Seamless Link-level Redundancy to Improve Reliability of Industrial Wi-Fi Networks

The adoption of wireless communications and, in particular, Wi-Fi, at the lowest level of the factory automation hierarchy has not increased as fast as expected so far, mainly because of serious issues concerning determinism. Actually, besides the random access scheme, disturbance and interference prevent reliable communication over the air and, as a matter of fact, make wireless networks unable to support distributed real-time control applications properly. Several papers recently appeared in the literature suggest that diversity could be leveraged to overcome this limitation effectively. In this paper a reference architecture is introduced, which describes how seamless link-level redundancy can be applied to Wi-Fi. The framework is general enough to serve as a basis for future protocol enhancements, and also includes two optimizations aimed at improving the quality of wireless communication by avoiding unnecessary replicated transmissions. Some relevant solutions have been analyzed by means of a thorough simulation campaign, in order to highlight their benefits when compared to conventional Wi-Fi. Results show that both packet losses and network latencies improve noticeably.Comment: preprint, 13 pages (Winner of the "2017 Best Paper Award for the IEEE Transactions on Industrial Informatics"

Experimental Evaluation of Techniques to Lower Spectrum Consumption in Wi-Red

Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates. In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.Comment: preprint, 13 page

QRscript specification

This specification document specifies the syntax and semantics of QRscript. The current document only shows the part related to the QRscript header, i.e., the first part of the binary code that must be inserted into the QR code. A QR code containing an executable code is called an executable QR code (eQR code). QRscript supports different dialects, i.e., sublanguages with implementation characteristics specific to the application field. The specifications of the individual dialects will be described in separate documents.Comment: Specification document, 13 page

Fixed-Length Payload Encoding for Low-Jitter Controller Area Network Communication

The controller area network (CAN) bit stuffing mechanism, albeit essential to ensure proper receiver clock synchronization, introduces a significant, payload-dependent jitter on message response times, which may worsen the timing accuracy of a networked control system. Accordingly, several approaches to overcome this issue have been discussed in literature. This paper presents a novel software payload encoding scheme, which is able to guarantee that no stuff bits will ever be added to the data field by the CAN controller during transmission and, hence, lessens jitters considerably. Particular care has been put in its practical implementation and its subsequent evaluation to show how the simplicity and inherent high performance of the scheme make it suitable even for low-cost, embedded architectures

QRtree -- Decision Tree dialect specification of QRscript

This specification document specifies the syntax and semantics of QRtree, which is a specific dialect of QRscript particularly suited to represent decision trees without chance nodes. The term dialect identifies one of the possible sub-languages that can be encoded inside of an eQR code via QRscript. This specification will describe an intermediate representation of QRtree, made through a language derived by the three-address code. It will then define the transformation rules from the intermediate representation to a binary code. The latter is a binary representation called eQRtreebytecode. These rules can also be applied inversely to transform the eQRtreeBytecode into the intermediate representation. This specification document will pay particular attention to the creation of a compact eQRtreebytecode, as the maximum number of bits that can be stored in a QR code is, at the time of writing, equal to 2953 bytes (in the case of QR code version 40 with a "low" error correction level).Comment: Specification document, 32 page

Guest Editorial Special Section on Communication in Automation

International audienceThis Special Section on “Communication in Automation” presents seven papers that deal with relevant aspects pertaining to the topics highlighted above. Quite obviously, they cannot provide a comprehensive overview on the whole subject (nor they are intended to). Nevertheless, they are able to give some useful insight about the most recent advances in this field. The papers included in this Special Section cover a quite wide spectrum of topics, ranging from wired industrial communication systems aimed at providing strict real-time behavior, to hybrid systems obtained by adding wireless extensions to the wired backbone, to completely wireless industrial solutions able to ensure high determinism. Novel approaches have been described as well, aimed at improving either routing in WSNs or CSMA schemes so as to make them more suitable for the use in industrial automation systems. Finally, a testing approach for safety-critical automotive networks has been introduced and formally validated, and an agent platform defined and implemented that requires less resources, while granting higher performances and a methodology proposed and verified for assessing the performance of WSNs under cross-channel interference

Ultra-Low Power and Green TSCH-Based WSNs With Proactive Reduction of Idle Listening

Wireless sensor networks are characterized by low power consumption because motes are typically battery-powered. Time slotted channel hopping (TSCH) relies on a fixed transmission schedule, which enables the receiver module of wireless motes to be switched off every time it is not needed. Unfortunately, in many practical contexts most of the reserved slots remain unused, which leads to appreciable energy waste. For periodic traffic, proactive reduction of idle listening (PRIL) techniques have been proven able to mitigate this problem. In this paper, PRIL multi-hop (PRIL-M) is introduced with the aim to improve existing PRIL techniques, by lowering energy waste further in large real-world mesh networks. PRIL-M is advantageous in all those contexts where ultra-low power consumption is more important than end-to-end latency. Applications that can benefit from PRIL-M include, e.g., environmental monitoring, where sensors are deployed over the target area and must operate for years without maintenance. A thorough simulation campaign showed that, in these scenarios, energy consumption of PRIL-M is 75% less than standard TSCH, while the average latency is about 20 times larger