The growing demand for highly reliable, low-latency communication in industrial and real-time applications poses significant challenges for traditional Wi-Fi networks, especially under dynamic traffic conditions. Multi-Connectivity (MC) presents a viable solution to enhance network performance by utilizing multiple transmission paths. This paper extends our previous work where we proposed Channel Capacity Index-Aware Adaptive Scheduler (CIAS), and evaluates static and adaptive scheduling, i.e., selecting which paths are used, on latency and reliability in non-periodic, sporadic, and attenuated scenarios, which are commonly observed in autonomous systems and industrial applications. We analyze the performance of static schedulers and compare them with CIAS, an adaptive cross-layer scheduling approach that dynamically selects the optimal MC scheme based on channel capacity. Our results demonstrate that CIAS consistently reduces latency and mitigates packet delays, particularly under high traffic loads, sporadic transmissions, and signal attenuation. Furthermore, CIAS enhances reliability by minimizing tail-end latencies and adapting to channel fluctuations more effectively than static schedulers. This study underscores the critical role of adaptive MC scheduling in improving wireless communication efficiency for time-sensitive applications that demand both low latency and high reliability.

Traditional Linux network stacks struggle to handle the high packet rates of modern Network Interface Cards (NICs), pushing high-performance users towards kernel bypass solutions. But kernel bypass solutions introduce compatibility issues requiring exclusive access to network interfaces, lacking access to privileged instructions, and breaking existing application compatibility. To partially address these issues, Linux introduced eXpress Data Path (XDP), enabling programmable, efficient, user-space packet processing but still failing to provide compatibility with traditional socket-based applications.We propose the XDP Packet Mill, a framework combining the performance benefits of XDP socket with seamless compatibility for existing applications. The Mill intercepts and processes packets via XDP, and it offers efficient, zero-copy primitives to drop, modify, forward, duplicate, slice, and merge layer-2 packets. This enables practical experimentation and deployment of advanced networking protocols, such as multi-path communication, without requiring non-standard application interfaces. Our evaluation shows the throughput characteristics of Mill in different XDP modes (native, SKB, zero-copy) in a realistic high-performance Ethernet setup. Mill aims to simplify the real-world deployment and experimentation of flexible networking protocols while preserving application compatibility.

In recent years, Multi-Connectivity (MC) has emerged as a promising approach to enhancing the reliability and resilience of communication networks. The effectiveness of MC depends on the statistical dependencies between the links and heavily on the selection of an appropriate MC strategy. We introduce Packet Duplication (PD) and Load Balancing (LB) in this paper. Each of these strategies offers distinct advantages, but a comprehensive comparison under varying network conditions and dependencies is missing. To address this gap, we investigate an idealized diamond network element, applying two strategies. Analytical results are provided, highlighting the mathematical relationship between effective rate and reliability, considering worst-, best-, and independent and identically distributed (i.i.d.)-dependencies between links. Numerical simulations demonstrate the dichotomy of the optimal strategy under different network scenarios. Interestingly, LB outperforms PD for the worst-case. Additionally, we extend our analysis by deriving reliability bounds as functions of the effective rate for arbitrary network structures in both PD and LB.

Vehicle-to-X (V2X) communication has become crucial for enhancing road safety, especially for Vulnerable Road Users (VRUs) such as pedestrians and cyclists. However, the increasing number of devices communicating on the same channels will lead to significant channel load. To address this issue this study evaluates the effectiveness of Redundancy Mitigation (RM) for VRU Awareness Messages (VAMs), focusing specifically on cyclists. The objective of RM is to minimize the transmission of redundant information. We conducted a simulation study using a urban scenario with a high bicycle density based on traffic data from Hannover, Germany. This study assessed the impact of RM on channel load, measured by Channel Busy Ratio (CBR), and safety, measured by VRU Perception Rate (VPR) in simulation. To evaluate the accuracy and reliability of the RM mechanisms, we analyzed the actual differences in position, speed, and heading between the ego VRU and the VRU, which was assumed to be redundant. Our findings indicate that while RM can reduce channel congestion, it also leads to a decrease in the perception rate of VRUs. The analysis of actual differences revealed that the RM mechanism standardized by ETSI often uses outdated information, leading to significant discrepancies in position, speed, and heading, which could result in dangerous situations. To address these limitations, we propose an adapted RM mechanism that improves the balance between reducing channel load and maintaining VRU awareness. The adapted approach shows a significant reduction in maximum CBR and a less significant decrease in VPR compared to the standardized RM. Moreover, it demonstrates better performance in the actual differences in position, speed, and heading, thereby enhancing overall safety. Our results highlight the need for further research to optimize RM techniques and ensure they effectively enhance V2X communication without compromising the safety of VRUs.

Collective Perception (CP) is a key use case for the Cooperative-Intelligent Transportation System (C-ITS) to improve traffic safety. With CP, vehicles and infrastructure share information about locally detected objects via direct broadcast communication to enhance each other's awareness and obtain perception beyond line-of-sight. However, when more and more vehicles deploy CP, the resource demand grows in terms of communication as more and more senders share their object observations. Moreover, computation requirements grow throughout a vehicle's lifetime as more observations must be processed and fused into a holistic Environment Model. This paper proposes Receiver-Side Object Filtering (RSOF), which filters received objects by relevance and quality, reducing computing power requirements and considering constant memory. The evaluation in a large-scale traffic scenario shows that RSOF significantly reduces the number of fusion operations required to process an increasing amount of received object data. Furthermore, an upper bound for memory and fusion operations is achieved.

Increasing the reliability of multihop industrial wireless sensor networks (IWSNs) is an important challenge to enable continuous data collection in industrial processes. One approach for increasing reliability is multiconnectivity (MC), which enables simultaneous data transmission through two independent network links. In practice, MC can be implemented on all OSI layers, resulting in different parts of the network stack being duplicated. In this article, we compare the implementation of MC above the MAC layer and above the network layer, corresponding to an implementation on a per-hop basis or an end-to-end basis in multihop networks. For a comprehensive consideration, the approaches are discussed analytically, simulated and deployed in a real-world scenario to provide foundational knowledge about the effects of different layer MC on reliability. We show that the per-hop approach offers higher reliability than the end-to-end approach in homogeneous networks, while both approaches outperform the single-connectivity baseline. In comparison, the end-to-end approach outperforms the per-hop approach and the baseline depending on the network topology in heterogeneous networks. Apart from the topology and the link quality, we reveal the influence of fragmentation on both approaches. All influencing factors, in combination with external factors introduced by a real-world deployment, led to a decreased data loss rate of up to 56% compared to the single-connectivity baseline.

In Europe, the C-ITS Security Certificate Management System supplies pseudonymous credentials to valid stations, allowing them to authenticate each other when exchanging messages. Detecting misbehavior and evicting offenders from the C-ITS is challenging but must be addressed to maintain security and safety. The offending station must be reported and found guilty by the Misbehavior Authority (MA) in order to revoke its credentials and protect other stations. Collecting necessary evidence is hindered by privacy requirements, allowing potential attackers to use pseudonyms to obfuscate the source of misbehavior. Privacy-Preserving Misbehavior Reporting (PriMiRe) enables the MA to aggregate and analyze evidence for unique senders without revealing their real or pseudonymous identities, thus maintaining privacy requirements. It is shown that PriMiRe requires minor changes to the existing architecture and protocols, and additional data storage requirements are modest.

Currently, Cooperative Awareness is being introduced to evermore commercially available vehicles, and Collective Perception is in the final phase of standardization to be ready as next step (Day 2) of vehicular Cooperative-Intelligent Transportation Systems. Afterwards (Day 3), Maneuver Coordination will be a key functionality for Connected Automated Vehicles. It will enable them to exchange planned trajectories and actively cooperate via Maneuver Coordination Messages (MCMs). Our study presented in this paper analyzes the capacity and performance of an ITS-G5 communication channel employed to exchange these messages, varying a set of different parameters. One of Europe’s most frequented highway intersections was modeled for the simulations, including realistic traffic patterns. Generic channel-centric metrics show that substantial channel loads can be caused, both by existing messages and by the MCM, such that multiple channels are required to host all services -depending on parameterization. New metrics specific to Maneuver Coordination, such as the Manuver Coordination Time, show a sufficient service performance even in a resource-constraint environment. However, it degrades quickly with increasing channel loads. The study provides insights on what to expect from Maneuver Coordination for researchers, engineers and regulators on both ends of the communication stack.

Simulation tools are frequently used to analyze vehicular networks. However, these tools are not ready yet to model the world in the necessary level of detail for Collective Perception. The network load generated by the Collective Perception Service highly depends on the sender's sensors, which are modeled insufficiently by current vehicular network simulators. This paper presents an Environment Model extension to Artery, a popular simulation framework for the ETSI C-ITS communication stack. It enables sensor-equipped vehicles to perceive objects from their perspective individually to improve the realism of perception. Furthermore, it adds new sensors that produce synthetic object data for detected objects based on the characteristics of various automotive sensors. A performance evaluation shows that the computational overhead for the extension is limited, so it is suitable even for large-scale simulation studies using Artery.

