WiFi? Why not?
May 2017, Industrial Wireless
Despite its image as a consumer-level technology, WiFi is actually an ideal basis for an effective, low-cost mobile data network with wide area coverage. When used correctly, WiFi is a perfect fit for many applications that need highly mobile network access, including automated warehousing and public transportation.
Fifty years ago, fully automated warehouses and robotic factories were only seen in movies. But with the progress in robotic and wireless technologies in the past five years, they have now become a reality. Mobile wireless technologies also open the door to numerous other attractive applications, such as vehicle tracking for public transport and freight networks. In fact, for many years, some degree of mobile wireless data communication has been possible in those applications. The cellphone network can provide the basic infrastructure for data coverage. But, regrettably, due to limitations of latency, bandwidth and cost, most industrial applications have been unable to take full advantage of practical, reliable and affordable real time mobile control and communication. In fact, in addition to these issues, cellular-based data may add unnecessary expense to many applications, if they only actually require wireless coverage over some parts of a relatively small, predefined area, such as a stockyard, vehicle depot, warehouse, bus route or metro line.
Today, with continuing improvements in WiFi/802.11 technology, including higher bandwidth protocols, IP-based networking and faster roaming between access points, users are finally able to use WiFi to construct a reliable mobile wireless communication system that takes advantage of all the latest innovations to deliver substantial cost savings, easier setup and maintenance, and greater operational efficiency.
However, outdoor and industrial WiFi applications do have some special demands when it comes to protecting radios and other electronics from manmade hazards, such as electrically-noisy or unstable power sources and intense radio frequency interference, and natural dangers, including lightning, and static electricity – not to mention environmental issues such as extreme temperatures, vibration, dust and humidity.
Electrical issues can be especially challenging and costly because they cause intermittent, hard-to-diagnose failures in random components, which may lead to repeated maintenance downtime and unnecessary replacement of affected equipment, if the root cause of the electrical disturbance remains undiscovered.
This whitepaper explains some typical applications and highlights the key factors to consider when designing a reliable mobile wireless communication network.
Mobile WiFi enables the IIoT
Although the ‘Internet of Things’ concept has been around for some years, global deployment of IoT networks has increased rapidly during the last 12 months, and the concept is spreading to industry with the Industrial Internet of Things (IIoT). The IoT centralises data through wireless technology and uses machine learning and big data analysis to turn that data into valuable information. Bringing this concept to legacy industrial applications can reduce costs, increase productivity and maximise uptime.
The IIoT often requires many devices to use WiFi simultaneously. The technologies and concepts in this white paper are key IIoT enablers, because they make it much easier for multiple, mobile devices to share WiFi without problems, thanks to new technologies like Turbo Roaming, and good practices like careful network design and avoidance of hidden nodes.
For mobile data communications, WiFi and cellular (mobile 3G/4G, etc) are the two most commonly-used technologies. For very wide-area coverage, such as freight vehicle tracking, cellular tends to be the best choice. But for local area mobile communication, such as smart warehouses, or for fixed-route vehicles, such as bus to depot/stop communication, WiFi is usually a better choice.
Unlike cellular, WiFi does not have monthly charges or data caps and there are no complications involving cellular service providers, billing, cell tower outages, and so on. Compared to Bluetooth and Zigbee, WiFi technology provides higher bandwidth and a relatively longer range – and it also has a proven history of backwards-compatible upgrades – so WiFi provides much greater headroom for future system enhancement and expansion. Unlike proprietary wireless data systems, WiFi is a standard protocol, based on the IEEE 802.11 specification, that is supported by hardware from many different vendors. So WiFi-based systems avoid the risk of vendor lock-in and ensure a longer design life than proprietary radio technologies.
As we have discussed, WiFi is currently the most suitable technology for local area mobile communication in many cases, because it offers a unique set of advantages. We can summarise WiFi’s main benefits as follows:
• Lower operational and maintenance cost.
• Future-proof technology with higher bandwidth available for future expansion.
• Very wide technology support from numerous vendors and hence longer system design lifetime.
Common WiFi mobility applications and their challenges
Material handling and automatic warehousing system
In a traditional warehouse, dispensers spend most of their time walking between shelves to store and retrieve items. As the scale of the warehouses increases, there is also an increase in the proportion of the time that staff must use moving from location to location, and an increase in costly human error due to misplaced items and other causes. Various types of AGV (automated guided vehicle) and AS/RS (automated storage and retrieval systems) have been introduced, using automation to resolve these problems.
One useful example is the automated warehouse system introduced by Kiva (now known as Amazon Robotics) and Amazon in 2011. These robots move the shelves horizontally to help staff to store and retrieve products more quickly and accurately. Even though this system does not utilise vertical space as well as other AS/RS systems, it can be deployed faster and provides better scalability for medium and small warehouses. A key factor required to make AGV, AS/RS or robotic systems successful is selecting the most suitable wireless technology and implementing it correctly. In our experience, we have seen several common wireless problems in warehouse applications:
Challenge #1: Roaming reliability – WiFi has limited signal coverage, so multiple access points are necessary for full coverage throughout an entire warehouse. It is critical to ensure that the clients can roam smoothly between these access points with minimal handover time.
Challenge #2: Power supply quality – robots and other mobile devices often have very limited space and weight-carrying capacity for a WiFi module, and the power system usually cannot be properly grounded. So system integrators must dedicate considerable effort to ensuring onboard devices cannot be affected by the inrush current (a surge of power commonly created when electrical devices switch on or start moving) that is created by the robot’s motors – otherwise there is even a risk that electronics could burn out or suffer significantly reduced lifespan.
Challenge #3: Communication blockage – Unfortunately, metal is extremely effective at blocking radio signals, and large metal objects, such as vehicles and metal shelving, are common in industrial, freight and transport environments. System integrators need wireless expertise and experience to devise the most efficient positioning of APs and antennas, in order to avoid the risk of communication blind spots caused by stationary or moving metal objects.
Challenge #4: System adaptability – there are many kinds of warehouses; some require special environments, such as very high or low humidity, or sub-zero storage temperatures. System integrators need to be able build a system that is adaptable to different customer needs and many different environments. So it is important to choose hardware that can handle extreme temperature ranges and has good ingress protection to keep out dust and moisture.
Building a reliable mobile WiFi system with the Moxa AWK-A series
Moxa’s AWK series devices meet these challenges through incorporation of the following:
• Advanced roaming technology with client-based Turbo Roaming.
• Rugged hardware design with dual isolation.
• DFS channel support.
• Industrial-grade production and reliability.
These features provide all the basic building blocks of a reliable, high-performance mobile WiFi network. The AWK-1131A can be integrated into mobile clients providing all of Moxa’s seamless roaming technologies, while the AWK-3131A and the AWK-4131A are ideal fixed access points for indoor and outdoor use respectively. All units have Moxa’s Dual Isolation technology, providing electrical isolation features suitable for their designated usage, with 500 V insulation and level 4 ESD protection. The AWK-4131A offers IP68 ingress protection – particularly suited to outdoor use where direct exposure to rain, strong winds and dust or grit is a common hazard. The other units are shielded by IP30 ingress protection.