Industry 4.0 Vision for the Supply of Energy and Materials. Группа авторов

coordinator. Since it offers various features for protocols of all the layers above MAC and PHY, it can be properly adapted to large deployments.

Zigbee operates on the frequency band of 2.4 GHz (i.e., the Industrial Scientific and Medical [ISM] band) and shares the spectrum with IEEE 802.15.1 and IEEE 802.11. This makes it susceptible to high mutual interference and noise and leads to frequent backoff for Zigbee MAC protocol [70]. Zigbee is not highly suited to provisioning easy channel access and delivery of data in delay-sensitive applications. Consequently, it is not suitable for industrial applications that require deterministic delay and high reliability [71].

To combat limitations of its MAC layer, Zigbee Alliance developed a variant called Zigbee PRO, which specifically supports industrial process and control applications [72]. Zigbee PRO can change network operating channels and enhances security features if it faces significant levels of interference or noise [73]. Zigbee Smart Energy (Zigbee SE) is another related protocol that relies on Zigbee IP and effectively manages the power consumption of nodes. Considering the cost efficiency, low-powered structure, and redundancy capability of Zigbee SE, it is suitable for demand–response and load control systems such as smart grids [74].

WirelessHART. This open standard specifically targets wireless instrumentation for factory automation [75]. The main motive behind WirelessHART was to deliver feasible solutions that address stringent timing requirements and severe interference conditions of the industrial ecosystem [76]. The PHY layer of WirelessHART is based on IEEE 802.15.4; however, it applies TDMA channel access for MAC protocol to guarantee collision-free channel access [62]. Therefore, WirelessHART communication is scheduled and offers strict time slots as well as network-wide time synchronization due to the adoption of the TDMA-based MAC layer. WirelessHART MAC protocol features some prominent properties such as channel blacklisting and channel hopping schemes, which enhance data bandwidth and system robustness. More importantly, the WirelessHART network layer supports self-organizing mesh networks to assist in automatic configuration, optimization, diagnostician, and healing networks.

Different from generic WSNs, the WirelessHART network design and employment includes eight different types of devices. The sensors and actuators are denoted as field devices, which are usually attached to the plant equipment or processes to collect data such as pressure, humidity, and fluid flow from physical environment. The remaining seven are deployed to assist in network management and functionalities such as network interoperation, security, and optimization. WirelessHART is mainly considered as a centralized wireless network and utilizes a central network management to keep communication and route scheduling up to date. Consequently, it is more suited to industrial applications where network graphs should be continuously adapted to network changes and demands. WirelessHART can serve a large number of devices and high network data rates by using multiple gateways connected to a HART over IP backbone or multiple access points [77].

      ISA100.11a. The International Society of Automation (ISA) developed industry standards that offer reliable and secure systems for automation and control applications. ISA100.11a is an industrial wireless communication standard ratified in 2009 and operates in a 2.4 GHz band (ISM band) [64]. A PHY layer of ISA100.11a is based on the IEEE 802.15.4 standard; however, its MAC layer is built on a modified, noncompliant MAC protocol of IEEE 802.15.4 and utilizes a combination of contention- and scheduled-based MAC scheme. To achieve real-time networking, a MAC protocol of ISA100.11.a exploits TDMA and carrier-sense multiple access (CSMA) along with additional spatial, frequency, and temporal diversity. Channel blacklisting and frequency hopping are also leveraged to address mutual interference from coexisting wireless systems and enhance network robustness [70].

The network of ISA100.11a consists of field and infrastructure devices. Both classes of devices are further divided into multiple types to assist in achieving a proper network architecture. Similar to WirelessHART, it exploits self-healing networks. The configuration of monitoring (e.g., slot allocation and scheduling), network runtime configurations, and execution of security standards policies are performed by the system manager as an infrastructure device. ISA100.11a connects field and plant networks via gateway devices. It embraces either distributed or centralized management; however, the proposed distributed management does not specify how network resources should be coordinated [78]. Different from WirelessHART, ISA100.11a provides graph and source routing while also offering options for configuration-based time-slot sizes, explicit congestion notification, and dual acknowledgment [77].

      Wireless networks for industrial automation-process automation (WIA-PA). The Chinese Industrial Wireless Alliance introduced WIA-PA in 2008 as the national standard that proposes architecture and communication specifications for industrial automation and process use cases. Later, this standard was approved by the IEC (International Electrotechnical Commission) [58]. The WIA-PA PHY layer complies with the IEEE 802.15.4 standard, though its MAC layer applies a hybrid scheme (a combination of scheduled- and contention- based mechanisms) on IEEE 802.15.4 MAC protocol. It also exploits TDMA, CSMA, and frequency-division multiple access (FDMA) approaches for channel access. Given that WIA-PA MAC layer leverages adaptive frequency hopping, time slot hopping, and adaptive frequency switching, it can cope with varying network conditions and is considered a self-healing network [78]. Similar to WirelessHART and ISA100.11a, this standard employs a reactive approach that exploits redundant routing and gateway devices to prevent failures in networks, further enhancing its reliability and self-organizing characteristics [78].

Physical devices in WIA-PA networks are categorized into five classes [76]: (1) handheld devices to monitor and control the production plants and configure network devices; (2) field devices (sensors and actuators) located in the field to control or monitor industrial processes; (3) routing devices; (4) gateway devices that connect WIA-PA networks to various plant networks; and (5) a host computer as the user interface for management and maintenance. Both centralized and distributed mechanisms are deployed in WIA-PA networks to perform network and security management. Typically, network manager configures the network, schedules communication, handles routing tables, and protects the overall network, whereas the security manager is responsible for security and authentication management in the network. To conserve energy in WIA-PA networks, two-level aggregation mechanism is exploited: packet aggregation at network and application layers. This is different from WirelessHART and ISA100.11a, which utilizes only a one-level packet aggregation scheme. Additionally, WIA-PA adopts two-stage communication resource allocation.

      1.4.1.2 IEEE 802.15.1 Standard

It was approved in 2002 and designed for short-range, low-power, and low-cost connectivity in WPAN applications. IEEE 802.15.1 is established on Bluetooth v1.1 foundation specifications that govern Bluetooth technology [79]. There are two main variations of this technology: classic Bluetooth and Bluetooth low energy (BLE). Classic Bluetooth supports devices with high demand of small transmission and low energy consumption, whereas BLE is ideal for applications that require communication of small quantities of data on an occasional or periodic basis.

Bluetooth classic. The Bluetooth PHY layer is adapted from the IEEE 802.15.1 standard and operates in the frequency band of 2.4 GHz. Its transmission technique exploits frequency hopping spread spectrum (FHSS). This results in the reduction of interference from nearby systems sharing the same frequency band (ISM band) and increases system robustness. Bluetooth defines two types of network topologies, namely, piconet and scatternet. Piconet is a single-hop topology that enables communication between one master node and multiple slave nodes. A scatternet topology is a cluster of Bluetooth piconets overlapping in space and time; there is only one master node, while a slave node could operate as slave in different piconets. Bluetooth MAC layer mainly focuses on establishing physical connections between the master and slaves, synchronizing network nodes with the master node’s clock, packet transmission on physical channels, and device management for energy-saving modes [80].

Bluetooth low energy (BLE). A smart variation of the IEEE 802.15.1 standard, also known as Smart Bluetooth, BLE supports industrial wireless communication [81]. It is designed for short-range communication and, compared with classic