The utilization of IoT devices is becoming omnipresent in industrial settings. However, adoption in more rural areas still poses challenges. Especially when processing data on the edge, privacy, data integrity, accountability and data ownership pose challenges since the devices may be easily accessed and manipulated. We present ContractBox, a system that provides accountable and trusted data sharing based on a publisher–subscriber system, as well as trusted computing on the edge. ContractBox uses a Trusted Execution Environment to guarantee the confidentiality and integrity of clients’ data and code. Furthermore, it provides security by using WebAssembly to execute the smart contracts in their own sandboxed environment. This design protects the host as well as co-located smart contracts from misbehaving executions. Lastly, it ensures the immutability and accountability of the published data by storing it in a blockchain. We show that ContractBox can process several thousand publications per second with various payloads and host multiple smart contract runtimes on a single edge device. ContractBox also achieves up to 35 times higher throughput than a comparable deployment of Hyperledger Fabric.

In industry 4.0 many industrial processes are enhanced by using the information continuously collected through connected sensors. While many use cases have been discussed and simulated, the transfer into real-world deployments and the discussion of associated challenges have been rather sparse.In this field report, we present our experiences on developing and deploying a versatile Wireless Sensor Network (WSN) for the monitoring of temperature, particle concentration, CO2concentration and other important environmental data. The WSN is accompanied by its backend and testbed infrastructure, which allows the continuous management and monitoring of the deployments. We describe the challenges faced and experiences gained during the deployment of 70 nodes at five different industrial scenarios and recap the lessons we learned.

A reliable energy supply is the foundation of many Wireless Sensor Networks that can not be powered from mains power permanently. Therefore, batteries have been widely used since many years. However, due to their environmental impact and limited lifetime, costs are high and they should be used most efficiently. Further, predictability is challenging and overprovisioning is common practice, which once again increases costs. Hence, energy harvesting has become very popular and can increase lifetime, reduce cost, but comes with additional challenges. Outdoor Wireless Sensor Networks operate in varying temperature ranges which has a noticeable impact on the energy sources. In this paper, we characterize different types of energy sources regarding their behavior under usage patterns and temperature changes,

The demand for wireless communication systems that provide low latency with high reliability is growing due to emerging applications such as wireless industrial control or mobile robotics. A promising approach to improve latency and reliability performance of wireless communications is Multi-Connectivity (MC), i.e., using multiple communication paths at the same time. The task group working on the upcoming 802.11be amendment is discussing multi-link operation as one of the main features. In previous work different static MC scheduling schemes have been evaluated and in different scenarios different schemes demonstrated to provide the best latency and reliability performance. Based on these findings and in coherence with the discussion about multi-link operation in the 802.11be task group an adaptive MC scheduling scheme is proposed in this work. Two variants are proposed and both perform a client-based decision. The first variant decides solely based on the parameters available at every station itself. The second variant also takes into account additional information about the network that are gathered and shared with the stations by the AP. System level simulations with ns-3 for an industrial scenario show that the adaptive MC schemes can significantly improve the latency and reliability performance, especially in scenarios with medium network load. The insights gained in this work can be used to develop multi-link operation concepts in order to improve latency and reliability performance in the upcoming 802.11be amendment.

Ranging and subsequent localization have become more and more critical in today’s factories and logistics. Tracking goods precisely enables just-in-time manufacturing processes. We present the InPhase system for ranging and localization applications. It employs narrowband 2.4 GHz IEEE 802.15.4 radio transceivers to acquire the radio channel’s phase response. In comparison, most other systems employ time-of-flight schemes with Ultra Wideband transceivers. Our software can be used with existing wireless sensor network hardware, providing ranging and localization for existing devices at no extra cost. The introduced Complex-valued Distance Estimation algorithm evaluates the phase response to compute the distance between two radio devices. We achieve high ranging accuracy and precision with a mean absolute error of 0.149 m and a standard deviation of 0.104 m. We show that our algorithm is resilient against noise and burst errors from the phase-data acquisition. Further, we present a localization algorithm based on a particle filter implementation. It achieves a mean absolute error of 0.95 m in a realistic 3D live tracking scenario.

While today only a small fraction of vehicles is equipped with communication technology, this will hopefully change in the near future. But when market penetration rates increase, so will the load in the allocated frequency spectrum. Therefore, Decentralised Congestion Control mechanisms have been developed to limit the channel load and are mandatory in Europe. When one vehicle hosts multiple services, each of which regularly needs to transmit messages, those mechanisms are not appropriate to distribute available resources among them as this can lead to the complete starvation of low priority services. Therefore, an additional entity located in the Facilities Layer is required. This paper introduces a Weighted Fair Queuing-based approach to such a resource allocator. An extensive simulation study analyses its performance and shows how it is able to fairly allocate resources according to the services' weights and completely mitigates the starvation issue.

Wireless communication systems which provide low latency with high reliability are required for emerging industrial applications such as closed-loop control systems or mobile robotics. Multi-Connectivity (MC), i.e., using multiple communication paths simultaneously, can be a measure to enhance latency and reliability performance of wireless communication systems. MC schemes can be applied on different layers of the communication stack. While Physical (PHY) Layer MC schemes combine the paths at signal or symbol level, in higher layer schemes, i.e., MC schemes on MAC Layer or above, the paths are combined at packet level. Higher layer schemes provide more degrees of freedom for dynamic scheme adaptation, while PHY MC schemes have more information available. MC schemes on different layers need to be compared to evaluate their suitability to enhance latency and reliability performance in different scenarios. In this work system level simulations are performed with the network simulator ns-3 to compare PHY Layer MC schemes, i.e., selection combining (SC), maximum ratio combining (MRC) and joint decoding (JD), with higher layer MC schemes, i.e., MP-UDP with packet duplication (PD). Our results suggest that the gain of PHY Layer MC schemes increases with decreasing SINR. The higher layer MC schemes provide diversity not only on PHY but also on MAC and higher layers and could thus decrease access and queuing latency. The gain of MP-UDP increases with increasing network load. The insights obtained in this work can be used to develop dynamic MC schedulers that activate or deactivate certain MC schemes or switch between MC schemes on different layers based on the scenario.

Many wearable applications utilize wireless communication to provide the user with comfort features. With a typically rather small consumer market using technologies in the ISM band is beneficial in order to be cost effective. Safety relevant wearable applications, such as a wireless airbag jacket, face the challenge of providing real-time communication in noisy and volatile environments. In this evaluation we analyze different Wireless Body Area Network (WBAN) technologies with respect to their performance for real-time applications in mobile scenarios. The well established approach of using frequency diversity for increased reliability in noisy environments is evaluated for mobile scenarios.

Intersections are prone to accidents due to poor visibility and complex traffic situations. Vehicle-to-X communication enables vehicles to announce themselves by sending Cooperative Awareness Messages or Basic Safety Messages and thus helps to greatly improve the time they are aware of each other before arriving at an intersection. However, similar to the drivers' vision, communication can be obstructed by buildings, too. To mitigate this issue, different approaches to message relaying have been suggested in the past. While they discussed the general idea, this paper gives a detailed proposal on how Road Side Units can aggregate and relay messages using the Collective Perception Service which is currently being standardised. A simulation study analyses the performance of direct and aggregated relaying using a complete ITS-G5 communication stack. Especially, the influence of Decentralized Congestion Control is discussed which earlier studies did not include. It is shown that aggregating Cooperative Awareness information in Collective Perception Messages can greatly improve the drivers' reaction time while at the same time adding only a small amount of load to the communication channel.

Vehicle-to-Vehicle communication is available in production cars only since end of 2019. Therefore, the load of these communication channels in real-world streets is very low nowadays. But market penetration rates will eventually increase and so will the channel loads. It is therefore crucial to design protocols and communication mechanisms in a way that they will perform well under high-load conditions, too. In order to test and evaluate them, a couple of simulators and traffic scenarios have been developed. However, so far researchers tend to re-create different versions of similar scenarios over and over again. This leads to results which are not easy to reproduce and compare to each other. Therefore, this paper proposes OrbWeaver: An open source tool automatically generating fully customisable, spider web shaped traffic scenarios which are suitable for high-load simulations. Simply by publishing the used input parameters, researchers can enable the community to easily generate the same scenario and compare their results. Three different scenarios generated with OrbWeaver are evaluated and their channel loads, message drop and transmission rates are compared, showing the feasibility of the generated scenarios for the evaluation of protocols under different network loads.

