During the last years WLAN (IEEE 802.11) has become the primary wireless access technology. However, the fast evolution of peak data rates and the wide deployment of WLAN hotspots results in the backhaul connecting such small cells becoming a bottleneck. To provide a high capacity backhauling, we propose COUWBAT, a COgnitive Ultra-Wide BAckhaul Transmission system, featuring extremely flexible usage of a very wide range of non-contiguous, dynamically allocatable spectrum for backhauling in rural areas where a wired solution is not economically feasible. The proposed cognitive MAC layer supported by protocol in-band signaling, ensures the continuity of connectivity with high capacity even in case of fast changes in spectrum availability. The proposed system was prototypically implemented and evaluated exhaustively analytically and also by means of network simulations using ns3. The source code of our simulation model is provided to the community as open source.

In dense deployments of residential WiFi networks individual users suffer performance degradation due to both contention and interference. While Radio Resource Management (RRM) is known to mitigate this effects its application in residential WiFi networks being by nature unplanned and individually managed creates a big challenge.We propose ResFi - a framework supporting creation of RRM functionality in legacy deployments. The radio interfaces are used for efficient discovery of adjacent APs and as a side-channel to establish a secure communication among the individual Access Point Management Applications within a neighborhood over the wired Internet backbone.We have implemented a prototype of ResFi and studied its performance in our testbed. As a showcase we have implemented various RRM applications among others a distributed channel assignment algorithm using ResFi. ResFi is provided to the community as open source.

Cognitive Radio (CR) will enhance the efficiency in spectrum usage by re-using temporally unused licensed spectrum. A promising transmission scheme to utilize even very fragmented and fast changing spectrum is Non-Contiguous OFDM (NCOFDM). Unfortunately, NC-OFDM requires tight synchronization between sender and receiver, i.e. the receiver needs perfect up-to-date knowledge about the set of subcarriers being used by the NC-OFDM sender. Therefore, a reliable and always available Control Channel (CC) is crucial for signaling the spectrum allocation information. Although, underlay Impulse-Radio Ultra-WideBand (IR-UWB) meets the theoretical requirements for such a CC in CR networks, i.e. communication range of up to 1km on a sufficient high data rate, there is a lack of practical studies of IR-UWB in real world environments, especially with respect to co-existence with NC-OFDM as in the envisioned CR multi-technology station. In this paper we present results of measurements in our state-of-the-art IR-UWB testbed. We show that IR-UWB can reach the required communication range of a few hundreds of meters in unobstructed as well as slightly obstructed Lineof- Sight propagation only. Although, IR-UWB is a wideband technology we show that it is severely affected by narrowband interference from close proximity sources which is typically the case in the envisioned multi-technology stations. Such a mutual disturbance can be mitigated by increasing the spatial separation between both air interfaces, orthogonalization in time or using only those parts of the radio spectrum for NC-OFDM which are outside the main IR-UWB transmission mask.

In many road traffic scenarios the ability to communicate among traffic participants is very helpful. Therefore, research and development in academia and industry in that field exists already for many years and is ongoing in several directions. Some examples are Vehicular Ad-hoc Networks (VANETs), e.g., using technologies like IEEE 802.11p, and vehicles communicating with backend systems, e.g., using 2/3/4G cellular networks.In opportunistic vehicular networks, vehicles may not only exchange data for the immediate use such as Cooperative Awareness Messages (CAMs) in the ETSI Intelligent Transport Systems (ITS). Instead, a more general type of network might be set up, also for application scenarios beyond direct road traffic related aspects. For instance, buses of public transportation systems could collect data from the field or distribute data among several buses. Thus, buses could become an important part of smart cities or Internet of Things (IoT) application scenarios.Important questions are then, e.g., how much data could be distributed in such a bus-based opportunistic network or how often is it possible to exchange data between buses. Usually, buses in urban public transport systems follow well planned but nevertheless highly dynamic schedules and trajectories. Thus, traffic conditions have a significant and complex influence on bus mobility, causing very characteristic movement properties that are considerably distinct from other road vehicles. Understanding these special characteristics is essential for the design and evaluation of opportunistic vehicular communication networks. For this purpose we inspect two large-scale bus movement traces and describe the available data and metadata. Moreover, we analyze and compare vehicle density, speed, update intervals, and characteristics that are specific to public transport.Especially for large cities, but even for smaller ones if many devices like vehicles, sensors, and various other IoT things are part of such a network, high-performance computing and simulation approaches are necessary to study, analyse, design, use and maintain such a system.

