Forbes Column

December 2, 2019
T-Mobile Nationwide 5G Launch Highlights Range vs. Speed

By Bob O'Donnell

If you’ve been following the news about the launch of 5G service and 5G-enabled devices in the US, you’ve undoubtedly heard a lot about speed. Specifically, there’s been a lot of discussion about the super-fast download speeds that some versions of 5G can enable.

Regular readers of this column know, however, that not all 5G is the same, nor are the characteristics of the different “versions” of 5G created equal (see The 5G Landscape, Part 2: Spectrum and Devices for an in-depth discussion of sub-6 GHz-based 5G and millimeter wave-based 5G).

The practical manifestation of these differences has never been clearer than with today’s nationwide launch of a 5G service from T-Mobile (both postpaid and prepaid) based on the 600 MHz spectrum. The use of the 600 MHz frequency puts it into the sub-6 GHz flavor of 5G overall, and specifically into what’s termed “low-band”, that is, anything under 1 GHz (aka 1,000 MHz).

What’s notable about T-Mo’s new service is that it offers a significantly wider coverage area than any other 5G service. T-Mobile is claiming it reaches over 200 million people in the US (60% of the population), including many parts of rural America. Plus, unlike millimeter wave (mmWave)-based 5G services from Verizon and AT&T, it works well both outdoors and indoors, because the signal easily passes through buildings, windows, etc. However, the speed of the service is only modestly faster (approximately 20% on average) than existing 4G LTE service from T-Mobile.

Here lies the crux of the current dilemma we have with 5G. Early promises of super-fast speeds are now facing the reality that those speeds are only available in limited outdoor urban environments, because they require the use of mmWave technology, which can’t travel very far. The 5G service that most people will have access to is going to be one that uses sub-6 GHz frequencies, and for a variety of reasons, including technical and historical ones, it doesn’t currently offer speeds as fast as some might expect (or at least hope for). Now, to be clear, in most cases it will still be better than what we’ve had, but it’s important for people to set (or reset) their expectations about what 5G is going to initially offer (see Real-World 5G Speeds Are Slower Than Expected for more.)

With this in mind, it’s worth diving deeper into the hows and whys of the new T-Mobile service, in part, because of how many interesting insights it provides into early 5G implementations. First things first, T-Mobile will not be charging extra for access to 5G service, which is great, but you will need to purchase one of two new 5G-compatible phones to take advantage of the new offering. The company has the OnePlus 7T Pro 5G McLaren available for $900 and a version of the Samsung Galaxy Note 10+ 5G for $1,300. It’s important to note that both phones only support sub-6 GHz frequencies and not mmWave—not even the mmWave frequencies that T-Mobile has already deployed in several cities around the country. In other words, these phones can “see” and work with one kind of T-Mobile 5G service, but not the other. (In places where they don’t sense a 5G signal, they simply revert back to 4G, as all 5G phones do.)

This dichotomy is one of many interesting realities about the early days of 5G. As of now, there are no phones available in the US that support both sub-6 GHz and mmWave. To complicate matters, there is another version of the Samsung Galaxy Note 10+ 5G available from Verizon that does support mmWave but does not support sub-6 GHz. Confused? Well, it has to do with a combination of what modem is being used in each version of the phone as well as a series of other chips that are collectively referred to as the RF Front End (RFFE) (see The 5G Landscape, Part 2: Spectrum and Devices for more details on how chips like modems and RFFEs work).

Qualcomm’s X50 modem, found in the Verizon version of the Note 10+ 5G, supports mmWave and some sub-6 GHz signals, while the newer X55 supports both mmWave and all types of sub-6 GHz signals (specifically, both FDD, or frequency division duplex, and TDD, or time division duplex). However, the modem has to be paired with the right antennas, filters, and other elements in order to work, and it’s both an engineering and cost challenge to get all of the frequencies to work in the same phone. As a result, the T-Mobile version of the Samsung Galaxy Note 10+ 5G only supports sub-6 GHz. (Interesting side note, the same is true for a new AT&T version of the Note 10+ 5G that works with its recently launched “low-band” 5G service based on 850 MHz.) One nice potential benefit for T-Mobile users is that both of its new phones do support the mid-band (around 2.5 GHz) sub-6 frequencies that Sprint currently offers as part of its 5G service, so if the merger between Sprint and T-Mobile goes through, the phones could potentially tap into those frequencies as well.