Emerging applications such as wireless industrial control or robotics raise strict requirements in terms of latency and reliability on wireless communication systems. It is still an open issue which wireless communication system can be used to enable industrial applications such as closed-loop control. A promising approach to improve latency and reliability of wireless communications is multi-connectivity (MC), i.e. using multiple communication paths simultaneously. Different scheduling schemes can be used to distribute the traffic over multiple links. The characteristics of these schemes and which one is best suited to enable reliable low-latency communications in different scenarios needs to be investigated. In this paper, we evaluate the latency and reliability performance of a local Wi-Fi and a private LTE network for traffic patterns as envisioned for industrial applications. Moreover, we assess the performance of different MC scheduling schemes operating on Application Layer over these two wireless links with focus on reliability and latency metrics. For the evaluated single-user scenario, WiFi provides a lower mean latency than LTE. The evaluation of MC scheduling schemes shows that packet duplication (PD) stabilizes the latency by mitigating outliers, while load balancing (LB) reduces the latency of nearly 50 percent of packets in a scenario with bad radio conditions. Our results suggest that using links with similar mean latency would be beneficial for all scheduling schemes.

Gait has been proposed as a feature for mobile device pairing across arbitrary positions on the human body. Results indicate that the correlation in gait-based features across different body locations is sufficient to establish secure device pairing. However, the population size of the studies is limited and powerful attackers with e.g., capability of video recording are not considered. We present a concise discussion of security properties of gait-based pairing schemes including quantization, classification and analysis of attack surfaces, of statistical properties of generated sequences, an entropy analysis, as well as possible threats and security weaknesses. For one of the schemes considered, we present modifications to fix an identified security flaw. As a general limitation of gait-based authentication or pairing systems, we further demonstrate that an adversary with video support can create key sequences that are sufficiently close to on-body generated acceleration sequences to breach gait-based security mechanisms.

Cyber-Physical Systems (CPSs) are used in various important application areas. Networking of several CPSs, the internal networking of CPSs components as well as the interconnection with other systems, is of major importance with respect to scientific, engineering and technical considerations; yet, it is also very challenging. In this paper we describe an architecture and methods which can be used for various networked CPSs. To base the system design and approaches on realistic requirements and devise suitable methods, we use tightly cooperating, mobile robots as application area. This is an example of challenging CPSs which put high demands on the networking methods. Nevertheless, the considerations are applicable to other CPSs as well. In order to enable networked mobile robots to perform individual and cooperative tasks, real-time support and network operations such as merge, split, and synchronize among clusters of such robots are needed. Further, management functions have to be provided which enable independent, but concurrent clusters to allocate and share scarce network resources. In the context of this paper, network resources are considered in a broad sense (e.g., time slots, frequency channels, codes) and assigned by a novel scheduling algorithm. Thus, a schedule means not only a sequence of time slots, but it takes all mentioned dimensions into account.

Smart Farming has the goal to support farmers in their various activities, i.e., achieve best results in quality and quantity of their products, with low and efficient resource usage, working in sustainable manners etc. For that, a lot of information is needed, e.g., about the current state of the monitored agricultural area. Typically this requires a large number of sensors which collect important sensor data at predefined intervals. For further evaluation such data is usually processed in a central place, for which it must first be transferred from the field to a data sink at the farm premises. Cellular networks could be used for such data transmissions, but the network deployment in rural areas is costly with less likely revenues. Thus, mobile operators are not eager to roll out their networks in rural areas so that they are often not well covered. In this paper we introduce PotatoScanner, a mobile Tolerant Wireless Sensor Node (DTWSN) that closes this gap and acts with the help of a field sprayer as a data mule for the collected data. In addition, PotatoScanner itself has sensors to obtain further information about the cultivated field. The paper provides an overview of the overall system and analyses the measurement data obtained in real operation over the past two years 2017 and 2018.

Multipath propagation introduces particular challenges for ranging schemes that exploit radio wave propagation. We investigate the impact of multipath propagation on phase-based ranging in the 2.4 GHz band. We show that a phase-based ranging system might report the length of a reflected signal path instead of that of the direct path. In our experiments, we identified three different measurement outcomes, depending on physical properties of the radio link between devices. Our findings show that multipath propagation can lead to severe measurement errors. To mitigate the effects, we propose a novel algorithm to compute the distance from measured phase angles. Our algorithm reduces measurement errors by 51 % compared to a state-of-the-art algorithm in a scenario with strong multipath effects.

Simulation is a common technique for the evaluation of new approaches and protocols in networked systems and provides many benefits. However, it is also well known that the relevance of the simulation results for real-world applications depends on the various models which are used within the simulation, e.g., for the characteristics of the radio communication. In this paper, we introduce the EMRM, an extension to the ray-tracing radio medium available in Cooja, to improve the modelling of wireless links in simulated WSNs. Our extension allows the simulation of environmental influences onto links on a per node basis, allowing the analysis of various effects observed in experiments in a virtual environment. Furthermore, the packet-based modelling of transmission errors is extended to provide the simulation of bit errors, allowing new usage scenarios, like for instance the simulation of error detection and FEC codes in Cooja.

The efficiency and effectiveness of network flooding protocols has recently been shown by many publications as well as real world deployments. One notable protocol is Glossy which combines Concurrent Transmission (CT) with Constructive Interference (CI). A drawback of Glossy is that up to now it has only been implemented and evaluated for one type of radio transceiver. In this paper we first present the Glossy implementation for an AT86RF233 radio transceiver which simplifies the packet forwarding due to a shared receive and transmit buffer. We evaluate our implementation against the original Glossy implementation in a minimalist setup as well as in a real world testbed. However, we observed a noticeable difference in the timing accuracy of the transceiver chips but without adverse effects on the network’s performance. For this reason, in the second part of this paper we provide a deeper investigation by using Software Defined Radios to emulate concurrent transmission for different types of transceivers. This work confirms the general benefit of constructive interference but also shows its limitations. Moreover, we give novel insight into hardware dependability of constructive interference in concurrent transmissions.

Many localization approaches need distance measurements to known locations as input. We present the Complex-valued Distance Estimation algorithm to compute the distance between two radio transceivers from phase measurements. Our proposed algorithm reliably computes the distance from a sampled phase response via Fast Fourier Transform. We compare the new approach with two other state-of-the-art algorithms by evaluating distance errors of real-world measurements in different scenarios. Our algorithm achieves high accuracy and precision with a mean error of 14.9 cm and a standard deviation of 10.4 cm. Further, we evaluate the ability of all algorithms to detect outliers with large errors in their results. We optimize our approach to reduce computation complexity via interpolation without affecting accuracy or precision.

During recent years, automation and optimized production processes within a variety of different agriculture sectors allowed farmers to achieve higher harvesting rates and therefore to maximize the outcome of their efforts. Besides harvesting, storing the crop is the next challenging step in improving agricultural practices. Monitoring and adjusting the environmental conditions in storage are important tasks to achieve an optimal and efficient storability. This paper focuses on the communication part of such a monitoring system. Modern warehouses are usually organized as box storage, which means that the crop to be stored is filled into boxes and then piled up in large warehouses. Selective ventilation and air conditioning ensure a maximum storage period. This paper examines which radio frequencies are suitable for transmitting sensor data from stored boxes to a sink. The obtained sensor data could be used, for example, to control the air conditioning of the warehouse more precisely. The investigations are carried out on potatoes as an example, for which first a simulation and then a prototypical sensor node is created.

Energy is the most limiting factor for remote outdoor deployments of Wireless Sensor Networks (WSNs). This paper proposes a novel routing algorithm for dual-platform nodes targeting WSN applications as found in smart farming applications. For scenarios in which high power components of nodes and radio links will be switched on at known points in time, our algorithm tries to make use of scheduled uptimes of nodes with the possibilities to turn other nodes on to send the nodes' data to a sink on time. We compare our method with a traditional flooding-based algorithm as well as with a greedy version which tries to transfer the data immediately. We show that our mechanism works energy-efficient while meeting all deadlines and keeping the amount of control traffic at a necessary minimum.

Secure spontaneous authentication between devices worn at arbitrary locations on the same body is a challenging, yet unsolved problem. We propose BANDANA, the first-ever implicit secure device-to-device authentication scheme for devices worn on the same body. Our approach leverages instantaneous variations in acceleration patterns from the user's gait to extract always-fresh secure secrets. It enables secure spontaneous pairing of devices worn on the same body or interacted with. The method is robust against noise in sensor readings and active attackers.

We describe a testbed for studying battery discharge behavior and the lifetime of wireless devices under controlled temperature conditions and present preliminary measurement results.

The Ballistocardiography (BCG) aims to analyze the ballistic forces on the heart in terms of vibrations that are transmitted to the body's surface. These vibrations can be measured by accelerometers. But instead of highly specialized analog sensors, we propose BCG based on commercially available digital accelerometers. To achieve this, we performed a bunch of trials to gain information about proper acceleration sensor technology, as well as needed requirements to create a full-fledged BCG sensor board. This sensor board as well as first results are presented within this paper.

