T-Mobile, Apple, Google lead the way on Wi-Fi calling

Republic Wireless Moto phones are enabled with Wi-Fi calling.

Once considered a threat to wireless operators, Wi-Fi is now part of their networks. AT&T (NYSE: T) added thousands of Wi-Fi hotspots when it acquired Wayport back in 2008. Sprint (NYSE: S) considers Wi-Fi a complementary "fourth layer" of its network. Google (NASDAQ: GOOG) put Wi-Fi front and center with its Project Fi, which, while it doesn't bill itself as a "Wi-Fi First" offering, it does rely heavily on Wi-Fi for calls and data.

Yet experts say it's just the beginning. The remainder of 2015 and beyond will see even more inroads in Wi-Fi -- namely in Wi-Fi calling -- as the processes mature and handovers improve. While Apple (NASDAQ: AAPL) released its Wi-Fi calling feature last year, its next iPhone release, expected in September, will come with its Continuity feature to support Wi-Fi calling on Macs or iPads even when the devices are on different Wi-Fi networks.

In fact, AT&T appears poised to join Sprint and T-Mobile US (NYSE:TMUS) in supporting Apple's Wi-Fi calling service. Verizon Wireless (NYSE: VZ) has said it plans to support Wi-Fi calling this year but hasn't revealed much beyond that.

While it might sound counter-intuitive, operators in general are interested in offering Wi-Fi calling because it's cheaper for their customers, especially when you consider the cost of international roaming. It helps carriers provide better coverage, and they don't have to spend thousands of dollars on new base stations. Plus, it's a harbinger of 5G, where all the connections will be treated as part of one big network.

Shane Buckley, CEO of Wi-Fi access point provider Xirrus, which created its EasyPass solution for better management of Wi-Fi devices, expects Apple's move with iOS 9 will create as big an impact or more so for the industry than its introduction of iMessage. "Wi-Fi calling is a big silver bullet," he said. "It's as impactful or more impactful to the industry as iMessage was when it was introduced a number of years ago," when text messaging was so expensive. "Wi-Fi calling has essentially the same attributes or value to the consumer. You're going to see the proliferation of these carriers who can now offer Wi-Fi call termination services."

But Wi-Fi calling still faces challenges. Quality of service has been a sticking point for years, and while progress has been made in refining the handoffs between cellular, there's room for improvement. The sheer proliferation of Wi-Fi can make it difficult to identify the right Wi-Fi access point -- private or public -- to hop onto. At a recent investor conference, Verizon Wireless COO David Small said that while Wi-Fi is useful for offload, Wi-Fi handoffs have not been perfected and Verizon considers the quality of service to be lower than its cellular network. 

"There's a couple of things our industry needs to work on in order for that to be successful," Buckley said. "You need application smart, application-aware wireless networks. If you have those, then you'll be able to deliver this Wi-Fi call over the Internet," and things like Google Fi potentially could take on carriers in voice. It's been done in a fixed environment in the home; "but doing it on your mobile device, this will be kind of a first."

Yet there's no denying that Wi-Fi calling is on the rise. In March, T-Mobile reported that 7 million Wi-Fi calls were being made every day on its network. Now that number has grown to 12 million, half of which use T-Mobile's next-generation Wi-Fi calling and connect to its LTE network.

T-Mobile's next-gen Wi-Fi calling

With next-gen Wi-Fi Calling, T-Mobile says it is pioneering seamless handover between its LTE network and any available Wi-Fi connection so calls don't drop between the two. Next-gen Wi-Fi Calling also features HD Voice quality when calling another HD Voice-capable user. T-Mobile says that means its customers can now maintain "crystal clear" HD Voice calls, whether connected to T-Mobile LTE or a Wi-Fi connection -- all using their existing T-Mobile number.

T-Mobile has been working on handoffs both in-house and with outside vendors for many years. In 2007, the operator launched its T-Mobile HotSpot @Home that encouraged customers to use Wi-Fi for domestic calls from their homes and the wide area network -- GSM/GPRS/EDGE -- when on the go.

"Our technology and network teams have been invested in Wi-Fi Calling for years and continue to innovate in this space, as seen with next-gen Wi-Fi Calling," Grant Castle, vice president of Engineering Services and Q&A at T-Mobile, told FierceWirelessTech in a statement. "We've put in considerable effort to ensure software updates to Wi-Fi Calling devices like the Samsung Galaxy S5, Samsung Galaxy Note 3 and LG G3 are working smoothly and deployed to our customers. We're working very hard to improve LTE coverage to cover 300M POPs by the end of the year, so there's a lot of design and validation that goes into both network changes and device software updates."

On the network side, T-Mobile introduced next-generation Wi-Fi calling as part of its Un-carrier 7.0 in September 2014 with support for Wi-Fi to VoLTE handoffs. "This year, we've been rapidly building out LTE," which now covers 290 million Americans and will reach 300 million Americans by the end of 2015. "That huge increase in LTE coverage is driving the number Wi-Fi Calling-to-VoLTE handoffs," Castle said.

On the device side, as more OEMs adopt support for next-generation Wi-Fi Calling, there will be even more seamless handoffs made between Wi-Fi and VoLTE. "We currently have 17 different devices that support Wi-Fi to cellular handoffs"--and nearly 11 million out of 34 million of these devices support seamless handoffs to VoLTE that result in fewer dropped calls, according to Castle. "As part of Un-carrier 7.0, we also introduced the Personal Cellspot, which optimizes a Wi-Fi signal for Wi-Fi calling devices."

