T-Mobile Relies on LTE for 5G Launch

Mike Dano
9/25/2019

According to a new set of tests, T-Mobile's licensed LTE network actually handled 15% of the data transmissions over its shiny, new 5G network.

How can this be?

According to extremely detailed testing conducted by Signals Research Group of T-Mobile's 5G network in New York City, the operator and its vendor partner Ericsson have chosen to simultaneously schedule traffic over both the operator's LTE and 5G networks. "Per the [3GPP] Release 15 specification, the allocation of data traffic over the two networks occurs at the PDCP [Packet Data Convergence Protocol] layer and it means that anytime someone observes/measures the throughput of the 5G NR network, they need to identify the amount of traffic going over LTE," the firm wrote.

That T-Mobile's 5G network uses LTE is not a surprise. The "non standalone" version of 5G, that T-Mobile and every other 5G operator is using right now, requires an LTE network to handle things like authentication. But SRG's Mike Thelander explained that T-Mobile is also opting to transmit data over 5G and LTE at the same time. He said Verizon is not doing this, according to SRG's tests, but that operators in South Korea are. He said operators can increase overall download speeds by sending data concurrently over LTE and 5G.

Another important takeaway from SRG's findings: "The 5G icon on the smartphone means absolutely nothing. We've documented 5G NR traffic when the 5G icon wasn't present, no 5G NR traffic when the 5G icon was present, including one instance when the traffic was going entirely over HSPA+." As SRG previously noted, T-Mobile isn't the only operator displaying 5G icons when 5G may not be available.

So what does T-Mobile have to say about all this? Nothing. The operator declined to provide to Light Reading any insight into how it's moving into the 5G world, how it's leveraging "dual connectivity" to glue together its LTE and 5G transmissions, and how it decides when and where to display the 5G signal icon to its customers.

Instead of addressing these questions about its own 5G network, T-Mobile last week embarked on an advertising campaign called "verHIDEzon" that sought to criticize Verizon for not publishing maps of its own 5G coverage areas.

It's worth noting here that, despite years of bluster from T-Mobile's executives on the topic of 5G, the company's actual 5G rollout is so far virtually identical to that of Verizon's. T-Mobile in June launched 5G in millimeter-wave spectrum in parts of Atlanta, Cleveland, Dallas, Las Vegas, Los Angeles and New York City, though it has said it will take 5G nationwide with its 600MHz spectrum next year. Verizon, meantime, is also launching 5G in millimeter-wave spectrum in parts of cities around the country, and has said it will expand 5G to additional spectrum bands at some unspecified point in the future. And both companies are using the same equipment vendors. The only technological difference, so far, is that T-Mobile is using 100MHz of millimeter-wave spectrum for 5G while Verizon is using 400MHz.

In terms of strategy though, T-Mobile has published maps of its 5G coverage while Verizon has only named the neighborhoods where its 5G signal is located. And Verizon is charging extra for 5G on some plans.

Embracing the messiness of 5G
In a report on the results of its T-Mobile 5G testing, SRG said that it recorded top speeds on T-Mobile's 5G network of 484 Mbit/s. Incredibly, though, the firm said that 5G wasn't the most spectrally efficient technology running on T-Mobile's network in New York City.

"Adjusting for channel bandwidth and after taking into consideration a full range of network conditions, we determined that LAA had higher spectral efficiency (bits/Hz/sec) than 5G NR," the firm wrote.

LAA has been widely embraced in the US by operators such as AT&T, T-Mobile and Verizon as a quick and relatively cheap method to add capacity to their networks. LAA essentially pushes users' LTE traffic into the unlicensed 5GHz band. If T-Mobile's New York network is the information superhighway, LAA adds additional lanes to that highway by transmitting signals in unlicensed spectrum bands alongside transmissions in T-Mobile's licensed spectrum holdings.

SRG reported that T-Mobile's 5G is using fully 100MHz of millimeter-wave spectrum, but that LAA was using between 20MHz and 60MHz. Thus, the firm said that the top speeds over T-Mobile's LAA connection of 209 Mbit/s actually represented a more efficient usage of spectrum at this point than the 484 Mbit/s over T-Mobile's 5G network.

But the complexities of T-Mobile's 5G don't end there. "With the current implementation of 5G NR and the limitations of initial devices/chipsets, a smartphone cannot concurrently use 5G NR and LAA," the firm wrote. "However, it can seamlessly move between LTE + 5G NR and LTE + LAA."

Did you get all that?

The bottom line
What SGR's results are really showing is that, here in the early days of 5G, the technology is nothing if not messy. Yes it's fast, but right now it's not as spectrally efficient as LAA. Yes it's new, but T-Mobile's implementation of 5G still leverages a 4G connection for a significant amount of data traffic (though T-Mobile is quickly moving to the standalone version of 5G, which would eliminate the need for LTE altogether). And no, the 5G icon simply cannot communicate these complexities to actual 5G users.

This is all to be expected from a technology that was obviously rushed to market. And if the evolution of 4G is any indication, 5G will continue to improve as new technologies arrive on the market, whether that's Massive MIMO or network slicing. Nonetheless, it's important to at least acknowledge the fact that 5G isn't monolithic, nor a panacea.

Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano

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Mike Dano
Mike Dano
9/26/2019 | 12:23:33 PM
Another update
I updated the above article again to provide a bit more detail on the role that LTE plays in 5G generally and with T-Mobile specifically.
Mike Dano
Mike Dano
9/25/2019 | 1:28:33 PM
Update
I updated the above article to note that Verizon is also charging extra for 5G on some plans.