The Routing Protocol for Low power and Lossy Networks (RPL) is a wide-spread, flexible routing protocol specifically designed for energy-constrained networks such as Wireless Sensor Networks (WSNs). The resilience of RPL has been verified in several existing evaluations, but how a simple node reset can impact the energy efficiency has not been investigated so far. Thus, in this paper we examine the energy costs of transient node failures in a RPL network. We show that such temporary node failures can have a significant impact on the network's total energy usage. As transient node failures are common in WSNs this work reveals an important weakness of RPL which can even be exploited for attacks.

Abstract Voice calls are still one of the most common use cases for smartphones. Often, sensitive personal information but also confidential business information is shared. End-to-end security is required to protect against wiretapping of voice calls. For such real-time communication, the ZRTP key-agreement protocol has been proposed. By verbally comparing a small number of on-screen characters or words, called Short Authentication Strings, the participants can be sure that no one is wiretapping the call. Since 2011, ZRTP is an IETF standard implemented in several VoIP clients. In this paper, we analyzed attacks on real-world VoIP systems, in particular those implementing the ZRTP standard. We evaluate the protocol compliance, error handling, and user interfaces of the most common ZRTP-capable VoIP clients. Our extensive analysis uncovered a critical vulnerability that allows wiretapping even though Short Authentication Strings are compared correctly. We discuss shortcomings in the clients’ error handling and design of security indicators potentially leading to insecure connections.

Electric vehicles (EVs) require a well-developed charging infrastructure. Particularly when used for the daily commute, most EV drivers will rely on a nightly charge in their garage, for instance. In typical European urban residential areas, however, private parking and charging resources are severely limited. Therefore, public on-street charging often is the only option. However, it faces several limitations that lead to an inefficient and unfair utilization of charging stations, or EV supply equipment (EVSE). For instance, EVSEs are often blocked by fully charged vehicles. We thus propose and evaluate a cooperative protocol for EVs that facilitates coordinated handovers of EVSEs. We integrate this protocol with the ISO 15118 standard and provide a detailed security analysis. In the evaluation, we show that coordinated handovers significantly improve both EVSE utilization (helping to amortize the expensive operating costs) and provide benefits for EV owners by providing sufficient charging resources. This reduces range anxiety and saves them from cruising for charging.

The fault-tolerant character of WSN protocols and applications that do not assume completely reliable systems legitimize undervolting - a highly efficient energy management technique where the supply voltage is set below the minimum specifications. As has been shown in earlier work, by using thereliable IdealVolting undervolting scheme the lifetime of WSN applications can be increased significantly while keeping the node in a safe state even under rough environmental conditions. To show the usability of undervolting in a real world WSN deployment, we performed a long-term study of IdealVolting in a Smart Farming application. All measurements were performed on a generic outdoor testbed for WSNs (PotatoNet) which is also presented within this paper. We collected a long-term dataset of a WSN running for one farming season on a potato fieldto compare the reliability and performance characteristics of IdealVolting against a regular powered WSN.

Being able to determine the location of a node is of great advantage in many IoT and WSN applications. For example, in health care scenarios or for autonomous configuration of IoT setups this information can be useful. One of the key challenges in localization is to estimate the distance between nodes. Most present indoor localization systems require additional hardware for this estimation which is costly in terms of money and energy consumption. To overcome this disadvantage, we developed a system which is able to perform distance measurements without adding any extra hardware and costs. It is based on phase measurements performed by the IEEE 802.15.4 transceiver chip that is normally solely used to realize communication. In the evaluation we investigate the performance of our system in different real world environments that are typical for IoT and WSN setups.

Congested roads not only lead to inattentive and inpatient drivers, but also have a significant negative economic impact. Especially during rush hour traffic at traffic light regulated intersections, inefficient cycle plans and the increased demand raise the need for mechanisms that increase the traffic efficiency. This paper presents a rule based algorithm for realizing platooning at traffic lights, in order to increase the throughput and to reduce the shock wave effect commonly observed at intersections. The algorithm makes use of Vehicle-2-X (V2X) communication technologies, by actively exchanging messages between the vehicles in order to set up the platoon. As a distinction to related work, the algorithm focuses on mixed traffic, in which not all vehicles are necessarily equipped with V2X technologies. The algorithm is implemented into an holistic simulation framework in order to study the effects of the parameters of the algorithm on the traffic efficiency.

Automated valet parking services provide great potential to increase the attractiveness of electric vehicles by mitigating their two main current deficiencies: reduced driving ranges and prolonged refueling times. The European research project V-Charge aims at providing this service on designated parking lots using close-to-market sensors only. For this purpose the project developed a prototype capable of performing fully automated navigation in mixed traffic on designated parking lots and GPS-denied parking garages with cameras and ultrasonic sensors only. This paper summarizes the work of the project, comprising advances in network communication and parking space scheduling, multi-camera calibration, semantic mapping concepts, visual localization and motion planning. The project pushed visual localization, environment perception and automated parking to centimetre precision. The developed infrastructure-based camera calibration and semi-supervised semantic mapping concepts greatly reduce maintenance efforts. Results are presented from extensive month-long field tests.

In this paper, we present the usage of our two-platform DTN node "Amphisbaena". It is designed for wireless outdoor operation without the need of an external energy supply. A Low Power Platform is running continuously and is able to power up a Linux based SBC on demand. Both parts are using the same communication protocol and appear as a single node to neighbors. In this demonstration we show the system in an example application, which allows to capture an image from a webcam attached to the High Power Platform. The request for the image is sent using a low power link while the answer is transferred using WiFi from the SBC.

In most Wireless Sensor Network deployments, the energy supply is a major challenge. Especially for nodes with high computational power or high bandwidth communication interfaces, the required size of batteries might increase to infeasible levels, even if the option of energy harvesting exists. For many use cases, some nodes are idling most of the time and transmitting only a few bytes from time to time. In this paper, we present a two-platform node consisting of a high-power and a low-power platform. Both platforms are using the same Delay-Tolerant Networking (DTN) architecture and the same protocols. A novel concept offers the opportunity for both platforms to appear as a single node to communication partners. The high-power part is running a full-featured Linux operating system, the low power platform is built around an energy-efficient 32-bit microcontroller and is able to fulfill tasks, which would have required to wake up the high power node in a conventional setup. Our system can increase the energy efficiency in WSN scenarios where the demand of bandwidth and computational performance is strongly fluctuating.

The deployment and especially the long-term operation of outdoor Wireless Sensor Network (WSN) testbeds is still a challenging task. If different monitoring tasks with significantly varying demands have to be performed, the handling of scarce resources like energy becomes difficult and might lead to questions about the reliability of the testbed. In this paper, we present "PotatoMesh", a remotely deployed WSN consisting of different classes of nodes. In addition to more regular sensor nodes like INGA [1], we introduce new 'two-platform' nodes which consist out of a higher and a lower processing & communication performance part. Several, different tasks can be assigned to the nodes. Depending on the needs of the tasks, they may be executed on the more energy-efficient low-power part or lead to the boot up of the high-power platform. Experiences made from this deployment are used to create new energy-efficient routing schemes for self-powered wireless network deployments.

In modern industry, robots and other highly automated machines are one of the most important parts in production. For future development in production techniques these machines will work in more flexible setups. To enable such setups wireless communication needs to fulfill strict real time requirements. In this paper we present a tool to verify whether a communication method fulfills the requirements. Furthermore, it helps during development of this communication by providing debug information. All data is provided to Wireshark, an easy to extend, open source protocol analyzer.

This demo paper describes the usability and effectiveness of our distributed energy measurement system for WSNs. The system is composed of several micro-controller-based oscilloscopes - named PotatoScope. The intention of PotatoScope was to enable a scalable and dependable energy measurement for challenging environmental conditions, e.g., WSN outdoor deployments. We will present the general architecture by using two of our nodes and demonstrate how to measure energy consumption of nodes in our testbed. Certainly, the PotatoScope can be used standalone to measure energy comsumption of other devices, such as other micro controllers or single-board computers, e.g. Raspberry Pis. The demo will introduce a GUI, that displays information directly on a computer. Both the PotatoScope, including the hardware layout and the firmware, as well as the distributed energy measurement system is free to be used in own projects.

Energy is one of the most critical resources in Wireless Sensor Networks (WSN). For any WSN deployment, being it for a productive use case or for a testbed, the ability to perform energy measurements is of major importance, e.g., to estimate the status of the WSN, the need for maintenance, or for remaining lifetime. This paper presents a distributed energy measurement system for outdoor applications. An existing testbed has been extended by the micro controller unit (MCU)- based oscilloscope PotatoScope. Measuring voltage and current of the sensor node, undervolting effects and energy consumption of realtime applications can be observed. The PotatoScope is capable of capturing the power dissipation precisely at a high temperature range of 100 K. Using high sample rates with up to 500 kHz, the system needs to be capable of storing and archiving the measured data. A final evaluation shows a 0.9% drift for voltage measurements and a 1.6% drift for current measurements over the range of 100K. Using an SD card, long-term measurements can be made with up to 500 kHz. Nevertheless, a live mode allows sample rates up to 2 MHz when using the PotatoScope with a computer.

