Introduction

4G-based Mission Critical (MC) services standards (a.k.a. PS- LTE) brought in a major shift in the critical communications industry landscape, bringing much-needed broadband capabilities to public safety services, leading to successful commercial deployments in several key markets. 3GPP 5G standardization, currently in Release 19 has progressed significantly since its beginnings in Release 15, adding a number of key 5G capabilities. As compared to 4G, 5G brings in 10 times higher bandwidth, 1/10th of the latency and enhanced by 100 times the reliability, availability and capacity. These advanced communication capabilities will turn out to be a game changer for public safety, railways and other critical communication sectors. Public safety agencies across the world are moving towards deployment of 3GPP based MC services. This is evident from the renewed 10-year strategic investment from the FirstNet Authority to transform and upgrade their existing networks to deliver full 5G capabilities [1].

Recently, Samsung Electronics announced that the company is teaming up with IBM as the mission-critical (MCX) solution provider to the UK’s Home Office, for a User Services deployment as part of the Emergency Services Network (ESN)[2]. Samsung’s MCPTX solution will enable intuitive multimedia sharing in real-time, allowing first responders to assess emergency situations more accurately as well as act with enhanced responsiveness. This milestone underscores Samsung’s commitment to advancing mission-critical networks globally, supporting government agencies to keep communities safe.

Key 5G capabilities transforming MC Services

3GPP introduced 5G capabilities to the MC services framework for both on-network unicast/multicast communication and off-network communication. The MC services layer is adapted to align with the underlying 5G system capabilities to support MC services over 5G. Necessary changes that are required at the MC services layer to utilize the 5G system capabilities are specified in 3GPP TS 23.289[3] for all the MC services and the sections below explain the MC services layer adaptation for each of the applicable 5G capabilities.

Summary of key 5G capabilities leveraged by MC services

●     Ultra-reliable low-latency communication (URLLC)

URLLC enables MC services to provide a seamless communication and coordination between first responders, control rooms and other mission critical agencies. 5G’s high bandwidth (1Gb/s) and data rate (20Gb/s) offers a significant leap for MC services when it comes to high definition voice, real-time video streaming/sharing, and large data transfer, thus enhancing situational awareness through which emergency teams can make well informed decisions when responding to emergency situations. Since this is part of the underlying 5G infrastructure, the benefits are implicitly available for MC services.

●     5G Quality of Service (QoS) Model

URLLC enables MC services to provide a seamless communication and coordination between first responders, control rooms and other mission critical agencies. 5G’s high bandwidth (1Gb/s) and data rate (20Gb/s) offers a significant leap for MC services when it comes to high definition voice, real-time video streaming/sharing, and large data transfer, thus enhancing situational awareness through which emergency teams can make well informed decisions when responding to emergency situations. Since this is part of the underlying 5G infrastructure, the benefits are implicitly available for MC services.

The 5G QoS model is designed with the new concept of QoS flows, where a flow is the finest granularity of QoS differentiation in the Protocol-Data-Unit (PDU) session. The 5G QoS model supports both QoS Flows that require guaranteed flow bit rate (GBR QoS Flows) and QoS Flows that do not require guaranteed flow bit rate (Non-GBR QoS Flows). With the 5G QoS model, the mission critical system can apply different QoS parameters for emergency and non-emergency communications. QoS Flow for an emergency communication is established with higher priority than normal communication, thus ensuring ultra-reliable communication. Standardized 5G QoS identifiers (5QI) and the corresponding QoS characteristics (Priority level, Packet Delay Budget, Packet error rate etc.,) for MC services are defined in 3GPP TS 23.501[4].

MC services layer adaptations include changes at the SIP core and MC service server to request network resources at the time of session establishment. Procedures are updated to allow for modification of resources after the session is established and is in-progress (e.g. a request to upgrade the normal MC service call to an MC service emergency or imminent peril call). The QoS characteristics of the required resources are sent directly to the PCF using the N5 reference point or the Rx reference point by the MC service server or SIP core and encompass media type, bandwidth, priority, application identifier and resource sharing information. Alternatively, QoS characteristics for resources can be exchanged indirectly utilizing the N33 reference point between the MC service server and NEF.

●     Network Slicing

Network slicing is an important feature that can enhance MC communications by providing a differentiated and dedicated slice exploiting a single physical network infrastructure. Slicing enables configuration of public-safety applications to use a dedicated slice, offering guaranteed bandwidth, ultra-low latency, and the highest priority communication to meet the stringent requirements of MC services. It ensures MC communications remain uninterrupted by network congestion and without any glitch.

Initial MC service User Equipment (UE) configuration data at the MC services layer is extended to contain Data Network Name (DNN) and the corresponding Data Network (DN) credentials along with the Single – Network Slice Selection Assistance Information (S-NSSAI) to be used for each MC service. Default Configured slice(s) information and the corresponding slice credentials can be pre-configured at the MC service UE.

