After discussing system availability in the last blog, I want to look at the reliability of private wireless connectivity. 3GPP standards are air-tight and deep by nature, but there are still many areas of differentiations when it comes to the implementation, which has a lot of impact on how a private wireless system performs. The further we go with the radio technology (5G and 6G), the more the implementation approaches will be critical to achieving the promise of new and even more complex capabilities such as MIMO (massive-input, massive-out radio), uRLLC (ultra-reliable low-latency communications), TSN (time-sensitive networks), and so on.

Different types of cells/radios matter for private wireless reliability

Public networks are reliable by nature but also benefit from additional “elements” of reliability by the fact that they are made of multiple layers of redundant services. In many countries today, you still have 2G and 3G running alongside 4G/LTE and 5G. Within each radio technology, there are also layers of connectivity using two or three separate spectrum bands (e.g., LTE can operate in 800MHz, 1800MHz and 2.6GHz). Finally, in some urban areas and hot spots, you can even have physically separated layers of the same technology in the same spectrum bands, for instance, LTE/4G macro radios (BTS) running at height in 2600MHz and LTE/4G small cells on the street, also running in 2600MHz. Because today’s smartphones can often support all of these standards and bands, if something goes wrong with one layer, you have multiple layers to use as an alternative – in fact, most phones nowadays can connect to multiple layers at the same time to boost performance. Most of today’s private wireless networks, in contrast, operate a single technology with a single band of spectrum. Thus, the reliability of this single layer coverage is very critical.

The impact of choosing the wrong type of radio for private wireless

For CSPs to provide basic coverage in houses, small shops and in small- to medium-size businesses, a new type of small cell was invented in 2005 called the Femtocell. Compared to traditional small cells that are macro BTSs shrunk in size with a less powerful radio (lower coverage), but the same features and capacity, Femtocells are even smaller radio access points with a minimum set of features and capabilities designed to provide cellular connectivity to just a few people in small and not very challenging radio environments. They need to be very cost effective for the business model to work, which means a much more relaxed approach to reliability, availability, and performance. Because of the layering in the public mobile network, if a Femto goes down, you will probably still be able to connect to another layer of the public network. And even if you cannot, the failure of the Femto only affects a few people for a short amount of time and, most of the time, not for critical use cases.

Femtocells are great, but only when used for the use cases for which they were created. Outside their “comfort zone” — the multi-layered public mobile network— they lack the performance and reliability, for example, that would be required by a typical Industry 4.0 application. This is similar to Wi-Fi – a great technology designed for IT needs, but rarely fit for OT needs. Today, there are many of these Femtocell (or cheap small cells) all-in-one chipsets available from chipset vendors. These vendors not only provide the reference design but also the baseline software stack. It means virtually any company, even not a radio expert, can work with a contract manufacturer to rapidly build a range of private wireless radios based on these chipsets and baseline software. This is what is fueling the explosion in the market of many smaller players, start-ups or established 3GPP core companies, suddenly coming up with their own radio portfolio.

The problem is that these companies (often coming from the core side or even Wi-Fi side) lack the experience of running telco-grade 3GPP networks; meaning, they underestimate the importance of good radios. They do not necessarily understand the difference between a Femtocell and a real macro-parity small cell. The impact on private wireless performance and reliability can be dramatic.

Telco-grade small cells and radios

Nokia has over 30 years’ experience creating and running telco-grade radio cells that reliably support hundreds and even thousands of simultaneous connections in the field, despite the difficult radio environments they operate in. The Nokia Flexi Zone all-in-one small cell range, which is built using the same purpose-built chipsets as our macro cells, can support transmission with up to 840 simultaneous users. Our other telco competitors’ all-in-one small cells, using off-the-shelf small cell chipsets, are already more in the range of 64–128 simultaneous users. And the smaller vendors, using off-the-shelf Femtocell chipsets, are often closer to 16–32 simultaneous users, which often isn’t enough considering all the systems, assets, sensors and people that need to be connected in a typical industrial site; the sensor set for a single digitalized legacy machine could eat up the capacity of a single Femto-based cell. In addition, since they lack the processing power to simultaneously serve more users, they are also unable to run the same feature set as real small cells.

The scheduler and why you should care

One of the greatest areas of differentiation when it comes to radio performance is the software and in particular the software for the scheduler, which is the application that manages users or devices connecting to the radio cell. In a nutshell, the better the scheduler, the more simultaneous devices can be served with reliable performance and the better the performance will be when the radio environment gets tough.

Scheduler design and implementation are a key differentiator between the large telco vendors; hence, it is a big R&D investment area and really influences field performance. How many users you can reliably support simultaneously, how much performance you will get in different areas of the cells, how well it manages interference, and even how far and/or deep the coverage goes are heavily influenced by the strength and capabilities of the scheduler.

The scheduler is something that network vendors have spent years developing since the early days of 3GPP technologies, and the oldest telco vendors have over 30 years of experience in developing and perfecting powerful, intelligent and feature-rich schedulers to deliver reliable performance in real conditions. This deep experience and software intelligence does not come as part of the included reference design and baseline software stack provided with the merchant Femto/small cell chipsets being used by many small cell vendors today. That is why, in challenging radio environments like industrial sites, there is a real-life performance difference, even beyond multi-user capacity, between a good radio and a bad one.

When it comes to Nokia, the scheduler performance has always been one of our strengths; we have plenty of independent public network testing showing the superiority of our scheduler. That is why, when we developed our range of small cells (largely used for private wireless), we decided to do what was needed to have the same scheduler and the same advanced features in our all-in-one Flexi Zone small cells as on our macro cells, so that the performance would not be sub-par. Nokia’s small cell performance clearly puts us leagues ahead of other private wireless vendors, and provides a world of difference from the smaller private wireless vendors, whose improvised radio portfolio is based on off-the-shelf Femto/small cell chipsets with baseline software and scheduler.

In conclusion, just as with availability, which I covered in the first blog, the reliable connectivity expected from private wireless is not something to take for granted when choosing a vendor. Meeting the 3GPP standard is no guarantee of actual performance. Look for a vendor that has deep experience designing and running critical networks and, ideally, running public mobile networks. This ensures that their solution will be carrier grade and high performance. Think about the end-to-end integration and testing they can provide. And don’t dismiss the importance of reliable, optimized and feature-rich software that has evolved over decades. The choice of system architecture and the quality of the radio should not be underestimated if you want to meet the critical requirements needed for today and tomorrow’s Industry 4.0 applications.