Cooperation between vehicles facilitates traffic management, road safety and infotainment applications. Cooperation, however, requires trust in the validity of the received information. In this paper, we tackle the challenge of securely exchanging parking spot availability information. Trust is crucial in order to support the decision of whether the querying vehicle should rely on the received information about free parking spots close to its destination and thus ignore other potentially free spots on the way. Therefore, we propose Parking Communities, which provide a distributed and dynamic means to establish trusted groups of vehicles helping each other to securely find parking in their respective community area. Our approach is based on high-performance state-of-the-art encryption and signature algorithms as well as a well-understood mathematical trust rating model. This approach allows end-to-end encrypted request-response communications in combination with geocast and can be used as an overlay to existing vehicular networking technologies. We provide a comprehensive comparison with other security architectures and simulation results showing the feasibility of our approach.

The energy consumption of Wireless Sensor Networks (WSNs) correlates with the voltage level at which the nodes are powered—a lowered voltage leads to a prolonged lifetime of nodes and networks. Operating nodes at voltage levels below the recommendation—so-called undervolting—saves energy but is accompanied by an increased risk of failures. In this article, we show that a WSN can still work reliably, even if the voltage recommendations are violated. We show that there is a correlation between temperature and error-proneness at the same voltage level and that ideal voltage levels depend on environmental conditions. Especially in outdoor deployments, temperatures fluctuate often and heavily. Additionally, we show that these ideal voltage levels are different for each individual node. To deal with these individual variations and varying temperatures, we present a supervised learning strategy that is able to keep the nodes in uncritical states even if environmental conditions are constantly and heavily changing while saving as much energy as possible by constantly adapting the voltage level of these nodes to an individually ideal level. All measurements were performed on sensor node prototypes that are also presented in this article. In detailed evaluations, it is shown (i) that a single node will never run in the same unsafe state twice, (ii) that only five known bias points are needed to predict nearly all temperature dependencies for an individual node, and, thus, (iii) that a system of undervolted nodes can be as reliable as a conventionally powered network while prolonging the lifetime by more than 40%.

Automated valet parking not only improves driving comfort, but can have a considerable impact on the urban landscape by reducing the required parking space. We present the first study of parking space optimization for automated valet parking with an in-depth theoretical analysis of the parking lot properties under various aspects, inluding the worst-case extraction time, total shunting distance, and the number of shunting operations (each per car). Most importantly, the proposed model bounds all these values. We verify the theoretical properties of our model in four simulated scenarios, one of which is based on real-world data from a downtown parking garage. We show that very good pick-up times of about 1 min are possible with very little overhead in terms of shunting distance and time, while providing a significantly improved parking density as compared to conventional parking lots.

Modern cars are already able to park in parking spaces adjacent to streets. Soon autonomous cars will be able to navigate themselves through parking garages to find a parking lot assigned to them. Indoor localization is essential to qualify cars and parking garages to perform this operation. Currently the reliability of many indoor localization schemes suffers from non-line-of-sight propagation paths. We present a position estimation algorithm for indoor localization systems based on phase measurements of electromagnetic signals. Our algorithm is designed to detect and exclude measurements originating from these non-line-of-sight paths to reduce their harmful influence on the localization.

Body area networks (BANs) consisting of small sensing and computing devices can help to improve medical care and well-being of humans. Obviously, the data recorded in BANs such as vital parameters are personal and should be private. To protect this privacy, such data are usually encrypted when transmitting it over a wireless link. In the past, many cryptographic algorithms and methods for the encryption and decryption of data have been proposed-and most of them have become obsolete. One-time pads (OTPs) were mathematically proven to be secure and impossible to crack. But, for most purposes, OTPs are complicated to handle, because if applied correctly, for each bit of plain text data, another bit of OTP must be available. Sensors in BANs usually do not generate an enormous amount of data. Hence, also the length of an OTP is not huge. Sustained progress in memory technology makes large amounts of nonvolatile memory available at cheap prices and small sizes. Thus, numerous OTPs can be preinstalled on BAN devices and ensure a long lasting and secure data transmission. In this paper, we present a concept for securing data transmission in BANs by utilizing OTPs. We delineate a system for generation, distribution, and utilization of OTPs in wireless sensor network (WSN) and BAN scenarios, and we show the implementation and evaluation of such a system.

Adapting the voltage level of a processing unit to the actual system load leads to an increased energy efficiency. The aim is to extend the battery lifetime, but existing voltage scaling approaches still act with reserve. To reduce the energy consumption even further, it is possible to power the electric circuits below the specified voltage levels. Considering the processing unit of wireless sensor nodes, this “undervolting” saves up to 42% of energy per clock cycle, and hence would lead to a significant longer lifetime of nodes and networks. Contrariwise, operating processors or nodes outside their specifications add some extra incertitude to the system. In this paper, we analyze the effects of undervolting for a typical wireless sensor node in theory and practice. Moreover, we give a detailed insight into the dependencies and used a prototype implementation to characterize the influence of lower than recommended voltage levels on the microcontroller unit (MCU). In addition, the impact of different temperatures is considered as well as the behavior of an undervolted transceiver unit and, therefore, the effects on the wireless communication. While classical computer applications may contain too many hazards to outweigh the improved energy consumption when using undervolting, we show that it is particularly suitable for wireless sensor networks (WSNs) with a huge potential of saving energy and the opportunity of novel power management approaches on every layer.

Typical home automation systems consist of dense populated sensors and actuators in wireless networks. In apartment houses, networks are often deployed closely to each other by different neighbors. In such scenarios wireless networks suffer from packet loss caused by interference with other networks. Packet loss causes unnecessary delay and energy consumption. To overcome this, transmission power control can be used to lower the interference. However, reducing the interference is a rarely used capability of transmission power control. This paper presents transmission power control based on a P-controller. The feedback loop for the signal-to-noise ratio is realized by modifying the link layer acknowledgments of IEEE 802.15.4. The evaluation of the system is performed in a real-world testbed. It shows the benefit of reducing the transmission power in dense networks. The application layer loss can be lowered by 5%.

In the past we presented a delay tolerant network that used public buses and trams in the city of Braunschweig to monitor air pollution. Today, as smartphones are becoming computationally more powerful and offer a variety of communication interfaces, it becomes attractive to investigate whether smartphones and vehicular nodes can cooperate with each other, forming a network that can provide better quality of service to applications. In this paper, we evaluate the feasibility of creating an integrated Delay- and Disruption-Tolerant Network (DTN) consisting of smartphones and the public transportation system. Most importantly we propose a Misbehavior Detection System (MDS) to protect the security of the hybrid network. The evaluation results show that our MDS is able to efficiently detect attackers and defend the hybrid network against the interference of malicious nodes.

Electric vehicles (EVs) still have relatively long and frequent charging cycles. Moreover, charging resources are typically limited and must therefore be used efficiently. The V-Charge project has the vision to provide a solution by combining autonomous valet parking with e-mobility, introducing improved parking and charging comfort. V-Charge proposes a solution for charging autonomous EVs in parking places and efficiently using scarce charging resources, thus simplifying the life of the customer and increasing the feasibility of EVs. For the management of parking lots and charging resources, V-Charge provides a server back end and a communication infrastructure. In this paper, we present our design of scheduling concepts for a coordinated charging strategy that is implemented by this back end. Through intensive simulations, we show that the V-Charge server is able to efficiently handle realistic parking volume and performs well in fulfilling customer requirements, e.g., energy demand for the next driving tasks. Moreover, we evaluate the suitability of various scheduling strategies in different usage scenarios. For the simulation setup, real-world parking statistics obtained from Hamburg Airport and the City of Braunschweig, Germany, are used.

Wireless sensor networks for industrial process monitoring and control require highly reliable and timely data delivery. To match performance requirements, specialised schedule based medium access control (MAC) protocols are employed. In order to construct an efficient system, it is necessary to find a schedule that can support the given application requirements in terms of data delivery latency and reliability. Furthermore, additional requirements such as transmission power may have to be taken into account when constructing the schedule. In this article, we show how such schedule can be constructed. We describe methods and tools to collect the data necessary as input for schedule calculation. Moreover, due to the high complexity of schedule calculation, we also introduce a heuristic. We evaluate the proposed methods in a real-world process automation and control application deployed in an oil refinery and further present a long-term experiment in an office environment. Additionally, we discuss a framework for schedule life-cycle management.

