The LTE iPhone experience: What to expect with iPhone 5

Coverage, data rates and new data behavior all being watched as iPhone 5 rolls out

You have it in the iPhone 5: the first LTE iPhone from Apple. Now what?

It depends.

LTE coverage

To use LTE, you need a 4G LTE wireless network. And not everyone will have one.

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Verizon has the largest LTE-only network -- meaning it's in more locations and more people potentially can use it: It claims 370 markets. AT&T is next, claiming 75 markets. Sprint for now is a distant third. All three are rapidly expanding the LTE coverage and capacity.

If you're an AT&T or Sprint (or even a Verizon) customer who is upgrading to an iPhone 5, you may not have LTE service in your area. In that case, your iPhone 5 can use high-performance HSPA+ if available or whatever other 3G connectivity the carrier has for your area.

One possible impact of the LTE iPhone: whether non-LTE subscribers at or near the end of their two-year contracts will switch cellular carriers to get LTE service in their area.

T-Mobile USA will start building its LTE network in 2013. In the meantime, it offers its expanding HSPA+ network (which some consider to be 4G). T-Mobile recently launched the "Unlocked & Unlimited" campaign, persuading users to buy a full-price unlocked AT&T iPhone and switch to T-Mobile's network. But some reports note that the iPhone doesn't support the larger part of T-Mobile's 3G network, so the connection options range from its 2G EDGE service to the HSPA+ service.

A new wide-ranging, real-world test of cellular data performance in the U.S., "The Need for Speed" by RootMetrics, found T-Mobile is delivering very good data performance: The percentage of connections running at over 5Mbps (an indication of "4G" capability) was 46.7% for T-Mobile, compared to 48.1% for AT&T and 77.4% for Verizon. A sign of its much broader LTE footprint, Verizon has a much higher percentage of connections over 15Mbps: 38% vs. 13% for AT&T and 6% for T-Mobile.

RootMetrics is one of several sites that offer tools to evaluate not just coverage but data rates in a given location, from different carriers.

LTE data rates

LTE is a big improvement for data, with higher download and upload speeds than 3G. WCDMA could offer 3-5Mbps but LTE can reach 5-12Mbps, according to Vish Nandlall, CTO North America for Ericsson. That's enough to make streaming high-definition video and audio a smooth, painless process, he says.

The RootMetrics data performance survey was conducted in 2012; it involved visiting 75 U.S. markets, and doing 500,000 indoor and driving tests of cellular connections (of any type) using off-the-shelf smartphones.

One chart looked at how consistently each carrier delivered fast and slow download speeds. For example, over-5Mbps connections occurred 77% of the time at Verizon, 48% at AT&T, 47% at T-Mobile and 17% at Sprint. As noted earlier, the higher-speed subset of this class -- over-15Mbps connections -- occurred 38% of the time at Verizon, 13% at AT&T, 6% at T-Mobile and zero at Sprint. Connections ranging from 1.5-5Mbps occurred 11% of the time at Verizon, 17% at Sprint, 30% at T-Mobile and 34% at AT&T.

Using more data

From the end user viewpoint, LTE means faster data speeds. Based on the usage pattern of other LTE devices in the U.S., iPhone users on average will about double their data use.

"LTE users are drawing about two times the amount of traffic, averaging about 1 gig per month," says Ericsson's Nandlall. Much of that increase is video. "You start to be able to do more, like high-definition FaceTime [Apple's video chat feature]," he says. "You can do better video recordings and upload them faster."

Verizon and AT&T have moved away from unlimited data plans and users need to view data differently because they're "engaging" the network differently, says Alex Pavlovic, director of marketing for Alcatel-Lucent's wireless division. "Operators probably need to spend the next two years educating customers to look at smartphone connectivity as a [usage-based] utility similar to electricity," he says.

You can talk, or you can surf

iPhone 5 will not let you do voice and data at the same time on CDMA2000 networks such as those from Sprint and Verizon. LTE , when available, will be for data, and voice calls will be handled by the carriers' 3G networks. Carriers eventually will add support for voice over LTE (VoLTE), now offered only by the regional carrier MetroPCS.

AnandTech's Brian Klug has a detailed post about Apple's decision, drawing on iPhone 5 test results posted by the FCC.

"[A]t a high level this is a design decision which makes the phone as small and light as it is (it really is light, almost alarmingly so) and enables it to support a wide number of LTE bands, rather than some major oversight like I've seen it portrayed," Klug writes.

