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.

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.

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.

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.

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.

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%.

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.

Context prediction is the task of inferring information about the progression of an observed context time series based on its previous behaviour. Prediction methods can be applied at several abstraction levels in the context processing chain. In a theoretical analysis as well as by means of experiments we show that the nature of the input data, the quality of the output, and finally the flow of processing operations used to make a prediction, are correlated. A comprehensive discussion of basic concepts in context prediction domains and a study on the effects of the context abstraction level on the context prediction accuracy in context prediction scenarios is provided. We develop a set of formulae that link scenario-dependent parameters to a probability for the context prediction accuracy. It is demonstrated that the results achieved in our theoretical analysis can also be confirmed in simulations as well as in experimental studies.