If there is one overarching theme to this report, that theme is speed. The U.S. mobile industry has gotten a jolt of bandwidth in the past year, causing average 4G download speeds among all four operators to climb. T-Mobile and Verizon have now crossed the 20 Mbps threshold for average 4G download speeds in our measurements — a milestone that seemed quite distant a year ago. Meanwhile we see even more powerful networks incubating in major U.S. cities, LTE reach continuing to expand and the reinvigoration of the country's smallest national operator Sprint.

In the latest State of Mobile Networks report for the U.S., OpenSignal parsed 8.1 billion data points collected from 385,679 devices in a 90-day test period between March and June to compare the 3G and 4G experience offered by AT&T, Sprint, T-Mobile and Verizon. In addition to our national results, we've also taken a detailed look at the major cities of the U.S., expanding our regional coverage to include 47 cities and four metrics. Let's start first with the impressive growth trends we're seeing in 4G speed.

A growth spurt in LTE speeds

The U.S. mobile industry has hit an important milestone since OpenSignal published its January State of Mobile Networks report for the U.S.: Two operators have crossed the 20 Mbps threshold in our 4G download measurements. This wasn't merely a case of T-Mobile and Verizon inching their speeds upwards in our results. Rather both operators saw significant jumps in their LTE speed scores in the last six months. T-Mobile users saw their average 4G download connection increase more than 2 Mbps to 21.6 Mbps since our last report, while Verizon users experienced a nearly 3 Mbps boost to bring their average LTE download speed to 20.6 Mbps. Seen in the context of a full year, their speed gains are even more telling. T-Mobile's measured LTE download speeds have increased 24% in just 12 months, while Verizon's have jumped a whopping 38%.

Verizon's improvement is particularly impressive given the trend we observed after it reintroduced unlimited plans last year. The launch of these plans coincided with a drop in its average speed measurements, most likely driven by users consuming more data on Verizon's networks. Our current data shows that Verizon has not only overcome those challenges, but it has left them far behind. If there is one hangover effect from the unlimited launch, it's that while Verizon's speeds suffered last year, T-Mobile established a big lead in our 4G download speed metric. It maintains that lead today, though the gap between T-Mobile and Verizon has certainly shrunk in our measurements.

Gains in 4G speed weren't confined to T-Mobile and Verizon. Despite its own battle with falling 4G speeds after it reintroduced unlimited plans, AT&T reversed that trend early this year and emerged the better in our 4G download metric. Its average LTE download speed grew 17% over 12 months to 15.1 Mbps in our measurements. Sprint actually saw the biggest year-over-year increase in 4G download speed of any of the four operators in our results. Its average LTE download connection jumped 48% to 14.5 Mbps and brought it within a megabit of catching up to AT&T in our rankings. If Sprint's speeds continue to improve at the present rate, it could easily become the third-ranked operator in 4G download speed by our next report.

What we're seeing in these trends is definitive evidence of increased 4G capacity and LTE-Advanced upgrades across all four operators' networks. Data consumption certainly isn't going down, nor is the number of 4G users dropping, so this can only mean network improvements. What's more, our regional results suggest this may only be the beginning of a larger growth spurt in speed. Operators typically focus their network upgrades in urban areas before expanding them across their national footprints, so larger cities serve as bellwethers of what's to come. In 10 of the cities we examined, either Verizon or T-Mobile (or both) averaged 4G download speeds of 30 Mbps or greater in our measurements. In the largest city in the U.S., New York, we clocked Verizon's average 4G downstream connection at 33.9 Mbps.

In our other speed metrics, T-Mobile once again emerged as the dominant operator. Its HSPA+ service ran away with our 3G download award, averaging speeds of 3.6 Mbps. Given its high ranks in 3G speed, 4G download and 4G availability, it was no surprise to see T-Mobile also win the overall download speed category, and it was the only operator in our results to average more than 20 Mbps across its networks.

Our final speed category, 4G upload speed, was also a lock for T-Mobile, but here we saw a surprising gap between the fastest and slowest averages. T-Mobile's winning 4G upload result of 7.5 Mbps was three times faster than Sprint's last-place result of 2.5 Mbps. This is likely explained by the unique nature of Sprint's primary LTE technology. As detailed in our recent blog analysis of U.S. upload speeds, Sprint is able to tweak its networks to prioritize download speed over upload speed. This is most likely the reason for its low score in our upload metric, and would also explain the big improvements in 4G download speed we've seen from Sprint lately.

T-Mobile, Verizon duel over 4G reach

T-Mobile and Verizon have long battled over our 4G availability award, but in our last report we saw T-Mobile gain the upper hand, beating Verizon by a fraction of a percentage point in our measurements. Verizon, however, has closed that narrow margin in the last six months. The two operators weren't just statistically tied, they were numerically tied. Overall our users on both T-Mobile and Verizon were able to latch on to their respective LTE connections 93.7% of the time. It doesn't get closer than that.

What's fascinating about this rivalry over 4G availability is that the two opponents have already achieved such a high level of LTE access, that any gains they make are often small. T-Mobile's 4G availability score increased by half a percentage point, while Verizon's score grew by barely a percentage point. At this level, LTE reach can only grow incrementally as operators optimize their networks to maximize access. But it seems to be a fight Verizon and T-Mobile feel is worth taking. T-Mobile has been using low-frequency airwaves to expand its LTE reach, and Verizon is making availability gains in this report right as it is emphasizing improvements in network reliability in a new TV ad campaign. For every percentage point of 4G availability they gain, their consumers spend on average 7 more hours each month connected to an LTE signal. By chasing higher levels of 4G reach, Verizon and T-Mobile will not only be able to provide a better mobile broadband experience to their customers but also hasten the shutdown of their legacy 2G and 3G networks.

