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In industrial applications of wireless sensor networks (WSNs), synchronized sampling of data on each sensor node is often required. Thus, the wireless communication protocol needs to support accurate timing synchronization. If due to a high sampling rate also high data throughput is required, WSNs based on the IEEE 802.15.4 physical layer often do not provide sufficient data rate. Wireless communications based on the well-established IEEE 802.11 wireless local area network (WLAN) standard provides high data throughput but not an accurate timing synchronization unless the protocol stack is severely changed. We propose two low-complexity consensus-based synchronization algorithms for the hybrid WSN introduced, which are executable at limited embedded computing capacity, e.g., on an 8-b microcontroller. A time division multiple access-based synchronization packet broadcasting with three-step-controlled or proportional-integral (PI)-controlled clock adjustment enables 1-kHz sensor sampling rate with a sampling jitter $\mu $ s for the three-step-controlled synchronization algorithm and $ for the PI-controlled algorithm.

We present the design of a suite of protocols for wireless sensor networks (WSNs) with respect to a complete life cycle of a WSN node from warehouse to the end of operation. While there are numerous publications on various, usually isolated, aspects of WSNs, the whole life cycle of a node from registration in an automation system via warehouse, calibration, mounting, performing measurements to finally unmounting, has not yet been sufficiently addressed as compound survey. Our application example is a WSN to be used in automotive test beds in which a large amount of testing with many different sensors is performed in controlled environments. While there is published work on WSNs for performing the measurements focusing on node hardware and MAC protocol, we now extend this work by accounting for the whole life cycle of operation of such a WSN and its nodes. This is mainly achieved by introducing optimized MAC protocols for wireless communication in all life cycle phases. Right from beginning of the life cycle the nodes are synchronized with a base node. Even during long offline periods nodes stay synchronized. The life cycle is modeled via a set of states, instantiated in state machines, which control operation in the base station and the nodes. Besides, considering the whole life cycle of the sensor nodes, our design minimizes energy consumption, largely avoids collisions due to suitable multiple access protocols, and allows tight synchronization even during long sleep periods. A demonstrator concludes the presentation and shows functionality and benefits of the concept.

From wearables to smart appliances, the Internet of Things (IoT) is developing at a rapid pace. The challenge is to find the best fitting solution within a range of different technologies that all may be appropriate at the first sight to realize a specific embedded device. A single tool for measuring power consumption of various wireless technologies and low power modes helps to optimize the development process of modern IoT systems. In this paper, we present an accurate but still cost-effective measurement solution for tracking the highly dynamic power consumption of wireless embedded systems. We extended the conventional measurement of a single shunt resistor's voltage drop by using a dual shunt resistor stage with an automatic switch-over between two stages, which leads to a large dynamic measurement range from μA up to several hundreds mA. To demonstrate the usability of our simple-to-use power measurement system different use cases are presented. Using two independent current measurement channels allows to evaluate the timing relation of proprietary RF communication. Furthermore a forecast is given on the expected battery lifetime of a Wifi-based data acquisition system using measurement results of the presented tool.

Wireless measurement systems will provide significant benefits to industrial applications, for production facilities as well as in mobile or R&D scenarios. However, in order to exploit the improvements by flexibility, scalability and easy reconfigurability brought by wireless sensor networks (WSN), industrial use cases often require a sustainable autonomous energy supply, while providing the reliability which is comparable with today's wired systems. In this work we introduce a sensor node implementation with a temperature measurement circuit design, optimized for low energy consumption, while providing industry-grade accuracy and resolution. A first implementation realizing the concept of a switched signal acquisition circuitry is discussed, demonstrating the impact of the energy harvesting and storage unit. In a second implementation, a coordinated signal conditioning and power management concept is introduced.

Wireless sensor networks (WSNs) currently see a strong increase in demand for various industrial applications like smart testing and production systems. Open frequency bands (e.g. 2.4 GHz) allow the use of commercial low-cost hardware, but need to be shared with other devices and systems, leading to interference and therefore transmission errors. Re-transmitting damaged packages might eventually succeed, but at the costs of increased latency and additional energy consumption of the node. As minimizing energy consumption is paramount for self-powered WSN nodes, interference avoidance is highly desired. In this work a channel management procedure for WSNs is proposed which can react to dynamically changing interference scenarios. A short monitoring period is used to sample received signal strength indication values of a set of candidate frequency bands. An extensive measurement campaign is performed and six analysis methods are compared, and effects of applying the resulting choice of “best” frequency bands to WSNs in an automotive testing environment are investigated. The best method allows a reduction of energy consumption of a node by about 15%.

