By Marcin Dryjanski, Ph.D., Grandmetric
In the past year, we have seen the rapid standardization of 3GPP Rel-15, 5G-NR, laying the foundation for the first 5G networks. Even before the introduction of 5G in Release 15, “5G phase 1,” aspects of further improvements already were in development, as not all features could be completed in time for Rel-15.
This article discusses the ideas and enhancements currently being worked on for 3GPP Release-16. These enhancements cover not only 5G-NR, but also LTE, which is being advanced in parallel. We focus on the selected Rel-16 work items (WI) and study items (SI), and split those into two chapters.
The first part elaborates on the 3GPP Rel-16 Work Items (also known as features) currently under 3GPP consideration to be included in this release :
- eNB(s) Architecture Evolution for E-UTRAN and NG-RAN
- LTE-NR & NR-NR Dual Connectivity and NR Carrier Aggregation enhancements
- Rel-16 Enhancements for NB-IoT Security Assurance Specification for 5G
- LAN support in 5G
- Integration of Satellite Access in 5G
- 5G positioning services
- NR intra-band Carrier Aggregation
- Dual Connectivity (EN-DC)
- Enhancements on MIMO for NR
- NR mobility enhancements
- Energy efficiency for 5G
The second part of the article focuses on the selected Study Items that 3GPP has chosen for Rel-16, including :
- Study on NR beyond 52.6 GHz
- Study on self-organizing networks (SON) for 5G
- Study on NR V2X
- Study on Cellular IoT support and evolution for the 5G System
- Feasibility Study on 6 GHz for LTE and NR in Licensed and Unlicensed Operations
- Study on NR-based Access to Unlicensed Spectrum
- Study on Non-orthogonal Multiple Access for NR
Release 16 Work Items
This chapter discusses further enhancements of both LTE and 5G-NR for 3GPP Rel-16 in terms of normative specification.
eNB(s) Architecture Evolution for E-UTRAN and Next Gen (NG)-RAN focuses and builds upon the Technical Report  in Rel-15, which studies the higher-layer functional split architecture of eNB. A new architecture with a central unit (eNB-CU) and a distributed unit (eNB-DU) has been designed to achieve better integration between the LTE eNB and NR gNB.
LTE-NR & NR-NR Dual Connectivity and NR Carrier Aggregation enhancements are dedicated to exploring enhancements for dual connectivity (DC) and carrier aggregation (CA). The focus is on the following four topics:
- Support of asynchronous and synchronous NR-NR Dual Connectivity
- Early Measurement reporting — to ensure quick and efficient setup of MR-DC and/or CA
- Efficient and low-latency serving cell configuration/activation/setup
- Fast recovery — in case of master cell group (MCG) failure, by utilizing a secondary cell group (SCG) link and the split SRBs during recovery
Rel-16 enhancements for NB-IoT — After successful commercialization of NB-IoT was introduced in Rel-13 and further improvements were made in subsequent releases, the following improvements are in discussion for Rel-16:
- Improved DL transmission efficiency and/or UE power consumption — by supporting mobile-terminated (MT) early data transmission, along with support for UE-group wake-up signal
- Improved UL transmission efficiency and/or UE power consumption — by supporting transmission in preconfigured resources (common or dedicated), in idle and/or connected mode, based on SC-FDMA waveform for UEs with a valid timing advance
- Scheduling enhancement — in the form of scheduling multiple DL/UL transport blocks, with or without DCI, for single-cell point-to-multipoint (SC-PTM) and unicast, along with discussion for semi-persistent scheduling (SPS)
- Network management tool enhancement — improvement of self-organizing network (SON) support
- Improved multi-carrier operation — For non-anchor carrier cases, support of Msg3 quality reporting and support for signaling to indicate on a non-anchor carrier for paging a set of subframes, which will contain narrowband reference signal (NRS) even when no paging NPDCCH is transmitted;
- Mobility enhancement — allowing for a NB-IoT mechanism that would assist idle mode inter-RAT cell selection for NB-IoT to and from LTE, LTE-MTC, and GERAN
- Coexistence with NR
5G Security Assurance Specification[s] (SCAS) aims to develop SCAS for 5G network products to identify threats to critical assets of the 5G system architecture, along with security/vulnerabilities related functional requirements and testcases.
5G LAN support focuses on developing initial requirements for the 5G system to support LAN-type services on 5G. The results of this WI will contribute to the update of 3GPP TS 22.261, addressing various aspects, such as 5GLAN creation and management, 5G private virtual network, 5GLAN service authorization, mobility and service continuity for 5G LAN-type service, etc.
