NGMN urges more options for transition to SA 5G

A new white paper (pdf) from the Next Generation Mobile Networks Alliance urges the industry to more fully develop multiple paths for operators to move from NonStandalone to Standalone 5G network architectures, particularly options that allow operators to avoid extensive use of Dynamic Spectrum Sharing.

Operators around the world initially deployed NonStandalone 5G that works in concert with an existing LTE core, essentially relying on 5G to be a “booster” technology (also referred to as an Option 3 architecture). Those early deployments helped the technology come to market faster than implementing a full, end-to-end 5G architecture with a 5G core from day one, but were always expected to be a midway point on the path to Standalone 5G. Now that the first wave of 5G NSA deployments have come to fruition, however, operators around the globe are looking at their next steps to move to Standalone 5G, which will fully support 5G features such as network slicing . In that context, the NGMN paper says that focus on the transition to 5G SA has largely focused on the 5G Standalone “Option 2” configuration path, with a 5G core and the use of DSS, which allows both LTE and 5G New Radio to operate in the same spectrum bands. The authors say that they are convinced that the Option 2 path will lead to “new 5G SA customers in many networks experiencing data rate performance levels below the level of existing NSA customers or even the ‘legacy’ LTE customers. This may make the introduction of the [5G core] unattractive for mainstream consumer use for several years until NR capable devices are penetrated into the device base to allow for sufficient spectrum to be refarmed.”

The paper was put together by NGMN carrier participants from Deutsche Telekom, BT, SK Telecom, TIM, China Mobile Research Institute and Hong Kong Telecom.

Option 2, the paper’s authors said, involves “an extensive use of DSS on multiple carriers to increase the amount of NR usable spectrum or on-demand fallbacks of NR SA users to LTE and NSA. While DSS is a valuable enabler for more rapid NR deployment, it has been demonstrated that DSS degrades spectrum efficiency and it is costly to deploy. Recent measurements also show NR data rates on the same DSS carrier are worse than LTE due to lacking interference cancellation technology in NR devices. This turn means that DSS cannot fully address the competitiveness issue and therefore, an extensive use of DSS on multiple carriers is not recommended.”

While many operators are expected to start SA deployments with localized “campus” private network environments where 5G SA can be built from scratch, the paper brings up the point that the benefits of Standalone 5G services for the broader consumer market are “somewhat intangible and are probably not sufficient to justify significant extra costs or lower performance within a RAN.” If a 5G SA deployment doesn’t at least meet the levels of performance and efficiency that NSA does, it undermines operators’ investments, the paper argues.

Multiple paths to 5G SA besides Option 2 have been laid out by 3GPP as part of the standardization process, the authors note; but, they add, “Unfortunately, major network and terminal suppliers have been unwilling to develop any of these options as the operators requested, and the lack of commonly agreed operator prioritization … has hindered the development of any of them.” The paper in particular backs 3GPP’s Option 4 as a “more strategic long-term option.” Option 4 makes 5G, with a 5G Core, the primary technology and relies on LTE as a booster.

The fact that most operators’ sub-3 GHz spectrum is in heavy use by their LTE subscribers means that 5G SA deployed via DSS could end up being uncompetitive compared to NSA, the paper argues. In addition, in analyzing the widespread use of DSS, the authors call out device implementations as part of the issue. They say that LTE Cell Specific Reference Signal filters for interference cancellation that are implemented in LTE devices “aren’t implemented in NR devices. That fact causes the high interference levels in NR devices which is an undesirable effect to be added to the overhead losses. Accordingly, the use of DSS even in unloaded networks will result in an unacceptable performance for NR UEs. Until LTE CRS filters are supported in the vast majority of NR devices, DSS is not a realistic option for operators to overcome the … performance shortfall.”

Read the full paper here.

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