Sprint's plan to add high-frequency radio capacity and coverage to its network means it is building for a 5G future, not a 4G past, according to the operator's CFO.

"We're not building a network that is 4G... 4G is almost a thing of the past. We are building a 5G network for the future, and 5G is fundamentally different from 4G," said Tarek Robbiati at the 2016 Deutsche Bank Media, Internet & Telecom Conference on Wednesday.

Robbiati is referring to Sprint's plan to lay the groundwork for 5G by adding large numbers of high-frequency small cells and distributed radio elements to the existing network of about 40,000 Sprint cell towers in the US. This will allow the operator to enable higher data speeds, but only if the radios are close to the subscribers.

Robbiati cited Sprint's existing 2.5GHz spectrum holdings as the foundation for this network "densification" push, though he gave no indication that Sprint is yet looking into even higher frequencies -- such as 28GHz -- something that its three major rivals are doing. In fact, Robbiati said that the operator's holdings of 90MHz of spectrum in the 2.5GHz band across the US was one of the reasons he took the CFO position in the first place.

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One thing he continually stressed in talking about the move from 4G to 5G is that network topology and design will morph to cope with the changing requirements of a new mobile world. Basically, network design will be very different in a city like New York, versus Miami, and different again for rural areas.

"The new networks of the 5G world are what we call... heterogeneous networks," Robbiati said. (See Heterogeneous Network (HetNet).)

Robbiati said the network densification program will take two to three years to complete. If the small cell push is as extensive as executives seem to be suggesting, the operator will no doubt gain land rights and experience it can apply to 5G networks in the future. Presently, however, the program seems solely centered on 4G LTE updates. (See Sprint CEO: Price Cuts First, Best Network Next .)

In fact, Sprint documents have previously indicated that it did not expect to deploy a 5G network in the US until after 2020. (See Sprint: 5G in the US After 2020?)

Nonetheless, with rivals focused on the 600MHz spectrum auction, which Sprint has decided to sit out, Robbiati says the operator's focus on dense, data-focused network updates will help improve its standing against rivals further. (See Sprint CFO: 600MHz Auction Will Not Deliver Enough Spectrum and Sprint Says It Will Sit Out Incentive Auction .)

"That [600MHz] spectrum will not be available for a window of time, three to four years... that's a fantastic window of opportunity for us," Robbiati said.

— Dan Jones, Mobile Editor, Light Reading