In mobile applications, like wireless sensor networks, it is often inevitable to use a location-independent source of energy. Wherever the batteries capacity or inefficient energy harvesting limits the lifetime, other solutions have to be implemented to increase the energy efficiency. Dynamic Voltage Scaling (DVS) is a well known technique with the ability to adapt the voltage level to the actual system load to save energy. While it has been used in many application areas, DVS has not been studied sufficiently for wireless sensor nodes. In this paper, we present a method to estimate the gain of DVS. We study DVS theoretically as well as in a practical manner, i.e., we using a prototype implementation of a DVS capable wireless sensor node. With the theoretical considerations we were able to optimize DVS for an 8-Bit ULP micro controller by a combination of DVS and dynamic power management (DPM). In addition, we proved the calculated results with an extensive practical evaluation of the concept using a prototypical implementation. Moreover, we analysed the effect of voltage scaling on other components of the sensor node (transceiver, sensors and memory).

In mobile applications, like wireless sensor networks, it is often inevitable to use a location-independent source of energy. Wherever the batteries capacity or inefficient energy harvesting limits the lifetime, other solutions have to be implemented to increase the energy efficiency. Dynamic Voltage Scaling (DVS) is a well known technique with the ability to adapt the voltage level to the actual system load to save energy. While it has been used in many application areas, DVS has not been studied sufficiently for wireless sensor nodes. In this demo, we show the benefits of DVS. We were able to optimize DVS for an 8-Bit ULP micro controller by a combination of DVS and dynamic power management (DPM). Moreover, we analyzed the effect of voltage scaling on other components of the sensor node (transceiver, sensors and memory).

Dependable Wireless Sensor Networks for industrial process automation, monitoring and control applications have high demands regarding network reliability in terms of timely delivery and packet loss. In large industrial facilities, interference between neighboring networks is a major problem that can be mitigated by reducing the radio transmission power to the necessary minimum. However, reliability of the network should not be compromised even in spite of packet loss bursts. In this paper we aim at keeping the link within certain burstiness bounds while still minimizing the transmission power. We present evaluation results showing that the burstiness changes with the receiver signal strength. Based on this observation we present two mechanisms for dependable wireless sensor networks and study the performance in our testbed.

Today, many sensor nodes are equipped with a microSD slot to provide a cost effective way to store large amounts of data. When using the FAT file system, data collected by a node can be easily read by a PC without the need for any special software or communication protocol. While several FAT implementations for microcontrollers do exist, they are not suited for real-time applications. For a WSN in an industrial scenario where a node needs to run a closed loop control program, logging to a non-real-time capable persistent storage system is not an option. In this paper we present RATFAT, an efficient implementation of a flexible real-time capable FAT file system for Contiki, that can be used for applications requiring real-time guarantees.

While for an automatic and autonomous indoor fall detection an enormous amount of different sensors is conceivable, for an outdoor fall detection only wearable sensors are applicable. For practical uses cases, it would be very beneficial if after a detected fall a medical alert is initiated. In indoor environments, a base station connected to a telephone line can handle these calls. On the road, this can be achieved by mobile phones or smartphones. In this paper we first estimate the suitability of several systems for an outdoor fall detection. Then, we propose a system for a mobile and stationary fall detection and alerting system. We implemented and evaluated this system, which is consisting of a smartphone and a wireless sensor node.

Future requirements for drastic reduction of CO2production and energy consumption will lead to significant changes in the way we see mobility in the years to come. However, the automotive industry has identified significant barriers to the adoption of electric vehicles, including reduced driving range and greatly increased refueling times. Automated cars have the potential to reduce the environmental impact of driving, and increase the safety of motor vehicle travel. The current state-of-the-art in vehicle automation requires a suite of expensive sensors. While the cost of these sensors is decreasing, integrating them into electric cars will increase the price and represent another barrier to adoption. The V-Charge Project, funded by the European Commission, seeks to address these problems simultaneously by developing an electric automated car, outfitted with close-to-market sensors, which is able to automate valet parking and recharging for integration into a future transportation system. The final goal is the demonstration of a fully operational system including automated navigation and parking. This paper presents an overview of the V-Charge system, from the platform setup to the mapping, perception, and planning sub-systems.

We consider the recognition of activities from passive entities by analysing radio-frequency (RF)-channel fluctuation. In particular, we focus on the recognition of activities by active Software-defined-radio (SDR)-based Device-free Activity Recognition (DFAR) systems and investigate the localisation of activities performed, the generalisation of features for alternative environments and the distinction between walking speeds. Furthermore, we conduct case studies for Received Signal Strength (RSS)-based active and continuous signal-based passive systems to exploit the accuracy decrease in these related cases. All systems are compared to an accelerometer-based recognition system.

The number of connected cars is growing continuously. Many car manufacturers offer systems, which provide online content to the passengers, mostly infotainment and information data. Although new wireless data communications technologies like LTE will offer much more performance, the increasing number of mobile data users in combination with higher individual data traffic will nullify the higher capacities. Mobile data bandwidth will remain a rare commodity. If next generations driver assistance systems should be supplied with data from central servers in time and according to their individual priorities, it is important to make optimal use of the available resources. Considering the changing channel conditions of the wireless links offers potential for improvements, since the channel quality has a direct influence on the utilization of the data channel. HSPA and LTE use the so called Channel Quality Indicator (CQI) as a measure of the channel conditions. Summarized in a map, server-side applications can use a priori knowledge of the location-dependent channel quality to optimize the data distribution to mobile clients. This paper describes the process of creating CQI maps for HSDPA networks, from the initial collection of raw data to the final validation of the proposed concept.

Vehicle-to-Vehicle (V2V) communication is envisioned to enable a vast range of road safety, traffic efficiency and infotainment applications for next-generation vehicular traffic. In this paper, we investigate the effects of vegetation on the performance of V2V communication based on a 5.9GHz measurement campaign conducted at different urban and rural intersections with different types of vegetation under non-line-of-sight (NLOS) conditions. We evaluate received power levels and packet delivery rates under varying conditions with respect to vehicle positioning, intersection layout and vegetation type. To capture the additional signal attenuation caused by foliage, the measurements for each intersection were conducted both in summer and in winter, which allows comparing the impact of leaved and leafless vegetation. Moreover, we derive the additional attenuation caused by vegetation and compare the measurement results with three well-known empirical models for vegetation-induced path loss. Based on the acquired sets of measurement data, we present a simple parametrized model for estimation of path loss caused by vegetation in V2V scenarios.

Delay or disruption tolerant protocols can be used in several application areas. In the area of Ambient Assisted Living (AAL) or healthcare, these protocols are well-suited to provide a seamless handover between online and offline monitoring of vital parameters or activity data; this also implies a synchronization of offline gathered data. In this paper, we analyze the expected data rates for several medical sensors and applications and give an insight into how to dimension such disruption tolerant protocols and systems. We also developed a scenario for activity recognition in which we constantly monitor the acceleration data of a wearable sensor node. We implemented and evaluated this scenario with our disruption tolerant protocol for wireless sensor nodes and show its overall functionality, its utility, and its limits.

Today's industrial facilities, such as oil refineries, chemical plants, and factories, rely on wired sensor systems to monitor and control the production processes. The deployment and maintenance of such cabled systems is expensive and inflexible. It is, therefore, desirable to replace or augment these systems using wireless technology, which requires us to overcome significant technical challenges. Process automation and control applications are mission-critical and require timely and reliable data delivery, which is difficult to provide in industrial environments with harsh radio environments. In this article, we present the GINSENG system which implements performance control to allow us to use wireless sensor networks for mission-critical applications in industrial environments. GINSENG is a complete system solution that comprises on-node system software, network protocols, and back-end systems with sophisticated data processing capability. GINSENG assumes that a deployment can be carefully planned. A TDMA-based MAC protocol, tailored to the deployment environment, is employed to provide reliable and timely data delivery. Performance debugging components are used to unintrusively monitor the system performance and identify problems as they occur. The article reports on a real-world deployment of GINSENG in an especially challenging environment of an operational oil refinery in Sines, Portugal. We provide experimental results from this deployment and share the experiences gained. These results demonstate the use of GINSENG for sensing and actuation and allow an assessment of its ability to operate within the required performance bounds. We also identify shortcomings that manifested during the evaluation phase, thus giving a useful perspective on the challenges that have to be overcome in these harsh application settings.

Wireless Sensor Nodes often need to store or cache measurement or operational data into some non-volatile memory. Many applications using low power sensor nodes are based on Contiki, which provides the COFFEE file system for data storage. As COFFEE introduces occasional long and hard to predict write delays, it can not be used in applications which have real time demands, such as sensor networks operating in industrial environments. In this paper we present an efficient implementation of a flexible Ring File System for Contiki, that can be used in real-time applications. Read and write times are predictable and adherence to Contiki's file system API allows it to be used as a drop-in replacement for COFFEE in many applications.

In most of today's healthcare and AAL scenarios a multitude of data is recorded by different sensors for various purposes. By definition, this data is mostly personal and can be assigned to certain persons, which again makes it interesting for shady data miners, hackers, or even health insurance companies. Thus, this data needs special care regarding privacy and security. On the other hand, if the systems are spread over a larger area, a remote access to such systems is essential for the operator. At least a basic system monitoring should be possible and backups to a distant location are beneficial if the distributed systems fail. In this paper we provide concepts and solutions how in distributed installations of personal AAL platforms privacy and security can be preserved, while remote backup and restore functionality and remote system monitoring can be provided.

