How to choose wireless standards in IIoT applications

This article offers useful guidance on what to consider when deploying wireless standards in Industry 4.0 applications, from the factory floor through to system level.

Field level I

Wireless data transmission starts from the sensors and actuators that lie at the heart of today’s production lines. Thanks to their energy harvesting modules, these critical edge devices can convert ambient light energy or heat differences into enough electrical power to transmit data packets over short-range wireless connections (within a few hundred meters). A local energy storage unit ensures backup power whenever the energy harvested from the environment is not enough.

There are different wireless network options available, including the Sub-GHz protocol EnOcean, Bluetooth 5 and ZigBee 3.0 on the 2.4GHz band. A compatible EnOcean module combination enables the energy harvesting process with ZigBee while Bluetooth enables straightforward P2P connections or interaction with a smart phone, tablet or laptop, and is also fully self-powered.

If a wider range is required or the 2.4GHz band is not an option, the EnOcean protocol offers a proven alternative. As a distributor, Rutronik is working with EnOcean and the EnOcean Alliance to supply solutions to software specific adaptations and more complex problems.

Field level II

We have seen how the wireless connection of sensors or actuators to a gateway, hub or edge computer can offer a maintenance-free and self-sufficient solution. But in larger and more complex networks, this approach has its limitations. Especially when it comes to non-time-synchronised mesh topologies, each wireless node must be permanently on to receive incoming data packets and process them immediately, which requires a permanent and intense energy supply.

Whereas available stationary wireless nodes can be powered by wired sources, ‘floating’ wireless nodes need to rely on mobile alternatives such as airfuel-charging technology, which allows greater movement than Qi charging technology. However, often the best compromise is the traditional battery. Many wireless standards, such as Bluetooth Mesh, WiFi Mesh and ANT Blaze, have a history based on a star topology, but, in recent years, have also been supplying mesh topologies.

Above: wireless infrastructures in Industry 4.0 applications now stretch from the factory floor through to system level

By contrast, ZigBee, Threat and some others were designed from the start for mesh networking communication. While WiFi Mesh manages with virtually no power supply, all the other mesh systems can operate for months on one battery charge. Compared with the home sector, where ZigBee controls the LED light sources, unrouted Bluetooth Mesh sets the standard for industrial lighting systems in warehouses and production facilities, open-plan offices and hallways. Unlike the conventional method of specifically routing data packets, unrouted data flow ensures rapid reaction and throughput times.

Smartphones and similar devices can be integrated easily into this type of network, providing another huge advantage over other wireless standards that rely on a router to connect with IT equipment.

Bluetooth Mesh is an intermediate layer which can in theory be placed on any Bluetooth 4.0 hardware. However, when designing a new system, it is a good idea to use more up-to-date Bluetooth 5 or 5.1 hardware.

Field level III

At trans-shipment points such as logistics centres, railway stations and ports, long-range wireless is the way to go. Of the technologies using public and license-free ISM bands, LoRa has become a popular choice in most central European countries. France and the Netherlands have mainly settled on Sigfox because of its good network expansion.

However, over the past year a new trend has emerged, with the CatM1 and Cat NB1 4G standards for narrowband IoT experiencing significant growth and the initial test phases already giving way to series production. While the LTE-M is available for tracking applications with cell changing, the LTE NB1 uses even less energy.

In many countries, the network is undergoing expansion with the deployment of low-power mobile wireless technology. German mobile wireless suppliers, for example, are focusing on the metering market; an electricity, gas or water meter is static so there is no need to change mobile wireless cells during a connection. Providers in other countries prefer to opt for tracking applications for moving objects and have focused on expanding category M1. Most mobile wireless module manufacturers support both networks.

