Voice-over-LTE (VoLTE) technology has been championed by carriers for several years now, but the mobile ecosystem as a whole is still moving rather slowly toward commercial services.  Back in 2011, for example, Verizon Wireless made the first voice call over a commercial LTE network.  For AT&T, its $14 billion Project Velocity IP expansion program that began last year includes the deployment of more than 40,000 small cells, which are instrumental in strengthening its VoLTE coverage.

VoLTE technology, which is a mobility-enhanced version of basic Voice-over-IP (VoIP), is still very new, and 4G voice service needs to work as well, if not better, than what consumers are used to. Operators know there is no room for error when it comes to voice calls, and getting VoLTE right required significant development and testing efforts.  But all is well now and 2013 has heralded the arrival of VoLTE services on a broader scale.  In June, South Korea Telecom, one of the first operators worldwide to launch VoLTE services, announced that it had more than 4.5 million active users of the technology.  Verizon this summer reiterated that its first VoLTE-compatible handset will launch by the end of the year, and AT&T is planning to launch VoLTE services in 2013 as well.  Meanwhile, T-Mobile, which completed its acquisition of MetroPCS in May, has said that it is working on a "VoLTE path," which would allow MetroPCS calls to roam onto the larger T-Mobile LTE network.

As the march toward VoLTE commercialization moves forward, few consumers realize that even as network operators continue to roll out their 4G LTE coverage, the new and blazing fast LTE-enabled smartphones don’t inherently support voice calls over the LTE network, and that when a voice call is needed, networks automatically ratchet down to older, circuit-switched 3G or 2G networks to transmit the call.  The benefits of VoLTE – the better call quality and lower power consumption – remain elusive for most users.

It All Starts with the Voice

But why so much talk about using a mobile broadband technology to improve lowly 20th century voice services?  The reason is that voice calls remain central to the smartphone and to the service provider business model.  Even if the Internet is never more than a swipe of the finger away, we still make actual phone calls when it matters most – when we need to reach a colleague, friend or family member, for example, or when we need to confirm that our message was received.  And although messaging apps like Snapchat and WhatsApp have risen in popularity, as has the constant urge to post status updates, at the end of the day our social world is based on the need for “full-duplex,” and only voice calls are real-time, interactive and instantaneously gratifying. 

Thus, while voice remains critical, “Can you hear me now?” is no longer really the central question.  Instead, the critical problem to solve, given the power-hungry multi-tasking needs of smartphone consumers, is what can be done to make voice services sound better, consume less battery, and cost the service provider less.

The good news is that VoLTE literally answers that call.  It provides a range of advantages that includes more spectrally efficient transmission than 3G calls; higher-quality phone calls; lower power consumption; and the enabling of interactive services.

Higher spectral efficiency: Thanks to its OFDMA airlink, LTE networks can transmit voice calls with as little as half the spectrum needed for 3G voice calls. Unlike the WCDMA airlink in 3G networks, an OFDMA airlink only sends and receives traffic when actual voice call packets are being transferred. WCDMA voice networks continuously send and receive airlink signals even if there is no voice traffic.

Better call quality: LTE networks support Quality-of-Service scheduling that ensures that voice packets are being transmitted with tightly controlled latency and jitter, which allows the voice call quality to approach that of a landline call. VoLTE also supports variable rates for the voice codec, which enables HD Voice services based on greater speech sampling bandwidth and reduced compression. 

Lower power consumption: LTE technology enables the phone to dramatically reduce power consumption during inactive periods when the phone is either not receiving or not transmitting voice traffic. This partial shutdown of the transceiver enables power savings of up to 40 percent when compared to 3G voice calls. 

Interactive services: Because LTE is a network designed to support low-latency IP traffic, voice is handled like just another data application on the network. And since a voice call consumes very little resources, there is ample bandwidth left for a phone to simultaneously send and receive additional data traffic and add messaging or video capabilities to a voice call, anytime and on demand. 

The trend is clear.  VoLTE enables superior voice calls while using less spectrum to do it, motivating both service providers and users to adopt this new service. 


Lars Johansson is Senior Director of 4G Product Marketing at Broadcom.