Qualcomm is now predicting that the first 5G smartphones will arrive on the market in 2019 but they will come with a feature that may surprise some: a constant connection to a 4G LTE network.

"We are targeting for 5G NR smartphones by the middle of 2019," Sherif Hanna, senior manager for the technical marketing of Snapdragon modems at Qualcomm, told Light Reading in New York City Tuesday. NR, by the way, refers to the 5G New Radio specification from the 3rd Generation Partnership Project (3GPP) . (See 3GPP Approves Plans to Fast Track 5G NR.)

Qualcomm unveiled its first 5G modem -- the X50 -- in October 2016. The silicon is expected to start sampling to phone makers in the second half of 2017, with device trials starting in 2018. (See Oh Snap! Qualcomm Unveils X50, Its First 5G Modem.)

Qualcomm says that 5G "dual connectivity" with 4G LTE is part of the 5G specification. But why would 5G phones need a persistent 4G connection baked into the spec?

It is because of the high-band millimeter wave (mmWave) connections planned to be used in Japan, South Korea and the US. These 28GHz and 39GHz connections can deliver extremely high data rates -- 1 Gbit/s and up -- over short ranges but are susceptible to atmospheric conditions and more. For instance, Qualcomm -- and, no doubt, many other vendors -- will be looking into how a user's hand might block a 28GHz signal in the real world.

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Light Reading.

So, an always-on LTE connection, which could be delivering gigabit downloads by the time 5G comes on the scene anyway, is the insurance policy that keeps a user online even if the mmWave signal drops.

This differs from the way 4G LTE was implemented on smartphones. 4G can "fall back" to 3G for voice calls and data connections, but the phone switches between the connections.

Dual connectivity will -- of course -- bring its own issues to the world of next-gen smartphones. Top of the list is probably how much power running two radios together will require.

This is something we're likely to get a clearer picture on as 5G test devices arrive in 2018.

See this demo video from Ericsson AB (Nasdaq: ERIC) for a demo of dual connectivity:

— Dan Jones, Mobile Editor, Light Reading