Special Articles on 3GPP Release 17 Standardization Activities
5G and 5G-Advanced Standardization Trends

3GPP 5G-Advanced Release 18

Hiroki Harada and Satoshi Nagata
6G-IOWN Promotion Department

Atsushi Minokuchi
Core Network Development Department

Shinji Takeda
Communication Device Development Department

Anil Umesh
Radio Access Network Development Department

Abstract
5G commercial services have been expanding in many countries around the world, and in Japan, the 5G network has been growing since the launch of commercial services in March 2020 in the form of expanded coverage, use of the millimeter-wave band, provision of standalone systems, and other features. At 3GPP, Release 17 specifications were completed in June 2020, and standardization activities on Release 18 specifications and beyond are now under way as “5G-Advanced” toward the further evolution of 5G. This article describes 5G and 5G-Advanced standardization trends at 3GPP.

01. Introduction

  • Mobile communications technology has been evolving ...

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    Mobile communications technology has been evolving and expanding into next-generation systems at roughly 10-year intervals, and in recent years, Release 15 (Rel-15) specifications completed in 2018 at the 3rd Generation Partnership Project (3GPP)*1 has been launched in commercial form in many countries around the world as the 5th Generation mobile communications system (5G). In Japan, NTT DOCOMO launched 5G commercial services in March 2020, and going forward, the goal is to achieve further advances in the mobile broadband services provided up to 4G and provide new value through platform technologies supporting industry and society by exploiting the technical features of 5G such as high data rate and high capacity, low latency and high reliability, and massive connectivity.

    Additionally, since the time that 5G commercialization first got underway, projects promoting the study of the next-generation system, 6G, have been launched in many countries around the world, and 6G-related white papers have come to be released in rapid succession by research institutes and leading vendors in Japan and abroad. NTT DOCOMO launched the first version of its “5G Evolution and 6G” white paper in January 2020. This white paper has been updated regularly and is currently at Version 5.0 [1]. Studies are now underway toward the commercialization of 6G in the 2030s while 5G continues to evolve in anticipation of 6G. Here, 6G and the evolution of 5G are expected to drive the provision of value to new markets as a wave leading to the next stage of mobile multimedia. At 3GPP, 5G functional extensions and performance improvements have been made in Rel-16 and Rel-17 specifications following Rel-15 specifications, and work on the drafting of Rel-18 specifications began in 2022 with Rel-18 specifications and beyond defined as “5G-Advanced.”

    In this article, we describe standardization trends in 5G and 5G-Advanced with a focus on the main contents of 5G standardization up to Rel-17, the targets of 5G-Advanced, and 3GPP Rel-18 study items and work items.

    1. 3GPP: An organization that creates standards for mobile communications systems.

    • 02. 5G and 5G-Advanced Standardization Trends

  • 2.1 Overview of 5G Standardization up to Rel-17

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    In Rel-15, the initial specifications for 5G, which focused mainly on enhanced Mobile Broad Band (eMBB)*2, standard specifications for New Radio (5G NR*3), a new radio access technology, and standard specifications for Long-Term Evolution (LTE) advanced technology were developed in June 2018. Then, in Rel-16 specifications, mobile broadband technology was further enhanced, and in addition, advanced technology in the form of Ultra-Reliable and Low Latency Communication (URLLC)*4 and technology for creating new business called Industrial Internet of Things (IIoT)*5 for promoting IoT in industrial fields were specified in June 2020.

    Next, in addition to making extensions in functions introduced in Rel-15 and Rel-16, Rel-17 aimed to support new scenarios and use cases by extending the frequency band available for use by 5G from up to 52.6 GHz to up to 71 GHz; supporting the Non-Terrestrial Network (NTN)*6 using satellites to expand coverage; adding a low-cost NR terminal category called Reduced Capability (RedCap) for wearable terminals, factory-oriented sensor devices, and monitoring cameras; supporting roaming*7 at the time of a disaster to aid network terminals affected by a massive outage; and studying a mechanism for the identification and authentication/approval of drones. The drafting of Rel-17 specifications was completed in June 2022. An overview of 5G enhancements in Rel-17 is provided in other articles of this issue [2]-[4].

