This article originally appeared on Forbes by Bob O’Donnell.
One of the many challenges that has plagued previous cellular network generation changes has been the need to do a hard switchover from one standard to the next. That was the case from 2G to 3G, as well as 3G to 4G. In other words, before 4G became real, all new network infrastructure equipment (see The 5G Landscape, Part 1: Infrastructure) and all new devices (see The 5G Landscape, Part 2: Spectrum and Devices) had to be installed and available before 4G could really get started. With the debut of 5G, however, the notion of network standard replacement goes away, because 5G doesn’t initially replace 4G. In fact, it actually builds upon and enhances 4G LTE networks, as will be explained shortly.
This is, in part, due to the fact that there are essentially two different implementations of 5G networks. The first version—and the one currently in use by all existing 5G networks—is referred to as non-standalone (or NSA). 5G NSA has some, but not all, of the capabilities of the full standalone (or SA) version of 5G. Having learned some hard lessons in previous network generation shifts, particularly with regard to how long the transitions took to fully complete, the telecom industry created the NSA version of 5G to serve as a transitional standard designed to smooth what could have been another hard shift from 4G to the full 5G SA standard.
In practical terms, this means that all the early implementations of 5G use a combination of 4G and 5G technology to function. Specifically, initial call and connection management for 5G devices is handled by the core 4G network and then switched over to 5G once the initial connection is made. In addition, all data uploads on early 5G phones actually use a 4G LTE connection—meaning upload speeds will be absolutely identical to what they would be with a 4G phone. But—and this is where it starts to get interesting—it does so with the latest and most advanced versions of 4G, which is sometimes called LTE Advanced. In other words, the deployment of 5G is actually encouraging the upgrading of 4G networks to their most advanced versions. LTE Advanced has been available for several years now and some carriers (notably AT&T in the US) are calling it 5Ge, or 5G Evolution, even though it is most definitely not an official 5G standard, but rather the latest iteration of 4G.
When 5G SA networks (and compatible devices) become available, all connections will switch over to a dedicated 5G network, including data uploads and additional capabilities promised for 5G will also become available. One critical thing to know about 4G LTE Advanced, 5G NSA, and 5G SA is that you only get the full benefits of the network type if the network infrastructure equipment you happen to connect to and the device you happen to be using both support the same standard. If they don’t, then you fall back to whatever network type that both sides of the connection support. In other words, if you have a 5G NSA phone, but happen to be in a geographical area where the local telecom carrier still only has 4G network infrastructure installed, you’ll only get a 4G connection. In fact, it’s even possible you would get a standard 4G connection and not even LTE Advanced if the cell towers haven’t been upgraded in a while. (Remember, it’s very expensive and time consuming for carriers to upgrade their network equipment, so it’s going to take them a while to upgrade their full network.)
In order to get the full benefits of a standalone 5G network, you need to have a 5G SA-capable phone—none of which have shipped yet, and the earliest of which won’t show up until very late this year, but primarily in 2020—and you need to be in an area where the carriers have upgraded their cell towers to support 5G SA as well. The network infrastructure support for full 5G SA isn’t likely to be available until 2021 in the US and, in many areas, may not be available until several years after that. The best you can do right now is to have a 5G NSA-equipped phone on a 5G NSA network.
By the way, just to clarify, the non-standalone versus standalone distinction has nothing to do with radio frequency spectrum. So, for example, you can have both mmWave and sub-6 frequencies on both NSA and SA 5G networks. This can potentially get confusing, because some of the marketing names that carriers are using to describe their networks can sometimes suggest a connection between spectrum and the type of network.
Remember, you can work backwards when it comes to network types and capabilities. For example, a standalone-capable 5G (SA) smartphone can connect to a 5G NSA network—but you won’t get the full benefits of standalone 5G. Generally speaking, the speed of connections won’t typically change between a 5G standalone network and a 5G non-standalone connection—that’s more dependent on the type of frequencies being used for the connection (mmWave, sub-6, etc.—again see The 5G Landscape, Part 2: Spectrum and Devices for an explanation). However, a few other highly touted features of 5G—notably low latency connections, network slicing, and URLLC (Ultra Reliable Low Latency Communications—a technology primarily designed for machine-to-machine, industrial, and IoT applications) are only available with 5G SA-capable infrastructure and 5G SA-capable phones and other devices. Future columns will describe these capabilities in more detail but suffice it to say that not all the full capabilities and benefits being touted for 5G will be available in the first few years of its existence.
