Contents With the global momentum that 5G has been driving, cyber-physical control applications have recently attracted a lot of attention. The basic idea is to utilize the communication technology between two entities even when they are logically and geographically separated so as to provide necessary command, control, and information in time and on time. The 3rd Generation Partnership Project's (3GPP's) effort on technical enhancement to accommodate time-sensitive networking (TSN) associated with clock synchronization will enable many industry applications, such as smart factory and critical infrastructure operations, and tele-health applications. Following this technology advancement, several challenging points have been widely identified among global forums toward the next generation, or 6G, to further enhance the capability of communication technology that can support new applications and usage scenarios in unstructured environments as opposed to those in structured and tame working environments as described in Next G Alliance Report: 6G Applications and Use Cases published by the Alliance for Telecommunications Industry Solutions (ATIS) [1]. We focus on communication technology aspects that are relevant to support a network of service robots (SOBOTs) that stay with humans and understand natural forms of interactions between humans and robots and/or between robots in order to make decisions and perform tasks as described in a recent IEEE article on SOBOTs [2]. In this column, we address the recent advancement in 5G communication technologies and their potential relation to system enhancements to support SOBOT operations. We begin by addressing the implications and expected roles of SOBOTs, which is followed by recent advancements in 3GPP standards and further consideration points.
Network of Service Robots: Expected Roles
With the global trends of aging populations described in the United Nations' Report on World Population Ageing, the old-age dependency ratio is expected to rise significantly in the next three decades: OAORs will be highest in Europe and North America in 2050 [1]. 3GPP has recently introduced new features that are relevant for smart working environments, such as smart manufacturing with industrial robots. However, there is a constantly growing demand in smart living environments for which the next generation telecommunication and computing technology should play a key role. By further investigating what humans will need from technology-oriented services (e.g., ambient assisted living) in a commonly agreed trend of population aging, critical roles tightly coupled with human-cen-tric intelligence are expected to be played through enhanced capability over what industrial robots can do in a structured setting, such as in manufacturing. A SOBOT, which was defined as a “robot in personal use or professional use that performs useful tasks for humans or equipment” by ISO 8373:2021, will play a key role to alleviate the burden that aging societies will face. SOBOTs are specifically designed to understand the need that humans directly or indirectly express through natural forms of interactions (e.g., natural language, gesture, or facial expression) and define roles to play on their own through independent and/or collaborative decision making. In this context, the intelligence that SOBOTs, including collaborative robots, have is specifically referred to as ambient intelligence, in which the focus is not on the capability of general intelligence but on what SOBOTs with ambient intelligence can do specifically for humans in human-centered usage scenarios.
Clock Synchronization and Time-Sensitive Networking
Clock synchronization is one of the key aspects necessary to provide communication services for applications that require TSN. Furthermore, timing resiliency is very important. The 5G system (5GS) supports clock synchronization and time-sensitive communication (TSC) [3]. TSC is a communication service that supports deterministic communication (which ensures a maximum delay) and/or isochronous communication with high reliability and availability. It is about providing packet transport with quality of service (QoS) characteristics such as bounds on latency, loss, and reliability, where end systems and relay/transmit nodes may or may not be strictly synchronized. To support QoS characteristics required for TSC, the 5G system supports the following features that can be used inde-pendently or in combination: delay-critical GBR QoS flow, hold and forward mechanism, and TSC assistance information.
To support various service requirements and deployment environment, 5G System supports different modes for clock synchronization, which are based on the features described in IEEE Std 802.1AS or IEEE Std 1588 as follows:
Time-aware system
Boundary clock
Peer-to-peer transparent clock
End-to-end transparent clock
The device-side TSN translator (DS-TT) and network-side TSN translator (NW-TT) are located at the edge of the 5G system to handle and generate Generalized Precision Time Protocol ((g) PTP) message. The DS-TT and NW-TT perform timestamping, and link and path delay measurement to support clock synchro-nization. The distribution of the master clock in the PTP domain is independent of the clock synchronization in the 5G system, as shown in Fig. 1.
Meanwhile, there are still some challenges on adapting to technologies supported by 5G, while there are some requirements from several verticals to support clock synchronization services including both the ability to improve resiliency of timing services and the ability to act as a backup for global navigation satellite system (GNSS) timing services. For example, the radio access network (RAN) and core network of the 5G system should learn about 5GS network timing synchronization status to be able to inform UEs, and devices attached to the UEs and AFs. Also, it is considered necessary to enable AFs to request clock synchronization service in a specific coverage area because the current exposure framework does not consider reliability aspects.
Features Relevant to Support SOBOTs
With some similar features required to support SOBOT operations, vehicle-to-everything (V2X) would add practical values in the service chain of SOBOTs. 3GPP enhanced the 5G system in order to facilitate vehicular communications for V2X services, over PC5 reference point (i.e. NR PC5 RAT, LTE PC5 RAT; RAT: radio access technology) and Uu reference point (i.e., NR, E-UTRA).
Regarding V2X communication over a PC5 reference point, two types of PC5 reference points exist: the LTE-based PC5 reference point as defined in TS 23.285 and the NR-based PC5 reference point as defined in TS 23.287. A UE can use either type of PC5 or both for V2X communication depending on the V2X services the UE supports. V2X communication over a PC5 reference point is supported when the UE is “served by NR or E-UTRA” (i.e., in coverage) or when the UE is “served by neither NR nor E-UTRA” (i.e., out of coverage).
V2X communication in the 5G system: a) V2X communication over pc5 (nr pc5/lte pc5); b) V2X communication over uu (nr/e-utra).
V2X communication over NR based PC5 reference point supports broadcast mode, groupcast mode and unicast mode. The per-flow PC5 QoS model is introduced for V2X communication over NR-based PC5 reference point. Various PC5 5G QoS identifier (PQI) values were standardized with mapped QoS characteristics to support V2X services (e.g., platooning, sensor sharing, cooperative lane change).
For V2X communication over Uu reference point in the 5G system, unicast is supported. Latency reduction for V2X message transfer to/from the V2X application server can be achieved by using various mechanisms such as edge computing defined in TS 23.501. Support of V2X communication over Uu reference point by using multicast-broadcast services is expected.
A variety of parameters need to be available to the UE for V2X communications over PC5 and Uu reference points including PC5 radio parameters used when the UE is out of coverage, mapping of V2X services to PC5 RATs, V2X application server address information, and so on. These parameters can be con-figured in the UE and provided by the V2X application server or the policy control function to the UE.
QoS support and prediction are important to support V2X services. The 5G system supports QoS sustainability analytics so that the V2X application server can request notifications on QoS sustainability analytics for an indicated geographic area and time interval in order to adjust the application behavior in advance with potential QoS change or degradation (e.g., adjust inter-vehicle gap).
Security for V2X communication over PC5 reference point is supported as specified in TS 33.185 and TS 33.536 while considering various security aspects such as privacy. For security of V2X communication over a Uu reference point in the 5G system, security or privacy procedures for Uu connectivity with 5G core network specified in TS 33.501 are used.