    2.2 Targets of 5G-Advanced

    It was decided at 3GPP to define Rel-18 and beyond as 5G-Advanced at the #46 meeting of the Project Coordination Group (PCG)*8 in April 2021. Prior to Rel-18, Rel-8 and beyond had been defined as LTE, Rel-10 and beyond as LTE-Advanced, Rel-13 and beyond as LTE-Advanced Pro, and Rel-15 and beyond as 5G. These names have been used to differentiate a group of releases providing new functions and services from past groups of releases. The last half of the 2020s is being targeted for the commercialization of 5G-Advanced, which is the next step toward 6G targeting the 2030s for commercialization. The 3GPP standardization timeline for the 2010s and 2020s is shown in Figure 1. The study/work items for Rel-18, the initial release of 5G-Advanced, were agreed upon in December 2021 and standardization activities for Rel-18 have begun. The plan is to complete these activities by December 2023. The schedule related to 6G in the figure is an estimate obtained by back calculating from 2030, which is the time targeted for commercialization. At this point in time, the 3GPP Release schedule going forward and its relationship with 6G are undecided, but it is thought that the standardization of 5G-Advanced will run from Rel-18 to Rel-20 immediately prior to the start of 6G specifications.

    Figure 1  3GPP standardization timeline for the 2010s and 2020s

    Figure 1  3GPP standardization timeline for the 2010s and 2020s

    How to conduct studies and the drafting of specifications for 5G-Advanced will be decided through discussions at 3GPP, but looking back at Rel-12 to Rel-14 immediately prior to 5G specifications, the items up for study and specification at that time took on three major roles as described below.

    1) Improve the Mobile Communications System of the Present Generation Currently in Commercial Service

    Assuming that several years have passed since commercialization of the mobile communications system of the present generation began, dealing with problems that came to light in practical operation, studying and drafting specifications for the standardization of performance improvements, and upgrading the commercial system of the present generation at an early date have the effect of solving operational problems while further promoting the migration from the prior generation system to the present generation system. Rel-12 of 4G, for example, includes specifications to support 256 Quadrature Amplitude Modulation (256QAM)*9 in the downlink and Carrier Aggregation (CA)*10 between Time Division Duplex (TDD)*11 and Frequency Division Duplex (FDD)*12 carriers. Commercial introduction of these functions served to improve 4G peak throughput and facilitate the migration from 3G to 4G.

    2) Support New Service Domains Such as IoT

    In Rel-12 to Rel-14, items that attracted particular interest in technologies to be studied and made into specifications were LTE Machine Type Communication (LTE-MTC)*13 and NarrowBand IoT (NB-IoT)*14 toward IoT and Low Power Wide Area (LPWA)*15 networks. It was expected that the drafting of specifications and commercialization of these technologies in time for the arrival of the IoT era would promote the expansion of the IoT market and drive its growth even today. In addition, inter-terminal communications technologies that were studied and made into specifications in the same releases served as a basis for introducing new service domains such as Public Safety LTE (PS-LTE)*16 and LTE Vehicle to X (LTE-V2X)*17. These technologies are expected to expand the market even further in the years to come.

    3) Study and Draft Specifications for New Technologies with a View to the Next-generation Mobile Communications System

    In Rel-12 to Rel-14, while not being widely introduced in the commercial 4G network, a number of new functions associated with what would be basic functions in 5G, the next-generation mobile communications system, were studied and made into specifications. Specifically, these included dual connectivity for simultaneously connecting to two base stations, Full-Dimension Multiple Input Multiple Output (FD MIMO)*18 considering beam forming*19 in three-dimensional space, Short Transmission Time Interval (Short TTI) that performs data transmission in units smaller than a subframe*20 for achieving low latency, and autonomous uplink that performs uplink transmission without using dynamic scheduling indication from a base station.