T-Mobile also is gearing up to test a Passpoint-capable Wi-Fi roaming service with cable operator Bright House Networks in Tampa and Orlando. The test will include up to 50,000 customers and will allow them to roam onto Bright House's 34,000 public Wi-Fi hotspots in the cities using the Passpoint standard, which will provide "extended coverage by seamlessly connecting calls, messages and data through T-Mobile Preferred Wi-Fi access points," according to the operator.

'Wi-Fi First' pioneers

Others -- mainly MVNOs -- are taking a Wi-Fi First approach, which refers to mobile devices and services that use Wi-Fi as the primary network and cellular networks only to fill in gaps. That's the case for several MVNOs, like Republic Wireless, FreedomPop and Scratch Wireless.

In July, Republic Wireless announced Project Salsa, an initiative to test its technology to seamlessly hand over cellular circuit-switched calls to the Wi-Fi network when possible. The trial involved several thousand customers who voluntarily opted into the company's Republic Labs initiative, which is designed to directly involve Republic customers in research and development of future products and features.

Mulcahy

"We believe in Wi-Fi first," said Jim Mulcahy, general manager at Republic Wireless, which uses Sprint's network when Wi-Fi is not available. Wi-Fi is better, faster, cheaper and ubiquitous and it allows the company to pass on savings to its customers, he said. Republic Wireless offers a $10 base plan with unlimited cellular talk and text and zero cellular data. Customers who opted into its Republic Refund plans averaged monthly bills of $14.88.

Republic Wireless also has gone through multiple variations of its algorithm in anticipation that customers would demand quality as good as what they would get on any of the big four carrier's networks. In November 2013, it introduced Wi-Fi-to-cellular seamless handover with the first generation Moto X, and it has been refining the process ever since. It has now filed more than 60 patent applications and has been granted more than 30.

Mulcahy and his team are determined to make possible things that haven't yet been done before, and they're constantly on a mission to refine their processes. "We think we've just scratched the surface," Mulcahy said. "We're going to keep hammering because we think the quality could be better and we think the offload could be better, but it's a journey."

Test and measurement lab specialist Spirent Communications has been testing cellular/Wi-Fi combinations for the past three or four years and still sees interest rising. In the last couple of years especially, a lot of carriers, access point manufacturers and others have been using Spirent's solutions to test their products, not just by themselves but alongside thousands of handsets accessing the network while it's fully loaded, according to Jon Baker, general manager of the mobility infrastructure business at Spirent.

Many of today's networks were built on the basis of coverage but now that they're being loaded, it's more about capacity. "Anybody can make one-to-one voice call or data call work, but how does it work when you have thousands of handsets actually sitting on the network," Baker said, adding that latency is a big issue when it comes to voice quality.

All about timing

Ken Kolderup, chief marketing officer at Taqua, which has worked with Sprint on its Wi-Fi calling service, said it's not really the handovers that are challenging. The standards about how to do handovers between voice over Wi-Fi and VoLTE, 3G and 2G are well defined and have been around for a while. Especially when it comes to 2G and 3G, the networks are mature and coverage is well established, so those handoffs aren't an issue.

Kolderup

"Once it's triggered it, it's actually a very good procedure. But it's determining when to do it," Kolderup said. "You don't want a bunch of unwanted handovers" because there may be economic reasons where an MVNO, for example, wants to keep as much traffic as possible on Wi-Fi to avoid paying the operator that owns the mobile network.

"Whenever you do a handover, there's always the possibility it's going to drop," he said. And when you consider where most Wi-Fi is located -- the home and office -- there's really a relatively low percentage of time when the caller is walking out of the coverage area. But if they are going to move off-site, there needs to be a mechanism for handing off when it's really necessary and not constantly handing off when it's not essential. The handoff itself takes some seconds to happen, so you don't want to force a handoff if it risks dropping the call.

Interestingly, voice over Wi-Fi also has to meet E-911 requirements, but the way the standards are written, the call first must be routed over the macro network; 911 calls are supposed to go over Wi-Fi only if there is no cellular coverage available, Kolderup said.

One of Taqua's selling points is a voice over Wi-Fi solution that doesn't require the operator to deploy IMS in order to make it work. It also offers a feature that allows the end-user to control when calls are made using Wi-Fi.

T-Mobile's Castle acknowledged a lot of improvements have been made over the years when it comes to handoffs. "It was a little bit of stop and go, but it's fully a 'go' now. The handoffs have improved and many of the technical aspects of getting next generation Wi-Fi Calling to work with VoLTE have been tackled," he said. "Initially, the transition from first generation Wi-Fi Calling to next generation Wi-Fi Calling had a few bumps such as an interim Wi-Fi Calling solution based on IMS that didn't support handoffs. Now, most of the effort is just making sure there's lots of LTE available to people wherever they are, so they can make those Wi-Fi to LTE handoffs."

While operators continue to refine the handoffs, tech giants like Apple and Google are not sitting by the wayside. No doubt, with Apple and Google throwing their respective weights behind Wi-Fi calling, more consumers will get on board as well.

T-Mobile, Apple, Google lead the way on Wi-Fi calling
Read more on