One obvious question that comes from all this is, how does one move from 4G to 5G NSA to 5G? The answer, of course, is that it depends. In the case of devices that connect to the network, such as smartphones, you need to have one that has a modem with built-in support for the various network types. Unfortunately, you can’t “upgrade” a modem to support new network types (just as you can’t upgrade a modem or its associated RF front end to support different types of radio frequency spectrum) after it’s been shipped. (For more details on modems and RF front ends, see The 5G Landscape, Part 2: Spectrum and Devices.) Most all of the 5G-capable phones currently being shipped use Qualcomm’s X50 modem, which only supports 5G NSA. To get standalone 5G support, you’ll need one with the forthcoming Qualcomm X55. In addition, later this year other companies, including MediaTek, will begin shipping both 5G NSA and 5G SA-capable modems that will start being incorporated into smartphones and other devices in early 2020.
In the case of network infrastructure, the story is a bit different. Because of the long lifetime and high cost of the equipment, network infrastructure vendors like Ericsson, Nokia, Samsung and others have been building software upgradable versions of their cell tower equipment for several years. In particular, there has been a great deal of effort to produce equipment that can be easily upgraded from 4G Advanced LTE to 5G NSA. This is yet another example of how the deployment of 5G is making 4G networks better, because this upgradability typically wasn’t available on standard 4G infrastructure—only on the newer, more advanced versions of 4G network equipment. As a result, it provided strong motivation for carriers to upgrade their networks.
One of the reasons software-only upgrades are possible is that a great deal of the sub-6 frequencies expected to be used for 5G are also currently being used for 4G. As a result, there isn’t a need to add new antennas and other radio access network, or RAN, equipment to support these frequencies when they want to switch their networks to 5G. (Note that new equipment is required for mmWave, hence the additional cost and slower pace of deploying these higher frequencies.) In many cases, this same equipment can then be once again upgraded to 5G SA, although there typically are other elements necessary to enable a fully standalone 5G network. It’s a classic chicken-and-egg situation, because there’s no need to turn on 5G SA infrastructure until there are enough 5G SA-capable phones in use to justify the effort and expense.
One other critical capability that’s making the transition from 4G to 5G easier is a technology first developed by Ericsson, but now being used by all infrastructure vendors, called DSS, or Dynamic Spectrum Sharing. The trick is that even though both 4G and 5G signals could potentially be used on the same frequency, the different makeup of the signals prevented them from being used at the same time. As a result, carriers were going to have to decide to split their spectrum at given frequencies into smaller chunks, then carry 4G signals in one part and 5G signals in the other. The problem was that this would negatively impact the vast majority of people continuing to use 4G devices by reducing the amount of total bandwidth available to them. Early 5G users, on the other hand, would have had a very lightly used network, which might have been nice for them, but expensive and inefficient for the carriers.
However, Ericsson figured out a clever way to dynamically and automatically divide the spectrum as network traffic demanded so that it could be used as efficiently as possible and allow both 4G and 5G network signals to work across whatever bandwidth was available. This is a tremendous boon to carriers, because it allows them to easily and quickly make 5G service available on at least some of their existing network infrastructure. To be clear, there is a bit of network overhead required to allow this capability. As with many aspects of cellular networks, devices and network infrastructure need to specifically be able to support the technology, but DSS is clearly an important factor in early 5G network deployments.
The final point to make about the connections between 4G and 5G is that much of development of 5G standards was done with the specific assumption that 4G service would continue to exist for some time to come. Even when completely standalone 5G networks and devices become available, most telecom companies, device makers and industry observers expect 4G to be an important part of the wireless landscape. One critical reason is that if there are areas where no 5G service is available, even 5G standalone devices will fall back to a 4G connection. Plus, there is a huge installed base of 4G devices that isn’t going to go away anytime soon, particularly in industrial applications, and they will continue to need networks to which they connect. The bottom line is that while 5G clearly points the way forward, it’s built on a foundation of 4G that will be a critical part of its operation and success.