Here's the background: Apple has announced two iPhone 5 hardware models, A1428 and A1429, with three different provisioning configurations. The hardware differences "accommodate a number of different LTE bands between the two." The software differences in how the two models are configured have to do with the initial provisioning of the phones and probably the version of Qualcomm's Advanced Mobile Subscriber Software (running on the baseband chip) that gets loaded at boot time, according to Klug.

With this approach, "Apple is able to support no fewer than 8 LTE bands with largely the same hardware -- the same display, chassis, battery, form factor, and PCB outline (different power amplifiers and filters are required), and roughly the same exterior antennas (gain is different on the primary bottom antenna between the two models, no doubt they're tuned differently)," Klug says. "Previously most handsets I've seen have been destined to work only on a single carrier, and thus implement at most one or two LTE bands." (You can check Apple's official list of supported LTE bands.)

According to Klug, today's simultaneous voice-data implementations -- SVLTE (simultaneous voice and LTE) and SVDO (simultaneous voice and EVDO) -- require a three-antenna solution and two transmit radio frequency chains for CDMA phones. Apple's approach avoids all that extra space-demanding hardware, because it sticks with widely used circuit-switched fallback (CS-FB) -- "This quite literally means you drop from 4G LTE to 3G WCDMA (where voice and data are already multiplexed) for the call, then hand back up to LTE when you're finished," says Klug.

"What it really boils down to is that by using this single Tx [transmit] chain, Apple is able to support a ton of LTE bands ... and also do it without making the iPhone very large," Klug says. "Moving to an architecture that works with SVDO and SVLTE would require an additional transmit path and antenna, and incur a size and weight penalty."

No LTE roaming either

LTE globally and in the United States is highly fragmented, says Eran Eshed, vice president of marketing for Altair Semiconductor, the Israel-based LTE chipmaker. Without going into details, there are two LTE flavors, and 15-20 different frequencies (some say 30 or more) around the globe designated for them. "In each band, you'd need different components and antennas in some cases to talk to each frequency," he says.

There have been ongoing efforts to "harmonize" a handful of bands for LTE, and some effort to push for an international "roaming band" -- based on 1800MHz -- that phones could support, he says. But nothing is expected soon.

Multi-mode phones will be able to fall back to 3G to support roaming, according to Eshed.

Even in the U.S., where AT&T and Verizon are deploying LTE in the 700MHz spectrum, roaming isn't possible. "You'd expect that one phone could support both, but there are two bands within that spectrum," says Ericsson's Nandlall. "An AT&T [LTE] phone will not roam to the Verizon band."

iPhone 5 impact on LTE networks

If asked, the carriers recite standard assurances that they've carefully designed their networks to handle LTE subscribers. If pressed, they'll repeat those assurances.

But there's going to be big surge of LTE-capable devices thanks to the iPhone 5.

Apple is widely expected to sell millions of the new iPhones in a matter of days: Some are projecting 10 million units. Some number of those may not reach their owners for two or three weeks but within a few months, the number U.S. LTE subscribers could double.

There are roughly 12 million-13 million LTE users in the U.S. now, estimates Bill Moore, CEO and president of RootMetrics in Bellevue, Wash. One analyst thinks Apple could sell up to 5 million units before September ends, and 15 million more in the last quarter of 2012. 

Those numbers could, in some locations at some times, congest the access to LTE base stations, or bog down the wireline backhaul from the stations to the carrier's core.

With the early iPhone, solely on AT&T's 2G/3G network, connections bogged down under unexpectedly heavy signaling loads, more than the higher data payloads. The 3G silicon and radio vendors have been addressing that. And LTE is much more efficient than 3G in this regard. In addition, the 3G data experience demonstrated the need for adequate LTE backhaul connections to prevent bottlenecks. And the nature of LTE creates much higher capacity at the outset, according to vendors.

None of the vendors or analysts contacted for this story think any of the U.S. LTE networks will implode. But there may be times or areas where users run into problems.

The next network phase for carriers will be adding capacity to their LTE macrocell networks by seeding larger numbers of smaller LTE radios. Carriers are also looking to shift traffic to Wi-Fi connections when possible, by deploying their own hotspots or partnering with Wi-Fi providers, and by automating subscribers' connections and authentication. The iPhone 5's support for Wi-Fi on the 5GHz band could prove to be a key feature for LTE users going forward.

John Cox covers wireless networking and mobile computing for Network World. : http://twitter.com/johnwcoxnww john_cox@nww.com

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