Integration of Satellite Access in 5G focuses on developing initial requirements for the 5G system to enable integration of satellite access when considering the different use cases mentioned in 3GPP TR 22.822. The following use cases are to be addressed, per 3GPP TR 22.822:
- Roaming between terrestrial and satellite networks
- Broadcast and multicast with a satellite overlay
- IoT with a satellite network
- Temporary use of a satellite component
- Optimal routing or steering over a satellite
- Satellite trans-border service continuity
- Global satellite overlay
- Indirect connection through a 5G satellite access network
- 5G fixed backhaul between NR and the 5G Core
- 5G moving platform backhaul
- 5G to premises
- Offshore wind farms
5G positioning services focus on developing initial requirements for the 5G system to support positioning services. There are various use cases, such as regulatory requirements for emergency services, as well as new services, that might require positioning support. The work carried out within this WI will be used to update requirements related to positioning in 3GPP TS 22.261 — apart from using the results and potential requirements identified in 3GPP TR 22.872.
NR intra band carrier aggregation — To achieve higher levels of carrier aggregation in NR with limited operating bands, it is important for the 5G system to support intra-band carrier aggregation (CA). This WI focuses on specifying the CA configurations and their specific RF requirements for both contiguous and non-contiguous cases, along with analyzing that the combinations introduced are not affected by RF limitations. Related conformance testcases also need to be investigated under the purview of this WI.
Dual Connectivity (EN-DC) aims to help define all the new 2 DL and 2 UL EN-DC configurations with different bands (i.e., 1 LTE band and 1 NR band). For a CA combination to be introduced in EN-DC configuration, it would be mandatory that the involved LTE or NR bands, along with their intra-band CA combinations, also be included in the specification.
Enhancements on MIMO for NR are dedicated to the improvement of MIMO performance in 5G NR. A lot of new items have been introduced in Rel-15, building on the Rel-14 enhancements in LTE, along with the change in the RF antenna array and introduction of Type-II channel state information (CSI). These changes help achieve better MIMO performance. The following areas have been identified for further improvement:
- MU-MIMO enhancements: by specifying the overhead reduction based on the Type II CSI feedback, considering the tradeoff between performance and overhead. Also, possible extension of Type II CSI feedback to rank > 2
- Enhancements on multi-TRP (Tx/Rx Point)/panel transmission, including improved reliability and robustness with both ideal and non-ideal backhaul
- Enhancements on multi-beam operation, primarily targeting frequency range 2 (FR2) operation
- CSI-RS and DMRS (both downlink and uplink) enhancement for peak-to-average power ratio (PAPR) reduction for one or multiple layers
- full power transmission in case of uplink transmission with multiple power amplifiers (assume no change on UE power class)
NR mobility enhancements — As Rel-15 5G-NR’s introduction was moved up and carried out under very tight timeline, current mobility aspects in NR simply were adopted from LTE. The handover mechanism similar to LTE is not ideal for 5G-NR FR2 with beamforming, as users might face higher interruption due to beam sweeping delay. Also, the UE might experience high signal degradation very quickly upon any slight change in the user’s direction due to the nature of beamforming.
The challenges of operating in FR2 to the mobility aspects and KPIs are significant, and novel solutions are required to deliver the 0 ms interruption promised by 5G, as well as reduce the frequency of such interruptions. The following improvements are being undertaken:
- Solution(s) to reduce interruption time during HO/SCG change by:
- Handover/SCG change with simultaneous connectivity with source cell and target cell
- RACH-less handover
- Solution(s) to improve the HO reliability and robustness by:
- Conditional handover
- Fast handover failure recovery
5G Energy Efficiency (EE) continues to be a focus of 3GPP, and this WI focuses on building the concepts, use cases, and requirements to achieving energy efficiency in the 5G system. Different parameters and requirements would be introduced to assess EE performance and compare it with other RATs.
Release 16 Study Items
This chapter details the selected study items (SI) for 5G, which normally result in new technical reports (TRs) or the extension of existing TRs.
Study on NR beyond 52.6 GHz — With NR already covering spectrum up to 52.6 GHz, this SI focuses on identifying the target spectrum ranges between 52.6 GHz and 100 GHz that could be utilized for NR transmissions. As the spectrum at this range is susceptible to higher phase noise, extreme propagation loss due to high atmospheric absorption, lower power amplifier efficiency, and strong power spectral density regulatory requirements, the study needs to come up with new requirements to operate in such conditions. Also, the SI will identify use cases that could utilize this spectrum efficiently.
Study on Self-Organizing Networks (SON) for 5G — Requirements that need to be fulfilled by the 5G NR network vary, from providing support for eMBB to URLLC and mMTC. All of these have fundamentally different QoS requirements and the 5G network must be tunable to provide optimal service for each class. This SI focuses on utilizing and enhancing SON capabilities to deal with the 5G networks’ complexities. 5G SONs would be built on the latest advancements in artificial intelligence (AI) and machine learning (ML), allowing them to predict need and act accordingly, driving optimal network efficiency.
