• It has produced a white paper which lays out the case 
• Operators obviously need to migrate spectrum from LTE to NR
• But pressure on operators to refarm must be ‘relaxed’ as long as some spectrum remains dedicated to LTE 

The Next Generation Mobile Networks (NGMN) Alliance has published a white paper urging the industry to support so-called Option 4 as a crucial stage in the development of 5G.  It says the establishment of Option 4 will allow the industry to “quickly and efficiently bring new 5G-based services to market.”

The White Paper is designed to set the scene for a trial of Option 4 this year to “encourage Option 4 development within the 5G ecosystem.”

“Development completion of Option 4 is urgently needed to enable all operators to invest in a new 5G core network without compromising user data rate performance,” said Arash Ashouriha, Chairman of the NGMN Alliance.  “Advanced 5G users using 5G Standalone should be able to access LTE on top of NR for a seamless service experience”.   

NGMN believes that Option 4 supporting a 5G core and dual connectivity with NR acting as a master, is required so that baseline 5G NR radio performance can be enhanced through the use of LTE on top. 5G Standalone users can then access both NR and LTE spectrum in the lower frequency bands supporting wider coverage when it is beneficial to do so.

So what is it? 

Option 4 might be seen as a crucial stage in the evolution of the network from 4G/LTE to new radio (NR) standalone (SA). Without it, the NGMA fears there will be an unfortunate tendency for some users to enjoy lower performance with ‘full’ standalone NR than users of the more advanced versions of LTE. Operators, it argues, need a strong and easily understood proposition around performance which should ramp up in a logical way as users move ‘up’ from one service and stage of 5G to the next. So users should be able to connect in parallel using both NR and existing LTE technology otherwise new 5G Standalone users will sometimes find themselves getting lower data rates than existing Non-Standalone 5G and LTE users. 

Goalposts on the move

The white paper authors point out that while the 5G New Radio (NR) radio interface brings significant improvements to the mobile network, including improved spectrum usage possibilities and lower latency support, its specifications were nonetheless,  created from the outset with LTE to act as an important 5G radio technology and to be integrated alongside NR. 

They explain that today, bands below 3 GHz are mainly used for LTE, and therefore NR standalone (SA) deployments will actually struggle to compete with the data rates and/or coverage of LTE in many locations, partly because the operation of the LTE network has been refined over the years. 

To make things more difficult, say the authors, operators have a high number of LTE customers with a really high penetration of LTE devices. Consequently, it will take time to refarm LTE bands to NR. It’s important to note, they say, that the NR spectral efficiency performance in these low frequency bands is not significantly better than LTE, thus there isn’t sufficient motivation for refarming especially given the large reduction in usable spectrum the refarming would entail. 

Raimund Walsdorf, Technology Architecture & Innovation Access & Home Networks, Deutsche Telekom and NGMN project lead said: “Option 4 development will support many network operators planning an initial 5G Standalone service launch today or a more widespread launch in the future. This option benefits operators to more efficiently migrate spectrum from LTE to NR, while also relaxing the pressure on operators to refarm from LTE to NR as long as spectrum remains dedicated to LTE”.

The full White Paper entitled, Option 4 as a 5G SA complement can be found here.