AT&T and Sprint also saw availability gains in our results. AT&T's 4G availability score grew from 87% to 88.4% in six months. But it was Sprint's availability results that increased the most, rising 2 full percentage points to 87.7%. Sprint's progress in this metric has been one of the big storylines of the U.S. mobile industry, especially in light of T-Mobile and Sprint's merger plans. Two years ago, Sprint's 4G availability languished below 70% in our measurements and it seemed unlikely that it could bridge the chasm between it and its competitors in LTE reach. In our most current data, Sprint is within a hair's breadth of being statistically tied with AT&T. What's more, if Sprint and AT&T keep up their current rate of 4G availability expansion, the U.S. could soon face the situation of having all four of its major operators cross the 90% threshold.

That brings us to latency, which measures a network's response time. The faster packets traverse the network, the less lag time consumers experience on real-time communications apps and the more quickly web pages and videos begin loading on the mobile internet. Last year, AT&T appears to have made major improvements to its network architecture that caused it to jump from last to first place in our 4G latency rankings. Our latest results show AT&T is solidifying this lead. Its 4G latency dropped 4 milliseconds to improve its score to 54.1ms. T-Mobile, however, continued its long series of wins in 3G latency, with a measured HSPA+ response time of 85.1ms.

Looking locally and abroad

In our regional examination of 47 major cities, we found the same battles between operators we saw in our national metrics playing out on the metro level. But in many cases the results themselves were amplified, reflecting the upgrades that operators have made to their urban networks.

In our 4G availability metric, the contest for the top spot was fought solely between Verizon and T-Mobile in 46 of the 47 cities we analyzed. Only in St. Louis did another operator take a share of the 4G availability prize as Sprint drew with Verizon. In the remaining markets, Verizon had the upper hand. It won our 4G award outright in 20 markets compared to the one market (Las Vegas) T-Mobile won outright. In the remaining 25 cities, Verizon and T-Mobile were tied statistically for the lead in our results. The level of 4G access in several of these markets was quite extraordinary. In many major cities, all four operators racked up 4G availability scores greater than 90%, and in 58 instances Verizon or T-Mobile were able to deliver a 4G signal to our users more than 95% of the time.

In 4G latency, AT&T's national dominance extended to the major cities. Ma Bell either won or shared our 4G latency award in 42 of the 47 metros. In two cities, Chicago and Milwaukee, our results show AT&T was able to provide sub-40ms connections, making it the only operator in the U.S. to hit that milestone.

Our regional 4G speed awards were more mixed than our other results, as every operator in the U.S. was able to flex its LTE muscles in at least a few markets. But T-Mobile and Verizon remained the predominant operators in our 4G upload and download speed columns. T-Mobile ranked highest in 4G download speed results in nine markets and highest in our 4G upload speed results in 10 markets. Meanwhile Verizon took the download prize in 13 cities and the upload award in 15 cities. In all of the remaining cities, either T-Mobile or Verizon — or as often was the case, both — were statistically tied in our upload and download measurements with another operator for the lead.

T-Mobile and Verizon also produced the fastest individual 4G speed scores across our 47 cities. Both operators provided our users with average LTE download speeds faster than 30 Mbps in Detroit and Minneapolis. Our results show Verizon also met that 30-Mbps benchmark in Baltimore, Chicago and New York City, while T-Mobile's list of 30 Mbps-plus cities included Cleveland, Grand Rapids, Jacksonville and Kansas City. We recorded AT&T's fastest 4G download score of 23.5 Mbps in San Diego and Sprint's fastest 4G score of 23.3 Mbps in Seattle. The location of the fastest network of all in our results was a surprise. T-Mobile's LTE service in Grand Rapids, Michigan, had the highest 4G download average in our results: 45.7 Mbps.

These faster 4G speeds we see emerging in U.S. cities are encouraging signs. They're evidence that national operators are moving further down LTE's evolutionary path, though the improvements we see in different cities could all be the result of different factors. In the last year, operators have plowed more bandwidth into their LTE networks, either from new spectrum or old 2G and 3G spectrum repurposed for 4G use. They've tweaked the technical capabilities of their networks with more sophisticated antenna technologies and more advanced modulation techniques. And they have used carrier aggregation technologies to lash together multiple frequencies at far-flung ends of the mobile spectrum band to create much more powerful LTE connections. Our measurements show those efforts are paying dividends.

In our next few U.S. reports, OpenSignal will be watching for further increases in 4G speed — to see whether we're tracking a continuing trend or just a one-off boost in LTE capacity. If the trend continues, the U.S. could reclaim some of its lost glory as a 4G innovator among the global wireless community. There is no question that the U.S. is a global leader in 4G availability. It's one of only five countries to maintain a national 4G availability greater than 90% in our most recent State of LTE report. But the U.S. has fallen far behind its fellow LTE early adopters in Europe and East Asia when it comes to technological capabilities such as speed and latency. Pushing past 20 Mbps is an early sign of progress, but if U.S. operators can expand the 30 Mbps-plus experience we're seeing in New York, Chicago, Detroit and Minneapolis across the country, then the U.S. could propel itself back into the 4G speed elite.