3GPP Release 16 brings significant enhancements and new features that will enable the 5G standard to expand beyond traditional communications.
5G New Radio (NR) is a fast-evolving standard. It emerged in late 2016 when work started on 3GPP Release 15 (Rel-15), which was completed in mid-2018 and is now stable and available to the market. Work on 3GPP Release 16 (Rel-16) started subsequently with physical layer aspects completed in December 2019, right before the pandemic, and the final version was issued in July 2020.
Although the second release of a new generation typically only brings enhancements to the initial one, Rel-16 is much different. This release not only introduces capacity and operational enhancements, but also expands 5G’s reach into new verticals.
Among the enhancements and new features that increase network capacity and operational efficiency, changes to multiple-input/multiple output (MIMO) are noteworthy. While Rel-15 introduced a MIMO framework that was significantly better than Long Term Evolution (LTE), several features did not make it into the release. Rel-16 addresses that issue by providing new types of channel state information (CSI) reports for multi-user MIMO (MU-MIMO), helping increase capacity by allowing more user equipment (UE) on the network.
Rel-16 also explicitly supports multiple transmission points (multi-TRP)/panel transmission by introducing the necessary signaling mechanism. It includes downlink (DL) and uplink (UL) control signaling for non-coherent joint transmissions and enhancements for multi-beam operations to reduce latency and signaling overhead.
There are also MIMO enhancements for power. Full transmit power UL enables certain UEs —such as partially-coherent and non-coherent UEs — to transmit more power in the UL by using all the power amplifiers at their disposal. These UEs only require a software upgrade to have this capability. Rel-16 also introduces a new reference signal (RS) design that lowers peak-to-average power ratio (PAPR) for better cell edge performance in power-limited scenarios.
In addition, you probably have heard of NR unlicensed (NR-U), another feature in Rel-16 that can increase network capacity by enabling NR to operate in unlicensed spectrum. This feature requires changes to the physical layer channels because of regulatory constraints. Rel-16 includes four implementation scenarios:
Rel-16 also introduces new reference signals to address specific interference scenarios. Cross link interference (CLI) enables the network to assess and mitigate DL/UL cross-interference between cells and UEs. The network can measure and understand DL/UL interference between surrounding cells and coordinate network exchanges to limit interference levels and improve overall system performance.
With remote interference management (RIM), the new signals help overcome ducting, an effect caused by changes in the refractive index of the atmosphere. Signals trapped in a duct propagate further than the normal range and can interfere with a cell further away. RIM helps the network better understand the environment and mitigate these issues.
In addition to increasing capacity and minimizing interference, power saving is a key area of focus of Rel-16. The release introduces a range of power-saving techniques for UEs and the network. You can use these techniques individually or together to enable UEs to save power. Physical downlink control channel (PDCCH) power saving is an important technique that refers to changes in the control signaling the network uses to indicate when a UE has to become active or can go to inactive or sleep mode.
Figure 3 PDCCH power saving enables a network to tell when a UE is active and inactive.
There are other mechanisms implemented in the release for the network and the UEs to agree on resource scheduling constraints that you can exploit to save power. With time domain resource allocation, for example, the network tells the UE that the data channel assignment will not start immediately after the DL grants the channel over PDCCH. This information enables the UE to take more time to decode the control channel and prepare the data transmission. It does not have to prepare for the worst-case scenario in which it must perform decoding of the control channel very fast, because the data channel could occur right after the control channel, saving power.
Figure 4 Time domain resource allocation enables the UE to decode the control channel and prepare for the data transmission slower, saving power.
Similarly, with MIMO layer adaption the UE does not have to prepare for the worst-case scenario that requires the use of all its antennas and RF chains. For example, a UE with four antennas does not need to prepare and power all four antennas and RF chains to be in use at any given time, if it knows that it will only be assigned two-layer transmissions. The UE can turn off unused receivers for longer periods of time to save power.
Figure 5 MIMO layer adaption enables UEs to turn off transmitters to save power.
While the enhancements and features reviewed so far increase capacity, mitigate interference, and foster UE efficiency, Rel-16 also provides features for vertical expansion. First, Rel-16 brings significant enhancements for ultra-reliable, low-latency communications (URLLC). Rel-15 only provided basic support for URLLC based on known use cases at the time. New use cases for factory automation and transportation have emerged, requiring lower latency and higher reliability than possible with Rel-15.
The release introduces new features and improvements across the specification to enable these new use cases. A major enhancement from the physical layer standpoint is prioritization of enhanced mobile broadband (eMBB) and URLLC traffic. Rel-16 enables multiplexing priorities for different types of traffic – intra-UE and inter-UE prioritization. Intra-UE prioritization, which refers to the multiplexing of eMBB and URLLC traffic inside a UE, stops a UE from transmitting low priority traffic in favor of a higher priority transmission within the same UE.
In contrast, inter-UE prioritization enables multiplexing eMBB and URLLC traffic between different UEs. The network can tell a UE scheduled to transmit low priority traffic to drop the scheduled transmission, freeing up the channel for another UE to send higher-priority traffic without interference. A pre-emption mechanism exists for the network to cancel delivered UL grants to other UEs because higher-priority traffic with low latency may come after scheduling eMBB traffic.
Figure 6 Inter-UE prioritization enables a UE with low priority traffic to stop transmitting so that another UE can transmit high-priority traffic.
Figure 7 Intra-UE prioritization enables a UE transmitting low priority traffic to switch to transmitting high-priority traffic.
Vehicle-to-everything (V2X) is another critical new feature for vertical expansion in Rel-16. Supported in Release 14 (Rel-14) and enhanced in Rel-15, V2X is now supported by the NR standard in Rel-16, with the goal of complementing LTE V2X for advanced use cases such as platooning, remote driving, and sensor sharing.
Enabling V2X for NR requires using the sidelink air interface to enable devices to communicate with each other without involving the network; cross-radio access technology (RAT) control, so that LTE can control NR and vice versa; quality of service (QoS) management; and compatibility and coexistence between NR and LTE V2X. In a nutshell, the release aims to facilitate LTE communication with NR devices for basic use cases and enable advanced use cases on NR V2X.
To achieve this goal, Rel-16 brings two new communication mechanisms not supported by LTE sidelink. These mechanisms provide the control necessary for implementing advanced V2X applications, which require transmissions to reach their intended destination. Unicast communications enable a device to communicate with another device and groupcast communications enable that device to communicate with a known set of devices. LTE only supported broadcast communications, which enable a device to communicate with other devices, but there was no control on which devices listened to these transmissions.
Figure 8 NR V2X enables two new ways for devices to communicate in addition to what LTE supports.
MIMO, NR-U, CLI, RIM, URLLC, and V2X are key new features brought by the second release of the 5G standard, making Rel-16 unlike any other second release for a cellular specification. While the release includes many minor improvements, it also brings significant enhancements and new features that will enable the 5G standard to expand beyond traditional communications and give birth to new applications. For a deep dive on 3GPP 5G releases, including a glimpse into the future, you can view the on demand 5G NR Standard Evolution 3GPP RAN1 Update presentation by Javier Campos, Keysight’s 3GPP RAN1 delegate.
This article was originally published on EDN.
Jessy Cavazos is part of Keysight’s Industry Solutions Marketing team.