Photo of a 3GPP meeting room with people sitting at tables and working on computers, overlaid with gear icons and wireless network terminology: RAN, 5G, V2X, Core, MCdata."

3GPP Quarterly Meetings Focus on 5G NR Sidelink Interfaces, Stage 2 Architecture Work

This blog is a repost from MissionCritical Communications, originally published on April 26, 2021. The original article can be accessed here.

This blog post is part of the "Tech Talk" series focused on the First Responder Network Authority’s (FirstNet Authority) standards development activities to support public safety. This post recaps discussions linked to public safety and other related topics from the 3GPP Plenary meetings that were conducted online in the first quarter of 2021. The FirstNet Authority represented public safety interests at the plenary meetings.

The first quarterly Third Generation Partnership Project (3GPP) Plenary e-meetings of 2021 recently concluded, with a focus on the upcoming June deadline for stage 2 (architecture) work. There were major discussions on the use of the 5G New Radio (NR) sidelink interface to support both user equipment (UE) to network (U2N) relay and UE to UE (U2U) relay.

The First Responder Network Authority (FirstNet Authority), AT&T, multiple vendors and at least 10 public-safety agencies from other countries strongly supported including both relay proposals in 3GPP Release 17 (R17). Because of this push, U2N will be part of R17, but U2U will likely wait to be included until R18. This means that 3GPP R17 will support the use of a UE to relay between the network and another UE that is out of network coverage, thus extending the on-network coverage. 3GPP R18 is targeted to support U2U relay to allow a UE to relay between two other UEs, thus extending off-network coverage.

Election of chairs and vice chairs for the three 3GPP Technical Specification Groups (TSGs) took place. Chairs and vice chairs are allowed to serve for no more than two consecutive two year terms. TSG Radio Access Network (RAN) will be chaired for the next two years by a Qualcomm representative; TSG Services and Systems Aspects (SA) will continue to be chaired for the next two years by a Huawei representative who was reelected; and TSG Core Network and Terminals (CT) will continue to be chaired for the next two years by a representative from Orange of France who was also reelected. It was decided that, given the current conditions, 3GPP will continue to use e-meetings at a minimum through the third quarter of 2021. A final decision about whether e-meetings or face-to-face meetings will occur in the fourth quarter will be made in June. The use of e-meetings has already led to significant delays in the R17 schedule, but progress is being made.

The following TSG reports provide details on each of the plenary meetings with a focus on public-safety activities. As in past plenary meetings, representatives from nearly all major mobile equipment vendors, chip manufacturers, software vendors and network operators from about 35 countries, as well as the FirstNet Authority and other foreign government agencies representing public safety interests, participated.

RAN Plenary

There were more than 900 registrants for the TSG RAN Plenary meeting. RAN is responsible for defining the functions, requirements, and interfaces of the 3GPP radio network.

Overall good progress was reported on 5G over non-terrestrial networks (i.e., over satellite), UE power savings, sidelink enhancements, 5G multicast and broadcast services (5MBS), dynamic spectrum sharing enhancements supporting the operation of 4G LTE and 5G NR in the same spectrum band addressing interference from LTE signals to 5G mobiles, and 5G NR positioning enhancements to improve location accuracy.

The RAN plenary approved a new work item to begin drafting technical specifications to support both layer-2 and layer-3 based solutions for U2N relay functionalities. This work item includes the U2N adaptation layer design and control plane procedures, U2N relay discovery, and re-selection. The work item includes objectives specific to layer 2 relaying such as specifying mechanisms for end-to-end quality of service (QoS) management and service continuity limited to intra-5G base station cases. It was also decided to re-use the design developed for LTE as the baseline architecture.

An existing work item on non-terrestrial networks was revised to add low Earth orbit (LEO) and geostationary orbit scenarios along with all non-geostationary orbit scenarios with circular orbit at altitudes greater than or equal to 600 kilometers. The work item also includes support for traditional handheld devices in Frequency Range 1 (FR1), which includes sub-6 GHz frequency bands.

Finally, the current work item on lower cost reduced capability UEs, such as wearables, industrial wireless sensors, and video surveillance devices, was revised to address the maximum bandwidth of 20 MHz in FR1 during and after initial access. For frequency bands where a legacy 5G NR UE is required to be equipped with a minimum of two receive antenna ports, the required minimum number of receive antennas supported by a reduced capability UE is one.

SA Plenary

There were more than 460 registrants in the TSG SA Plenary meeting, which is responsible for the overall architecture and service capabilities of 3GPP based systems. The meeting continued its primary focus of progressing R17 architecture specifications and R18 requirements.

The SA2 working group declared that all technical reports for R17 have reached at least 95% completion, and related technical specifications for these technical reports are all in progress. Technical studies for 5MBS and 5G proximity services (ProSe) were completed in the SA2 working group and were approved by the SA Plenary during this meeting. The 5MBS feature will provide the ability for multiple UEs to receive the same transmission, thus saving bandwidth.