Study on NR V2X focuses on NR’s role in the deployment of advanced V2X services as part of the 3GPP V2X phase 3. These advanced V2X services represent those developed beyond the scope of LTE Rel-15 V2X, and would require an enhanced NR system and new NR side-link to meet the stringent requirements. Among those requirements is the need to have a flexible design to support services with low-latency/high-reliability requirements, as well as support for higher capacity and better coverage.
Study on Cellular IoT support and evolution for the 5G System — The cellular IoT landscape has experienced many changes since Rel-13 and Rel-14 of LTE, most notably the introduction of eMTC and NB-IoT. These enhancements to cellular IoT in LTE brought with them additional changes related to power saving, overload control, and high-latency communication on the core network (CN) side. It has been agreed that 5G, within its framework, would be able to support the requirements for cellular IoT. To achieve this, the SI focuses on identifying solutions for the 5G CN (5GC) that will enable it to provide at least the same basic set of features required to make cellular IoT possible.
Feasibility Study on 6 GHz for LTE and NR in Licensed and Unlicensed Operations is related to initiatives undertaken by various bodies, such as CEPT and FCC, to use the 6 GHz frequency range for deploying wireless access systems. This SI aims to foster a common understanding regarding usage and requirements for this band across different regions. The frequency range of interest is 5.925-7.125 GHz, which could be utilized for existing technologies — such as LTE/LAA/eLAA — as well as new-generation NR and NR-unlicensed (NR-U) technologies (Note: for unlicensed access, LTE LAA and LTE eLAA can utilize the frequency range from 5.925-6.425 GHz).
Study on NR-based Access to Unlicensed Spectrum — As seen in the last releases of LTE, especially Rel-13 and Rel-14, access to unlicensed spectrum in order to get higher bandwidth at a low cost to operators is a novel proposition. Continuing this trend, for NR to glean the same benefits from unlicensed spectrum, this study explores possible deployment methods, along with the requirements for a NR-based unlicensed access. The bands of interest would be sub-7 GHz unlicensed bands, such as 5 GHz and 6 GHz.
This SI also takes into consideration dual-connectivity scenarios where NR-LAA is anchored to a legacy LTE carrier, along with CA opportunities within NR. The standalone deployment of NR in unlicensed spectrum also is discussed. Finally, the study should deliver a unified solution that meets various countries’ regulatory requirements for accessing the unlicensed spectrum via methods such as listen-before-talk (LBT), all while fitting within NR’s framework.
Study on Non-orthogonal Multiple Access for NR — The concept of using non-orthogonal multiple-access (NOMA) gained momentum during Rel-14, as it was part of a SI then. The benefit of having NOMA, especially in terms of UL, is that it enhances the sum throughput, along with system capacity. To deal with the interference caused by the non-orthogonal transmissions using overlapping resources, the transmitter would need to use schemes such as spreading and interleaving. This SI is further evaluating the NOMA schemes, focusing on uplink, and providing recommendation on them.
As can be seen, a lot of items currently being discussed by 3GPP for Release 16 that would enhance the existing LTE and 5G RATs towards achieving the goals of IMT-2020. 3GPP Release-16, or “5G phase 2,” is slated for completion by December 2019, and should be fully compliant with IMT-2020 requirements. It will be interesting to see the outcome of these WIs and how they influence their respective RATs.
We can see that some of the items target improvements to the current 5G system (like the use of even higher frequencies, SON, and IoT improvements), while others expand the 5G system scope (like NOMA, unlicensed spectrum, V2X). Let us also not forget that the enhanced LTE (i.e., this from 3GPP Rel-15 and 16) also is a part of SRIT (set of radio interface technologies), which will be submitted by 3GPP to ITU-R as a 5G technology , and thus should be discussed together with NR when speaking about current and future releases in 3GPP.
About The Author
Marcin Dryjanski is the co-founder, principal consultant, and a board member at Grandmetric, where he provides consulting services and training courses on LTE and 5G-related topics, as well as leads company’s wireless research on Grandmetric’s IoT platform. Marcin has held Senior IEEE Membership since 2018 and has served as a R&D Engineer, Lead Researcher, R&D Consultant, Technical Trainer and Technical Leader. Marcin has co-authored several research papers targeting LTE-Advanced Pro and 5G radio interface design, and is co-author of a book From LTE to LTE-Advanced Pro and 5G. Marcin was a Work Package leader in 5GNOW, a EU-funded research project aiming at radio interface design for 5G. He earned a Ph.D., with honors, from Poznan University of Technology in 2019.
 M. Rahnema, M. Dryjanski, “From LTE to LTE-Advanced Pro and 5G”, Artech House, 2017.