Cognitive Radio (CR) is a promising approach to overcome the spectrum crunch faced by today's enterprise and residential WiFi (IEEE 802.11) due to rapid growth of wireless devices and traffic load. However, the expected high-density CR Networks (CRN) will suffer from similar problems as we see today with WiFi, i.e. any uncoordinated spectrum access will inevitably result in interference between Secondary Users and hence in a low spectral efficiency. In this paper we take advantages of the ideas of Software-Defined Networking (SDN) and cloud computing technology to manage interference in CRN deployments in residential areas. Specifically, we propose a flexible SDN-based CR architecture where a cloud-based centralized controller, the Spectrum Broker (SB), takes control over the spectrum assignment for the CR Base Stations (CR-BS). To enable that, the CR-BSs under control report aggregated wireless statistics to the SB. Moreover, by configuring proper rules in OpenFlow-enabled CR-BSs, the SB controller can get up-to-date information about the network traffic condition in the CRN. With this information the SB can perform a very fine-grained topology-, traffic- and channel-aware spectrum allocation. Our architecture, as well as the proposed spectrum allocation scheme, were analyzed by means of emulation within Mininet. Results demonstrate a gain of up to 5x as compared to a static spectrum allocation scheme.

Cognitive Radio is a broadly discussed approach for better spectrum utilization by allowing Secondary Users (SU) the temporary usage of non-occupied spectrum licensed to Primary Users (PU). With the Non-Contiguous OFDM transmission technique even strongly fragmented spectrum can be efficiently accessed by SUs. In this paper, we consider a set of independent, autonomous groups of SUs (networks consisting of a base station and a set of client stations) to operate in a shared set of temporary reusable frequencies. We present a fair, distributed spectrum allocation algorithm with low computational complexity and low control data overhead. Our approach assures that in case a PU is reclaiming some spectrum this will affect all co-located SU groups in the same fair manner. Simulation results demonstrate the convincing efficiency of this algorithm as compared with a centralized, optimal solution.

In the last years, the measurement of environmental data in city areas has become an important issue to municipalities due to several national, European and even international climate directives. However, stationary measuring stations are inflexible, cost-intensive and limited to monitoring environmental data in distinct key areas. In this paper we present a decentralized architecture for environmental monitoring in metropolitan areas using Car2X communication techniques. This architecture , called EMMA, can be integrated in e.g. existing public transportation networks by equipping buses with sensor nodes that communicate with each other. Thus, the system is able to obtain area-wide measurements that are distributed within the ad-hoc network. A central visualization engine is used to analyze and publish the measured data and therefore allows to react to high pollution levels by e.g. closing streets for trucks. A field test revealed that the idea behind EMMA and the soft-and hardware used to realize our prototype implementation works as designed and is ready for more advanced testing like a large-scale field deployment. 1 Motivation Measuring environmental data like particulate matter, ozone, CO x or N O x-emissions is an important task in most modern societies. Densely populated areas need constant monitoring of environmental conditions to assure the citi-zen's health as well as compliance with political directives. Each sensor can only analyze its immediate surroundings and thus a complete coverage of the whole metropolitan area is very difficult and expensive. So usually only some key spots are monitored. In this paper we describe a new way to approach this problem. EMMA (Environmental Monitoring in Metropolitan Areas) is a mobile and distributed system which provides almost complete coverage of the whole metropolitan area with sensorial data in an easy to implement and cost effective way. It uses an existing conventional network such as the public transportation system to send mobile sensor nodes to all residential areas. By doing this, a relatively small number of sensors is sufficient and hardly any data network infrastructure is needed as

IEEE 802.11 WLANs are currently one of the most popular wireless technologies, but their immediate success results in dense deployments and high demand of user traffic. This in turn leads to decrease in throughput and poor spectrum utilization. Especially in the 2.4 GHz ISM band, where the spectrum is a very scarce resource, all available WLAN channels should be exploited in the best possible way to achieve higher utilization. One way to reach this goal is the usage of partially overlapping channels (POC). Most of the previous work related to POC is based on two major studies addressing 802.11 b, but none of them evaluates the POC behavior in the 802.11 g networks. Moreover, most of the previous results are based on simulations. The main contribution of this work is an experimental evaluation of POC in 802.11g networks. In this paper we confirm quantitatively that 802.11b reacts as expected from the previous studies, while 802.11 g reacts entirely different to the presence of adjacent channel interference. That leads to the conclusion that the usage of POC for 802.11g is not recommended.

Due to the intrinsic properties of vehicular disruption tolerant networks, contacts between nodes exist only for a very limited amount of time. Therefore, for good performance it is important to transmit messages efficiently, and to minimize the waste of capacity by finishing the transmission before the contact ends to lower the amount of data that is discarded or fragmented at the end of a contact. We investigate the performance improvements of various bundle transmission schedulers in simulations with real-world mobility. Moreover, we propose a new generic approach to scheduling. Although our approach has a positive effect, the evaluation also implies that the influence of transmission scheduling in realistic scenarios is lower than generally expected.

The measurement of environmental data in city areas has become an important issue to municipalities due to several national, European and even international climate directives. However, fixed measurement stations are inflexible, cost-intensive and limited to monitoring environmental data in distinct key areas only. Large-scale data collection with a high spatial resolution requires mobile measurements, which are an active area of research but still offer many challenges. In this paper we give an overview of current approaches and challenges.