During the last few years, vehicle-to-vehicle (V2V) wireless communication has become a key objective for enabling future cooperative safety applications, such as intersection collision warning. In this paper, we present the results of a 5.9 GHz V2V performance measurement campaign at four different urban intersections under NLOS conditions using commercial off-the-shelf wireless interface cards which meet the 802.11p and ITS-G5 specifications. Particularly, we quantify the packet delivery ratio (PDR) and received signal strength indication (RSSI) levels associated with different scenario conditions with respect to vehicle positioning, intersection geometry and traffic density. We determine reliable communication ranges which constitute an important metric for V2V collision avoidance applications.

Delay Tolerant Networking (DTN) enables transfer of data where conventional network protocols fail to deliver data because no continuous end-to-end connectivity is available. While the Bundle Protocol (BP) has been established as the standard DTN protocol in many application areas, Wireless Sensor Networks (WSN) often use proprietary protocols with a subset of the BP features. In this paper we use an exemplary application to demonstrate how the BP can be beneficial for many WSN-based projects. We show, how low-power sensor nodes can transport bundles by exploiting existing movement in the environment. More importantly we show, how 8-bit WSN nodes can seamlessly interact with standard BP implementations running on standard PCs. Our application, a sensor that is installed on the roof of a 15-story building, is using an elevator to transport bundles carrying measured values to our lab. We analytically compare the BP to existing protocols for WSNs, evaluate our application scenario and give insight into principal limitations.

In this demo we present IBR-DTN for Android: IBR-DTN is a fully featured RFC5050 compliant Bundle Protocol implementation that can run on un-rooted Android devices starting from Android Version 2.3 (Gingerbread). IBR-DTN for Android supports all features of the IBR-DTN version for PCs and embedded systems. It is available in the Google Play Store for free.

In this paper we present an approach to piggyback link quality measurements to IEEE 802.15.4 acknowledgement frames by generating acknowledgements in software instead of relying on hardware support. We show that the software-generated ACKs can be sent meeting the timing constraints of IEEE 802.15.4. This allows for a standard conforming, energy neutral dissemination of link quality related information in IEEE 802.15.4 networks. This information is available at no cost when transmitting data and can be used as input for various schemes for adaptive transmission power control and to assess the current channel quality.

In this demo, we present some exemplary applications for INGA, a new and affordable wireless sensor node for general applications. INGA's hardware design is completely under open source license and it runs the open source operating system Contiki "out of the box". Several up-to-date sensors are included in the basic design and we developed it for research, medical applications and universal usage.

The goal of the GINSENG project is a performance-controlled sensor network suitable for applications with specific network performance requirements, such as plant automation and health monitoring. Any such sensor network must include a deterministic MAC protocol that can meet the application's targets in areas like delivery delays and reliability. We present a description and preliminary evaluation results of GinMAC, designed to be such a MAC protocol. Also included are details of a deployment to the GALP oil refinery in Sines, Portugal.

Mobile internet has rapidly evolved in the past years with an ever increasing number of novel technologies and services. Today's mobile devices often support multiple communication technologies for accessing Internet services. However, they all do not tap the full potential of these capabilities as users often have to manually select networks and only one network is used at a time. Different approaches in the area of Always Best Connected propose strategies for user-centric network selection, but most of them focus either on application-oriented or device-centric approaches. The muXer project aims at combining both aspects and increasing the efficiency of network usage. In this paper, we introduce the muXer Global Arbitration Process (GAP) that balances application-oriented ratings of networks while optimizing the usage of communications resources and simultaneously meeting the application and user requirements. Besides deciding which single network an application should use, GAP considers network bundles as well as a proactive delaying of data transfers as additional options to reach a global optimum for all applications running on the device. We compare GAP with other network selection strategies and present benchmarks showing that these aspects bring a clear efficiency gain.

Highly interactive real-time music applications like network music performance (NMP) currently lack appropriate audio codecs that meet both demands for low delay and high audio quality. Music audio codecs introduce unacceptable processing latencies, while low-delay speech codecs provide insufficient audio quality. In this article we describe how we integrated the WavPack audio coding scheme into our NMP system for interactive distributed network centric music performances. Our evaluation shows that WavPack performs very well in such types of delay-critical applications. In NMP it provides high compression ratios and good audio quality without additional buffering delays.

Network-centric Music Performance (NMP) enables Internet-based multiparty music performance through cyberspace. Our goal is to support real-time distributed natural audio delivery over the network, using audio compression schemes with exceptional audio quality. Among many challenges, a tight delay bound between the production and perception of the audio is a dominant requirement. The demo video shows a recorded session of a live network-centric music performance demonstration involving a SDSL access network. It demonstrates that musicians can play together smoothly on a virtual stage provided by NMP. Beyond our previous work of realizing NMP in local and wide area research networks, this is the first time NMP has been enabled with a commercially available synchronous DSL access network. The positive ratings by the musicians confirm that NMP is ready for large-scale commercial deployment once such access technology is widely available and affordable to the end users.

Digital video streaming has attracted large interest in research as well as in commercial areas in recent years. The evolution of digital video coding and broadband Internet access enables a large number of users to access high quality video streams with several devices varying from mobile phones to notebooks. However, digital video streaming still has high resource requirements concerning the transmission and decoding of the streams. Especially mobile devices often cannot comply with such resource demands. This paper briefly describes our multimedia gateway implementation which provides video adaptation to mobile clients by using multidimensional compressed domain transcoding mechanisms.

We present an open source tool called MPEG analyzer that is able to visualize various MPEG-2 encoding characteristics while playing a video stream. Our tool has been developed during a student lab and is intended to support teachers and lecturers in teaching the functioning of MPEG-2 encoding techniques.

Internet protocol-based multimedia applications are gaining momentum thanks to the great proliferation of the Internet and mass deployment of broadband. The abundance of rich content, heterogeneity of networks, user terminals, and services, along with the surges of multimedia traffic, have convoluted ever-increasing complexity and costs in the operation and management of multimedia systems. Autonomic communications (AutoComm) promotes the autonomy of communication networks with minimum human administration. In a multimedia system that features AutoComm, the networks and their elements strive to realize efficiency, immunity, resilience, and evolvability through intrinsic self-governance. By encapsulating complexity within the networks, exploiting their intelligence, and using technology to manage technology, human administrative efforts can be greatly reduced while management efficiency can be maximized. In this paper, we want to illustrate how traditional way of management and control of multimedia networks can be gradually replaced by network autonomy and self-management. Related work is extensively reviewed and compared to our approach. Initial experiment results are presented as proof of concept.

The growth and evolution of the Internet and the rapid adoption of new wireless, mobile, and self-organizing networks and new services are constantly adding complexity and costs in network management. The traditional manual and static network management paradigm fits poorly into the changing environment where human efforts should be kept at a minimum, and gradually replaced by technologies themselves. We introduce a novel network self-management scheme. Our goal is to seek the synergy between autonomic management, policy-based manage- ment, and autonomic control. They all form the Architecture for Network Autonomy (ANA) that strives to realize proactive policy- based network management for autonomic communications. In this paper, we study the related work, describe the design considerations of ANA as well as its current implementation status, and present the initial results gathered. The Internet continues to grow and evolute, with rapid adoption of new wireless, mobile, and broadband networks. The trend of everything over IP and IP connects everything is being made self-evident by a myriad of sensors, devices, terminals, hosts that are penetrating into each single domain of modern work and life. Numerous services and applications, span WANs, LANs, vehicles, offices, homes, down to human bodies. All of this has convoluted the crisis of Internet manage- ment, in particular the spatio-temporal complexity of network dynamics, and the management and control difficulties. The traditional way of manual planning, configuration, trouble- shooting, and performance tuning will be exorbitantly ex- pensive or even dominate operational cost, as opposite to hardware/software improvements that continuously help to reduce capital expenses. The shortage of skilled labor and the limits of human management of complex systems are complicating the problem further. Besides the looming complexity, the relatively static and time-consuming procedure of conventional network manage- ment calls for new efforts to react to the dynamics and scale of the networks (considering their sheer sizes and traffic volume) in a timely manner. Even more essential is the mapping and bridging between the high-level management constraints and low-level configuration rules, with the latter being the implementation of the former. In doing so the users and administrators can remain control at a high and abstract level by specifying only objectives, and the system will self-govern itself towards realizing the high-level policies, and behaves as expected. Such paradigm requires new system architecture, network model, protocol stack, as well as algorithms for network self-management. In the rest of this paper, we first review the related work in Section 2 that covers three main areas, namely autonomic communications, policy-based management, and the semantic web technologies. Based on this, we present the architecture for network autonomy in Section 3. This is followed by Section 4 on the details of the design and implementation of our prototype. We also show some initial evaluation results in Section 5. Finally, Section 6 highlights the concluding remarks and outlines the directions of future work.

