA VE system concerning IP traffic in highly dynamic vehicular environments we propose a link status aware MAC queue architecture. Stochastic simulation results are presented to prove the concepts and validate the proposed solutions.

Vehicular wireless media network (VWMN): a distributed broadband MAC for inter-vehicle communications

The allocation of 75MHz spectrum in the 5.9GHz band for Dedicate Short Range Communications (DSRC) in North America makes it possible to deliver high data rate multimedia applications via vehicle-to-roadside and even vehicle-to-vehicle wireless links. However, Medium Access Control (MAC) protocols mostly studied for DSRC systems are designed for safety relevant applications and insufficient for high data rate multimedia applications. In this work we propose a novel MAC solution, namely Vehicular Wireless Media Network (VWMN), based on a distributed beaconing scheme. The VWMN MAC is designed to support both time critical safety relevant applications and high data rate multimedia applications in Vehicular Ad hoc Networks (VANETs), especially with multiple channels and in multi-hop scenarios. The most challenging issues faced by Inter-Vehicle Communications (IVC), i.e. synchronization and dynamic topology control, are discussed as well based on the VWMN MAC with proposed solutions.

On the Performance of Hybrid Wireless/Wired Mesh Networks

Wireless mesh networks (WMNs) transparently extend the coverage of a portal via mesh points (MPs) which relay data over multiple hops to the associated stations. While this concept lowers costly wire installations, capacity is reduced by the multiple transmissions. Therefore, multiple portals are needed to limit the route length, resulting in a wireless network supported by a wired backbone. In this paper, we analyze how the variation of the average ratio of MPs per portal effects the network performance. To do so, a realistic system model is defined which incorporates the typical characteristics of a wireless link based on IEEE 802.11a. Then, we use an analytical framework which allows to compute the capacity in an arbitrary network topology under the conditions of the system model. The comparison of the average system capacity with different ratios shows that the performance gain diminishes with increasing number of portals: While the step from one to two portals doubles the capacity, there is only a small difference between 1 and 0.5 MPs per portal. Furthermore, a simple cost model provides insights to the economical feasibility of WMNs: in the case that an MP costs about 10% of a portal, the optimal ratio is found to be around 5 MPs per portal.