Gaetano Patti

Introducing support for scheduled traffic over IEEE audio video bridging networks

The IEEE 802.1 Audio/Video Bridging (AVB) protocol successfully supports audio/video streaming over Ethernet networks and is also a promising candidate for industrial automation. However, several industrial automation applications feature requirements that cannot be fulfilled by the current AVB standard. The next generation of IEEE 802.1 standards, which will specifically target the requirements of automotive and industrial control, is under specification within IEEE 802.1 Working Group. Inspired by such an ongoing work, this paper addresses the introduction in IEEE AVB networks of scheduled traffic, i.e., high priority traffic that is transmitted according to a time schedule so as to ensure no interference from other traffic classes. The paper describes the proposed approach, discusses the design choices and presents a performance assessment based on OMNeT++ simulations.

Simulative assessments of the IEEE 802.15.4e DSME and TSCH in realistic process automation scenarios

Industrial Wireless Sensor Networks (IWSNs) are found in many application domains that require low latency, robustness, and determinism. The IEEE 802.15.4 standard is not able to cope with the requirements of these applications. For this reason, the IEEE 802.15.4e amendment was introduced, which provides novel MAC-layer profiles that are optimized for a broad range of application domains, including process automation. This paper focuses on two of these profiles, i.e., the Deterministic and Synchronous Multi-channel Extension (DSME) and the Time Slotted Channel Hopping (TSCH). The aim of the paper is twofold. First, assessing their behavior in realistic process automation scenarios. Second, comparing their performance in terms of end-to-end delay, reliability and scalability. The ultimate aim of the work is identifying the limits of those protocols, thus paving the way to further work addressing suitable approaches to tackle them.

Introducing multi-level communication in the IEEE 802.15.4e protocol: The MultiChannel-LLDN

The Low Latency Deterministic Network (LLDN) protocol is defined in the IEEE 802.15.4e, which is an amendment to the IEEE 802.15.4 standard specifically devised to support the requirements of industrial applications. The LLDN provides a TDMA-based medium access mechanism in which the network cycle time grows linearly with the number of nodes. As a result, to offer low cycle times to applications requiring a high number of nodes, the LLDN specifications suggest to create multiple networks operating on different channels by embedding multiple transceivers in the coordinator. However, such an approach entails high costs and increases the design complexity. Moreover, the LLDN protocol foresees a star topology that limits the network area coverage. This paper proposes a novel approach, called a MultiChannel LLDN, based on a hierarchical network structure in which nodes communicate on different channels at the same time. The approach supports a high number of network nodes while maintaining short cycle times without the need for multiple transceivers in the coordinator and also provides backward compatibility with the standard LLDN. The paper presents the MultiChannel LLDN and comparative performance assessments.

Performance assessment of the PRIME MAC layer protocol

The PRIME (PoweRline Intelligent Metering Evolution) protocol is a very popular multicarrier narrowband PLC protocol that fits the needs of advanced metering infrastructure applications. This paper proposes a performance assessment of the PRIME MAC layer protocol obtained through OMNeT simulations in different scenarios. The contribution of the paper is twofold. The first contribution is an approach to overcome a well-known problem of discrete-event simulators, i.e., the fact that they do not provide functionalities to emulate the continuous effects of signal propagation. To solve this problem, in this paper the channel is modeled based on measurements, made on real testbeds, so our simulator embeds data taken from experiments performed in a real scenario. The second contribution is the assessment of the impact of the modulation scheme on the performance of the PRIME protocol.

A Bluetooth Low Energy real-time protocol for Industrial Wireless mesh Networks

Low energy consumption and low cost are some of the primary issues that have to be addressed in Industrial Wireless Sensor Networks (IWSN). Such networks are being increasingly used to acquire sensory data that need to be processed in real-time. The Bluetooth Low Energy (BLE) protocol is an attractive solution for implementing low-cost IWSN with reduced energy consumption and high flexibility. However, the current BLE standard does not provide real-time support for data packets and is limited to a star topology. This paper presents a real-time protocol for industrial wireless mesh networks that is developed on top of the BLE and overcomes these limitations. The paper describes the protocol and provides analysis and experimental results.

Priority-Driven Swapping-Based Scheduling of Aperiodic Real-Time Messages Over EtherCAT Networks

Real-time Ethernet (RTE) technologies are becoming increasingly popular, as they provide high bandwidth and are able to meet the requirements of industrial real-time communications. Among RTE protocols, the EtherCAT standard is suitable for motion control and closed-loop control applications, which require very short cycle times. As EtherCAT was specifically devised for periodic traffic, aperiodic real-time transmissions are far from being efficient, as they entail long cycle times. To overcome this limitation, this paper presents a general framework for priority-driven swapping (PdS)-based scheduling of aperiodic real-time messages over EtherCAT networks, which uniformly covers both dynamic and static priority and allows for very short cycle times. This paper provides a description of the PdS framework, a schedulability analysis for both static priority and dynamic priority scheduling, and simulative assessments obtained through OMNeT++ simulations.