Emerging Wireless Body Area Sensor Networks are a promising technology which enables health monitoring of elderly people and enhances their independent living. In this paper, we propose the system architecture and protocol stack of a Wireless Body Area Sensor Network for health monitoring of elderly people. The architecture can be deployed in both indoor and outdoor environments and enables transmission of both routine and emergency vital signs.

The need for mobility awareness in ad hoc routing protocols is widely proclaimed. In this paper we present AODV-AP, a scheme to make AODV nodes aware of the accessibility of the neighbor nodes in the network. Nodes acquire the accessibility information of the other nodes through routine routing operations and keep it in their routing tables. later, this information can be utilized to enhance routing operations. One possible use of this accessibility information, restrict the route discoveries for inaccessible nodes, is also evaluated in this paper. Simulation results show that the use of accessibility knowledge in the route discovery process largely reduces the MAC and Routing overhead. Similarly, the Normalized Throughput with respect to MAC overhead is up to 3 times higher than that in standard AODV which reflects the effective use of network resources.

Abstract 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.

The increasing number and diversity of wireless mobile devices are driving a revolutionary change in the way users are accessing and using services and resources. Mobile ad hoc networks (MANETs), temporarily created by mobile devices, offer opportunities for sharing services and resources made available by member nodes. Especially, real-time applications have great potentials in mobile ad hoc environments as MANETs form an ideal technological basis for ad hoc real-time interaction among people. However, real-time applications require low latency connections with a minimum of jitter and packet loss rate from the underlying network. To meet these demands is a challenging task in mobile ad hoc networks due to the high level of node mobility, properties of the wireless communication channel and the lack of central administration. In this paper, via a simulation study we analyze and evaluate some Quality of Service (QoS) extensions, like priority queuing or rate control policies, to ad hoc routing in IEEE 802.11 wireless mobile ad hoc networks from the aspects of real-time applications. We show how these QoS extensions can improve the performance of AODV routing protocol and why we selected AODV as the starting point of our work.

Real-time interactive multimedia applications are highly delay-sensitive, and packets that are out of delay boundaries are usually obsolete. However the current Internet Protocol lacks a way to control the lifetime of the packets explicitly. We propose a packet lifetime control mechanism called Explicit Delay Control (EDC) that embeds a Maximum Tolerable Delay (MTD) field in an IPv4 option. At each network node, the MTD is deducted by the singlehop delay. Packets that expire their lifetime are discarded and non-congestion related delay losses are signaled to the sender to reduce inaccuracy in delay estimations and to adapt to path changes. We implemented EDC in the Linux kernel. Our evaluation has shown that EDC is an effective scheme to ensure the “legality” of the packets, reduce the waste of bandwidth and processing time in the networks, and alleviate congestions.

Network management requires a lot of manual work. Due to ongoing growth of the Internet, more self-management is needed in order to deal with the growing complexity. Policy-based management is an approach to simplify management by the use of rules. Policy refinement, i.e. breaking down high-level policies to technical configurations is still a task that needs manual work. We propose an architecture that uses Web services and automatic Web services composition as a complementary technique to policy refinement in order to automate policy-based management.

Over the last couple of years, multi-player games have become more and more popular. Additionally, new mobile devices now have sufficient resources to play these multi-player games in mobile and wireless networks. As the classic centralised game server design is unsuited for mobile ad-hoc networks, a group of nodes can take the role of a distributed game server. This group of nodes can provide the necessary redundancy which is needed in the dynamic environment of a mobile ad-hoc network.

Wireless video streaming is an area of extensive research due to the error-prone nature of the radio channel with variations in throughput and delay. In mobile networks, handovers may lead to further service degradation. Therefore adaptation has to be applied in order to cope with these challenges. This paper introduces a new two-level proxy architecture, which addresses the aforementioned issues. The first level proxy provides media adaptation to the requirements of its clients by using transcoding techniques and thereby supports many different mobile devices. The second level proxy is supposed to perform adaptation to the radio channel by using FGS-coding as well as unequal error protection. We also discuss handover QoS issues and approaches for signaling with service composition. Our two-level design is highly flexible and provides efficient, scalable and low-latency mobile streaming video. Besides, it provides better core network resource utilization while solving wireless channel problems where they occur.

Secure communication is very important in computer networks and authentication is one of the most eminent preconditions. However, common authentication schemes are not applicable in ad hoc networks because public key infrastructures with a centralized certification authority are hard to deploy there. We propose and evaluate a security concept based on a distributed certification facility. A network is divided into clusters with one special head node each. These cluster head nodes execute administrative functions and hold shares of a network key used for certification. New nodes start to participate in the network as guests; they can only become full members with a network-signed certificate after their authenticity has been warranted by some other members. The feasibility of this concept was verified by simulation. Three different models for node mobility were used in order to include realistic scenarios as well as make the results comparable to other work. The simulation results include an evaluation of the log-on times, availability, and communication overhead.

Resource management in active network nodes is challenging because more types and amount of resources are needed compared with traditional networks, and the consumption of different types of resources is not equally balanced. Hence, it is possible and important to consider the relationship between different types of resources, needed by an application. Adaptation of applications resource usages in network nodes enables the applications to react promptly to the resource status in the network nodes and therefore offers a better performance guarantee and more flexibility to the applications. This paper studies the resource management in active network nodes considering the relationship among different types of resources. The resource vectors (RVs) are introduced to describe the resource requirements of applications and their adaptation capabilities. And an adaptive resource management mechanism based on RV is proposed and the implementation of it in an active node is given.

Multiplayer games, i.e., games where several persons interact simultaneously over networks like the Internet, receive much interest. One of the reasons is that competing with human counterparts is typically considered as much more interesting and challenging than playing just against a computer.A major problem of network-based multiplayer games is caused by the network transmission delay. This means that it takes a while until information, e.g., about the movement of the opponents objects and their new position, reaches the receivers. This delay causes several difficulties and leads to paradoxical situations. For example, consider a racing game with two players, shortly after the start both believe that they have the lead because it takes a while until the position of the counter player reaches the local player. Approaches to provide for a global consistent state of the game by introducing a local presentation delay have been proposed, however, these increase the application-level delay even more.Therefore, it is important to investigate the impact such delays can have on the performance of multiplayer games and the attractiveness of these games for the human players. Such a study is the purpose of this work. We concentrate on real-time games for the Internet where significant delays can occur. The evaluation is performed through measurements using a car racing simulator.

Large scale video-on-demand systems require that the servers offering the video retrieval and playback services are arranged as a distributed system in order to support a large number of concurrent streams.If such a system is hierarchical, an end-node server handles the requests from a particular area, the next server in the hierarchy takes the request over for several end-node servers if those can not answer the request and so on.This architecture provides for cost efficiency, reliability and scalability of servers.The end-node servers store only a limited set of the overall available information which changes over time due to user interests.If a video is requested which is not available, this server contacts the next server in the hierarchy.To decide the size and location of the video servers and the location of videos in the hierarchy, the access behaviour of users must be considered.Various models for the simulation of user behavior (and thus, of the load induced on the video servers) have been presented in the literature.Only a few of these models are designed to take long-term effects into account because the basis for most of the models are short-term influences on a single' video server and the load on this single machine.In this paper we describe a new user behavior mode1 and show that various assumptions made within other models are unrealistic.

Multimedia communication deals with the transfer, protocols, services, and mechanisms of discrete media data (such as text and graphics) and continuous media data (like audio and video) in/over digital networks. Such a communication requires all involved components to be capable of handling a well-defined quality of service (QoS). The most important QoS parameters are used to request: (1) the required capacities of the involved resources, (2) compliance to end-to-end delay and jitter as timing restrictions, and (3) restriction of the loss characteristics. In this paper, we describe the necessary issues and study the ability of current networks and communication systems to support distributed multimedia applications. Further, we discuss upcoming approaches and systems that promise to provide the necessary mechanisms and consider which issues are missing for a complete multimedia communication infrastructure.

Continuous media such as audio and video require a certain quality-of-service (QoS) when transferred through computer networks. The selection of a network route for a particular media stream should hence take into account which route is best-suited for providing this QoS. QoSFinder is a method for QoS-based routing of multimedia streams. It is based on a path vector protocol that takes into account throughput, delay, and loss rate of individual route segments. A simulation of QoSFinder shows that its heuristic is superior to metrics that are only based on one of these parameters. QoSFinder increases the probability of finding suitable paths through networks for distributed multimedia applications.

Multimedia applications handling audio and video data have to obey time characteristics of these media types. Besides a basic functionality to express time relations, correctness with respect to time constraints requires mechanisms which lead to favoured processing of multimedia operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related quality of service requirements. This paper discusses mechanisms to express time in multimedia systems and describes an implementation of a CPU scheduler designed to run under IBM's UNIX derivate AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.