Marc Emmelmann

A radio over fiber network architecture for road vehicle communication systems

The road vehicle communication system is an infrastructure network to be deployed along the roads for future intelligent transportation systems. Recently, in order to provide high bandwidth data traffic a radio over fiber based network at millimeter-wave bands has been proposed. In this network a control station is connected to functionally simple base stations via optical fibers. Due to millimeter-wave properties the cell size is very small; therefore, the system is characterized by small cell and high mobility. As a result, it is obvious that mobility management becomes very significant. In this paper we propose a medium access control scheme featuring fast handover and dynamic bandwidth allocation using the ability of centralized control of radio over fiber networks.

Vehicular Networking: Automotive Applications and Beyond

During the last 15 years, the interest in vehicular communication has grown, especially in the automotive industry. Due to the envisioned mass market, projects focusing on Car-to-X communication experience high public visibility. This book presents vehicular communication in a broader perspective that includes more than just its application to the automotive industry. It provides, researchers, engineers, decision makers and graduate students in wireless communications with an introduction to vehicular communication focussing on car-to-x and train-based systems. • Emphasizes important perspectives of vehicular communication including market area, application areas, and standardization issues as well as selected topics featuring aspects of developing, prototyping, and testing vehicular communication systems.

Influence of velocity on the handover delay associated with a radio-signal-measurement-based handover decision

Velocity has a non-neglectable influence on the handover delay experienced by a user if the handover is triggered on a radio-signal-measurement (RSM) based handover scheme. Assuming currently used RSM schemes employing signal aver- aging (low-pass filtering) and a hysteresis margin, the analytical description of the delay is derived as a function of the velocity. The latter is used to determine the minimal overlapping of two adjacent radio cells required for a seamless, i.e. interrupt- free handover. Results show that the required overlapping for a zero-delay handoff does not scale with the handover frequency. Especially for small radio cell sizes, the overlapping may easily exceed 60% of the cells diameter. The improvement gained by dynamically adapting RSM-schemes parameter, i.e. the hystere- sis margin, to the current velocity is neglectably small. Hence, a RSM-based handover decision is not suitable for high handover frequency scenarios and should be supported by other handover trigger mechanisms. I. INTRODUCTION Upcoming wireless local area networks (WLANs) will provide throughput rates of several 100 Mbit/s (2) or even push this limit even beyond 1 Gbit/s. (1) As these future networks cannot infinitely increase the emitted radiation power, the coverage area of each WLAN radio cell will most likely shrink especially if higher frequency bands (e.g. the 30, 40, or 60 GHz) are employed in order to provide these high data rates in the future. (1) Along with the fact of extremely reduced cell sizes comes another challenge: to support users mobility possibly at high velocities. In an office environment, attenuation may limit the cell size to only a few meter whereas in sub-urban or rural areas, the latter will most likely be larger by a factor in between 100 and 1000. In both cases, the dwell time of a mobile user in a cell may be in the order of only a few seconds which emphasizes the need for an efficient scheme providing a seamless handover to consider VoIP over WLAN as an alternative to traditional cellular telephone systems. (3) Even though the mobiles velocity influences the han- dover frequency, it is still an open issue if a seamless, i.e.

Moving toward seamless mobility: state of the art and emerging aspects in standardization bodies

The challenge to provide seamless mobility in the near future emerges as a key topic in various standardization bodies. This includes first of all the support of seamless handover between homogeneous networks. Distinct technologies—such as IEEE 802.11WLANs (Wi-Fi) and IEEE 802.16 MANs WiMAX—have recently augmented such support to existing standards to enable seamless homogeneous handover. Cellular networks, in contrast, already included this inherently from the start. Currently considerable effort goes into coupling of different radio access technologies. Therefore, the second key topic in standardization is seamless heterogeneous handovers. IEEE, IETF, as well as 3GPP consider different approaches toward architectures and protocols enabling seamless mobility management. In this work, we discuss recent and on-going standardization activities within IEEE, IETF, and 3GPP toward seamless homogeneous as well as heterogeneous mobility support.