Wireless sensor networks (WSNs) are typically used to measure physical quantities of their environment at locations characterized by poor accessibility and lacking of wired infrastructure. To extend the operational time, energy harvesting systems (EHSs) support the power supply by transforming environmental energy into electrical energy. In the best case, a self-sufficient supply of the sensor node is possible. Information about the harvestable energy is necessary to design WSNs and EHSs properly. However, detailed information is often not available and special equipment is necessary to measure it. Therefore, this paper presents a simple method to estimate and track the harvestable power. The results can be used offline for design and simulations of nodes or networks, or online for work-load-distribution or energy aware network routing.

In this paper a novel synchronization method for wireless sensor networks with star topology is presented. We address timing synchronization using low frequency real-time clocks in all nodes. A beacon-driven TDMA-protocol for bidirectional node/base communication is used. Between the beacons, which are sent by the base station, lie the superframe time intervals to handle data transmission from node to base. We discuss the protocol and its energy saving advantages including the challenges of synchronization. We reduce the required communication for synchronization based on long term synchronicity of the node to save energy. Due to the individual node clock, the accurate superframe time interval usually will consist of a rational number of clock ticks. We propose to use a ΔΣ-converter to generate a sequence of superframes with different time durations, but each consisting of integer multiples of clock ticks, which - on average - achieve the accurate superframe duration for any rational number of clock ticks. We show by theory and measurements that our novel approach leads to a variance of the synchronization error which is constant at a value of 0.25 clock cycles. The variance is independent of the rate at which the nodes listen to the beacon of the base station.

We analyse the use of a ΔΣ-modulator in the nodes of a wireless sensor network, which is a new method to achieve long term synchronization. We consider star topology WSNs (Wireless Sensor Networks) with a central base station and address timing synchronization using low frequency realtime clocks. The WSN uses a beacon driven TDMA-protocol for bidirectional node/base communication. Between the beacons, which are sent by the base station, lie the superframe time intervals to handle data transmission from node to base. The ΔΣ-modulator is used to generate — at average — the accurate superframe duration for any rational number of clock ticks, by generating a sequence of superframes with different time durations, but each consisting of integer multiples of clock ticks. We discuss the synchronization accuracy based on the internal arithmetic of the ΔΣ-modulator and show by theory a relation between synchronization accuracy and word length of the internal arithmetic. Additionally the fractional part of a crystal clock module is responsible for variations in the synchronization quality. We present an equation that allows us to interpret measurements showing periodic variations of synchronization quality.

Cyber-physical systems often include small wireless devices to measure physical quantities or control a technical process. These devices need a self-sufficient power supply because no wired infrastructure is available. Their operational time can be enhanced by energy harvesting systems. However, the convertible power is often limited and discontinuous which requires the need of an energy storage unit. If this unit (and thus the whole system) is de-energized, the start-up process may take a significant amount of time because of an inefficient energy harvesting process. Therefore, this paper presents a system which enables a safe and fast start-up from the de-energized state.

Wireless Sensor Networks (WSNs) are at the verge of a broad acceptance in demanding industrial applications. Nodes must fulfill key requirements like reliability and deterministic communication, but also energy autarky in order to allow maintenance-free systems. In this paper a system combining low power, robust communication with appropriate methods for energy harvesting and energy management is suggested. By comparing two alternative variants for powermanagement, constraints of a solar-cell powered node design are derived. The resulting system demonstrates energy sufficiency at standard industrial indoor lighting conditions of 1300 lx for sensor nodes sampling temperature values at 10 Hz and transmitting once per second.

Wireless sensor and actuator networks (WSAN) for industrial applications usually have tighter requirements on dependability, synchronization, and real-time capability as compared applications in environmental monitoring or health care. For WSAN research and development, testbeds are a valuable tool as they enable controlled operation under conditions close to reality. In this contribution we present TWECIS, a testbed targeting the investigation of Wireless Energy Constrained Industrial Sensor and Actuator networks. We describe the concept, its architecture and the used hardware. Unique feature of TWECIS is the use of an industrial Real Time Ethernet system which offers the evaluation of the timing behavior of the nodes with a jitter below 100 ns. In addition TWECIS offers synchronized network-wide current measurements on all testbed nodes in a range from 1 μΑ to 100 mA for accurate power consumption profiling, remote and parallelized programming of nodes, remote in-circuit debugging, monitoring of UART output, and centralized storage of all captured data.

