Peter Stenumgaard

Challenges and conditions for wireless machine-to-machine communications in industrial environments

Wireless solutions are rapidly growing in machine-to-machine communications in industrial environments. These environments provide challenging conditions in terms of radio wave propagation as well as electromagnetic interference. In this article, results from the characterization of radio channel properties are summarized in order to provide some guidelines for the choice of wireless solutions in industrial environments. In conclusion, it is essential to know the sensitivity of industrial processes to time delay in data transfer. Furthermore, it is important to be aware of the radio interference environment and the manner in which different wireless technologies react upon interference. These steps will minimize the risk of unforeseen expensive disturbances in industrial processes.

A simple impulsiveness correction factor for control of electromagnetic interference in dynamic wireless applications

The emerging software defined radio technologies will be an enabler for a new generation of dynamic wireless systems. It will also open up the possibility of allocating frequencies in a, more dynamic way than today. From an intersystem-interference point of view, this can cause unforeseen problems to occur due to the increased complexity in such applications. In such applications, a measure indicating whether or not a frequency band is possible to use from an electromagnetic interference point of view, must be found. A simple approach is to use the measured total average interference power within the receiver band. Since the interference impact on modern digital communication systems from an interference signal does not only depend on the power but also on the actual waveform of the interference signal, some kind of quality measure of the average-power approach would be convenient to use. In this paper, we introduce a simple quality measure of the average-power approach so that a rough adjustment for the interference-waveform properties can be done.

Sources of disturbances on wireless communication in industrial and factory environments

Electrical and mechanical machinery, highly reflective industrial facilities and co-existing communication systems are the major sources of disturbances in wireless industrial applications. Characterization of industrial environments is important for the development of standards, to assess current and future deployment of wireless technologies, and to provide systems integrators and end user with guidelines. In this paper some deductions from measurements carried out at three industrial environments using traditional electric field strength, amplitude probability distribution (APD) and multipath time dispersion measurements are presented. These measurements have given surprising and interesting results.

An improved method to estimate the impact on digital radio receiver performance of radiated electromagnetic disturbances

Present emission standards are developed with respect to analog communication services. Therefore, knowledge of how relating present standards to the impact on digital radio receivers must be available for system design purposes. For a digital radio receiver, the bit error probability (BEP) is often used to show the impact of the receiver performance from a disturbing signal. A simple, previously proposed method relates present emission standards to the BEP for broad-band (BE) disturbance. This method has to be modified for use on narrow-band (NB) disturbance such as the NB spectral components from periodic signals. A method based on a modification of the earlier method is presented for this NB disturbance. This represents typical disturbance from information technology equipment working with periodic signals. The conclusion is that the method presented delivers a useful value of the BEP, which can be used when radiated emission requirements are to be chosen on electronic equipment co-located to digital radio systems.

Using the root-mean-square detector for weighting of disturbances according to its effect on digital communication services

The issue of finding a new electromagnetic interference (EMI) measurement detector with proper weighting properties for the effect of disturbances on digital communication services is of great importance for the development of future emission standards. We investigate the root-mean-square (RMS) detector as a possible candidate for future emission measurements. This investigation is done for type of disturbances typical for information technology (IT) equipment, i.e., a repetitive pulse waveform. We show that the tolerated RMS value of the disturbance level related to a certain bit-error probability is in practice independent of the pulse width of a repetitive pulsed disturbance signal. Furthermore, the variation of this tolerated RMS value with the pulse-repetition frequency of the disturbance can easily be modeled. These properties make it possible to express the maximum allowed disturbance level in terms of the output from the RMS detector. The conclusion is that the RMS detector is a promising candidate for future emission standards where the disturbance effect on digital communication services is considered.