Investigation of IEEE 802.11k-based Access Point Coverage Area and Neighbor Discovery

Possessing knowledge about access point coverage areas and neighbors is of essential need for the provisioning of, e.g., location based handovers or push services. A convenient method for their discovery is the usage of information obtained by the mobile devices which are currently associated with the access points. The time span being required for the discovery of coverage areas and neighbors is fundamental in order to assess the suitability of such a method in a dynamic environment. In this paper, exemplary numerical results of the required bootstrapping phase for the information determination are presented. Additionally, a relatively simple enhancement of the algorithm computing the coverage areas is introduced, reducing the number of vertices for the description of the areas. Besides, the paper shows how the upcoming IEEE 802.11k standard enables APs to query mobile devices for location and neighbor information and hence presents for the first time an entirely standard compliant acquisition scheme.

Multi-user OFDMA Frame Aggregation for Future Wireless Local Area Networking

State-of-the-art wireless local area networking enables frame aggregation as approach to increase MAC efficiency. However, frame aggregation is limited to the aggregation of packets destined for the same station. In order to serve different stations, the access point still has to contend for the channel multiple times. In this paper we propose and evaluate a novel approach that enables multi-user frame aggregation. We combine this concept with channel-dependent OFDMA resource assignments, yielding a higher PHY efficiency (by exploiting multi-user diversity and instantaneous channel state information) as well as a higher MAC efficiency. The downside to this approach is the increase in protocol overhead to enable such multi-user OFDMA frame aggregation. However, we show that the proposed approach outperforms state-of-the-art 802.11n for different packet sizes and stations to be served.

Opportunistic scanning: Interruption-free network topology discovery for wireless mesh networks

This paper presents the concept and preliminary performance evaluation of a stochastic network discovery approach named opportunistic scanning. Therein, a station only pauses its communication for an extremely short time interval to scan for other technologies / systems. The selected scanning duration is short enough not to be noticeable by higher layer applications. We place this concept into the 802.11 mesh network context and evaluate 802.11 power saving as one possible signaling protocol used to pause the communication between the scanning station and its interlocutor. We herein derive the theoretical performance limits of opportunistic scanning in combination with 802.11 power save and present first results classifying the time required to find a neighboring technology / system at a given probability.

System design and implementation of seamless handover support enabling real-time telemetryhighly mobile users

IEEE 802.11 is one of the most mature WLAN technologies and system components are available at very low cost. This makes it prevealing to reuse 802.11 (hardware) components for system designs apart from traditional WLAN application areas and environments. This paper presents a novel predictive fast handover protocol enabling seamless handover support for real-time telemetry applications for highly mobile users. The employed system architecture is based on 802.11 commercial off-the-shelf components with a modified firmware. We conduct a performance evaluation using a proof-of-concept implementation. The employed methodology and metric is for the first time in strict accordance the proposed approach of the IEEE standard on wireless performance prediction. Results show that the handover delay is below 1 ms.

Dynamic single-user ofdm adaptation for ieee 802.11 systems

Earlier paper have demonstrated that the achievable throughput of OFDM systems can benefit significantly from individual modulation/transmit power selection on a per sub-carrier basis according to the actual gain of individual sub-carriers (so called dynamic OFDM scheme). Usage of such approach requires, however, providing support for additional functionality like: acquisition of the sub-carrier gains, signaling of the used modulation types between the sender and receiver, etc. Therefore dynamic OFDM is actively pursued for future radio interfaces, rather then considered as extension of existing OFDM based standards. In this paper we present for the first time a proposal how the widely accepted IEEE 802.11a/g systems might be extended to support the dynamic OFDM in a single-user (point-to-point) setting while assuring backward compatibility. We address these issues by a) presenting a set of protocol modifications; and b) a performance evaluation of the suggested extension (referred further on to as single-user 802.11 DYN mode) demonstrating the potential of performance improvement.

Influence of network load on the performance of opportunistic scanning

This paper presents a detailed performance evaluation of a novel stochastic network discovery approach denoted as opportunistic scanning. Therein, a station only pauses its communication for an extremely short time interval to scan for other technologies / systems. The selected scanning duration is short enough not to be noticeable by higher layer applications with strict QoS constraints.We apply this concept to 802.11-based networks using power saving as one possible signaling protocol to pause the communication between the scanning station and its interlocutor. Within this paper, we present a detailed simulation-based performance analysis of the opportunistic scanning approach showing its effects on real-time services such as VoIP streams. Our results show that opportunistic scanning behaves sturdy against background traffic. This novel approach enables successful network discovery within a 850-milisecond time span while guaranteeing QoS constraints of such a higher layer real-time application.