3GPP Rel-18: 5G-Advanced RAN Features
3GPP Rel-18 is the first release of the 5G-Advanced standard. On the 17th of December 2021, 3GPP TSG (Technical Specification Group) RAN plenary (3GPP RAN TSG #94e) approved 28 Release-18 projects (i.e., Study- and Work-Items, SI/WI) with the following split among RAN groups: 12 RAN1-led projects, 10 RAN2-led projects, 5 RAN3-led projects, and 1 RAN4-led project (with further RAN4 items to be approved in March 2022) . Those topics include Artificial Intelligence/Machine Learning (AI/ML) for New Radio (NR) and NG-RAN, Non-Terrestrial Networks (NTN) and MIMO enhancements, evolution for sidelink, UAV, RedCap, SON, QoE, XR services, to name a few. In this post, we elaborate on each of the approved WI/SI entering 5G-Advanced standardization.
Note: this is a follow-up article from the preliminary discussion on 5G-Advanced, which we sketched back in May 2021. Interested readers are recommended to take a look here: 3GPP Rel-18: The Preliminary Discussions.
3GPP Rel-18 Timeline
The current timeline for the Rel-18, as per  is as follows:
- Rel-18 Stage 1 – Currently ongoing (Stage 1 means „an overall service description from the user’s standpoint” )
- Rel-18 Stage 2 Functional Freeze – March 2023 (Stage 2 means „overall description of the organization of the network functions to map service requirements into network capabilities” )
- Rel-18 Stage 3 Freeze – December 2023 (Stage 3 means „the definition of switching and signalling capabilities needed to support services defined in stage 1” )
- Rel-18 Protocol Coding Freeze (ASN1 and Open API) – March 2024
Note: this post covers the 5G-Advanced features as approved by TSG RAN. There will be a separate article, which will cover the approved Rel-18 SA WIs/SIs.
3GPP Rel-18 RAN Features
The current set of WI/SI (Work Items/Study items) for 3GPP Rel-18 RAN features is split into four RAN working groups (WGs) as per the figure below. Those are discussed in detail in the following subsections. Note: After the description, the relevant reference to the particular Study- and Work-Item description document is provided in square brackets.
WI/SIs to be led by RAN1
RAN1 is responsible for the specification of the physical layer including physical channels and modulation, PHY layer multiplexing and channel coding, PHY layer procedures and measurements as well as PHY layer-related UE capabilities. Within 5G-Advanced Rel-18 scope the following projects are to be covered by RAN1:
- New WI: MIMO Evolution for Downlink and Uplink: aims at addressing, among others, the following: CSI reporting enhancement for high/medium UE velocities by exploiting time-domain correlation/Doppler-domain information to assist DL precoding, targeting FR1; larger number of orthogonal DMRS ports for downlink and uplink MU-MIMO; enhancements of CSI acquisition for Coherent-JT targeting FR1 and up to 4 TRPs, assuming ideal backhaul and synchronization as well as the same number of antenna ports across TRPs; UL DMRS, SRS, SRI, and TPMI (including codebook) enhancements to enable 8 Tx UL operation to support 4 and more layers per UE in UL targeting CPE/FWA/vehicle/Industrial devices; simultaneous multi-panel UL transmission for higher UL throughput/reliability, focusing on FR2 and multi-TRP, assuming up to 2 TRPs and up to 2 panels, targeting CPE/FWA/vehicle/industrial devices. [3GPP RP-213598, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI: Artificial Intelligence (AI)/Machine Learning (ML) for NR Air Interface: aims at exploring the benefits of augmenting the air-interface with features enabling support of AI/ML-based algorithms for enhanced performance and/or reduced complexity/overhead. This SI’s target is to lay the foundation for future air-interface use cases leveraging AI/ML techniques. The initial set of use cases to be covered include: CSI feedback enhancement (e.g., overhead reduction, improved accuracy, prediction), Beam management (e.g., beam prediction in time, and/or spatial domain for overhead and latency reduction, beam selection accuracy improvement), positioning accuracy enhancements. For those use cases the benefits shall be evaluated (utilizing developped methodology and defined KPIs) and potential impact on the specifications shall be assessed including PHY layer aspects, protocol aspects (e.g. capability information, configuration, timing, inference, data management), interoperability and testability aspects. In addition to that the study shall cover characterization of the steps for ML/AI related algorithms and framework characteristics as well as identification of UE-gNB collaboration shall be evaluated, along with the lifecycle management for AI/ML models, datasets and notation and terminology. Note that as is typically the case, the actual AI/ML models/algorithms are not to be specified and will be left to implementation. [3GPP RP-213599, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI: Evolution of NR Duplex Operation: with the objective to study subband non-overlapping full duplex and potential enhancements on dynamic/flexible TDD including inter-gNB and inter-UE CLI handling (including intra subband and inter subband CLI) with feasibility of and impact on RF requirements