Industrial Wireless Part 3: Choosing Between Wi-Fi and Cellular
| By: Kristin Lewotsky, Contributing Editor
Editor’s Note: In part one of this three-part article, we covered industrial wireless communications over unlicensed spectrum. In part two, we took a deep dive into cellular technologies in the form of 4G LTE and 5G wireless. In part three, we focus on how to decide when cellular technology is a fit and if so, how best to implement it in your facility.
It’s an engineering truism that there is no perfect solution, just the best choice for the project at hand. Although wireless technologies like Bluetooth, Wi-Fi, and the various low-rate wireless personal area networks (LR-WPANs) and low-power wireless LAN standards such as Long-Range Wide-area Network (LoRaWAN) have their sweet spots, some facilities and applications need more. Cellular networks offer high data rates, low and predictable latency, and broad coverage, combined with the built-in security and reliability that are a requirement for the industrial sphere. They are also purposely built for mobile applications, adding a degree of functionality not offered by the alternatives. In a recent survey of 600 manufacturing executives, 74% plan to upgrade their communications and control networks as part of their digital transformations.1 More than 90% of respondents are considering 4G or 5G networks. The key is to know when to choose cellular, which generation to choose, and how to configure for success.
Wi-Fi and Bluetooth have become ubiquitous in the industrial landscape but they do have limitations. Wi-Fi has nominally high peak data rates (3.5 Gbps for Wi-Fi 5 and 9.6 Gbps for Wi-Fi 6). These are theoretical numbers, however. Their operational speeds will be significantly reduced by factors like overhead and the number of devices in the network. That’s not much of an issue for your household Wi-Fi but on a factory floor where wireless may be connecting dozens of sensors or hundreds of automated mobile robots (AMRs), data rate and latency matter. Security can also be a concern, as can reliability, particularly in the dynamic industrial environment.
For the right application and project, cellular wireless, particularly in a private network, can be a better choice. Cellular signals are much higher power than Wi-Fi and Bluetooth, which are limited to milliwatts. As a result, low-frequency and mid band cellular signals can pass through barriers like walls, trees, or other structural elements. This makes cellular networks effective in industrial environments with machinery, high ceilings, and lots of metal structures. They can also be useful for communications with devices embedded inside equipment. They can also replace a plant’s current push-to-talk communications system, saving money, increasing reliability, and reducing complexity.
The trade-off for these benefits can be higher costs and greater complexity, although both depend on the details of a given project and facility. Let’s take a look at conditions that would make cellular communications the most effective choice for a particular facility and project.
1. When you need to connect a lot of devices
Because the speed of a Wi-Fi network drops with the number of devices, facilities often need to set up multiple networks to connect everything. This limited ability to scale can be a problem as more and more companies begin to move through their digital transformations. “Based on the testing we've done, Wi-Fi 5 basically saturates at about 5 to 10 devices per access point,” says Stephane Daeuble, head of enterprise solution marketing at Nokia. “With Wi-Fi 6, the data shows saturation at around 16 devices.” Adding another machine or more sensors can require installing new access points in an environment in which the spectrum is already crowded.
It starts with the question of scale. A small business with only a few pieces of equipment can still operate effectively with Wi-Fi networks. Past a certain point, cellular is the most effective technology for guaranteeing a robust high-speed – and scalable – connection to hundreds or even thousands of devices. “We've been able to replace up to 20 Wi-Fi access points with a single 4G or 5G access point,” says Daeuble. “Private wireless can be pretty reliable connecting up to several hundred things to a single access point.”
2. When you’re operating over a large area or one with many obstructions
Signal strength makes cellular networks particularly effective at providing coverage for very large structures and campuses. When Erickson built a 5G factory in Lewisville, Texas, for example, it installed a private 4G LTE and 5G cellular network to provide connectivity for the 300,000 square-foot facility.
To evaluate the coverage of Wi-Fi compared to cellular, Nokia ran a series of side-by-side tests comparing the performance of a Wi-Fi access point to that of a 4G LTE access point operating over the same unlicensed frequency band. “We got roughly 2x more radius of coverage [with the 4G LTE unlicensed access point] and about 4x the area in total,” says Daeuble. For the cellular network, his team used the MulteFire, which acts as a standalone access point running a version of LTE over unlicensed spectrum.
Particularly at lower frequencies, cellular signals are very good at penetrating obstructions such as walls, foliage, and metal. The exception to this is the millimeter-wave band used in some higher-speed 5G networks. Millimeter-wave signals very high data rates but the trade-off is that they require direct line of sight or reflection in order to effectively connect (see Table 1).
Table 1: Performance trade-offs in spectrum bands
3. When you are connecting mobile devices
Many industrial environments today make use of AMRs. Although Wi-Fi can be used to network these devices together, large facilities and/or large numbers of devices frequently require multiple Wi-Fi access points. Problems can arise when an AMR reaches the “handover” point between two access points. If the mobile device loses its Wi-Fi connection due to low signal strength or interference, the robot will default to a safe state, stopping until it is reset or nudged to a location with sufficient signal strength. For warehouses and factories that depend upon hundreds or even thousands of AMRs, these glitches at the handover points can present a major problem.