Long story short, it’s worth finding out what modem your new 5G smartphone has in it, but just knowing the modem model number isn’t enough. You also have to find out what frequency bands the phone supports. This also highlights that, in these early days of 5G, it’s going to be a lot harder to switch carriers because of the technical limitations of these phones. We’re going back to the days of picking your carrier first and then your phone—at least for the time being.

Another very interesting aspect of the T-Mobile 5G launch is how the technology behind this new network works. Despite initial appearances, the range of the signal has nothing to do with the fact that it’s 5G—it’s completely because lower frequencies travel much further than higher frequencies and 600 MHz is on the very low end of frequencies available for use on cellular networks. In T-Mo‘s case, it has a range of 600 MHz frequencies that it is using for both 4G and 5G services, and both types of signals can travel approximately the same distance if they’re transmitting at roughly the same frequency. What’s particularly unique about this launch is that the company is using a dedicated chunk of this low-frequency spectrum just for 5G. Most carriers who have rights to spectrum below about 2.5 GHz (the current upper limit used by 4G services) have used it all for 4G. T-Mobile, on the other hand, chose to reserve a portion of its 600 MHz frequencies just for 5G, and that’s what it’s using to launch this service.

From a network architecture perspective, T-Mobile is using a technology called 5G NR Dual Connectivity—available on 5G Non-Standalone (NSA) Networks—to combine a channel of 4G bandwidth with this dedicated channel of 5G bandwidth (see How Fast Will 5G Really Be? for more on the many different ways that 5G networks can send signals in a speedier fashion). Dual Connectivity (or more properly, 5G EN-DC, which stands for Evolved-Universal Terrestrial Radio Access-New Radio Dual Connectivity) is what enables T-Mobile to deliver a level of performance that it says will, on average, be 20% faster (but potentially as much as 2x faster) than 4G service in the same location. Basically, you’ll be getting the 5G bandwidth added to the existing 4G bandwidth. While this is conceptually similar to another technology called Carrier Aggregation, or CA, Dual Connectivity works across “G’s”, while CA only lets you combine several 4G channels or several 5G channels—you can’t mix 4G and 5G signals with CA.

Dual Connectivity is also different than another network technology called Dynamic Spectrum Sharing (DSS) that lets carriers use the same frequencies to transmit and receive both 4G and 5G signals at the same time. Many carriers that are launching sub-6 GHz 5G services are planning to use DSS, because, even though it requires a bit of processing overhead, it theoretically enables carriers to leverage a single set of frequencies to carry both types of signals. That, in turn, makes it easier to launch 5G services without having to either buy new spectrum or go through the slow, painful process of reallocating (also called “refarming”) existing radio frequencies from 4G to 5G.

It’s important to note that, over time, T-Mobile can enable some of these other network technologies to improve the speed of this “low-band” 5G network (just as AT&T plans to do). Ultimately, though, T-Mobile’s goal with this launch isn’t to enable a super-speedy network right away, but rather to set the baseline for a longer-term strategy of developing services that leverage a range of different frequencies, including low-band, mid-band (from Sprint) and mmWave. The path to the promised land of 5G is a long one, and as this launch illustrates in several different ways, it’s still in the very early stages. However, it’s certainly interesting to see the approach T-Mobile has taken with its 5G strategy, and it will be fascinating to see how consumers react to it.

Forbes columnist Bob O'Donnell is the president and chief analyst of TECHnalysis Research, a market research and consulting firm that provides strategic consulting and market research services to the technology industry and professional financial community.