considering the self-interference. [3GPP RP-213591, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: NR Sidelink evolution: aims at specifying: mechanism to support NR sidelink CA operation based on LTE sidelink CA operation (e.g. LTE sidelink CA features for NR, i.e., SL carrier (re-)selection, synchronization of aggregated carriers, handling the limited capability, power control for simultaneous sidelink TX, packet duplication), support of sidelink on unlicensed spectrum (including channel access mechanisms from NR-U, physical channel design framework), enhanced sidelink operation on FR2 licensed spectrum (support of sidelink beam management, including initial beam-pairing, beam maintenance, and beam failure recovery, etc), mechanism(s) for co-channel coexistence for LTE sidelink and NR sidelink, UE Tx and Rx RF requirement for supporting new features introduced in this WI, sidelink frequency bands for single-carrier operation and frequency band combinations for carrier aggregation operation. [3GPP RP-213678, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI/WI: Expanded and improved NR positioning: is an SI to be followed up by WI after 9 months. The study item covers the following three main topics: solutions for sidelink positioning (i.e. target performance requirements, evaluation methodology with which to evaluate SL positioning for the uses cases and coverage scenarios, reusing existing methodologies from sidelink communication and from positioning, performance and feasibility of potential solutions for SL positioning, considering relative positioning, ranging and absolute positioning), improved accuracy, integrity, and power efficiency (including integrity for RAT dependent positioning techniques, accuracy improvement based on PRS/SRS bandwidth aggregation for intra-band carriers, accuracy improvement based on NR carrier phase measurements); positioning support for RedCap UEs. [3GPP RP-213588, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI/WI: Further NR RedCap UE complexity reduction: is an SI to be followed up by WI after 6 months. The study part includes: further UE complexity reduction techniques by considering network impact, coexistence of Rel-17 and Rel-18 RedCap and non-RedCap UEs in a cell, UE impact, specification impact, etc.; developing potential solutions covering: UE BW reduction to 5MHz in FR1 in combination with relaxed UE processing for PDSCH/PUSCH/CSI, and reduced UE peak data rate in FR1 by restricting BW for PDSCH/PUSCH in combination with relaxed UE processing for PDSCH/PUSCH/CSI. [3GPP RP-213661, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI/WI: Network Energy Savings: is an SI to be followed up by WI after 9 months. The study phase cover the following topics: definition of a base station energy consumption model (including relative energy consumption for DL and UL (considering factors like PA efficiency, number of TxRU, base station load, etc), sleep states and the associated transition times, and one or more reference parameters/configurations), definition of an evaluation methodology and KPIs (i.e. system-level network energy consumption and energy savings gains, as well as assessing/balancing impact to network and user performance (e.g. spectral efficiency, capacity, UPT, latency, handover performance, call drop rate, initial access performance, SLA assurance related KPIs), energy efficiency, and UE power consumption, complexity), study techniques on the gNB and UE side to improve network energy savings in terms of both BS transmission and reception (including achieving more efficient operation dynamically and/or semi-statically and finer granularity adaptation of Tx/Rx in one or more of network energy saving techniques in time, frequency, spatial, and power domains, with potential support/feedback from UE; information exchange/coordination over network interfaces). [3GPP RP-213554, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Further NR coverage enhancements: aims at defining coverage enhancements for uplink, including PRACH (e.g. multiple PRACH transmissions with same beams for 4-step RACH procedure, PRACH transmissions with different beams for 4-step RACH procedure), power domain (like increasing UE power high limit for CA and DC, reduce MPR/PAR, including frequency domain spectrum shaping with and without spectrum extension for SC-FDMA and tone reservation) and SC-FDMA (i.e. support dynamic switching between DFT-S-OFDM and CP-OFDM). [3GPP RP-213579, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI/WI: NR Network-controlled Repeaters: focuses on the following scenarios and assumptions: NW-controlled inband RF repeaters used for extension of network coverage on FR1 and FR2 bands; single hop stationary NW-controlled repeaters which are transparent to UEs and can maintain the gNB-repeater link and repeater-UE link simultaneously. The study scope covers: identification of side control information for NW-controlled repeaters including assumption of max transmission power with: Beamforming information, timing information to align transmission / reception boundaries of NW-controlled repeater, information on UL-DL TDD configuration, ON-OFF information for efficient interference management