How Verizon LTE Phones Could Offer Simultaneous Voice and Data

The HTC ThunderBolt, poised to soon storm Verizon’s (s vz) new LTE network, may be the first smartphone to allow simultaneous voice and data use on the network. In a Q&A session at the Consumer Electronics Show (CES) earlier this month, the operator said that some, but not all, 4G phones launched in the first half of 2011 would offer this feature. News of this feature on the ThunderBolt was found by Android Central in an alleged leaked slide for Verizon employee training on this particular phone. But how would it work?

Using a Verizon handset for voice and web surfing at the same time hasn’t been possible in the past, because Verizon uses one network for both voice and data. So current CDMA handsets on Verizon must pause their cellular data connection in order to use the network for voice. If the leaked training slide is accurate, Verizon and HTC have come up with a solution for that limitation. While it could be some type of VoIP offering over LTE such as VoLTE (Voice over LTE), I suspect it isn’t, for a few reasons.

The GSMA, the governing body of GSM telecommunications systems, launched a VoLTE initiative only last year. The intent is to create a set of standards for voice communication over LTE networks, which unlike current 3G networks, are completely IP-based. It’s going to take time for those standards to evolve, and I simply don’t see Verizon trying to set the standard for the rest of the world, especially since the operator is just now beginning to adopt GSM technologies.

Adding to that challenge is the lack of LTE network coverage; Verizon’s next-generation network currently covers 38 markets and about one-third of the U.S. population. The carrier expects to cover 140 additional markets by the end of 2011. How would a VoLTE-capable phone handle a voice call when leaving a 4G coverage area? The digital call would have to seamlessly route over to the analog network and that’s simply too complicated. As it is today, available LTE data sticks take time to switch back and forth from 4G to 3G, for example, and any delay would create a poor voice experience.

More likely to me is the idea of managing voice and data through completely separate radios within a handset such as the ThunderBolt. In an LTE coverage area, the data connection would be handled on the faster 4G network and voice would simply be handled as it is today: on the CDMA network. Through software management and multiple radios, this solution seems most likely to me in the short term to provide simultaneous voice and data on Verizon’s network. It’s worth noting that among the new LTE handsets, only the ThunderBolt is using Qualcomm’s (s qcom) new silicon, combining a Snapdragon system-on-a-chip with a Gobi-enabled LTE modem.

We should know soon if indeed the ThunderBolt will handle voice and data at the same time because my sources say that among the four new LTE handsets Verizon will launch in the first half of 2011, the ThunderBolt is the most likely one to launch first. That makes sens,e because aside from Motorola (s mmi), no other smartphone vendor has partnered as much with Verizon than HTC in the past year or two. The other two LTE handsets expected by June are coming from LG and Samsung, which don’t have as much of a smartphone history with Verizon.

It’s possible that some early standard of VoLTE will appear on the ThunderBolt, but my money is on a multiple radio solution that totally separates voice and data to handle simultaneous use. And if I’m correct, that means you’ll only be able to talk and surf on such devices where you have both 3G and LTE coverage. Consider it a stop-gap measure until a true VoLTE standard evolves, which gives Verizon more time to build out its LTE network.

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