●     5G Multicast Broadcast Services (5MBS)

5MBS is a point-to-multipoint service that allows data transmission from a single source entity to multiple recipients, either to all users in a broadcast service area or to users in a multicast group. 5MBS enables mission critical services to provide optimized downlink delivery of user traffic in group calls and communications. Specifically, it enables efficient usage of network resources for group based voice, data and video MC communications and supports large numbers (100 times greater than 4G) of first responders concentrated within a small area attending an emergency incident. It is also possible to switch between broadcast and unicast delivery within the same session. 5GS supports both multicast and broadcast services whereas LTE eMBMS was limited only to broadcast services.

In order to utilize the 5MBS feature offered by the 5G system as defined in 3GPP TS 23.247[5], the MC services layer has specified the interactions between the MC service server and MC service clients for (pre-defined and dynamic) session creation, activation, deactivation and deletion of the 5MBS sessions. A MC service client can report the monitoring state (i.e., the reception quality of the 5MBS session) back to the MC service server, based on which, the MC service server can choose to switch the downlink data delivery to the MC service UEs from unicast to multicast/broadcast and vice-versa.

Faster delivery method switching is achieved in 5GS compared to LTE since the decision to switch between PTP (point-to-point) and PTM (point-to-multipoint) is handled by NG-RAN. The Location reporting mechanism is enhanced to leverage the changes in UE Radio Access Type (RAT) Type. Based on the RAT type change location reporting trigger and the reported RAT type of the UE, the MC service server can choose to perform inter-system switching below.

    ▪      5G MBS session to LTE eMBMS bearer
    ▪      5G MBS session to LTE unicast bearer
    ▪      LTE eMBMS bearer to 5G MBS sessions (either broadcast or multicast)
    ▪      LTE eMBMS bearer to 5G unicast PDU session

●     5G Proximity based Services (ProSe)

Proximity based Services (ProSe) are provided by the 5G System based on UEs proximity to each other. It allows establishing direct connections between devices in scenarios outside the coverage area, thus ensuring first responders with the connectivity they need, especially in hazardous situations.

5G ProSe supports UE-to-UE relay to support connectivity between 5G ProSe-enabled UEs when in out-of-coverage, and UE-to-Network relay to support 5G ProSe Remote UEs connectivity to the network. 5GS brings significant enhancements to make the Device-to-Device (D2D) communication match or exceed the KPIs offered by legacy LMR (Land Mobile Radio) technologies.

MC service UE(s) utilize the discovery procedures specified in 3GPP TS 23.304[6] to discover a potential UE-to-UE relay or UE-to-Network relay supporting MC service in its proximity and establishes active communication.

Additional MC Enhancements

In addition to integrating the core 5G capabilities, the MC service framework has been further enhanced with the following key capabilities:

●     Adhoc group communication

Adhoc Group Communication was introduced in Release 18, which enables authorized users to combine a random set of MCX Users into a group communication. An adhoc group is spontaneously created during the communication and is deleted once the communication is terminated. In Release 19, adhoc group communication is enhanced with the support of procedures related to standalone file distribution using http, modification of criteria for selecting the participants during call, multi-talker floor control, migration during call etc..

●     MC gateway UE

The MC gateway UE enables MC service access for a MC service user residing on non-3GPP devices, which may or may not have the ability to host MC service clients. In order to be able to participate in a MC service, the MC gateway UE provides the necessary functions such as 3GPP transport resources, location management, MC traffic forwarding etc., to enable the MC service access for such MC clients.

●     IOPS mode of operation for 5GS

The goal of the Isolated Operation for Public Safety (IOPS) capability is to maintain communication between public safety users even when the backhaul connectivity to the core network is not fully functional. It operates in an isolated mode, ensuring communication via isolated base stations without backhaul communications. This feature was earlier available for LTE and in Release 19 the procedures are enhanced to support IOPS mode of operation over 5GS.

●     Recording and logging

This functionality, specified in Release 19, enables the MC service organizations to log the metadata of the group communications and private communications and to record the transmissions of the group communications and private communications under the organization's authority. The metadata includes start time, date, MC User ID, functional alias(es), MC Group ID, Location information of the transmitting Participant, end time or duration, end reason, type of communication (e.g., MC Service Emergency, regroup, private) and success/failure indication.

●     Sharing administrative configuration

Sharing administrative configuration between interconnected MC systems enables MC administrators and authorized MC service users of the primary MC system and the partner MC system to negotiate and apply configuration changes between interconnected MC systems, in order to fulfil preconditions for the cooperation between interconnected MC systems.

Conclusion

Advancements in 5G technology bring implicit benefits to the critical communications industry. High speed and ultra-reliable connectivity with virtually zero latency enables MC services to be more sophisticated, reliable and smarter. Through massive Machine Type Communications (mMTC), it will now be possible to scale-up the deployment of Internet of Things (IoT) devices thereby enabling the first responders to make better and timely decisions to handle first-responder situations. 5G also brings increased coverage for both macro cells and D2D communications.

Public safety organizations are gearing up to embrace 5GS and additional MC capabilities that enhance mission critical services. Samsung continues to be at the forefront of 3GPP standardization efforts and development of mission critical products and solutions catering to the emerging needs of public safety agencies and their users.