Low-power wide-area networks (LPWANs) enable a vast number of sensors to be connected in a low-maintenance, low-cost, and easily deploy-able way. Conventional cryptogra-phy measures used to provide secure communication in such networks, often result in a higher on-air time, which directly increases the energy consumption. Also the additional message size needed may exceed the actual payload. This paper combines the concept of sensor data watermarking together with side-channel utilization to satisfy integrity protection of sensor data without the need to sacrifice payload size for message authen-tication codes (MACs). Practical experiments using LoRaWAN over The Things Network (TTN) show that watermarks can be embedded in a side-channel without significantly changing the channel characteristics thus making the security fully transparent to the original data transmission both in terms of payload and timing characteristics.

Indoor localization is a core technology for many position-aware applications. This is often based on the mea-surement of the signal strength at the receiver end, which is available for many commercial radio protocols without additional costs, e.g., for WiFi, Bluetooth or Zigbee. However, a major limitation with received signal strength (RSS)-based methods are high inaccuracies resulting mainly from physical propagation effects. But these effects are not the only cause for erroneous position estimates. In this paper we first present a RSS measure-ment system and localization setup based on Software Defined Radio (SDR)s, which reduces protocol-specific influences such as transmit power management. In addition, the RSS value can be measured with a much higher resolution and sampling rate, which gives more headroom to analyze its statistical and temporal properties. The measurement data is then evaluated to get an insight on the errors and disturbances commonly associated with RSS localization schemes. This allows us to identify a problem in the basic way RSS-based localization methods process the measurement data, which could be partially responsible for the high variance typically associated with RSS measurements and the elusive fast fading effect. The goal of this work is to investigate some fundamental aspects of RSS localization to better understand the limitations of the technology.

With technological revolutions like the Internet of Things and Industry 4.0 on the doorstep, localization of network nodes is more important than ever. Indoor localization systems mostly work with omnidirectional antennas for simplicity reasons. Using directional antennas has advantages, though, and devices with such antennas will be included in IoT systems someday. In this paper, the focus is on dynamic changes in the configuration of localization systems. Adding an antenna must be handled fast and efficiently. Frequent recalculations of the configuration could be necessary, and limited resources make a reduction of the computational effort desirable. In this work we look at possible methods to cut the computational effort while minimizing the penalty on accuracy. Since accuracy is of utmost importance for indoor localization, there is a fine line which is important to find.

Within this paper a concept for a NFC compatible wireless power transfer system is presented that is able to supply sensors embedded over 10 cm deep into concrete. The goal is on the one hand the use of only commercially easily available components and on the other hand the integration of an energy storage system to enable a self-sufficient function without active energy transfer. Therefore, we discuss the basic requirements to achieve magnetic coupling of reader and transponder and present a system concept for a wireless power transfer system that is tested in measurements with two different embedding depths. Depending on the thickness and water content of concrete, power transmission ranging up to almost one Watt has been achieved in a proof of concept implementation.

Low-data rate networks typically cannot afford the overhead entailed with security measures because of lack of bandwidth. In this paper we propose a method for embedding digital watermarks in LoRaWAN based sensor systems. With the presented approach, the transmitted messages themselves do not need to be modified. Rather, the inter-packet interval between individual packets is used as a side-channel to carry the security-relevant information. We first examine the specific characteristics of LoRaWAN which are typical also for similar low-data rate wireless networks and then present a feasible, lightweight approach for the generation of the digital watermarks. Subsequently, we analyze first simulation results of two different differential methods for the watermark implementation.

With increasing deployment of wireless devices also localization gets a consequential boost in industrial and other IoT environments. Localization so far in most cases assumes omnidirectional antennas. This paper investigates a generalized Received Signal Strength (RSS) fingerprinting localization algorithm for antennas with arbitrary radiation patterns in order to include IoT devices with directional antennas in localization.Focus is set on the recursive algorithm which improves performance of the traditional fingerprinting methods. First a machine-learning aided analysis of the overlapping reception areas of the antennas is conducted for quickly determining possible initial positions of the nodes to be localized. Then, for reaching higher resolution, different up-scaling techniques and gradient search is applied. In particular, the localization accuracy vs. computational efficiency is investigated which is an important trade-off for many applications.