Like 2G, 3G and conventional 4G modules, LTEM1 transceivers are often combined with GNSS (Global Navigation Satellite System) into a single housing to track and monitor the position and motion of containers, vehicles, high-end goods, people and animals. The position is defined and transmitted via the mobile wireless network. Until a few years ago, GPS was a navigation system that was almost without competition, but GNSS alternatives such as Russia’s Glonassand, China’s Beidou and Europe’s Galileo have since emerged. In mid-2019 Galileo made greater tracking accuracy available free of charge, meaning that this system is now ahead of the curve in terms of free use of layer 1 data. In addition, Galileo is the only system to provide an authentication function, which ensures that the received signals are genuine - meaning they do not originate from a counterfeit transmitting station.

Above: The development of multiple standards for wireless data transmission are one of the key drivers behind the ongoing trend towards the Industrial Internet of Things (IIoT)

Generally, the best option is to install as many systems in parallel as possible; this enables the most recent multi-GNNS receivers to work faster, more efficiently and accurately. Yet, it is important to be ready for future changes and react accordingly if one of the systems fails. The NB1 or M1 modem available in the module can be used to change the firmware settings. For applications using GNSS with LoRa, Sigfox, WiFi or Bluetooth, it is necessary to ensure a corresponding option to access the GNSS unit’s operating mode in the host controller; usually it is enough to create an NMEA control command, to choose which systems to use, and which to ignore.

Process level: enter 6th generation WiFi

All the data from the individual workstations are brought together at the processing level. As the data collected at the field-level sensor is often raw, preliminary processing takes place to obtain meaningful information from it. In many applications this process enables users to compare field data that is received in parallel. To cope with such computing-intensive tasks, heavier-duty x86-based systems are often used. Here the trend is towards interconnection, from system-level to wireless technologies.

The 6th WiFi generation is not just faster than the earlier ones, it also brings better connection management for subscribers, which scores particularly well in professional installation scenarios. Another benefit is its improved frequency assignment with the upcoming 5G network.

Working with its technology partner, Intel, Rutronik has been able to provide its customers with market-ready WiFi 6 solutions from the start, including m.2 PC cards for industrial PCs, Panel PCs and NUCs.

System level: location, location, location

The choice of technology at system level is heavily dependent on the complexity and local circumstances, such as the size of the manufacturing site or the operational frequency plan. WiFi 6 may be the best choice for smaller dynamic operations, while larger companies with very static installations may want to consider a cabled solution. Yet, as soon as 5G becomes widely available and affordable, it may become necessary to rethink these installations too.

Operative level: the earlier generation is still an option

When communicating between different plants, the information tends to be heavily condensed beforehand so conventional LTE is normally enough to cope with the data throughput and latency periods – even in major international corporations. Transmitting important key operational data wirelessly via an LTE router is already possible.

Power consumption and the modem are negligible costs considering that the computers always operate from the mains, and only a very few LTE modems or LTE routers are deployed. Different solutions from different manufacturers such as PC cards, external modems and routers can be combined, for example, a server may be configured with an LTE modem and a WiFi 6 card.

The latest wireless trends in automation

Following its success in consumer smartphones, another technology is now becoming increasingly popular in industrial environments; 13.56MHz technology enables secure exchanges between active reader and passive transponder as well as between two active readers. It is compatible with almost all modern tablets and smartphones meaning that affordable standard hardware becomes readily available; there is often no need to deploy more expensive special devices such as an RFID gun. Besides the cost of the hardware, this option provides software programming benefits too.

Those wishing to use RFID for longer distances or to scan several transponders at once will still need to use another frequency. In this case the transponders are not supplied by the reader’s electromagnetic field, communicating via load back coupling, but have their own power supply (usually a battery or solar power) and communicate in a 2.4GHz band based on Bluetooth or a similar proprietary wireless protocol.

Where neither fixed cabling nor energy harvesting are available, and even affordable wireless connections such as BLE deplete the batteries too quickly, increasing numbers of industrial players are choosing the ANT protocol. For example, the first Time-of-Flight sensors will soon be available for high accuracy distance mapping with very low energy consumption. In addition, ANT is available ex works in most Android smartphones, and with multiprotocol SoC solutions that can transmit data traffic in Bluetooth networks without incurring further hardware costs.