3GPP releases 16 & 17 overview – the 5G NR evolution

According to the latest Ericsson Mobility Report, global traffic levels hit 38 exabytes per month at the end of 2019, with a projected fourfold increase to 160 exabytes per month expected by 2025 [1]. Fortunately, the 5G system is designed to handle this massive increase in data traffic in a way that ensures superior performance with minimal impact on the net costs for consumers.

The evolution of 5G New Radio (NR) has progressed swiftly since the 3GPP standardized the first NR release (release 15) in mid-2018. Not only is release 16 nearly finalized but the scope of release 17 has also recently been approved. Making wise decisions in the months and years ahead will require that mobile network operators and other industry stakeholders have a solid understanding of both releases.

NR development started in release 15 [2] [3] with the ambition to fulfill the 5G requirements set by the ITU (International Telecommunication Union) in IMT-2020 (International Mobile Telecommunications- 2020). The overall design consists of several key components. The extension to much higher carrier frequencies is an important one due to the continuing demand for more traffic and higher consumer data rates and the associated need for more spectrum and wider transmission bandwidths. The ultra-lean design of NR enhances network energy performance and reduces interference, while interworking and LTE coexistence will make it possible to utilize existing cellular networks. The forward compatibility of NR design will ensure that it is prepared for future evolution. Low latency is also critical to improve performance and enable new use cases. Extensive usage of beamforming and a massive number of antenna elements for data transmission and for control-plane procedures are also notable components of NR design.

Figure 1 shows the time plan for the evolution of NR over the next few years. Release 16, the first step in the NR evolution, contains several significant extensions and enhancements. Some of these are extensions/improvements to existing features, while others are entirely new features that address new deployment scenarios and/or new verticals.

Figure 1: NR evolution time plan

5G NR release 16 – enhancements to existing features

The most notable enhancements to existing features in release 16 are in the areas of multiple-input, multiple-output (MIMO) and beamforming enhancements, dynamic spectrum sharing (DSS), dual connectivity (DC) and carrier aggregation (CA), and user equipment (UE) power saving.

Multiple-input, multiple-output and beamforming enhancements

Release 16 introduces enhanced beam handling and channel-state information (CSI) feedback, as well as support for transmission to a single UE from multiple transmission points (multi-TRP) and full-power transmission from multiple UE antennas in the uplink (UL). These enhancements increase throughput, reduce overhead, and/or provide additional robustness [4]. Additional mobility enhancements enable reduced handover delays, in particular when applied to beam-management mechanisms used for deployments in millimeter (mm) wave bands [5].

Dynamic spectrum sharing

DSS provides a cost-effective and efficient solution for enabling a smooth transition from 4G to 5G by allowing LTE and NR to share the same carrier. In release 16, the number of rate-matching patterns available in NR has been increased to allow spectrum sharing when CA is used for LTE.

Dual connectivity and carrier aggregation

Release 16 reduces latency for setup and activation of CA/DC, thereby leading to improved system capacity and the ability to achieve higher data rates. Unlike release 15, where measurement configuration and reporting does not take place until the UE enters the fully connected state, in release 16 the connection can be resumed after periods of inactivity without the need for extensive signaling for configuration and reporting [6]. Additionally, release 16 introduces aperiodic triggering of CSI reference signal transmissions in case of the aggregation of carriers with different numerology.

User equipment power saving

To reduce UE power consumption, release 16 includes a wake-up signal along with enhancements to control signaling and scheduling mechanisms [7].

5G NR release 16 – new verticals and deployment scenarios

The most notable new verticals and deployment scenarios addressed in release 16 are in the areas of:

• Integrated access and backhaul (IAB)
• NR in unlicensed spectrum
• Features related to Industrial Internet of Things (IIoT) and ultra-reliable low latency communication (URLLC)
• Intelligent transportation systems (ITS) and vehicle-to-anything (V2X) communications
• Positioning.

Integrated access and backhauling

IAB provides an alternative to fiber backhaul by extending NR to support wireless backhaul [8]. As a result, it is possible to use NR for a wireless link from central locations to distributed cell sites and between cell sites. This can simplify the deployment of small cells, for example, and be useful for temporary deployments for special events or emergency situations. IAB can be used in any frequency band in which NR can operate. However, it is anticipated that mm-wave spectrum will be the most relevant spectrum for the backhaul link. Furthermore, the access link may either operate in the same frequency band as the backhaul link (known as inband operation) or by using a separate frequency band (out-of-band operation).

Architecture-wise, IAB is based on the CU/DU split introduced in release 15. The CU/DU split implies that the base station is split into two parts – a centralized unit (CU) and one or more distributed units (DUs) – where the CU and DU(s) may be physically separated depending on the deployment. The CU includes the RRC (radio resource control) and PDC (packet data convergence) protocols, while the DU includes the RLC (radio link control) and MAC (multiple access control) protocols along with the physical layer. The CU and DU are connected through the standardized F1 interface.