    2.3 Rel-18 Study/work Items

    At 3GPP, a Rel-18 workshop was held by Technical Specification Group Radio Access Network (TSG RAN)*21 in June 2021 and by Technical Specification Group Service and System Aspects (TSG SA)*22 in September 2021. In addition, discussions on Rel-18 study/work items based on proposals from various companies continued to be held after these workshops, and as a result, Rel-18 study/work items were approved in December 2021 and March 2022. The Rel-18 standardization schedule is summarized in Ref. [5] and all Rel-18 study/work items are listed in Ref. [6]. The study/work items for Rel-18 attempt to achieve a balance between diverse viewpoints, such as evolution of mobile broadband and 5G rollout to a variety of industries, short-term and medium-term/long-term needs, and device evolution and network evolution. Among this large number of study/work items, the following introduces several items based on the targets and expectations of 5G-Advanced described above.

    1) Improved Performance in Uplink Communications

    Following the introduction of commercial 5G, peak data rate and effective data rate improved compared with 4G, but this improvement has been mainly in downlink communications, while the effective data rate in uplink communications has been hardly different from 4G at several tens of Mbps. In general, there is more downlink traffic than uplink traffic, and transmission power in the downlink (at the base station) is greater than transmission in the uplink (at the portable terminal). It can therefore be said that the difference in data rate and communications quality between the downlink and uplink is inevitable from the viewpoints of efficient allocation of radio resources*23 and difference in transmission power.

    On the other hand, there is a demand for improved performance in uplink communications in a number of 5G use cases such as real-time streaming, information gathering from sensor terminals, and the use of 5G as an alternative to fixed-line communications as in the case of home routers.

    Against this background, proposals were received from many companies to study performance improvements and draft specifications with respect to uplink communications in Rel-18, and a number of items were eventually agreed upon. Specifically, support of simultaneous transmission by multiple antenna panels and MIMO transmission by more than four layers envisioning home routers, vehicle-mounted terminals, and industrial devices, effective frequency usage by dynamic switching among multiple carriers for uplink use, and extensions for improving terminal transmission power are being studied toward the drafting of specifications [7]-[9].

    2) IoT Support by NR

    From the viewpoint of telecom operators, making a smooth transition to a new-generation mobile communications system from the past generation is extremely important. Continuing to maintain and operate multiple generations of a mobile communications system is hardly efficient. For this reason, many operators have announced that they will terminate 3G services in the 2020s after introducing 5G commercial services. In addition, there were many cases in which 5G was introduced as a Non-StandAlone (NSA)*24 system using both LTE and NR to produce a smooth transition from 4G; however, the replacement of such systems with SA systems using only NR is progressing, and terminating 4G services around 2030 when 6G is to be launched is being studied.

    At the same time, there is a demand for low-cost and low-power IoT devices capable of long-term operation, so the problem arises in which replacing the current mobile communications system with a new generation system does not proceed well so that using a mobile communications system of a past generation continues for some time. For example, IoT devices introduced in the latter half of the 2010s can be used in about ten years, which means that their replacement may have to take place in the latter half of the 2020s. At that time, however, circumstances may be different as to whether LTE IoT devices are to be continued, and in the event that the use of those LTE devices are actually continued without introducing new NR IoT devices and networks, it may not be possible to terminate 4G services by the latter half of the 2030s.

    Against this background, Rel-17 in 5G targeted a middle ground between conventional LTE specifications for IoT and NR specifications mainly for eMBB, and prescribed specifications for simple RedCap NR terminals that can achieve lower costs by holding back on performance and supported functions. Furthermore, in Rel-18, the study and drafting of specifications for even simpler NR terminals known as enhanced RedCap (eRedCap), which may replace some of the conventional LTE based devices and networks for IoT, were proposed and agreed upon [10]. Targets for NR and LTE terminal specifications are shown in Figure 2.