As the name suggests, cellular networks are composed of networks of communications cells. They were built from the beginning to support smooth handovers as mobile devices travel from one cell to the next. This works as well for an AMR crossing from cell to cell in a large warehouse as it does for a mobile handset in a car driving down the highway.
4. When you need higher data rates or higher volumes
Although Wi-Fi 6 was developed to provide a major performance boost over previous generations, in some cases, it just isn’t enough. “We typically see cellular in places where those unlicensed technologies can't provide the data throughput and connectivity you need for your application,” says Justin Shade, senior product marketing specialist for wireless products at Phoenix Contact (Middletown, Pennsylvania). “If you want to do a firmware update or remote connect to a drive or a PLC and Wi-Fi doesn't give you the signal strength to get the data rate you need, a cellular connection can provide it.”
The speed of the latest generations of cellular networks enables them to transfer massive volumes of data, once again providing a major advantage over Wi-Fi for the right application. “Especially when it involves gigabytes or terabytes of data per week or per month, that’s where private mobile networks based on cellular technology really shine,” says Harald Remmert, senior director of technology, Digi International (Hopkins, Minnesota). “And on top of that you have the range and quality of service that Wi-Fi, for example, is not able to provide. You have a level of security that for cellular is just baked in with a SIM card. Wi-Fi or other technologies cannot provide security at that level.”
5. When you need high reliability
Cellular technology is designed to serve a number of applications for which reliability is essential, such as first-responder networks. For industrial operations depending on equipment availability, losing the network can shut down the process just as quickly as any other type of downtime. Increasingly, manufacturers are considering a move to private cellular networks to ensure operational continuity. “We see a lot of customers who are now replacing their Wi-Fi networks with private cellular networks,” says Peter Linder, head of 5G marketing at Ericsson (Plano, Texas). “WiFi is great as a secondary infrastructure, but not as a primary infrastructure and that’s why we see the strong momentum for 4G and 5G in terms in general right now.”
4G versus 5G
The next major decision is to determine whether to use 5G and 4G LTE. Aimed at business and industrial applications from the start, 5G has been designed to deliver major advances in three key areas:
- Enhanced mobile broadband (eMBB): Downlink speeds as high as 10 Gbps
- Massive machine-type communications (mMTC): Coverage of up to 1 million devices per square kilometer
- Ultrareliable low-latency communications (URLLC): 1-ms latencies with 99.9999% reliability
When mature, 5G will simplify connecting the hundreds and thousands of smart devices that will form the industrial Internet of Things (IIoT). 5G will enable entirely new use cases and remake markets. Indeed, one recent analysis forecasts that between 2021 and 2025, 5G will add $1.5 trillion to the US GDP.2
Today, however, 5G is only at the beginning of its rollout, which will take place in stages over multiple years. Release 15, which launched 5G, focuses primarily on eMBB. The capabilities of most interest to the industrial community—MTC and URLLC—will not be available until later releases (see table 2). In other words, most of what 5G currently offers in the industrial space is faster data rates rather than any advance in controls capabilities. Meanwhile, 4G LTE, which launched in 2011, has had a decade to mature. The most recent version, LTE Advanced Pro (colloquially known as 4.9G), even received some updates in Release 15.
Table 2: Performance comparison of 4G LTE and 5G
4G LTE Advanced Pro currently operates with latencies on the order of 10 ms to 20 ms – once again, not fast enough for true wireless control but good enough for many applications. [Note: 4G LTE Advanced Pro will eventually evolve to latencies on the order of 2 ms.] The peak download rate will be 1 Gbps and it is specified to reach a connection density of 100,000 devices per square kilometer. Given these performance metrics, 4G LTE Advanced Pro currently serves most industrial use cases while offering a lower price, footprint, and complexity than 5G.
“We have 290 customers today who have deployed private wireless in multiple sites and in all of those cases, we have never encountered something that we could not do with 4.9G LTE,” says Daeuble. “Although often we start the conversation with 5G, the reality gets very quickly back to 4.9G LTE because there’s already so much you can do today. You can get started on your industry 4.0 transformation. You can get a lot of competitive advantage in terms of flexibility, efficiency, sustainability, safety, and security. Then when the time is right, you'll add 5G to your network.”
For now, 5G should be reserved for applications that can benefit from the boost in data rate. For many connected worker use cases, for example, 4.9G can do just fine. For augmented reality/virtual reality applications requiring high-definition video and a high degree of interactivity, 5G may be a better solution.
For another example, consider dockside cranes. A current system might have half a dozen cameras to assist with the fine motion control required to accurately position loaded containers at very low speeds. The increased bandwidth provided by 5G makes it possible to increase the number of cameras and angles available while also serving up HD video.
HD video can also dramatically improve quality inspection and process control. A 5G data pipe can support ultrafast transfer of high volumes of data for analysis by AI. The system can be used to not only identify flawed product but to determine corrective action needed to quickly address any process issues.