In this paper, we present a highly accurate but still cost-effective measurement solution for tracking the highly dynamic power consumption of wireless embedded systems. We extended the conventional measurement of a single shunt resistor's voltage drop by using a dual shunt resistor stage with an automatic switch-over between both stages, which leads to a large dynamic measurement range of 50 dB (1 μΑ to 100 mA) with an average measurement error smaller than 1.2 %. Using two zero-drift current sense amplifiers for measuring the voltage drop over two different sized shunt resistors together with a 16 bit SAR ADC for each of both amplifiers leads to a far better thermal noise behaviour and a higher total measurement resolution compared to a single shunt solution, providing a minimum invasive measurement system with a maximum voltage drop of 100 mV. Using a state-of-the-art Ethernet connection allows our measurement system to forward the power samples with up to 250 kHz sampling rate to any remote networked computer.

In industrial applications of wireless sensor networks (WSNs) synchronized sampling of data on each sensor node is often required. Thus the wireless communication protocol needs to support accurate timing synchronization. If due to a high sampling rate also high data throughput is required, WSNs based on the IEEE 802.15.4 physical layer often do not provide sufficient data rate. Wireless communication based on the well established IEEE 802.11 (WLAN) standard provides high data throughput but not an accurate timing synchronization unless the protocol stack is severely changed. We propose a hybrid WSN which uses WLAN for high rate data transmission combined with a proprietary wireless communication system operating on Sub-GHz short range devices for synchronization. A consensus-based synchronization algorithm is used to be independent from the number of WSN nodes and node failure. The proposed hybrid WSN performs a two-step synchronization algorithm which can easily be executed on an 8-bit microcontroller and achieves a sampling jitter smaller than 50 μs.

The range of applications for wireless sensor networks (WSNs) is continuously growing and is expanding into new branches and markets rapidly. Largely different requirements regarding network structure, powering possibility, latency, data rates, and reliability, lead to the need of suitable systems and protocols. An approved way to implement an energy aware wireless network is the Time Division Multiple Access (TDMA) strategy. In this work we propose two different TDMA schedules for highly reliable sensor data collection with sample rates of 10 Hz and analyze and compare them regarding reliability and energy consumption. A standard coin cell can power a sensor node for more than 2 month with a sensor data loss smaller than 10−3 percent at 3% PER in the radio channel.

A major task of wireless sensor networks (WSNs) is to collect data under a range of ambient conditions and with many different dynamics from a variety of sensors which are distributed, for instance, around an industrial plant. Focusing on real-time data collection for control applications, we present a spatial extension to our previously published self-organized TDMA-based WSN with star topology implemented on low-complexity commercial off-the-shelf hardware. Employing repeater nodes for two-hop neighbors retains both the real-time behavior and self-organization of the initial protocol. Under ideal conditions, the radius of the area covered by the WSN can be doubled while the increase in power consumption due to the repeater nodes remains moderate.

We present a novel ultrasonic (US) indoor localization system based on the time-of-arrival (TOA) principle realized with radio frequency (RF) synchronization. The US signal is assembled as a Gold sequence of chirp signals to guarantee a high signal-to-noise ratio (SNR) and, at the same time, provide the position estimates of multiple mobile transmitters (MTs). By exploiting the TOA in the time domain and the Doppler shift in the frequency domain, position and velocity of the MT can be determined simultaneously. The concept is proven by means of both simulated and measured data and performs excellently even in a harsh industrial environment.

Wireless sensor networks (WSNs) are becoming increasingly attractive for industrial applications, where the requirements with respect to data rates, latency, and reliability are especially challenging. Due to cost reasons in such applications Standard hardware has to be used. As well known protocols like ZigBee or Wireless HART are not able to offer high data rates with short and deterministic delays, we propose in this contribution a time division multiple access-based approach for efficient data transmission in WSNs with a broad range of sample- and transmission rates. Our proposal is based on beacon-triggered time-intervals, supports wireless sensor nodes with a wide range of data rates and enables self organized joining and leaving of nodes. We present measurement results of a demonstration system in star topology using evaluation boards of the CC2510, a low-power System-on-Chip solution with integrated micro-controller and RF-transceiver, with two different sleep mode strategies to minimize power consumption.