The SA2 working group reported that technical specifications work has already started for the 5MBS and 5G ProSe features and has reached 20% to 30% completion. A great deal of discussion regarding the scope of the relay function in R17 took place during this plenary meeting. Taking into consideration the workload for RAN working groups to deliver R17 and the dependency of relay functions on some RAN working groups, it was agreed to include the U2N relay in R17 and to likely defer the U2U relay to R18. In addition to direct UE-to-UE communication, 5G ProSe will ultimately support both U2N and U2U relays.

In the SA1 working group, studies regarding off-network operation for railways and the sharing of mission-critical administration configuration between interconnected MC systems continued. The off-network operation for railways is applicable to public-safety use of 5G ProSe. The ability to share mission-critical administration configuration information between mission-critical systems can greatly reduce overhead and support mutual aid scenarios. Requirements were also added for the mission-critical gateway UE function to allow multiple gateways to operate in the same area and for mission-critical UEs to use more than one gateway at the same time.

In the SA6 working group, the study on architecture issues and solutions for the mission-critical gateway UE continued, including the new requirements from SA1. Also, in SA6, good progress is being made on the normative work for mission-critical services over 5G. It is expected that SA6 will complete the first phase of mission-critical services over 5G in R17 with a scope of on-network, unicast operation. Work continues on a study of the off-network and multicast aspects while 5G mission-critical enablers, such as sidelink and the 5MBS feature are still under development in other working groups. The plan is to complete work on the subsequent phases of MC services over 5G in R18.

Normative work is continuing in the SA3 working group on enhancements to improve security for mission-critical media content storage, as well as the 5G ProSe and 5MBS features. This work maintains the mission-critical security architecture alignment with architecture features being defined in SA6. Progress is being made studying security issues and potential solutions for the security aspects of the enhancements to 5G ProSe. The security solutions will be required when 5G ProSe normative work completes in other groups. These solutions will address security issues that those groups have highlighted, specifically issues around the layer 2 versus layer 3 relay architecture debate. Other ongoing normative work in SA3 is focusing on various 5G system security enhancements for R17.

In related work, the Alliance for Telecommunications Industry Solutions (ATIS) Joint LMR LTE (JLMRLTE) working group is developing an architecture study on interworking between 3GPP mission-critical services and legacy LMR services such as Project 25 (P25) systems. The work in the JLMRLTE working group is organized in phases. The third phase has recently completed and has been delivered to the Telecommunications Industry Association (TIA). On the basis of these inputs, TIA is developing the necessary standards enhancements in areas such as the suite of wireline interface specifications that will define the interworking of P25 systems with 3GPP 4G LTE systems via an interworking function (IWF).

TIA has also recently completed their work on the phase 3 inputs and has published two new addenda to support interworking:

  • ‟BACA-B-3 - Inter-RF Subsystem Interface Messages and Procedures for Voice Services, Mobility Management, and RFSS Capability Polling Services – Addendum 3 – Interworking with an IWF.ˮ and
  • ‟BACD-B-3 - Inter-RF Subsystem Interface (ISSI) - Messages and Procedures for Supplementary Data – Addendum 3 – Interworking with an IWF.ˮ

The features supported by these specifications include the most common P25 trunking features and a subset of P25 conventional features. Work is continuing in the JLMRLTE working group with the next phase focused on completing interworking with LMR conventional systems including systems based on TIA-603 (analog FM).

CT Plenary

There were 302 registrants for the TSG CT Plenary meeting, which covers the protocol details that follow the requirements and architectural work performed in the SA TSG.

At this meeting, two new technical specifications to support the protocol work on 5G ProSe began in the CT1 working group. Work will begin on the creation of those technical specifications in the next few months, as the stage 2 architectural work becomes sufficiently stable.

The majority of work on mission-critical features in TSG CT over the past quarter has focused on correcting errors found in the technical specifications. These errors have been identified as a result of both implementation efforts by 3GPP companies and European Telecommunication Standards Institute (ETSI) Plugtest events. Correcting errors is a high-priority effort. Of the 24 issues found with mission-critical standards during past ETSI Plugtest events to test mission-critical implementations against each other in a lab environment, only two issues now remain unresolved. The FirstNet Authority has led offline efforts to coordinate experts from multiple companies to cooperatively resolve these issues. This effort has resulted in solutions for several issues being approved at this Plenary meeting.

There were also a number of smaller features added to mission-critical services, such as the interaction of private call forwarding with functional aliases and adding detection of entering/exiting a geographic area relative to emergency alerts and group affiliation. The majority of R17 protocol work is awaiting the completion of the associated stage 2 architectural work that is scheduled for June. As a result, the period from July through March, which is the target date for R17, will see significant protocol work in CT1 for mission-critical services.

Further information on the 3GPP’s work and organization can be found here.          

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