Why the Industry Cannot Agree on How 5G and 6G Should Work Together

One of the important challenges facing 6G is how it will be introduced alongside existing 5G networks. Operators have invested heavily in 5G infrastructure and will want to reuse as much of it as possible, rather than building entirely new networks from scratch.

I have previously discussed Multi-Radio Spectrum Sharing (MRSS) and Dual Stack, as well as the NGMN recommendations on 6G migration. MRSS remains the preferred starting point for introducing 6G alongside 5G, but it may not be sufficient for every operator or deployment scenario.

At the 3GPP RAN Plenary #113 meeting, held in Madrid in September 2026, companies discussed several additional migration approaches. Interestingly, despite considerable work on this topic, they could not agree on which additional approaches, if any, should be supported. The decision has now been postponed until December 2026.

The disagreement is not about whether 5G and 6G should coexist. Everyone recognises that they will need to operate alongside each other for many years. The debate is about how closely the two networks should work together and whether the additional complexity is justified.

To understand the discussion, it is useful to remember how 5G was introduced.

Early 5G deployments generally used a Non-Standalone (NSA) architecture in which the smartphone connected to both 4G and 5G. The 4G base station acted as the anchor, managing the primary connection, while 5G provided additional data capacity.

This allowed operators to deploy 5G quickly, but it also meant that the network remained dependent on 4G. The subsequent transition to 5G Standalone (SA) introduced another deployment stage, with additional complexity for network equipment, smartphones and operators.

For 6G, the agreed direction is to support standalone operation from the beginning, rather than requiring a 5G radio anchor. MRSS and mobility between 5G and 6G are also part of the baseline migration approach. However, sharing spectrum is not the same as combining two radio connections.

With MRSS, 5G and 6G devices can use resources within the same spectrum band. With Dual Connectivity, a single device can use radio resources from both generations simultaneously. This distinction is important because the debate in 3GPP is primarily about whether additional ways of combining or maintaining 5G and 6G connections are necessary.

Three main options have been under consideration (as shown in the image on the top).

The first, referred to as Option 1, uses 6G as the anchor, with an existing 5G connection providing additional capacity.

Imagine an operator introducing 6G using a new frequency band. Although this provides access to the new technology, the operator might initially have only a limited amount of spectrum available for 6G. Meanwhile, it already has several 5G carriers providing substantial capacity.

Under Option 1, a smartphone could connect primarily to the 6G network while also using some of those existing 5G carriers to improve throughput. The 6G radio network remains in control, while 5G acts as an additional source of capacity.

This approach has received support from companies including Samsung, Qualcomm, NTT DOCOMO, SK Telecom, Verizon and BT. The argument is that 6G should be the primary technology from the beginning, but operators should still be able to take advantage of their substantial investments in 5G radio infrastructure.

The second approach, Option 2, reverses the arrangement. 5G remains the anchor, while 6G provides additional capacity. This resembles the original 4G-to-5G NSA migration, with the older generation providing the primary connection and the newer generation supplying additional radio resources.

Such an arrangement might allow operators to introduce 6G in selected locations without immediately requiring widespread 6G coverage. However, it raises an obvious concern: would the industry be repeating the experience of early 5G, with another complicated transition needed later?

The third possibility, Option 3, takes a different approach. Instead of tightly combining 5G and 6G within the radio access network, the smartphone maintains connections to both generations through their respective core networks. This is generally discussed in terms of Dual Stack or Dual Registration.

One potential use case is to continue using 5G for voice calls while using 6G for data. This could be attractive during the early stages of 6G deployment, particularly if operators want to retain existing Voice over NR (VoNR) capabilities without immediately introducing equivalent services over 6G.

A simplified version of Option 3 was retained for further consideration at the September meeting. Under this version, the smartphone would have separate registrations with the 5G Core and 6G Core, but there would be no requirement to combine or split user data traffic between the two networks.

This is narrower than some of the more ambitious Dual Stack approaches previously discussed. It is primarily about maintaining services across two generations, rather than aggregating their data capacity.

Companies including China Mobile, Orange and several satellite connectivity players have expressed interest in dual-registration approaches. In particular, Boost Mobile, AST SpaceMobile, Skylo and EchoStar submitted a proposal asking for the core-network implications of Dual Stack to be examined. However, not everyone believes that these additional approaches are necessary.

Nokia has argued that the industry should avoid introducing multiple migration architectures that could increase complexity without delivering sufficient benefits. Ericsson has also opposed additional Dual Connectivity and Dual Stack options.

Their concern is understandable. Every additional network architecture needs to be implemented by equipment suppliers, supported by smartphones, tested for interoperability and maintained by operators. Adding features that ultimately see little commercial deployment could increase costs without delivering meaningful improvements.

This brings the debate back to MRSS. If 5G and 6G can efficiently share spectrum, and smartphones can move between the two networks when necessary, perhaps additional migration mechanisms are not essential.

On the other hand, spectrum sharing alone does not necessarily allow a smartphone to combine capacity from existing 5G carriers and new 6G carriers. Some operators therefore see 6G-anchored Dual Connectivity as an important capability, particularly during the early stages of deployment.

There is also an additional technical question about split bearers. In simple terms, a split bearer allows the network to distribute data belonging to one connection across two radio links. Supporting this between 5G and 6G would require the two networks to coordinate how that traffic is handled.

Without such functionality, some of the potential benefits of Dual Connectivity could be more limited. The industry therefore needs to decide not only which network should act as the anchor, but also how traffic should be handled between the two generations.

The outcome of the September meeting was that no additional migration option was selected. The 3GPP RAN plenary agreed to postpone the decision until RAN#114 in December 2026. The question of split-bearer support for Options 1 and 2 was also left for further consideration.

For the simplified Option 3, 3GPP's Service and System Aspects Working Group 2 (SA2), which deals with core-network architecture, has been asked to examine its feasibility. The final decision on this particular approach rests with the system architecture side of 3GPP.

Meanwhile, MRSS remains the baseline, with work continuing to make spectrum sharing between 5G NR and 6G Radio (6GR) more efficient. One important outcome from the September discussions was agreement that 6G should support efficient sharing of at least downlink control-channel resources between the two radio technologies.

The Next Generation Mobile Networks Alliance (NGMN) also updated its 6G migration guidance in September 2026. Its message remains consistent: MRSS should be the preferred approach, and any additional migration option should demonstrate clear benefits in terms of deployment requirements, technical feasibility, hardware implications and total cost of ownership.

What makes this debate interesting is that there is no universally correct answer. An operator with extensive 5G coverage and limited new 6G spectrum might see considerable value in combining the two generations. Another operator might prefer a simpler standalone architecture, particularly if its existing infrastructure can support efficient MRSS.

Similarly, equipment suppliers have to consider the additional development and testing work associated with supporting multiple architectures, while chipset manufacturers must consider the implications for device cost, complexity and power consumption.

The decisions being made now will influence how the first commercial 6G networks are introduced in the early 2030s.

While much of the publicity around 6G focuses on new spectrum, artificial intelligence, higher speeds and advanced applications, operators will ultimately need a practical and affordable way of introducing the technology.

Perhaps one of the most important lessons from 5G is that introducing more architectural options does not necessarily result in a better or faster migration. The interesting question for 6G is whether the industry can agree on a simpler approach before the first commercial deployments begin.

For now, that question remains unanswered.

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