Figure 2 illustrates the basic structure of a network utilizing IAB. The IAB node creates cells of its own and appears as a normal base station to UEs connecting to it. Connecting the IAB node to the network uses the same initial-access mechanism as a terminal. Once connected, the IAB node receives the necessary configuration from the donor node. Additional IAB nodes can connect to the network through the cells created by an IAB node, thereby enabling multi-hop wireless backhauling. The lower part of the figure highlights that an IAB node includes a conventional DU part that creates cells to which UEs and other IAB nodes can connect. The IAB node also includes a mobile-termination (MT) part providing connectivity for the IAB node to (the DU of) the donor node.

Figure 2: High-level architecture of IAB

New Radio in unlicensed spectrum

Spectrum availability is essential to wireless communication, and the large amount of spectrum available in unlicensed bands is attractive for increasing data rates and capacity for 3GPP systems. To exploit this spectrum resource, release 16 enables NR operation in unlicensed spectrum, targeting the 5GHz and 6GHz unlicensed bands. It supports both standalone operation, where no licensed spectrum is necessary, and licensed-assisted operation, where a carrier in licensed spectrum aids the connection setup. This greatly adds to deployment flexibility compared with LTE, where only licensed-assisted operation is supported.

Operation in unlicensed spectrum is dependent on several key principles including ultra-lean transmission and use of the flexible NR frame structure. Both of these were included in release 15. Channel access mechanisms based on listen-before-talk (LBT) are probably the most obvious area of enhancement in release 16. NR largely reuses the same LBT mechanism as defined for Wi-Fi and LTE in unlicensed spectrum. Interestingly, it was demonstrated during standardization that replacing one Wi-Fi network with an NR network can lead to improved performance for the remaining Wi-Fi networks [9] as well as for the NR network itself.

Industrial IoT and ultra-reliable low-latency communication

The IIOT is a major vertical focus area for NR release 16. To widen the set of potential IIoT use cases and support increased demand for new use cases such as factory automation, electrical power distribution and the transport industry, release 16 includes latency and reliability enhancements that build on the already very low air-interface latency and high reliability [10] provided by release 15. Support for time-sensitive networking (TSN), where very accurate time synchronization is essential, is also introduced. Figure 3 illustrates TSN integration in 5G NR.

Figure 3: Overview of the TSN integration

Although many of the URLLC-related improvements are small in themselves, taken together they significantly enhance NR in the area of URLLC [11].

The inter-UE downlink (DL) preemption that is already supported in release 15 is extended in release 16 to include the UL, such that a UE’s previously scheduled lower-priority UL transmission can be preempted (that is, cancelled) by another UE’s higher-priority UL transmission. Release 16 also supports standardized handling of intra-EU UL resource conflicts.

To reduce latency, release 16 supports more frequent control-channel monitoring. Furthermore, for both UL configured grant and DL semi-persistent scheduling, multiple configurations can be active imultaneously to support multiple services. These enhancements are especially useful in combination with TSN traffic, where the traffic pattern is known to the base station.

Intelligent transportation systems and vehicle-to-anything communications

ITS, which provide a range of transport and traffic-management services, are another major vertical focus area in release 16. Among other benefits, ITS solutions improve traffic safety as well as reducing traffic congestion, fuel consumption and environmental impacts. To facilitate ITS, communication is required not only between vehicles and the fixed infrastructure but also between vehicles. Currently, 25 use cases for advanced V2X communications have been defined, including vehicle platooning and cooperative communication using extended sensors [12].

In release 15, communication with fixed infrastructure is provided by the access-link interface between the base station and the UE. Release 16 adds the option of the NR sidelink (PC5), which can operate in in-coverage, out-of-coverage and partial-coverage scenarios, utilizing all NR frequency bands. It supports unicast, groupcast and broadcast communication, and hybrid automatic repeat request (hybrid-ARQ) retransmissions can be used for scenarios that require more robust communication. Groups can be either configured or formed, and the group members communicate using groupcast transmissions. A truck platoon, for example, could be configured using dedicated hybrid-ARQ signaling between the receivers and transmitter, or formed in a dynamic manner based on the distance between the transmitter and receiver(s).

Positioning

For many years, UE positioning has been accomplished with Global Navigation Satellite Systems assisted by cellular networks. This approach provides accurate positioning but is typically limited to outdoor areas with satellite visibility. There is currently a range of applications that requires accurate positioning not only outdoors but also indoors. Architecture-wise, NR positioning is based on the use of a location server, similar to LTE. The location server collects and distributes information related to positioning (UE capabilities, assistance data, measurements, position estimates and so on) to the other entities involved in the positioning procedures. A range of positioning methods, both DL-based and UL-based, are used separately or in combination to meet the accuracy requirements for different scenarios.

DL-based positioning is supported by providing a new reference signal called the positioning reference signal (PRS). Compared with LTE, the PRS has a more regular structure and a much larger bandwidth, which allows for a more precise correlation and time of arrival (ToA) estimation. The UE can then report the ToA difference for PRSs received from multiple distinct base stations, and the location server can use the reports to determine the position of the UE.

UL-based positioning is based on release 15 sounding reference signals (SRSs) with release 16 extensions. Based on the received SRSs, the base stations can measure and report (to the location server) the arrival time, the received power and the angle of arrival from which the position of the UE can be estimated. The time difference between DL reception and UL transmission can also be reported and used in round-trip time (RTT) based positioning schemes, where the distance between a base station and a UE can be determined based on the estimated RTT. By combining several such RTT measurements, involving different base stations, the position can be determined.