Schedulability analysis of Ethernet Audio Video Bridging networks with scheduled traffic support

The IEEE Audio Video Bridging (AVB) technology is nowadays under consideration in several automation domains, such as, automotive, avionics, and industrial communications. AVB offers several benefits, such as open specifications, the existence of multiple providers of electronic components, and the real-time support, as AVB provides bounded latency to real-time traffic classes. In addition to the above mentioned properties, in the automotive domain, comparing with the existing in-vehicle networks, AVB offers significant advantages in terms of high bandwidth, significant reduction of cabling costs, thickness and weight, while meeting the challenging EMC/EMI requirements. Recently, an improvement of the AVB protocol, called the AVB ST, was proposed in the literature, which allows for supporting scheduled traffic, i.e., a class of time-sensitive traffic that requires time-driven transmission and low latency. In this paper, we present a schedulability analysis for the real-time traffic crossing through the AVB ST network. In addition, we formally prove that, if the bandwidth in the network is allocated according to the AVB standard, the schedulability test based on response time analysis will fail for most cases even if, in reality, these cases are schedulable. In order to provide guarantees based on analysis test a bandwidth over-reservation is required. In this paper, we propose a solution to obtain a minimized bandwidth over-reservation. To the best of our knowledge, this is the first attempt to formally spot the limitation and to propose a solution for overcoming it. The proposed analysis is applied to both the AVB standard and the AVB ST. The analysis results are compared with the results of several simulative assessments, obtained using OMNeT++, on both automotive and industrial case studies. The comparison between the results of the analysis and the simulation ones shows the effectiveness of the analysis proposed in this work.

SchedWiFi: An innovative approach to support scheduled traffic in ad-hoc industrial IEEE 802.11 networks

The spread use of IEEE 802.11 networks in industrial automation raised the need to support multiple traffic classes with different requirements. This paper proposes a novel approach, called SchedWiFi, that provides flexible support to the scheduled traffic class, i.e., a high priority traffic class that is transmitted according to a fixed schedule, over IEEE 802.11 ad-hoc industrial networks. SchedWiFi operates on the IEEE 802.11n physical layer, thus providing high datarate, and supports multiple traffic classes with different priorities. SchedWiFi modifies the EDCA mechanism allowing to transmit scheduled traffic without requiring any predefined superframe structure, or timeslots, thus allowing for more flexible schedule of non-ST traffic.

A Priority-Aware Multichannel Adaptive Framework for the IEEE 802.15.4e-LLDN

The low-latency deterministic network (LLDN) protocol defined in the IEEE 802.15.4e amendment is intended for factory automation applications that require very low latency and large networks, such as automotive manufacturing. However, LLDN does not provide priority support to properly deal with real-time traffic or dynamic channel configuration capabilities to cope with unreliable channels. Moreover, it offers a limited scalability, as the cycle time grows linearly with the number of network nodes. This paper proposes the priority-aware multi-channel adaptive (PriMulA) framework, which introduces in the LLDN priority-aware scheduling, multichannel communication, adaptive channel selection, and channel blacklisting. PriMulA supports a higher number of network nodes than the LLDN protocol while keeping short cycle times. In addition, PriMuLA avoids deadline miss and improves the network reliability. It maintains the interoperability with LLDN standard nodes and can be implemented on commercial off-the-shelf devices. This paper presents the framework, a schedulability analysis, comparative simulations, and a proof-of-concept implementation.

A three-tiered architecture based on IEEE 802.15.4 and Ethernet for precision farming applications

This paper proposes a three-tiered network architecture to support precision farming applications over large cultivated fields. The hybrid network combines IEEE 802.15.4 Wireless Sensor Networks, operating in a multichannel mode, with Switched Ethernet. The network design has to fulfill several objectives, such as, achieving a tradeoff between energy saving for battery-operated devices and timeliness of precision farming applications over large areas, while providing scalability, robustness and cost efficiency. The work presented in the paper is based on real-world specifications provided by end users, i.e. qualified farmers, during a comprehensive investigation and requirement analysis phase. The paper first discusses the constraints that drive the network design and then presents the three-tiered architecture. Finally, the performance of the network, obtained through OMNeT++ simulations, are discussed.