Ultimately, it comes down to the specific needs of the use case. “There are a lot of automation applications today that can use 4G, such as remote access, remote control, and sensors,” says Remmert. “If you need end-to-end low latency, then a standalone 5G network might be better. And 5G network slicing will allow you to tailor your network even further to your specific application needs.”
Public or Private Cellular?
At first glance, using a public network seems like the easiest entry point. It doesn’t require investment in spectrum, infrastructure, or in-house expertise. Back when every device on the network was treated as equal, gathering data from sensors using a public data plan could be cost prohibitive. These days, data plans for items like sensors have dropped considerably, however. Public networks present other, greater concerns for the industrial user, though, including resource contention, security, and the ability for the network to serve the needs of a specific location or use case. Private networks provide an increasingly accessible alternative.
Private networks require greater upfront investment from the user but are highly scalable long term. Dedicated spectrum eliminates concerns about resource contention. The network owner can allocate network capacity and customize performance metrics such as latency and data rates for uplink and downlink.
In the manufacturing survey, the top two motivations for installing private wireless networks were to capture data for digitalization, particularly the digital twin, and to address issues with AMRs (see Figure 1). They also wanted to use connectivity to improve worker effectiveness. Only then were they interested in more sophisticated capabilities such as reconfigurable machinery, etc.
Figure 1: Survey of 600 manufacturing executives revealed that private 4.9 G networks can address many current networking needs. (Courtesy of Nokia)
As far as the network architecture itself, typically the private network core (blue box) connects to the Internet through firewall. Management tools are typically cloud-based applications. Access points are used to create a cellular network across the facility or campus (see Figure 2). User equipment incorporates modems and Sim cards that enable them to securely connect; a device without the properly enabled Sim card will not be able to access the network.
Figure 2: A typical private cellular network (Courtesy of Phoenix Contact)
A variety of deployment models are available. Companies can take advantage of third-party providers who own the assets and operate the service as a turnkey offering. The enterprise can use an integrator to build the network and then contract with one or more wireless providers for services across specific spectrum bands. Alternatively, the enterprise can handle everything, from buying frequency at auction to installing and managing the hardware.
Companies can either try out the technology in a flagship location and apply lessons learned to subsequent deployments, or they can start out with a handful of use cases as a foundation, then broaden out over time.
Tips for Getting Started
Start with the use case
Don’t begin with a preconception about which wireless generation is best. Start with the use case. What problems are you having in the plant? Can cellular networking solve them? What are your end goals in terms of the digital transformation? How are needs likely to scale in future? This information should be used to determine whether a cellular network is appropriate and if so, which generation.
Perform a detailed cost analysis.
In a side-by-side comparison of cost per access point, cellular is more expensive than Wi-Fi. For an appropriately sized project, the cost disparity shrinks once the analysis takes into account the increasing coverage, improved penetration, and its ability to take over any voice network requirements. “Because cellular is so reliable and it's able to handle interference so much better than Wi-Fi, once you’ve deployed your network, you're done,” says Daeuble. “You don't need to add another access point or tweak the net a different way just because you deploy a new machine. So, for any facilities beyond, say, around 25,000 m², private wireless will typically be more cost effective.”
Analyze the application and the location
In a wide-open area, particularly outdoors, a single antenna may be able to get the job done. In a facility full of obstructions, for example with metal shelving, columns, or multiple rooms, network planning will be more complex. The installation might require multiple antennas, or small cells, throughout the warehouse to provide sufficient coverage. In general, using multiple frequencies will optimize performance.
Don’t go it alone
Any IT shop in the world knows how to set up a Wi-Fi network. Cellular networks involve a steeper learning curve. At minimum, work with your vendor or consider using an integrator. Partners who are experienced in the technology can help identify problems in advance and guide you through proof of concepts.
Although it might make sense to do a broad deployment at a greenfield facility, especially at Brownfield locations, it’s okay to start small. “There’s a lot of value in automating and digitally transforming an existing facility,” says Remmert. “It doesn’t have to be expensive. It doesn’t have to be the latest and greatest 5G. Start with 4G. Try a few different things. Bring bright people from your company together and then have them see what's possible.”
it’s important to note that cellular technology shouldn’t be thought of as replacing Wi-Fi and other alternatives. Those technologies still have important roles to play, not just for IT applications but also on the factory floor with less important processes. Cellular technology should be considered as an addition to Wi-Fi for mission-critical and business processes in properly scaled projects.
As for 5G, it may be a niche solution at present, but the broader capabilities are coming. The key is to lay the groundwork now. Consider the use cases, reach out to the IT department. Consider the need for future scalability and what technology will best support it. Most of all, get started. “Even if the [mMTC or URLLC] were ready today, you wouldn’t be able to deploy the technology tomorrow,” says Shade. “You need to plan for it, obtain funding, install hardware, and deploy your network. These things can take 12-16 months, so if you know that you’re going to need the capabilities coming out with the next release, start having the conversations now.”
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