Sprint has two paths to HD voice–1X Advanced and LTE

Sprint is turning up the volume on its upcoming LTE rollout, dropping hints that the iPhone 5 will be an LTE device.  However, the company also has a CDMA HD voice play as it upgrades its 3G network using Qualcomm chips and the 1X Advanced standard.

The path to HD voice through LTE is relatively straightforward: Deploy LTE and Voice over LTE (VoLTE) ready devices, then deploy VoLTE as an app on the phone and network. AMR-WB is the default codec for VoLTE calls, so HD voice appears as VoLTE appears.

Converge! Network Digest conducted a video interview with Sprint Vice President of Network Development and Engineering Iyad Tarazi back in October 2011, shortly after the company announced its network upgrade/buildout plans under the title of Network Vision.

The YouTube piece, available here, doesn’t get to a discussion of HD voice until around 10 minutes into the clip.  Tarazi states 1X Advanced allows for “high definition voice” even on CDMA, while deploying voice (VoLTE) on an LTE network simplifies the device since voice is just another app, and can be made available to other applications on the device.

VoLTE will be introduced in the first half of 2013, at least “to a subset of devices,” Tarazi says, and Sprint expects to support voice over multiple delivery streams, in VoLTE, 1X, and OTT (yes, over the top) services. Over the long term, VoLTE will be the dominant technology, but it “will take quite some time” to get there.

Qualcomm and other sources note that handsets and other devices incorporating 1X Advanced support are already being shipped or “seeded” into various markets around the world. 

But Qualcomm also notes that a carrier may not choose to use 1X Advanced to deliver HD voice using its EVRC-NW codec.   Instead, carriers could choose to substitute the EVRC-NW codec to deliver narrowband voice – which uses only a third to a fourth of the bandwidth of existing narrowband codecs – and apply the freed RF bandwidth to data services.

There’s no guarantee Sprint will deploy HD voice on its CDMA network using 1X Advanced. However, it might wish to do so in order to provide a short-term differentiator when compared to other CDMA-based (Verizon) services and to provide rough parity with VoLTE in terms of voice quality.

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