and improved energy efficiency, power control information for efficient interference management; L1/L2 signalling to carry the side control information; and NW-controlled repeater management (e.g. identification and authorizaiton). [3GPP RP-213700, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Enhancement of NR Dynamic spectrum sharing (DSS): aims at improving the DSS feature from the perspective of NR spectrum efficiency for LTE-NR co-existence and covers the following items: NR PDCCH reception in symbols with LTE CRS REs (i.e. investigate enabling LTE CRS to puncture NR PDCCHA); and UE support, and configuration with, two overlapping CRS rate matching patterns regardless of support or configuration of multi-TRP. [3GPP RP-213575, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI: Low-power Wake-up Signal (WUS) and Receiver (WUR) for NR: aims at studying power saving schemes which do not require existing signals to be used as wake-up signal (WUS). The following study objectives are to be covered: evaluation methodology for low-power WUS/WUR for power-sensitive, small form-factor devices including IoT use cases (such as industrial sensors, controllers) and wearables; evaluation of low-power wake-up receiver architectures; wake-up signal designs to support wake-up receivers; L1 procedures and higher layer protocol changes to support the wake-up signals; and UE power saving gains compared to the existing Rel-15/16/17 UE power saving mechanisms and their coverage availability, and latency impact. [3GPP RP-213645, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Multi-carrier enhancements for NR: the objective is to specify solution for multi-cell PUSCH/PDSCH scheduling (one PDSCH/PUSCH per cell) with a single DCI, and specify enhancements for multi-carrier UL operation including: UL Tx switching schemes, including mechanisms to enable more configured UL bands than its simultaneous transmission capability and to support dynamic Tx carrier switching across the configured bands for both single TAG and multiple TAGs configurations; switching time and other RF aspects, and RRM requirements for above UL Tx switching schemes across up to 3 or 4 bands. [3GPP RP-213577, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
WI/SIs to be led by RAN2
RAN2 is responsible for the specification of the air interface architecture and L2/L3 protocols and the Radio Resource Management procedures. Within 5G-Advanced Rel-18 scope the following projects are to be covered by RAN2:
- New WI: Further NR Mobility Enhancements: objectives are to specify: mechanism and procedures of L1/L2 based inter-cell mobility for mobility latency reduction (including configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells, dynamic switch mechanism among candidate serving cells, L1 enhancements for inter-cell beam management, Timing Advance management, CU-DU interface signaling to support L1/L2 mobility); mechanism and procedures of NR-DC with selective activation of the cell groups; CHO including target MCG and target SCG; RRM core requirements, like L1/L2-based inter-cell mobility, enhanced CHO configurations; and to study impact of FR2 RRM mobility measurement acquisition and reporting on FR2 SCell/SCG setup/resume delay for a UE connecting from idle/inactive mode, and improvement in FR2 SCell/SCG setup delay from defining new UE measurement procedures and RRM core requirements. [3GPP RP-213565, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI: XR Enhancements for NR: aims at studying the following aspects: XR-awareness in RAN (like: XR traffic characteristics, QoS metrics, and application layer attributes for the gNB to be aware of, XR-specific traffic handling); XR-specific Power Saving (i.e. power saving techniques to accommodate XR service characteristics (e.g., periodicity, multiple flows, jitter, latency, reliability), like C-DRX enhancement or PDCCH monitoring enhancements); XR-specific capacity improvements (i.e., more efficient resource allocation and scheduling for XR service characteristics, like SPS and CG enhancements, dynamic scheduling/dynamic grant enhancements). [3GPP RP-213587, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: NR sidelink relay enhancements: goal is to specify solutions to enhance NR Sidelink Relay for V2X, public safety and commercial use cases including the following: mechanisms to support single-hop Layer-2 and Layer-3 UE-to-UE relay (i.e., source UE -> relay UE -> destination UE) for unicast; mechanisms to enhance service continuity for single-hop Layer-2 UE-to-Network relay; Study the benefit and potential solutions for multi-path support to enhance reliability and throughput (e.g., by switching among or utilizing the multiple paths simultaneously); Support of sidelink DRX for Layer-2 UE-to-Network sidelink relay operation; RRM core requirements for relay discovery and (re)selection in UE-to-UE relay. [3GPP RP-213585, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: NR NTN (Non-Terrestrial Networks) enhancements: aims to specify enhancements for NG-RAN based NTN including for the following scenarios: GSO and NGSO (LEO and MEO) with transparent payload; earth fixed tracking area andEarth moving cells for NGSO; FDD