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The First 5G Radio Standards: A Strong Beginning with Much More to Come

By Mr. Alexander Chassaigne Ricciulli (Telefonica), Mr. Javier Lorca (Telefonica), and Prof. Ana Garcia Armada (Universidad Carlos III de Madrid)

Wireless communications are nowadays at the heart of any economic, industrial and societal progress in the world. Telecommunications operators are constantly fostering the development of interoperable technologies to enable them to provide wireless services everywhere, at any time, through any kind of terminal device, and with great quality. This goal can only be achieved with appropriate telecommunication standards, whose development is a consensus-driven activity led by operators, equipment manufacturers and technology providers in all over the world. The technical group in charge of developing all cellular technical specifications is the 3rd Generation Partnership Project (3GPP).

Currently, 3GPP is making significant progress in defining the technical specifications of the 5th Generation (5G) cellular communications, aimed to be a successor of current 4G technology. Such efforts have already begun to crystalize in several important milestones for the wireless industry.

The last 3GPP Radio Access Network (RAN) Plenary Meeting was held on June 2018. The most important achievement of this meeting was the completion of the 5G New Radio Rel-15 specifications for standalone (SA) mode, six months after completing the non-standalone (NSA) variant on December 2017.  The completion of this specification gives the industry the green light to fully accelerate the design and implementation of equipment to reach the goal of commercialising first products in the 2019 time-frame.

The Release-15 Full Specification includes the highest priority architecture options (see Options 3 (NSA), Options 2 (SA) and 5 (SA) below), however, a late drop was introduced to complete non-standalone options 4 and 7, and is scheduled for December 2018.

Furthermore, a package of new projects for Rel-16 specifications was approved, representing the second phase of 5G, which will expand the mobile ecosystem and add new services, enabling new business models.

“The freeze of Standalone 5G NR radio specifications represents a major milestone in the quest of the wireless industry towards realizing the holistic 5G vision,” said Balázs Bertényi, Chairman of 3GPP TSG RAN.  “5G NR Standalone systems not only dramatically increase the mobile broadband speeds and capacity, but also open the door for new industries beyond telecommunications that are looking to revolutionize their ecosystem through 5G.”

Mr. Enrique Blanco, Telefónica’s Global Systems and Networks Director, added, “Telefónica greatly appreciates the efforts made by the industry for completing this major milestone towards 5G. Telefónica acknowledges the full potential of 5G, and encourages the industry to keep developing ambitious ideas in order to deliver outstanding connectivity and bring the best possible experience to our customers. Telefónica is fully committed to working with the industry in this direction.”

What are the network architecture options included in Rel-15?

For the early introduction of 5G, two radio technologies should be aggregated: Long Term Evolution (LTE) and New Radio (NR). Besides, two core network concepts have to be considered: Evolved Packet Core (EPC), which is the LTE core, and the 5G Core (5GC), the new core.

The way to combine these elements gives rise to several possible architecture options. In this paper we explain the Rel-15 3GPP’s prioritized options.

The most obvious way to combine these four ingredients are the Standalone (SA) options 1 and 2. Option 1 is based on the legacy radio and core (LTE/EPC), while option 2 means connecting the two newly developed ones (NR/5GC). Then, option 2 will fully support all 5G new applications. It is the only option for new operators that do not have a previous LTE infrastructure.

Option 3, Non Standalone (NSA) is the most straightforward way to start deployment and it is likely to be the first option implemented. It leverages existing 4G infrastructure and can be used to quickly connect 5G hotspots to provide enhanced and new services.

In option 4, 5GC replaces the EPC so that the control is taken by 5G that is used for more than just providing coverage, in contrast to option 3.

In option 5, the LTE radio is connected in standalone mode with the 5GC and option 7 is similar to option 3 with 5GC replacing the EPC. Figure 1 shows an overview of the architectures presented above. Options 6 and above 7 are not currently being discussed.

Figure 1: 4G and 5G Deployment Options.  Source: GSMA

What are the main features of 5G NR?

3GPP RE-15 establishes a solid foundation for 5G NR, introducing several new features mainly in the architecture, spectrum and frame structure. Here are some of the most interesting features.

From the architectural standpoint, two deployment options, namely Non-Standalone (NSA) and Standalone (SA) are being standardized, as mentioned above. The possibility of starting the deployment with an NSA version facilitates the early implementation of 5G. Also, cloud/centralized-RAN (C-RAN), and High Layer functional split (option 2) concepts are introduced in a native way in the architecture of 5G NR, paving the path to a more efficient, flexible and scalable network and evolving from the distributed RANs of today to the fully-virtualized and open Cloud RAN of the future. By exploiting a combination of virtualization, centralization and coordination techniques, the open Cloud RAN can provide a more cost-effective solution with reduced time to market for new services, in addition to flexibility and scalability.

The 5G NR allows us to use new spectrum, including millimeter-wave frequencies (above 24 GHz), C-band and frequencies below 3 GHz.  Combining low and high frequency bands will support a wide variety of services, providing the required coverage for IoT and capacity for broadband services with the creation of multiple coverage layers.

Figure 2:  Multiple Capacity and Coverage Layers Enabled by New Spectrum

The frame structure has been designed in a new way using shorter slots and a self-contained sub-frame design (which make TDD switching more flexible and faster) as key enablers for lower latencies. The slot aggregation can be used to offer higher data rates. The mixed numerologies allowing for diverse sub-carrier spacing in the multi-carrier signal (15KHz, 30KHz, 60Khz, 120KHz, 240KHz) provide added flexibility to accommodate different services (from low latency to high spectral efficiency) and diverse spectrum. A new lean design with a careful placement of signaling channels reduces the power consumption.

Efficient channel coding schemes have been introduced to provide robust performance and flexibility. Polar codes added to the control plane complement the LDPC (Low Density Parity Check) codes used to protect the user plane with significant efficiency gains and low complexity over LTE turbo codes.

Multiple input–multiple output (MIMO) techniques are key in the design of 5G NR and are included in a native way in the design. Improved multi-user MIMO and beamforming (massive MIMO) increase coverage and capacity by efficiently utilizing a large numbers of antennas. Furthermore, beamforming will enable mmWaves bandwidth for extreme capacity and throughput.

New Radio redefines the reference signals. Cell-specific reference signals (CRS) are not used anymore and new demodulation reference signals (DMRS) are defined for control and data channels.

Which main features are still under development?

With this extensive list of new additions it may seem that the standard is almost complete. Yet there are many features under development that are not included in this first drop of specifications.

In a short time we will see MIMO enhancements including improved multi-user MIMO, the use of multi-panel antennas and beam management. Frequencies beyond 52.6 GHz will potentially be specified with other types of waveforms. Specifications for reduced power consumption – including the UE power saving and a wakeup mechanism – as well as a Flexible Duplex mechanism that has better duplexing flexibility in unpaired and paired spectrum are also under development.

Regarding new services, ultra reliable low latency communications (URLLC) require enhancements such as time sensitive networking, high accuracy synchronization and jitter control. Also, for massive machine type communications (mMTC) the coexistence between NR and LTE-M (eMTC)/NB-IoT) is being addressed.

Internetworking with non-3GPP systems such as WiFi, vehicular communications (complementing LTE V2V/V2X), multicast services and multimedia broadcast, unlicensed spectrum access, NR voice (VoNR) and positioning using the NR radio interface are also under development.

Conclusions

The NR includes many interesting new features that will expand the value of mobile networks, but many more are yet to come … It is an exciting time to be working on wireless!