DTN nodes often idly wait for contacts and unnecessarily consume energy during these periods. For solar-powered nodes this means that solar panels and batteries could be much smaller with an efficient energy management, reducing the physical size of these nodes. We present our design of a solar-powered DTN node including a module that handles solar charge management, energy management and a discovery mechanism to wake sleeping nodes. Moreover, the system senses the remaining battery capacity, and keeps a reserve for emergency communications. Our evaluation shows that the power management module's design is energy-efficient and performs as intended. Furthermore, we evaluate the discovery mechanism. The results show that the capabilities of the module offer a promising new approach to the implementation of energy efficient routing in DTNs.

Realistic scenarios are essential for the simulation-based evaluation of opportunistic routing protocols in vehicular networks. Synthetically generated scenarios are easy to obtain but fail to reproduce the complexity of the real world. Therefore, the generally accepted procedure is to use traces recorded in experiments. Unfortunately, this is almost impractical for large-scale scenarios. The advancing pervasion of ICT in transportation systems results in new opportunities for the research community to collect mobility traces from real systems. Using the example of one of the world's largest public transportation network, we demonstrate our approach to acquire realistic traces which are more extensive than existing traces. Moreover, we demonstrate how this data can easily be integrated into the established delay tolerant network (DTN) simulation tool 'The ONE'.

Communication is crucial to the coordination and efficient operation of public transport systems. However, deployment of infrastructure based communication systems is very expensive. Delay tolerant vehicular networks are a promising alternative since only very few infrastructure elements are required. This paper presents a DTN routing algorithm for urban public transport systems. Beginning with an analysis of node mobility, system characteristics are derived and exploited to improve routing performance. To increase realism in the performance evaluation and comparison a new approach is taken for the generation of mobility traces. A map based on real cartographic data is combined with line definitions, stops and timetables of real public transport systems. A micromobility simulator then produces large scale mobility traces which are fed into a DTN simulator. We compare various DTN routing schemes with our algorithm. Moreover, the impact of disturbances in the public transport system on the routing performance is examined. The results show that our routing algorithm can outperform previously proposed algorithms even if 20% of all vehicles are behind schedule.

In our demonstration we present an implementation of DTN for embedded systems and demonstrate how a WLAN access point can be turned into a stand-alone DTN-node for mobile applications. The modular software design of "IBRDTN" is centered on the efficient use of resources and interoperability with the DTN2 reference implementation. Our modules comprise a DTN Core, Bundle Router, Persistent Storage and a Convergence Layer Manager. IBR-DTN is work in progress, but the comparison of the features and performance to DTN2 is already very promising. Finally, we present a practical evaluation in a mobile scenario in which a vehicle mounted node passes a stationary node.

The 2007 DARPA Urban Challenge afforded the golden opportunity for the Technische Universität Braunschweig to demonstrate its abilities to develop an autonomously driving vehicle to compete with the world's best competitors. After several stages of qualification, our team CarOLO qualified early for the DARPA Urban Challenge Final Event and was among only eleven teams from initially 89 competitors to compete in the final. We had the ability to work together in a large group of experts, each contributing his expertise in his discipline, and significant organisational, financial and technical support by local sponsors who helped us to become the best non-US team. In this report, we describe the 2007 DARPA Urban Challenge, our contribution "Caroline", the technology and algorithms along with her performance in the DARPA Urban Challenge Final Event on November 3, 2007.

Measuring environmental data in city areas has become an important issue for municipalities due to several climate directives. As fixed measuring stations are inflexible, cost-intensive, and limited to monitoring a specific spot, we developed a distributed environmental monitoring network called Environmental Monitoring in Metropolitan Areas (EMMA). This architecture is based on the delay tolerant networking approach and can be integrated into existing Public Transportation Networks (PTNs). Buses or other vehicles can be equipped with sensor nodes that gather data and forward messages. In order to evaluate the basic ideas of this project we performed a series of real-world experiments. Besides analyzing the behavior of 802.11-based Wireless Local Area Network (WLAN) between moving vehicles in a controlled environment, we also evaluated the communication performance in urban environments. Moreover, we examined the qualification of a Disruption Tolerant Networking (DTN) implementation for spreading measurement results throughout the network. The suitability of EMMA's architecture has been successfully demonstrated by these experiments. Copyright © 2007 John Wiley & Sons, Ltd.

Vertical handovers between heterogeneous communication networks are required to provide seamless Internet access to mobile users. In this paper we present an approach for dynamic transport layer handover by utilizing the multihoming capabilities of SCTP. The architecture allows for selecting the most suitable communication path for an application depending on the user’s preferences, the application’s requirements as well as the current network characteristics. The evaluation results of the prototype implementation show that SCTP is very suitable for transport layer handovers and more robust against interferences than TCP.

In our demonstration we present an implementation of DTN for embedded systems and demonstrate how a WLAN ac- cess point can be turned into a stand-alone DTN-node for mobile applications. The modular software design of "IBR- DTN" is centered on the efficient use of resources and inter- operability with the DTN2 reference implementation. Our modules comprise a DTN Core, Bundle Router, Persistent Storage and a Convergence Layer Manager. IBR-DTN is work in progress, but the comparison of the features and performance to DTN2 is already very promising. Finally, we present a practical evaluation in a mobile scenario in which a vehicle mounted node passes a stationary node.