mode; UEs with GNSS capabilities; both “VSAT” devices with directive antenna supported in FR1; only “VSAT” devices with directive antenna supported in above 10 GHz bands. The enhancements cover the following features: Coverage enhancement, NR-NTN deployment in above 10 GHz bands, network verified UE location, NTN-TN and NTN-NTN mobility and service continuity enhancements. [3GPP RP-213690, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: IoT NTN enhancements: covers enhancements to both NB-IoT NTN and eMTC NTN including: performance enhancements in terms of throughput (like, disabling HARQ feedback to mitigate impact of HARQ stalling on UE data rates, improved GNSS operations for a new position fix for UE pre-compensation during long connection times and for reduced power consumption); mobility enhancements (like, Support of neighbor cell measurements and corresponding measurement triggering before RLF); GNSS optimization operation with sparse use of GNSS and power efficiency for long-term connection; and further enhancements to discontinuous coverage. [3GPP RP-213596, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: NR support for UAV (Uncrewed Aerial Vehicles): covers the following items to be specified: enhancements on measurement reports (e.g., UE-triggered measurement report based on configured height thresholds, reporting of height, location and speed in measurement report, flight path reporting); signaling to support subscription-based aerial-UE identification; enhancements for UAV identification broadcast; UE capability signaling to indicate UAV beamforming capabilities. [3GPP RP-213600, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Dual Tx/Rx MUSIM (Multi SIM): the goal is to provide enhancements for MUSIM including procedures to operate in RRC_CONNECTED simultaneously in network A and network B, specifically: define mechanism to indicate preference on temporary UE capability restriction and removal of restriction (e.g. capability update, release of cells, (de)activation of configured resources) with network A when UE needs transmission or reception (e.g., start/stop connection to NW B) for MUSIM purpose; RAT concurrency: network A is NR SA (with CA) or NR DC, while network B can either be LTE or NR; applicable UE architecture: Dual-RX/Dual-TX UE. [3GPP RP-213584, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: In-Device Co-existence (IDC) enhancements for NR and MR-DC: the goal of this WI is to address interference between 3GPP and non-3GPP RAT (e.g. Wi-Fi) (i.e. UE detects internal issue caused by coexistence related to usage of radio resources that UE cannot resolve itself and thus provides info to gNB to assist in restricting radio resource usage), including, e.g.: enhancements to FDM solution, to allow more granular indication of affected frequencies (e.g. granularity of BWP or PRB level) or introduction of TDM solution (e.g. indication of UE preferred TDM pattern for UL/DL). [3GPP RP-213589, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Mobile Terminated-Small Data Transmission (MT-SDT) for NR: MT-SDT (i.e. DL-triggered small data) allows: reducing signalling overhead and UE power consumption by not transitioning to RRC_CONNECTED and reducing latency by allowing fast transmission of (small and infrequent) packets, e.g. for positioning. This work item aims at specifying support for paging-triggered SDT including: MT-SDT triggering mechanism for UEs in RRC_INACTIVE; MT-SDT procedure for initial DL data reception and subsequent UL/DL data transmissions in RRC_INACTIVE. [3GPP RP-213583, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Enhancements of NR Multicast and Broadcast Services (MBS): targets to specify: support of multicast reception by UE in RRC_INACTIVE; Uu signalling enhancements for UE to use shared processing for MBS broadcast and unicast reception (i.e., including UE capability and assistance information reporting on simultaneous unicast reception in RRC_CONNECTED and MBS broadcast reception from the same or different operators); enhancements to improve the resource efficiency for MBS reception in RAN sharing scenarios. [3GPP RP-213568, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
WI/SIs to be led by RAN3
RAN3 is responsible for the specification of the overall RAN architecture and protocols for the network interfaces. Within 5G-Advanced Rel-18 scope the following projects are to be covered by RAN3:
- New WI: Mobile IAB (Mobile Integrated Access and Backhaul): aims at: defining procedures for migration/topology adaptation to enable IAB-node mobility, including inter-donor migration of the entire mobile IAB-node; enhancements for mobility of an IAB-node together with its served UEs, including aspects related to group mobility; mitigation of interference due to IAB-node mobility, including the avoidance of potential reference and control signal collisions. Mobile IAB-nodes should: support in-band and out-of-band backhauling; serve only UEs (including the legacy ones) – i.e. should have no descendent IAB-nodes; support UE HO and DC. [3GPP RP-213601, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI/WI: AI/ML for NG-RAN: the aim of this WI is to specify data collection enhancements and signaling support within existing NG-RAN interfaces and architecture for AI/ML-based Network Energy Saving, Load Balancing and Mobility Optimization.