T-Mobile had the biggest turnaround in our Fastest Mobile Networks study this year, and it isn't done. In a series of exclusive interviews before the UnCarrier 5.0 event in Seattle today, T-Mobile's network heads revealed some of the company's upcoming secret weapons, and promised that the next year will see major moves on one of T-Mobile's biggest pain points: coverage.

"We're very confident with the LTE build we have underway this year, that if you re-ran your tests in less then six months we would rise to No. 1 nationally," T-Mobile's CTO Neville Ray said.

T-Mobile's LTE network now reaches more than 227 million of the 318 million U.S. residents. The company today announced that it had "wideband LTE" in 16 major metro areas and voice-over-LTE (VoLTE) in 15. (See the map below.) That makes its network "data strong, it said.

"We've been mobilized around building an extremely capable, data strong network. That's been the goal and objective of this team," Ray said.

Starting with Speed

Wideband LTE, in T-Mobile's parlance, is an LTE network with channels larger than 10 MHz - either 15 MHz or 20 MHz. Other carriers are moving to wider channels, as well. Verizon Wireless calls its version XLTE, and says it's available in 250 markets. Sprint calls its version Spark, and has it in 24 cities.

But channel width isn't everything. We were impressed with T-Mobile's speed in our nationwide network tests this year; the smaller carrier almost always beat Sprint Spark, and sometimes beat Verizon's wideband XLTE network. Ray says that's because T-Mobile has more capacity per user, not just fewer users on its network.

T-Mobile insists it has a capacity advantage over AT&T and Verizon because of its denser network. Since T-Mobile was built with smaller cells to operate over 1700MHz and 1900MHz rather than 700MHz and 850MHz, the company has more cell sites per square mile and can pack more data capacity into each city, Ray said.

"We have more sites than the Verizon guys do, and we have a lot more density with the metropolitan DAS [distributed antenna system]," Ray said. "The Verizon guys are chasing us. And the AT&T story is that as they started to drive more and more activity into the smartphone space their performance would dip."

Sprint Spark, meanwhile, uses the very high-frequency, short-range 2500MHz band from Clearwire's old WiMAX network. That requires even more cell sites, and our tests this year showed that Sprint has been having trouble building that out across whole cities.

Another T-Mobile capacity secret is 4x2 MIMO, which improves performance at the edge of cells and which no other carrier is implementing. It's already built into most of T-Mobile's phones, said Mark McDiarmid, T-Mobile's vice president of radio engineering.

"This is a huge technical breakthrough which our competition has completely missed. You see dramatic gains at the cell edge of many tens of percentage points of average throughput," he said.

With plenty of capacity, T-Mobile is remaining committed to unlimited data on smartphones."Our commitment to unlimited, unrestricted at a very fair price with no overages is firmly in place," according to McDiarmid.

Vibrant VoLTE

T-Mobile has led with cutting-edge voice technologies for a while now. It was the first carrier to introduce Wi-Fi calling, and the first to deliver nationwide HD voice. Now it's starting to turn on VoLTE, which is going to further improve call quality, according to engineering vice president Grant Castle.

"We've already turned in a 23.85 kilobit codec for all VoLTE calls. That is double the bandwidth of the existing HD Voice. While everybody's trying to catch up with us on HD Voice, we're going to double down on it," he said.

That means clearer calls - at least, between T-Mobile users. But so far, HD voice hasn't operated between carriers, and it sounds like it will still be a while before it does.

"We certainly recognize the benefit of interworking, and there's no technical reason not to implement interworking in HD Voice. We get inquiries from other operators for interworking and increasingly we're starting to make connections," he said.

One thing you're less likely to see is Rich Communication Services, heavily plugged by Qualcomm a few years ago as a reason for carriers to sign up for VoLTE. RCS would have introduced presence, video, and multimedia messaging into traditional voice calling, but apps like Facebook Messenger, Skype, and WhatsApp seem to have taken over those roles, Ray said. "The challenge we have on RCS is that we have such a rich app environment in both iOS and Android today," Ray said.