    Figure 2  Targets for NR and LTE terminal specifications

    Figure 2  Targets for NR and LTE terminal specifications

    3) IIoT Support by 5G System (5GS)*25

    IIoT that supports communications involved in various types of control within a closed industrial network is considered to be a new 5G service. At 3GPP, the drafting of specifications for time synchronization and deterministic communications deemed essential to providing such a service has been proceeding since Rel-16. These specifications were completed in Rel-17. Details on these initiatives are provided in another article of this issue [11].

    Then, in Rel-18, to further enhance the performance of IIoT provided by 5GS, a study on improving low-latency characteristics in end-to-end communications within 5GS was agreed upon [12]. Specifically, it was decided to study interworking*26 between the core-network*27 control plane*28 and the Time Sensitive Networking (TSN) transport network*29 set in N3*30 and notifying of the downlink packet RAN transmission schedule from RAN to application functions. In IIoT, terminal groups, as opposed to individual terminals, are controlled, and it was agreed that this would also be studied in Rel-18 [13].

    4) Study of New Technology Areas in Anticipation of 6G

    Based on medium- and long-term needs, Rel-18 includes items in new technology areas designated only for study and not for specification within the Rel-18 period. For example, with regard to the application of Artificial Intelligence (AI) and Machine Learning (ML)*31 to the radio interface, it was agreed to conduct studies with use cases in mind such as feedback of channel state information, beam control, and terminal positioning [14]. Additionally, as extensions to duplex operations in the downlink and uplink, it was agreed to conduct studies on extending available time resources especially on the uplink and improving uplink performance. This would be accomplished by frequency multiplexing downlink and uplink resources in the TDD band and by supporting simultaneous transmission/reception (full duplex) on the base station side [15].

    In addition, the study of AI/ML technologies is progressing steadily with the entire 3GPP system in mind. In Rel-17, studies began on the use of those technologies for generating various types of analytical information using control plane functions in the core network, and the NetWork Data Analytics Function (NWDAF)*32 specified in Rel-16 was divided into the functions of model training, inference, data collection, and data storage. Details on this initiative are provided in another article of this issue [3]. In Rel-18, the studies mentioned above are progressing, and it was agreed to conduct studies on sharing trained models between different vendors, expanding federated learning, linking with data analysis functions on the operation side, etc. [16]. A consensus was also reached on studying functions for supporting external AI/ML model service providers in Rel-18 [17].