[3GPP RP-213602, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Further enhancement of data collection for SON/MDT in NR and EN-DC: aims at specifying data collection enhancement in NR for SON/MDT purposes. This covers the following: e.g., support of data collection for SON features, including “left-over” features (i.e. MR-DC and MRO successful PScell change report, fast MCG recovery, NR-U) and MRO enhancement for inter-system handover voice fallback (including UE reporting specification necessary to enhance the mobility parameter tuning or inter-node information exchange specification, including possible enhancements to interfaces); Support of SON/MDT enhancements for RACH enhancements, NPN; Support of signaling-based logged MDT override protection to address the scenario where the signaling based MDT configured in LTE, the UE comes to connected in NR. [3GPP RP-213553, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New WI: Enhancement on NR QoE management and optimizations for diverse services: aims at introducing enhancements to the existing NR QoE framework and at introducing the support for new types of 5G services, such as AR, MR, cloud gaming, as well as the support for RRC_CONNECTED, RRC_INACTIVE and RRC_ IDLE for the MBS (Multicast/Broadcast) service. This includes e.g., the mechanism of how to configure and report legacy QoE and RAN visible QoE measurements, and how to align the QoE with radio-related measurements; support for QoE measurement configuration, measurement reporting over MN/SN for NR-DC scenario, as well as support for RAN visible QoE report over MN/SN, mobility continuity, the alignment of QoE report and MDT, etc; support the network to collect QoE measurement for high speed scenarios, e.g. high speed train. [3GPP RP-213594, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- New SI: Enhancement for resiliency of gNB-CU-CP: the NG-RAN architecture includes the split option, with a single gNB-CU-CP connected to multiple gNB-CU-UPs and gNB-DUs. Therefore, failures at the gNB-CU-CP may cause interruption of UP traffic and disconnection of UEs. Due to the above, this SI aims at studying and identification of failure scenarios associated with gNB-CU-CP based on the current NG-RAN architecture. [3GPP RP-213677, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
WI to be led by RAN4
RAN4 is responsible for the specification of the Radio Frequency (RF) aspects, the definition of minimum requirements for transmission and reception parameters, Radio Resource Management (RRM), and for channel demodulation and Channel State Information (CSI) reporting. Within 5G-Advanced Rel-18 scope, the following is to be covered by RAN4:
- New WI: NR support for dedicated spectrum less than 5MHz for FR1 – aims at identifying and specifying changes to NR PHY layer to operate in spectrum allocations from 3 MHz to less than 5 MHz. Those can be used for concurrent operation of FRMCS and GSM-R (co-located deployments) in bands n100, n8, n26, n28. This would effectively lead to migration from GSM-R sytems towards FRMCS. [3GPP RP-213603, 3GPP TSG RAN Meeting #94e, Dec. 6 – 17, 2021]
- Other RAN4-led projects to be approved in March 2022.
As per the above description, the first release of 5G-Advanced as per 3GPP Rel-18 will cover interesting topics like the inclusion of AI/ML within RAN and even air interface. This is part of the automation framework, which is getting more advanced within the 5G system and is accompanied by other relevant features like enhancements to QoE and SON/MDT. Other set of topics include novel architectural aspects, like Mobile IAB, UAV, Network Controlled Repeaters, Sidelink, and NTN. In the IoT sector, also aspects like coverage enhancements, Small data transmission, RedCap, positioning, or NTN within the IoT area are dealt with. Finally, the MBB related features include MIMO and CA enhancements along with MBS and XR enhancements.
The next post covers the other part of the 5G-Advanced standard as per 3GPP Rel-18, namely System Architecture (SA) features. To read it, click here: 5G-Advanced: 3GPP Rel-18 SA2 Features – RIMEDO Labs
Marcin Dryjanski received his Ph.D. (with distinction) from the Poznan University of Technology in September 2019. Over the past 12 years, Marcin served as an R&D engineer and consultant, technical trainer, technical leader, advisor, and board member. Marcin has been involved in 5G design since 2012 when he was a work-package leader in the FP7 5GNOW project. Since 2018, he is a Senior IEEE Member. He is a co-author of many articles on 5G and LTE-Advanced Pro and a co-author of the book „From LTE to LTE-Advanced Pro and 5G” (M. Rahnema, M. Dryjanski, Artech House 2017). From October 2014 to October 2017, he was an external advisor at Huawei Technologies Sweden AB, working on algorithms and architecture of the RAN network for LTE-Advanced Pro and 5G systems. Marcin is a co-founder of Grandmetric, where he served as a board member and wireless architect between 2015 and 2020. Currently, he serves as CEO and principal consultant at Rimedo Labs.