Measurement Analysis and Channel Modeling for TOA-Based Ranging in Tunnels

A robust and accurate positioning solution is required to increase the safety in GPS-denied environments. Although there is a lot of available research in this area, little has been done for confined environments such as tunnels. Therefore, we organized a measurement campaign in a basement tunnel of Linköping university, in which we obtained ultra-wideband (UWB) complex impulse responses for line-of-sight (LOS), and three non-LOS (NLOS) scenarios. This paper is focused on time-of-arrival (TOA) ranging since this technique can provide the most accurate range estimates, which are required for range-based positioning. We describe the measurement setup and procedure, select the threshold for TOA estimation, analyze the channel propagation parameters obtained from the power delay profile (PDP), and provide statistical model for ranging. According to our results, the rise-time should be used for NLOS identification, and the maximum excess delay should be used for NLOS error mitigation. However, the NLOS condition cannot be perfectly determined, so the distance likelihood has to be represented in a Gaussian mixture form. We also compared these results with measurements from a mine tunnel, and found a similar behavior.

Characterisation of highly absorbent and highly reflective radio wave propagation environments in industrial applications

Experience has shown that Bluetooth, Wireless LAN (WLAN), Digital Enhanced Cordless Telecommunications (DECT) and other Industrial, Scientific and Medical (ISM) frequency band wireless technologies developed for office use, have encountered problems when used in critical industrial applications. The development of more reliable wireless solutions requires extensive knowledge of industrial environments with regards to both electromagnetic interference and wave propagation. This study presents the results of the analysis of two important classes of industrial environments having opposite characteristics, one being highly absorbent and the other being highly reflective, with respect to radio wave propagation. The analysis comprises both multipath and path loss characterisation. The results show that wireless solutions with different fundamental properties must be chosen for each of these environments to ensure high reliability. The conclusions of this work can be used as an important reference for further research in this area, as well as the design of new standards and guidelines for selecting wireless solutions in similar industrial environment classes.

A possible concept of how present radiated emission standards could be amended in order to protect digital communication services

Present radiated emission standards are developed to protect analog communication services. Finding a new detector for electromagnetic interference (EMI) measurements with adequate weighting properties to quantify the effect of disturbance on digital communication services, is one important issue in the evolution of present radiated emission standards in order to protect digital communication services. Recent measurement and simulation results indicated that the RMS detector exhibits a response that can be correlated to the interference impact on digital communication systems that do not use error-correcting codes, or codes of block or convolutional type. In this paper, we show that this conclusion is also valid for systems using the more complicated concatenated codes. The codes investigated so far cover a representative and relevant selection of codes employed in practical digital systems. Therefore, the proposed concept to amend existing radiated emission standards is considered valid.

Improved impulsiveness correction factor for controlling electromagnetic interference in dynamic spectrum access applications

Initiatives to open certain frequency bands for dynamic spectrum access (DSA) are ongoing. Examples are the wireless access policy for electronic communications services and white spaces coalition. A key issue in DSA is how to measure occupancy and interference in an open frequency band to decide whether or not it can be used for a certain service. Such measurement must be easy to perform and provide a result that can be used as decision metric. An earlier proposal, based on a so-called impulsiveness correction factor, with this purpose has been shown to work properly if the interference is dominated by a single pulsed signal. In this study, the former approach is extended to the case in which the interference signal consists of a multiple of interference signals. This extension is shown as a closed expression involving only parameters that can be determined from an interference measurement.

EMI disruptive effect on wireless industrial communication systems in a paper plant

It is well known that industrial and factory environments present considerable challenges for wireless communications. Because every industrial environment is different, and may offer a unique set of obstacles to effective wireless communication, a site characterization is needed at first step in determining improvements of existent wireless technologies to increase the reliability. In this work electric field strength and APD measurements have been performed to characterize electromagnetic interference in an industrial paper plant. Common characteristics of the industrial environments affecting wireless communication were identified. Additionally, results show high interference levels at the frequencies for the DECT band 1880-1890 MHz. The interference level is correlated to the working mode of the electrical engines used in the process.