Mobile industry grapples to resolve new air interface question for 5G

FRANKFURT, Germany--The mobile industry appears largely in agreement that 5G will require a new air interface or waveform in order to handle the challenges presented by proposed new use cases, but as yet it is not clear what this new waveform will be.

At the NGMN Alliance's industry event here this week to discuss the implications of the alliance's recently published 5G white paper, some of the market's leading operators and vendors attempted to clarify what they felt would be required in the 5G era after 2020.

Philippe Keryer, chief strategy and innovation office at Alcatel-Lucent, said LTE Advanced already provides many of the key enablers for 5G and noted that the journey from LTE to 5G would be an evolutionary process. However, he also said there is still a set of requirements that would not be possible to fulfill easily without the correct interface.

"We do believe there is a need to introduce an improvement of the air interface to deal with the requirements of the white paper," he said. Under discussion is a modification of the LTE interface with universal filtered OFDM (UF-OFDM), he added.

Telstra CTO Hugh Bradlow also said 5G is expected to be an evolution of OFDM and LTE. However, he added that it will be important to remain open to new ideas and developments. For example, Telstra has just invested in a company called Cohere that plans to bring a new modulation called Orthogonal Time Frequency and Space (OTFS) to market.

"We see an opportunity for innovation in this space," Bradlow added.

Nokia CTO Hossein Moiin agreed that "we can safely assume there will be" a new air interface because the current one will not deal with some of the requirements in the NGMN white paper, such as very high capacity and extremely low latency of 1 millisecond. The new interface would also coexist with existing interfaces such as LTE and include components such as massive MIMO and beam forming, Moiin added. Beyond that he would not be drawn on the exact shape the next waveform would take.

"We will come to a consensus on what will be the new air interface that will meet the majority of these requirements," he said.

Moiin noted that spectrum remains the big unknown in the 5G standardisation process. For example millimetre wave frequencies above 6 GHz--which many in the industry believe are necessary to meet future 5G use cases--would not be issued before 2019. Indeed, it is not even assured that the mobile industry would be successful in obtaining frequencies in the higher bands.

Moiin does not appear to be too worried: "Some unlicensed spectrum is available," he said, "and we can repurpose spectrum should all hell break loose and we don't get anything!"

However, he said the mobile industry has a good track record in the past of getting the spectrum it needs, and competition for spectrum at this level is likely to be less fierce, he added.

Moiin said he now has a much clearer picture of what 5G will be compared to a year ago. "I did not know what 5G was last year," he said. "Today I can see an outline of a shape of 5G."

In terms of the 5G timeline, event participants largely agreed that 3GPP Release 15 towards the end of 2018 and Release 16 at the end of 2019 would contain the main elements of the standard. Full network deployments are predicted to start in around 2021 to 2022.

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