Common localization approaches are usually based on omni-directional antennas. There are various algorithmic methods, all of which assume strictly uniform radiation in all directions. However, in general, the output characteristics of these (nominally omnidirectional) antennas are not completely omnidirectional or even highly directional depending on the specific design. This article investigates the use of clustering algorithms to identify different areas of joint signal parameters that can be used for an RSS-based localization method. A set of clustering algorithms is investigated, and their properties to cluster RSS maps for localization applications are compared. In particular, their score for cluster quality and their execution speed relevant for deployment in embedded systems has been evaluated.

Within this paper a novel approach for localization of roaming nodes is presented that uses static directional antennas at the receiver side to measure the received signal strength (RSS). In contrast to omni-directional antennas it is not possible to formulate an analytical relationship of distance to received signal power. The characteristics as well as benefits and challenges of directional antennas are analysed and a concept for an iterative approach is presented that uses a stored antenna pattern to estimate the transmitter position. Finally, a Bluetooth based measurement setup is presented, that will be used for the upcoming validation of the proposed algorithm.

The increasing presence of wireless communication in factories has encouraged the introduction of novel applications on the factory floor. Highly accurate clock synchronization of wireless devices is necessary for timely communication between these devices and in some cases such as time-based localization, a major pre-requisite. One critical factor affecting synchronization performance is propagation delay variations suffered by a packet when it moves from its source to the destination. In this preliminary study, a set of measurements have been carried out to find out the extent of these variations. A highly accurate timestamping unit is used to detect the departure and arrival of a packet on the wireless channel, as the timestamping unit undergoes relative motion in an office environment. The results indicate that propagation delay variations are less affected by mobility than by reflections of signals from surrounding surfaces and objects. Future work will investigate whether the above observation is correct by employing higher speed mobility.

Network-based clock synchronization is an important prerequisite for many application areas and more and more required for the factory floor for network arbitration, control, and monitoring. Limitations of existing clock synchronization protocols are that they either support high redundancy and robustness or high precision. This paper presents an approach to integrate slave-side robustness into high precision clock synchronization. To achieve this goal, a system design facilitating the IEEE 1588 Precision Time Protocol (PTP) is proposed, which supports multiple masters in parallel and provides highly reliable and robust clock synchronization, while at the same time demanding no changes to the network and timing infrastructure. The slave-side robustness can be further enhanced to provide improved monitoring support for IEEE 1588. This makes the solution especially appealing for large-scale networks where retrofitting must be done efficiently and the network infrastructure is not under the control of the end device operator.

In the presence of multipath propagation received signals are composed of multiple echoes which are correlated to the direct signal. When using bandlimited signals for time-of-arrival (ToA) locating in indoor environments, the radio bandwidth is often not sufficient to decompose the received signal and to identify the first arriving path. This paper presents a ToA estimation approach based on a high-resolution correlation receiver with subsample interpolation. It is combined with a multipath error estimator based on the inverse channel impulse response determined by an equalizer. Simulation results confirm that the proposed approach can reduce the multipath error by a factor of 3.42 compared to matched filtering. Finally, measurements using an FPGA-based prototype implementation for wireless LAN show the applicability of the proposed approach for real-time locating systems.

With the evolving technologies smart metering, or generalized the smart grid, it becomes reasonable to think about integrating household devices into a Demand Side Management (DSM) network. This paper gives an overview about the state of the art in the area of DSM. Subsequently, it is shown what is needed to convert a standard, commercial-off-the-shelf refrigerator into a networked smart fridge. Following this, a simulation model and a basic algorithm for load control of a refrigerator is presented and analyzed. Finally, possible improvements of hardware and the algorithms are proposed.