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Analyzing AT&T’s spectrum usage to understand its 5G rollout plans

Opensignal is investigating how different U.S. carriers have been using their spectrum holdings to launch 5G services. In this first analysis, we have looked into AT&T’s spectrum use of its 850MHz band, which the operator used to launch its low-band 5G service in December 2019, in order to shed light on AT&T’s 5G approach.

U.S. carriers are waiting for new sub-6GHz spectrum to be auctioned for 5G or for the arrival of Dynamic Spectrum Sharing (DSS) technology which will enable more flexibility. The new auctions will likely occur later this year with the June 2020 CBRS auction and the December 2020 C-Band spectrum auction but that spectrum will not likely be available for use until a later date.

For now, if a U.S. carrier wishes to launch 5G on sub-6GHz bands, which offer good reach, the carrier needs to repurpose existing spectrum that the carrier owns and may be using for 3G or 4G users’ service. By analyzing the cities where the amount of 4G spectrum used has changed, Opensignal data can highlight the pace of AT&T’s 5G network deployments and help to predict which cities the operator is readying for 5G before the actual launch. 


AT&T is managing 850MHz spectrum between 3G, 4G and 5G users

AT&T has spectrum licensed on the 850MHz band in 155 markets of the top 200 Cellular Market Areas (CMAs), by population, which we analyzed. The operator owns 25MHz in 135 markets, 50MHz in 13 markets and has part of the band licensed in the remaining seven markets. In all except seven of the 155 markets where AT&T owns spectrum on the 850MHz band we have seen the operator using part of that spectrum for 4G, and part of it for 3G.

However, starting in November 2019, we observed AT&T reduce its 4G spectrum in use on the 850MHz band from 10MHz to zero in a number of markets. At the same time, the operator continued to use the other part of the band for 3G. Those are the same markets where AT&T launched its low-band 5G network in December 2019, suggesting that AT&T is now using that 10MHz of spectrum — which it stopped using for 4G — for its 5G service, while keeping the other part of the band for 3G, to support its 3G customers until the planned shutdown date of early 2022.

AT&T has retired 10MHz of 4G spectrum ahead of 5G launch

Since November 2019, we have observed AT&T reducing its 4G spectrum on the 850MHz band in more than 40 additional markets. In some of those markets, the operator subsequently launched its 5G service.

For example, in New York City we collected 4G measurements on the 850MHz band until mid-November 2019 when we stopped receiving 4G measurements on that band. AT&T then launched its 5G service in New York in late December, about a month after we observed the operator clearing the spectrum used for 4G in that band.

There is usually a gap of a few weeks, or even a month or two, between the operator clearing the spectrum used for 4G and the subsequent launch of 5G. This indicates that this data can help us understand the extent and likely pace of AT&T’s 5G network rollout, and could suggest the markets where AT&T will launch 5G next. Conversely, our data could also indicate where AT&T is not imminently launching its 5G service on the 850MHz band because we have not observed AT&T reduce the amount of spectrum used on the 850MHz band for 4G. 


In time, DSS and spectrum auctions will reduce the need to juggle existing spectrum

Low and mid-band spectrum is limited in the U.S. for now. While 2020 will likely see new sub-6GHz spectrum being auctioned in the U.S., it will take time for operators to deploy those new bands in their 5G networks. 

Despite some concerns about the technology, dynamic spectrum sharing (DSS) will likely make a difference by enabling carriers to deploy both 4G and 5G in the same spectrum band and dynamically allocate that spectrum between 4G and 5G smartphone users as needed. Verizon has stated its support for using DSS to launch 5G using its existing 4G spectrum bands. 

To date, each U.S. carrier has taken a different initial approach to 5G. Opensignal has measured the early results of these different strategies. One operator has launched 5G on mmWave only, one has launched on mid-band, while the other two have used the existing sub-6GHz spectrum holdings they originally had for 4G service, alongside mmWave.

Opensignal will keep investigating U.S. carriers’ 5G spectrum strategy and their impact on users’ mobile experience.