Continue Reading: So What About Coverage?>

So What About Coverage?

So What About Coverage?

These moves don't matter without sufficient coverage, and that's where T-Mobile falls behind as a national carrier.

We drove thousands of miles for our Fastest Mobile Networks test, and the map below shows T-Mobile's challenge. The green areas are T-Mobile LTE coverage. Yellow are HSPA+ and UMTS - fast 3G. Red are 2G EDGE.

We found that while T-Mobile had excellent coverage and speeds in our 30 test cities, coverage dropped to 2G EDGE about 30-40 miles outside many major cities. It fell to EDGE 30 miles outside of Kansas City, 35 miles from Jacksonville, and 38 miles from Las Vegas.

Compare that to AT&T and Verizon, and you see a stark difference. AT&T's network also drops out of LTE outside major cities, but it falls much more gently to HSPA+, which is still a 3G experience. Verizon's LTE network is nearly nationwide.

There are about 310 million people living in America. T-Mobile currently covers 227 million with LTE, 240 million with HSPA+, and 285 million with GSM and EDGE.

T-Mobile is attacking its coverage issues from several different angles, execs said. They're starting by installing LTE in the 1900MHz band on existing 3G and EDGE towers, Ray said. All they have to do is put an LTE box at the base of each tower; the tower antennas and customers' phones already support the technology.

"We cover 285 million [people] today with our mid-band spectrum portfolio," Ray said. "Some of that PCS spectrum, because it's so lightly loaded, we're going to convert that to LTE. GSM/EDGE will become LTE. It won't all happen this year, but as we move into '15, you'll see that program wrap up."

The next step will be turning on the 700MHz Band 12 spectrum that T-Mobile bought from Verizon, which the carrier will start doing in the fourth quarter of this year, Ray said. Existing Qualcomm chipsets already support Band 12, so it may be available as an upgrade to existing phones.

The 700MHz spectrum will improve range and in-building performance. As lower-band spectrum is better at penetrating walls, AT&T and Verizon (which hold most of the low-band spectrum in the U.S.) have long had an advantage there.

"We're going to do this T-Mobile style: we're going to do this quick," Castle said.

Bringing It Home

I didn't ask the network guys flat-out about what they think of Softbank's Masa Son wanting to merge Sprint with T-Mobile. Rather, I asked them about one of Son's obsessions: the idea that mobile carriers can compete with home broadband.

Son says that if he's allowed to combine the two carriers, he'll offer a wireless competitor to cable and DSL. So far, wireless carriers' home offerings aren't terribly competitive. While the average home user downloads more than 20GB per month (according to AT&T), T-Mobile doesn't offer home hotspot plans with more than 11GB available.

Castle said T-Mobile's unlimited phone and tablet plans are already replacing home broadband for almost 20 percent of its customers - those customers just aren't using PCs or smart TVs at all. And Ray said - I've heard this before - that a good LTE network can skim off low-intensity users who don't want to stream or download video in their homes.

"It's not a binary discussion in my head at all," Ray said.

Still, though, McDiarmid cautioned that any high-volume wireless solution would be more expensive than cable or DSL, because cable broadband is "subsidized" by "overpriced" TV packages.

Things may get much more interesting if T-Mobile moves into unlicensed spectrum. We're not talking about traditional Wi-Fi. Framing it as a "conceptual discussion," McDiarmid led me down a rabbit hole of running T-Mobile LTE over the 5GHz Wi-Fi band. While the company doesn't have anything to announce yet, he said "LTE unlicensed is complementary to Wi-Fi" and "it may be something we consider, yeah."

"If you factor in the 500MHz of unlicensed spectrum, there really isn't any reason why wireless networks can't compete with fixed broadband," McDiarmid said.

For more, watch PCMag Live in the video below, which discusses T-Mobile's new features, including its "data strong" plans.

Further Reading