China Mobile Shows off the Promise of VoLTE

Have you ever had a mobile call that sounded like the other person was talking with a scarf over their mouth? With 3G technology, that experience is not at all uncommon. That’s because most 3G calls use narrowband codecs that compress the bandwidth of our voice. In moderate to poor areas of coverage, the compressed voice signal may be further degraded by RF-related signaling errors, resulting in a muffled or distorted sound to the speaker’s voice.

Those muffled calls may soon be a thing of the past—or at least far less common. Thanks to the efficiency of 4G LTE technology, many operators will be able offer “HD” calling as a standard option on their 4G LTE networks. HD calls use wideband codecs that represent the human voice much more faithfully. That means phone calls sound much clearer and more lifelike even if the radio signal starts to degrade moderately. While some 3G networks will offer HD calling as a premium service, it isn’t expected to be a default calling option as with LTE.

Cell phones being tested with NomadHDWe demonstrated just how much better voice services over 4G LTE (VoLTE) can sound at the PT/EXPO COMM CHINA 2014 this past September in Beijing. This photo shows a real-time snapshot of our Nomad voice experience probe measuring speech quality on China Mobile’s commercial 3G network and trial VoLTE network.

To measure the speech quality, we used four HTC (M8) smartphones to make mobile-to-mobile calls on both the 3G voice and VoLTE networks. We used the industry standard POLQA algorithm to evaluate the speech quality of each call on a 1–5 scale (1 is bad, 2 is poor, 3 is fair, 4 is good, and 5 is excellent). We also used wideband speech samples (48 kHz bandwidth) in testing both services, to provide a direct comparison of quality.

Over many hours of testing, we found that the China Mobile VoLTE service was able to consistently deliver a 4.0 speech quality score—roughly the same as talking over a high-quality landline device. By contrast, the 3G commercial service consistently delivered a lower score of approximately 3.3, which is considered very good for a mobile network in an indoor location but far below land-line quality.

Mobile subscribers in China and the rest of the world can expect a big leap forward in sound quality as VoLTE rolls out. That means it won’t sound like someone’s talking through a scarf—unless they actually are!

Our thanks to the China Mobile Research Institute for inviting us to support their demonstration of the benefits of VoLTE technology at the PT/EXPO COMM CHINA 2014 show.

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