    1. eMBB: Generic term for mobile communications requiring high-data-rate and high-capacity features.
    2. 5G NR: A radio system standard drafted for 5G. It speeds up communications by using higher frequency bands (for example, the 3.6 GHz, 4.5 GHz, and 28 GHz bands) compared with 4G and enables low-latency and high-reliability communications with the aim of achieving advanced IoT.
    3. URLLC: Generic terminology for communications requiring low delay and high reliability.
    4. IIoT: Generic term for communications oriented to industrial equipment and devices in factories, etc.
    5. NTN: A network that extends the communications area to diverse locations including the air, sea, and space using non-terrestrial media such as satellites and high-altitude platform stations without limiting the coverage area to land.
    6. Roaming: A mechanism that enables users to use services similar to their subscribed carriers within the service areas of alliance partner carriers, but outside the service areas of their subscribed carriers.
    7. PCG: The highest decision-making body in 3GPP. It performs overall 3GPP activity planning, progress management, etc.
    8. 256QAM: A type of modulation scheme. 256QAM modulates data bits through 256 different amplitude and phase signal points. A single modulation can transmit 8 bits of data.
    9. CA: A technology for increasing bandwidth by simultaneously transmitting/receiving signals over multiple component carriers.
    10. TDD: A bidirectional transmit/receive system. This system achieves bidirectional communications by allocating different time slots to uplink and downlink transmissions on the same frequency.
    11. FDD: A single transmission system using different frequencies in the uplink and downlink.
    12. LTE-MTC: An LTE communications specification for performing IoT-oriented data communications using a portion of the ordinary LTE band.
    13. NB-IoT: An LTE communications specification for performing low-speed data communications for IoT (sensors, etc.) using a frequency band that is even narrower than LTE-MTC.
    14. LPWA: Wireless communications technology that can support a wide communications area on the kilometer level with low power consumption.
    15. PS-LTE: Generic term for networks or services rolled out using LTE for the sake of public safety for use in police work, fire fighting, etc.
    16. LTE-V2X: A generic term for vehicle-related technologies including Vehicle to Vehicle (V2V) for performing direct communications between vehicles, Vehicle to Infrastructure (V2I) for performing direct communications between a vehicle and roadside equipment (wireless communications facilities installed along a road), Vehicle to Pedestrian (V2P) for performing direct communications between a vehicle and a pedestrian, and Vehicle to Network (V2N) for performing base-station-mediated wide-area communications via the LTE network.
    17. FD MIMO: Among MIMO transmission methods that transmit signals using multiple transmitting/receiving antennas, this method uses multiple antenna elements in both the horizontal and vertical directions in three-dimensional space.
    18. Beam forming: Technology for generating a directional pattern for transmission and/or reception by using multiple antennas (by means of controlling amplitude and phase of each of multiple antennas) and increasing or decreasing antenna gain in regard to specific directions.
    19. Subframe: A unit of radio resources in the time domain consisting of multiple Orthogonal Frequency Division Multiplexing (OFDM) symbols (14 OFDM symbols in LTE).
    20. TSG RAN: A group in 3GPP in charge of drafting technical specifications, namely, radio interface specifications and radio-access-network interface specifications.
    21. TSG SA: A group in 3GPP in charge of drafting technical specifications, namely, specifications related to service requirements, architecture, and security.
    22. Radio resources: General term for radiocommunications resources (radio transmission power, allocated frequency, etc.).
    23. NSA: A connection format to the 5G radio access network assuming parallel use of LTE (enhanced LTE (eLTE)).
    24. 5GS: A 5G network system consisting of a core network, radio access network, and communication terminals.
    25. Interworking: Interaction between communications systems.
    26. Core network: A network that comprises the constituent elements of a mobile communications system. It governs registration control, session control, service control, etc. and transfers user data between the radio access network and external networks.
    27. Control plane: The part of the core network that performs a series of control processes such as registration control, session control, service control, etc.
    28. TSN transport network: The network that, among the transport networks connecting the radio access network and core network or among the transport networks interconnecting equipment in different networks, is equipped with TSN functions.
    29. N3: An interface for transferring user data between the radio access network and core network.
    30. ML: A mechanism for making a computer learn useful evaluation criteria from sample data.
    31. NWDAF: A network function specified in 5GC that returns the results of collecting and analyzing various types of data within the network.

    • 03. Conclusion

  • This article described the main contents of 5G ...

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    This article described the main contents of 5G standardization up to Rel-17, the targets of 5G-Advanced, and 3GPP Rel-18 study items and work items as standardization trends in 5G and 5G-Advanced. NTT DOCOMO is committed to promoting 5G and 5G-Advanced standardization at 3GPP and contributing to the further evolution of mobile communications.

  • REFERENCES

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    14. [14] 3GPP RP-221348: “Revised SID for AI/ML for NR air-interface,” Jun. 2022.
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    16. [16] 3GPP SP-220678: “Study on Enablers for Network Automation for 5G - Phase 3,” Jun. 2022.
    17. [17] 3GPP SP-220071: “Revised SID on System Support for AI/ML-based Services,” Mar. 2022.

VOL.24 NO.3

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