If your travel plans over the next week or so include Mobile World Congress (MWC) in Barcelona, then one thing I am sure you will know is that 5G will be a hot topic. The 5G requirements are now well-aired and the triumvirate of use cases (enhanced mobile broadband (emBB), ultra-low latency reliable communications (URLLC) and massive machine type communications (mMTC) are commonly understood.
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But as we prepare, let’s take a breath and ask one simple question, where are we right now in terms of standardization for 5G?
There is no one-stop shop standardization body where everything 5G is being specified. As I see it, many bodies are and will continue to contribute to the genesis of this next generation. However, one body still stands above the rest in terms of defining 5G, the 3rd Generation Partnership Project (3GPP). Looking specifically at progress provides probably the best and easiest benchmark for assessing where we are today on the road to 5G.
What is 3GPP?
3GPP is the international standards body that covers cellular communications network technologies. This includes the radio access, core network and service capabilities. Standards are developed driven by contributions into technical specification groups encompassing Radio Access Network (RAN), Services and System Aspects (SA) and Core Network and Terminals (CT).
5G Radio and System Architecture (SA) studies in 3GPP kicked off back in December 2015. The RAN group focuses on the development of a new radio and a new radio architecture and the SA groups focuses on the development of core network functions that are responsible for the establishment, maintenance and termination of end-to-end connections.
Where are we in the Radio Access Network?
The 3GPP RAN groups are about to complete their study phase, the focus of this study phase has been primarily about developing an understanding of what is required at the radio architecture and protocol structure level to fulfill key requirements from the 5G use cases.
It has been agreed to approach the standardization of the RAN in two phases.
The first phase, which corresponds to Release 15, is meant to provide operators with a minimum set of features that enable 5G capabilities. In addition, this phase targets eMBB and URLLC use cases. Since Release 15 is expected to be completed by Q4 2018, the detailed design of Phase I is also expected to be done by then.
The second phase targets features that will allow the 3GPP 5G Radio to comply with stringent IMT-2020 requirements. This second phase will be developed in Release 16 and is expected to be ready by December 2019—in time for IMT-2020 submission.
As might be expected, the Phase 1 focus has been on the eMBB use case. At a seminal meeting in October 2016, the Channel Coding technologies for this use case were tentatively decided: LDPC for the data channel and, a little surprisingly, Polar Codes for the control channel. The Physical Layer that includes new waveforms is still under study for this use case and all the others, too.
The leading candidates at the moment (not selected yet) targeting this main use case would appear to be DFT-S-OFDM-based waveform, which is complementary to CP-OFDM waveform. On the architectural aspects of the RAN, new options with both centralized and distributed properties are being studied and evaluated for their flexibility and resource efficiency properties (e.g., support of radio network slicing).
Finally, a new Radio Access needs to be able to work with both legacy and next-generation core networks; therefore, provisions are also being studied to ensure that the 5G Access Network is appropriately backward-compatible.
It is important to keep in mind that the progress I am referring to covers just the study phase on the development of 5G Radio Access technology. The detailed design phase is still to come and will likely take up to a year, i.e. all Release 15, and it is expected to be completed by December 2018. This first phase will include, as previously mentioned, both eMBB and URLLC use cases.
What about progress on the core network?
The core network teams are following a similar path with a study followed by more detailed design. The system study for this initial phase has been completed and includes a set of features and functions that enables basic connectivity in a flexible and efficient way. The normative phase was kicked off at the beginning of this year, so it is moving a little faster, it would seem, than the RAN area.
Similar to the 3GPP RAN groups, SA groups have covered key foundational functionality during the first phase of the 5G study. Unlike their RAN counterpart, however, which will only start detailed design after the Q1 2017 3GPP plenary meeting, the 3GPP SA groups started the normative phase of the 5G System design in January this year. This normative phase, which covers the first phase of the overall design, will include the followed detailed specification activities:
- Independent device registration and device connectivity, maximizing resources, by maintaining connectivity only when the device needs to transmit data. These features are key for the deployment of future massive machine type communication.
- Flow-based, bearer-less connectivity, enabling flexible forwarding of data sessions, allowing the establishment of data sessions running multiple data flows on a “single pipe” or tunnel. This feature removes the need to set up and tear down connections every time a new service is requested or an existing service is no longer needed, effectively reducing latency, an aspect that is key in the deployment of URLLC and Critical Communications.
- A service-based architecture that enables quicker time to market when designing and deploying new features that can interwork with existing services already deployed. These services may be deployed using network slicing capabilities through the allocation of functions and system resources intended to satisfy a variety of use cases.
- Efficient User Plane Path handling that enables intelligent forwarding of data sessions allowing the delivery of eMBB services closer to the end user.
Putting it all together to deploy the first 5G-capable 3GPP systems
In June 2016, an RAN-SA joint session was held during 3GPP Plenary to help synchronize plans, objectives and overall focus as to what features need to be in place to ensure that the first 5G-capable system could be deployed in record time. The result of that synchronization and alignment exercise yielded a common understanding that included key delivery dates, as well as the minimum level of functionality that needs to be in place to enable the deployment of the first 5G-capable 3GPP systems.
Three main points were identified to be completed by March 2017:
- SA needed to complete the System Study by Q4 2016. This was achieved.
- RAN needed to complete the New Radio Study by the end of Q1 2017. This has been achieved.
- Report from all 3GPP on forward compatibility of standalone and non-standalone radio solutions to be ready by the end of Q1 2017. Note that the non-standalone solution implies requirement for connectivity through the legacy LTE systems, while the standalone solution implies connectivity toward the 5G Core Network. This is in the works, and it is expected to be a key discussion point during the coming 3GPP March 2017 Plenary meeting.
The last point is likely to be the focal point of the coming 3GPP plenary meeting. Compatibility is the key challenge. Given that RAN and SA groups have been working largely independently from one another with little interaction, it is likely several issues of contention will be identified during the coming meeting, such as issues related to common quality of service approaches, new data transport models and a new overall end-to-end system architecture. These have been introduced by the 3GPP SA groups, and some of these issues are already moving forward.
It is fair to say that some good progress has been made, but there is still a long way to go. Cutting through the 5G hype, 3GPP has just about completed its study phase, but many big decisions are still only on the horizon. 5G will be rolled out in phases, and it is fair to say that Phase 1, which will bring support for some high-priority use cases, is on track, at least in standards, for completion in December 2018.
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